Robert J Steidl

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Scholarly Contributions

Chapters

• Mannan, R. W., & Steidl, R. J. (2022). Habitat. In Wildlife management: Contemporary principles and practices, 2nd edition. John Hopkins University Press.
• Archer, S. R., Andersen, E. M., Predick, K. I., Schwinning, S., Steidl, R. J., & Woods, S. R. (2016). Woody plant encroachment: causes and consequences. In Rangeland Systems: Processes, Management and Challenges(pp in press). Springer.
• Mannan, R. W., & Steidl, R. J. (2017). Demography of Raptor Populations in Urban Environments. In Urban Raptors. Island Press.
• Steidl, R. J., & Mannan, R. W. (2018). Demography of Raptor Populations in Urban Environments. In Urban raptors: Ecology and conservation of birds of prey in an urbanizing world(pp 51-63). Island Press, Washington, DC. doi:10.5822/978-1-61091-841-1_4
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  Lands modified by humans vary widely in their environmental features, from areas that retain much of their natural character to areas in the urban core that retain little natural character. For example, a city that was built on lands that were once covered by a forest might be dominated at its core by pavement and buildings and support only a few trees, many of which are nonnative species. Areas surrounding the urban core usually are residential neighborhoods composed of private homes and small parks, where trees are more common. On the outskirts of the city are exurban areas dominated by natural forest vegetation with only scattered houses and other human structures. Consequently, urban areas often represent a gradient of development1 that spans an array of natural and anthropogenic features, many of which influence the probability of an area being inhabited by a species (figure 4.1). Some raptors are capable of inhabiting urban environments at one or more points along this gradient, provided the areas support their specific habitat resources and match their tolerance of human activity.2,3
• Archer, S. R., Andersen, E. M., Predick, K. I., Schwinning, S., Steidl, R. J., & Woods, S. R. (2017). Woody plant encroachment: causes and consequences. In Rangeland Systems: Processes, Management and Challenges(pp 25-84). Springer.
• Mannan, R. W., & Steidl, R. J. (2013). Habitat. In Wildlife management: Contemporary principles and practices. John Hopkins University Press.
• Steidl, R. J., Shaw, W. W., & Fromer, P. (2009). A Science-Based Approach to Regional Conservation Planning. In The planner's guide to natural resource conservation: the science of land development beyond the metropolitan fringe(pp 217-233). Springer, New York, NY. doi:10.1007/978-0-387-98167-3_12
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  Although single-species approaches have played an important role in conservation in the United States, the Endangered Species Act provides a mechanism for conservation at larger scales through Habitat Conservation Plans (HCPs). HCPs not only offer the potential for comprehensive conservation planning for a wide range of species across broader geographic scales but also provide assurances that eliminate risks related to endangered species concerns for nonfederal landowners, developers, and planners. Given their benefits, dozens of municipalities have adopted HCPs to address planning issues related to rare and vulnerable species. The challenge, however, is to develop conservation plans that reliably meet broader-scale conservation and planning objectives while not increasing risks posed to vulnerable species. Consequently, we designed a science-based framework from which to develop regional conservation plans, including HCPs. We designed a rigorous process that classifies areas based on their relative conservation value as part of a conservation strategy for more than 20,000 km2 of Sonoran desert in Pima County, Arizona. This chapter describes our approach including the fundamental planning elements selected, the process used to quantify the relative biological importance of each landscape unit, and how we assembled landscape elements into units that form the framework of the Sonoran Desert Conservation Plan.

Journals/Publications

• Zylstra, E. R., Allison, L. J., Averill-Murray, R. C., Landau, V., Pope, N. S., & Steidl, R. J. (2022). A spatially-explicit model for density that accounts for availability: a case study with Mojave desert tortoises.
  . Ecosphere..
• Steidl, R. J., & Andersen, E. M. (2022). Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival. Ornithological Applications. doi:10.1093/ornithapp/duac049
• Andersen, E. M., & Steidl, R. J. (2020). Plant invasions alter settlement patterns of breeding birds. Ecosphere. doi:https://doi.org/10.1002/ecs2.3012
• Andersen, E. M., & Steidl, R. J. (2020). Power to detect trends in abundance within a distance sampling framework. Journal of Applied Ecology. doi:https://doi.org/10.1111/1365-2664.13529
• Steidl, R. J., & Andersen, E. M. (2020). Plant invasions alter settlement patterns of breeding grassland birds. Ecosphere, 11(1). doi:10.1002/ecs2.3012
• Steidl, R. J., Steidl, R. J., Mcintosh, M. E., Mcdade, L. A., Boyd, A. E., & Arnold, A. E. (2020). Growth and demography of a declining, endangered cactus in the Sonoran Desert. Plant Species Biology, 35(1), 6-15. doi:10.1111/1442-1984.12251
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  Increases in the incidence and severity of drought threaten the viability of rare plants in arid regions. The endangered Nichol's Turk's head cactus (Echinocactus horizonthalonius Lemaire var. nicholii L. Benson) occurs only in four small, isolated populations in the Sonoran Desert of North America. Since 1995 we have monitored a population in southeastern Arizona (USA). Here we report 23 years of observations on abundance, growth, mortality, flowering and recruitment. Abundance of plants decreased from 132 in 1996 to 40 in 2017, with 100 individuals recruited and 203 dying during the study. Individual plants grew slowly, increasing annually by an average of 0.22 cm (95% confidence interval, 0.18–0.26 cm) in diameter and 0.27 cm (0.20–0.33 cm) in height. Growth was slowest when drought was most severe and slowed as plants reached maximum size. Annual mortality increased markedly across the study period and did not vary with plant size. Annual probability of flowering increased as plants increased in diameter but not in height, and varied with precipitation and drought but not with mean annual temperature. Recruitment was higher when average temperature was higher and the number of recruits per capita increased across the study period. The annual rate of change in abundance averaged −6%, but shifted markedly from −1% during 1995–2008 to −11% during 2008–2017. Our results indicate that the population's decline was not a consequence of failed recruitment but of increased mortality, which we discuss in the context of climate and herbivory.
• Zylstra, E. R., & Steidl, R. J. (2020). A Bayesian state-space model for seasonal growth of terrestrial vertebrates in dynamic environments. Ecological Modeling. doi:https://doi.org/10.1016/j.ecolmodel.2020.108975
• Andersen, E. M., & Steidl, R. J. (2019). Woody plant encroachment restructures bird communities in semiarid grasslands. Biological Conservation. doi:https://doi.org/10.1016/j.biocon.2019.108276
• Andersen, E. M., Cambrelin, M. N., & Steidl, R. J. (2019). Responses of grassland arthropods to an invasion by nonnative grasses. Biological Invasions. doi:https://doi.org/10.1007/s10530-018-1831-z
• McIntosh, M. E., Boyd, A. E., Arnold, A. E., Steidl, R. J., & McDade, L. A. (2019). Demography of a declining, endangered cactus in the Sonoran Desert. Plant Species Biology, 2109, 1-10. doi:https://doi.org/10.1111/1442-1984.12251
• Steidl, R. J., & Andersen, E. M. (2019). Power to detect trends in abundance within a distance sampling framework. Journal of Applied Ecology, 57(2), 344-353. doi:10.1111/1365-2664.13529
• Steidl, R. J., Zylstra, E. R., Swann, D. E., Hossack, B. R., & Muths, E. (2019). Drought‐mediated extinction of an arid‐land amphibian: insights from a spatially explicit dynamic occupancy model. Ecological Applications, 29(3). doi:10.1002/eap.1859
• Zylstra, E. R., Swann, D. E., & Steidl, R. J. (2019). Surface-water availability governs survival of an amphibian in arid mountain streams. Freshwater Biology. doi:https://doi.org/10.1111/fwb.13204
• Zylstra, E. R., Swann, D. E., Hossack, B. R., Muths, E., & Steidl, R. J. (2019). Drought and metapopulation dynamics of a desert-dwelling amphibian. Bulletin of the Ecological Society of America.
• Zylstra, E. R., Swann, D. E., Hossack, B. R., Muths, E., & Steidl, R. J. (2019). Drought-mediated extinction of an arid-land amphibian: insights from a spatially explicit dynamic occupancy model. Ecological Applications.
• Campbell, S. P., Zylstra, E. R., Darst, C. R., Averill-Murray, R. C., & Steidl, R. J. (2018). A spatially explicit hierarchical model to characterize population viability. Ecological Applications, 28(8), 2055-2065. doi:10.1002/eap.1794
• Steidl, R. J., Zylstra, E. R., & Swann, D. E. (2018). Surface‐water availability governs survival of an amphibian in arid mountain streams. Freshwater Biology, 64(1), 164-174. doi:10.1111/fwb.13204
• Steidl, R. J., Zylstra, E. R., Campbell, S. P., Darst, C. R., & Averill‐Murray, R. C. (2018). A spatially explicit hierarchical model to characterize population viability. Ecological Applications, 28(8), 2055-2065. doi:10.1002/eap.1794
• Zylstra, E. R., Campbell, S. P., Darst, C. R., Averill-Murray, R. C., & Steidl, R. J. (2019). Demography of Sonoran desert tortoises. Bulletin of the Ecological Society of America, 100(1). doi:https://doi.org/10.1002/bes2.1470
• Steidl, R. J., Taylor, M. J., Andersen, E. M., & Arnold, A. E. (2017). Using cytochrome b to identify nests and museum specimens of cryptic songbirds. Conservation Genetics Resources, 9, 451-458.
• Litt, A. R., & Steidl, R. J. (2016). Complex demographic responses of a small mammal to a plant invasion. Wildlife Research, 43(4), 304–312. doi:10.1071/WR15147
• Campbell, S. P., Zylstra, E. R., & Steidl, R. J. (2015). Fecundity of desert tortoises: a synthesis of reproduction and first year survival. Herpetological Conservation and Biology, 10(2), 583–591.
• Gray, K. M., & Steidl, R. J. (2015). A plant invasion affects condition but not density or population structure of Sonoran desert tortoises.. Biological Invasions, 17, 1979-1988.
• Koprowski, J. L., Posthumus, E. E., & Steidl, R. J. (2015). Red squirrel middens influence abundance but not diversity of other vertebrates. PLoS One, 10(4). doi:10.1371/journal.pone.0123633
• Posthumus, E. E., Koprowski, J. L., & Steidl, R. J. (2015). Red squirrel middens influence abundance but not diversity of other vertebrates. PLoS One.
• Powell, B. F., & Steidl, R. J. (2015). Structure of montane riparian bird communities in the Sky Islands of Arizona, USA. Southwestern Naturalist, 60(1), 65–71.
• Zylstra, E. R., Steidl, R. J., Swann, D. E., & Ratzlaff, K. (2015). Hydrologic variability governs population dynamics of a vulnerable amphibian in an arid environment. PLoS One, 10(6). doi:10.1371/journal.pone.0125670
• Steidl, R. J., Conway, C. J., & Litt, A. R. (2013). Power to detect trends in abundance of secretive marsh birds: effects of species traits and sampling effort. Journal of Wildlife Management.
• Steidl, R. J., Conway, C. J., & Litt, A. R. (2013). Power to detect trends in abundance of secretive marsh birds: Effects of species traits and sampling effort. Journal of Wildlife Management, 77(3), 445-453.
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  Abstract: Standardized protocols for surveying secretive marsh birds have been implemented across North America, but the efficacy of surveys to detect population trends has not been evaluated. We used survey data collected from populations of marsh birds across North America and simulations to explore how characteristics of bird populations (proportion of survey stations occupied, abundance at occupied stations, and detection probability) and aspects of sampling effort (numbers of survey routes, stations/route, and surveys/station/year) affect statistical power to detect trends in abundance of marsh bird populations. In general, the proportion of survey stations along a route occupied by a species had a greater relative effect on power to detect trends than did the number of birds detected per survey at occupied stations. Uncertainty introduced by imperfect detection during surveys reduced power to detect trends considerably, but across the range of detection probabilities for most species of marsh birds, variation in detection probability had only a minor influence on power. For species that occupy a relatively high proportion of survey stations (0.20), have relatively high abundances at occupied stations (2.0 birds/station), and have high detection probability (0.50), ≥40 routes with 10 survey stations per route surveyed 3 times per year would provide an 80% chance of detecting a 3% annual decrease in abundance after 20 years of surveys. Under the same assumptions but for species that are less common, ≥100 routes would be needed to achieve the same power. Our results can help inform the design of programs to monitor trends in abundance of marsh bird populations, especially with regards to the amount of sampling effort necessary to meet programmatic goals. © The Wildlife Society, 2013.
• Steidl, R. J., Litt, A. R., & Matter, W. J. (2013). Effects of plant invasions on wildlife in desert grasslands. Wildlife Society Bulletin, 37, 527-536.
• Zylstra, E. R., Steidl, R. J., Jones, C. A., & Averill-Murray, R. C. (2013). Spatial and temporal variation in survival of a rare reptile: A 22-year study of Sonoran desert tortoises. Oecologia, 173(1), 107-116.
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  PMID: 23011852;Abstract: Although many species may be vulnerable to changes in climate, forecasting species-level responses can be challenging given the array of physiological, behavioral, and demographic attributes that might be affected. One strategy to improve forecasts is to evaluate how species responded to climatic variation in the past. We used 22 years of capture-recapture data for Sonoran desert tortoises (Gopherus morafkai) collected from 15 locations across their geographic range in Arizona to evaluate how environmental factors affected spatial and temporal variation in survival. Although rates of annual survival were generally high (Φ = 0.92), survival of adults decreased with drought severity, especially in portions of their range that were most arid and nearest to cities. In three locations where large numbers of carcasses from marked tortoises were recovered, survival of adults was markedly lower during periods of severe drought (Φ = 0.77-0.81) compared to all other periods (Φ = 0.93-0.98). Assuming continued levels of dependency of humans on fossil fuels, survival of adult tortoises is predicted to decrease by an average of 3 % during 2035-2060 relative to survival during 1987-2008 in 14 of the 15 populations we studied. This decrease could reduce persistence of tortoise populations, especially in arid portions of their range. Temporal and spatial variation in drought conditions are important determinants of survival in adult desert tortoises. © 2012 Springer-Verlag.
• Zylstra, E. R., Steidl, R. J., Jones, C. A., & Averill-Murray, R. C. (2013). Spatial and temporal variation in survival of a rare reptile: a 22-year study of Sonoran desert tortoises. Oecologia, 173, 107-116.
• Litt, A. R., & Steidl, R. J. (2011). Interactive effects of fire and nonnative plants on small mammals in Grasslands. Wildlife Monographs, 1-31.
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  Abstract: Invasions by nonnative plants have changed the structure of many terrestrial ecosystems and altered important ecological processes such as fire, the dominant driver in grassland ecosystems. Reestablishing fire has been proposed as a mechanism to restore dominance of native plants in grasslands invaded by nonnative plants, yet fire may function differently in these altered systems, potentially affecting animals in novel ways. To assess whether invasions by nonnative plants alter the effects of fire on animals, we performed a manipulative experiment in semi-desert grasslands of southeastern Arizona that have been invaded by a perennial, nonnative grass from Africa, Lehmann lovegrass (Eragrostis lehmanniana). We applied fire to 36 of 54 1-ha plots established along an invasion gradient where dominance of E. lehmanniana ranged from 0% to 91% of total live plant biomass. Over the 5-year period from 2000 to 2004, we used mark-recapture methods to assess how population and community attributes of small mammals varied along the gradient of nonnative grass and in response to fire. We quantified changes in presence of 17 species, abundance of 9 species, total abundance of all species combined, species richness, and species composition. Based on 11,226 individual mammals from 24 species, we found that effects of nonnative-grass dominance varied with habitat preferences of each species, resulting in composition of the small-mammal community changing predictably along the invasion gradient. As dominance of nonnative grass increased, presence and abundance of granivorous heteromyids and insectivores (e.g., Chaetodipus, Perognathus, Onychomys; pocket mice and grasshopper mice) decreased, whereas presence and abundance of omnivorous and herbivorous murids (e.g., Reithrodontomys, Sigmodon; harvest mice and cotton rats) increased. Species richness of the small-mammal community averaged 8.4 species per plot and was highest at intermediate levels of nonnative-grass dominance where vegetation heterogeneity was greatest. Abundance of all small mammals combined averaged 26.9 individuals per plot and did not vary appreciably with nonnative-grass dominance. During the 4- to 8-week period immediately after fire, abundance of 6 of the 9 most common species changed, with 5 species decreasing and 1 species increasing on burned plots relative to unburned plots. During this same time period, species richness of small mammals decreased by an average of 3 species (38%) and total abundance of all species combined decreased by an average of 16 individuals (61%) on burned plots relative to unburned plots. Effects of fire on vegetation biomass, on presence of 9 of 17 mammalian species, and on abundance of 4 of 9 mammalian species remained evident â¥2 years after fire. Effects of fire on most small-mammal species varied with the degree of nonnative-grass dominance, suggesting that fire functioned differently in areas invaded by nonnative plants relative to areas dominated by native plants. Specifically, effects of fire on presence of 12 of 14 species and abundance of 7 of 9 species varied along the gradient of E. lehmanniana. During this post-fire period, however, composition of the small-mammal community in areas dominated by nonnative grass transitioned towards composition of areas dominated by native grasses, suggesting that fires had some restorative effect on habitat for small mammals. The relative strength of this effect will likely depend in general on the structural and compositional contrasts between invaded and native plant communities. Despite the reported ineffectiveness of fire at reducing dominance of nonnative plants, restoring fire to grasslands invaded by nonnative plants can help maintain the mosaic of vegetation conditions necessary to support the diverse assemblage of animals that inhabit these fire-governed ecosystems. © 2011 The Wildlife Society.
• Litt, A., & Steidl, R. (2011). Ecological effects of fire on small mammals in grasslands invaded by nonnative plants. Wildlife Monographs.
• Flesch, A. D., & Steidl, R. J. (2010). Importance of environmental and spatial gradients on patterns and consequences of resource selection. Ecological Applications, 20(4), 1021-1039.
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  PMID: 20597287;Abstract: Strategies to conserve rare species require identifying resources that function as important habitat elements and that promote high demographic performance. Assessing the relative importance of resources, however, can be confounded by natural variation in resource availability and by the hierarchical spatial structure in which resources are organized. Because availability and relative importance of resources often vary across environmental and spatial gradients, we used gradients together with resource selection functions and variance decomposition to assess the relative importance of resources to nest site selection and reproductive performance of Ferruginous Pygmy-Owls (Glaucidium brasilianum). We measured habitat characteristics of 106 nests and paired available sites at five spatial scales across a 220-km gradient of precipitation and vegetation in northwest Mexico, in a region adjacent to the southwestern United States where pygmy-owls have declined to near extinction. Resources explained 76-85% of variation in nest site selection and 21-31% of variation in reproductive performance across all spatial scales combined. Although we found evidence of resource selection at each scale, the magnitude of selection and influence of resources on reproductive performance were greatest where availability of selected resources were low and where temperature extremes and predation risk likely increased the relative importance of these resources. At larger scales, geographic changes in resource use corresponded with changes in availability, whereas at smaller scales, resource use varied little despite changes in availability, suggesting higher specificity and importance of resources at smaller scales. At the smallest scale, owls selected nest cavities with smaller entrances, larger volume, greater height, and orientations that produced cooler microclimates in the hottest regions of the study area; these choices promoted higher reproductive performance. Cavity resources explained more variation in selection and reproductive performance than resources at larger scales, highlighting their importance as conservation, targets. High correlation of resource characteristics among spatial scales, however, indicated that selection of resources at small scales depended on characteristics of resources at larger scales. Assessing how resource selection changes in response to underlying variation in resource availability can help prioritize resources most important for conservation and management. © 2010 by the Ecological Society of America.
• Litt, A. R., & Steidl, R. J. (2010). Improving estimates of abundance by aggregating sparse capture-recapture data. Journal of Agricultural, Biological, and Environmental Statistics, 15(2), 228-247.
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  Abstract: Inferences about abundance often are based on unadjusted counts of individuals observed, in part, because of the large amount of data required to generate reliable estimates of abundance. Where capture-recapture data are sparse, aggregating data across multiple sample elements by pooling species, locations, and sampling periods increases the information available for modeling detection probability, a necessary step for estimating abundance reliably. The process of aggregating sample elements involves balancing trade-offs related to the number of aggregated elements; although larger aggregates increase the amount of information available for estimation, they often require more complex models. We describe a heuristic approach for aggregating data for studies with multiple sample elements, use simulated data to evaluate the efficacy of aggregation, and illustrate the approach using data from a field study. Aggregating data systematically improved reliability of model selection and increased accuracy of abundance estimates while still providing estimates of abundance for each original sample unit, an important benefit necessary to maintain the design and sampling structure of a study. Within the framework of capture-recapture sampling, aggregating data improves estimates of abundance and increases the reliability of subsequent inferences made from sparse data. Additional tables and datasets may be found in the online supplements. © 2009 International Biometric Society.
• Litt, A. R., & Steidl, R. J. (2010). Insect assemblages change along a gradient of invasion by a nonnative grass. Biological Invasions, 12(10), 3449-3463.
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  Abstract: Because invasions by nonnative plants alter the structure and composition of native plant communities, invasions can alter the function of ecosystems for animals that depend on plants for food and habitat. We quantified effects of an invasion by a nonnative grass on the insect community in grasslands of southeastern Arizona. We sampled insects on 54 1-ha plots established across a gradient of invasion by Lehmann lovegrass (Eragrostis lehmanniana Nees), a perennial species native to southern Africa. Between 2000 and 2004, we captured 94,209 insects representing 13 orders, 91 families, and 698 morphospecies during 2,997 trap nights. Richness of families, richness of morphospecies, and overall abundance of insects decreased as dominance of nonnative grass increased. With every 100 g/m2 increase in biomass of nonnative grass, the average number of insect families decreased by 5%, morphospecies decreased by 6%, and overall abundance decreased by 14%. In areas dominated by nonnative grass, 2 of 8 orders and 6 of 27 families of insects were present less frequently and one family was present more frequently; 5 of 8 orders and 6 of 27 families of insects were less abundant and 3 families were more abundant than in areas dominated by native grasses. As a result, this plant invasion altered the structure of the insect community, which has consequences for animals at higher trophic levels and for ecosystem processes, including decomposition and pollination. Because complete eradication of nonnative plants might be possible only rarely, maintaining stands of native vegetation in invaded areas may be an important practical strategy to foster persistence of animals in grasslands invaded by nonnative plants. © 2010 Springer Science+Business Media B.V.
• Wallace, J. E., Steidl, R. J., & Swann, D. E. (2010). Habitat characteristics of lowland leopard frogs in mountain canyons of Southeastern Arizona. Journal of Wildlife Management, 74(4), 808-815.
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  Abstract: Many aquatic species in the arid southwestern United States are imperiled, persisting primarily in isolated, low-order streams that are increasingly vulnerable to stochastic disturbances. During 2003 and 2004, we surveyed 39 mountain canyons in southeastern Arizona, USA, for lowland leopard frogs (Rana yavapaiensis), a species that has declined in abundance and distribution across its range in the United States. We quantified habitat features at 2 spatial scales, canyon and pool, to identify features that distinguished sites inhabited by frogs from those uninhabited by frogs. Canyons inhabited by frogs had watersheds that averaged 8.1 km2 larger (SE 2.52), pools that averaged 37.8 m3 greater (9.30) in volume, gradients that averaged 4.1 (1.40) less steep, and locations that averaged 3.2 km closer (1.06) to the nearest valley stream than did uninhabited canyons. Plunge pools inhabited by frogs averaged 13.5 (5.66) more perimeter vegetation, 11.2 (5.34) more canopy cover, and 1.9 (0.60) more refuges than uninhabited pools. In general, canyons that provided more perennial water during dry summer months and plunge pools that provided more bank heterogeneity were more likely to be inhabited by frogs. Conservation of lowland leopard frogs and other aquatic species that inhabit xeric systems in the southwestern United States depends principally on maintaining riparian ecosystems that provide habitat for these species and the adjacent uplands that influence the structure and function of these systems. Therefore, both riparian areas and their adjacent uplands must be managed to maintain habitat for organisms that inhabit these rare and diverse ecosystems. © The Wildlife Society.
• Zylstra, E. R., Steidl, R. J., & Swann, D. E. (2010). Evaluating survey methods for monitoring a rare vertebrate, the sonoran desert tortoise. Journal of Wildlife Management, 74(6), 1311-1318.
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  Abstract: Effective conservation requires strategies to monitor populations efficiently, which can be especially difficult for rare or elusive species where field surveys require high effort and considerable cost. Populations of many reptiles, including Sonoran desert tortoises (Gopherus agassizii), are challenging to monitor effectively because they are cryptic, they occur at low densities, and their activity is limited both seasonally and daily. We compared efficiency and statistical power of 2 survey methods appropriate for tortoises and other rare vertebrates, line-transect distance sampling and site occupancy. In 2005 and 2006 combined, we surveyed 120 1-km transects to estimate density and 40 3-ha plots 5 times each to estimate occupancy of Sonoran desert tortoises in 2 mountain ranges in southern Arizona, USA. For both mountain ranges combined, we estimated density to be 0.30 adult tortoises/ha (95 CI 0.170.43) and occupancy to be 0.72 (95 CI 0.560.89). For the sampling designs we evaluated, monitoring efforts based on occupancy were 836 more efficient than those based on density, when contrasting only survey effort, and 1730 more efficient when contrasting total effort (surveying, hiking to and from survey locations, and radiotracking). Occupancy had greater statistical power to detect annual declines in the proportion of area occupied than did distance sampling to detect annual declines in density. For example, we estimated that power to detect a 5 annual decline with 10 years of annual sampling was 0.92 (95 CI 0.750.98) for occupancy and 0.43 (95 CI 0.350.52) for distance sampling. Although all sampling methods have limitations, occupancy estimation offers a promising alternative for monitoring populations of rare vertebrates, including tortoises in the Sonoran Desert. © 2010 The Wildlife Society.
• Steidl, R. J., & Litt, A. R. (2009). Do plant invasions change the effects of fire an animals?. Fire Ecology, 5(1), 56-66.
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  Abstract: Fire and invasions by nonnative plants can change the structure and function of ecosystems, and independent effects of each of these processes have been well studied. When fire is restored to areas where it has been excluded and the native plant communities have been invaded by nonnative species, changes in vegetation structure and composition are likely to alter the fire regime. These changes, in turn, might alter the effects of fire on wildlife and wildlife habitat. In this paper, we develop a framework to evaluate whether fire and plant invasion act as independent, additive processes, or whether applying fire in invaded areas results in novel effects on wildlife. We explore changes in abundance of three small mammal species in response to experimental fires set along a gradient of dominance by Lehmann lovegrass (Eragrostis lehmanniana), an African bunchgrass that has invaded semidesert grasslands of the southwestern USA. For two of three species of small mammals, the effect of fire on abundance varied with the degree of invasion, suggesting a fire x invasion interaction. In systems dominated by nonnative plants, fire can function differently than it did prior to invasion, especially for animals with habitat requirements that match conditions created by the invading plant species. Consequently, prescriptions for restoration fires will need to consider the novel effects of fires on native plants and animals in areas where the plant community has changed.
• Zylstra, E. R., & Steidl, R. J. (2009). Habitat use by sonoran desert tortoises. Journal of Wildlife Management, 73(5), 747-754.
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  Abstract: The distribution of desert tortoises (Gopherus agassizii) spans a wide range of biotic and abiotic conditions in the southwestern United States and northwestern Mexico, with physical and behavioral differences distinguishing tortoises inhabiting the Mojave Desert from those inhabiting the Sonoran Desert. Relative to tortoise populations in the Mojave Desert, populations in the Sonoran Desert have not been well-studied. To assess how habitat use of desert tortoises in the Sonoran Desert was influenced by topography, vegetation, geomorphology, and soil, we surveyed 40 randomly located 3-ha sites for presence of adult tortoises within a site-occupancy framework. We modeled both occupancy and detection probability as a function of environmental features, and compared those results with a logistic regression model that assumed detection probability was equal to 1. Results from both approaches agreed, suggesting that habitat selection of tortoises in the Sonoran Desert was influenced primarily by topographic and geomorphologic features rather than by vegetation. Specifically, tortoises were more likely to occupy sites that were steep (we detected tortoises on 29 of sites with mean slope 15°) and predominantly east-facing (53 of sites with 20 facing E), and less likely to occupy north-facing slopes (100 of sites with 60 facing N). Our results contrast with patterns of habitat use in the Mojave Desert where tortoises primarily occupy valley bottoms. Habitat use of tortoises in Sonoran and Mojave Desert populations differ considerably, contributing to the mounting body of evidence suggesting that these geographically distinct populations may represent separate species.
• Flesch, A. D., & Steidl, R. J. (2007). Detectability and response rates of ferruginous pygmy-owls. Journal of Wildlife Management, 71(3), 981-990.
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  Abstract: Survey techniques that are both reliable and efficient are necessary to accurately estimate population parameters, especially for rare species. Cactus ferruginous pygmy-owls (Glaucidium brasilianum cactorum; hereafter pygmy-owls) have declined in southwestern North America and are surveyed often to comply with federal law. We studied owl responses to broadcasted calls to quantify how detectability and response rates (owls/station/transect) vary with environmental, spatial, temporal, and weather-related factors. We surveyed owls along 392 transects (1,113 km) throughout Sonora, Mexico, including a subset of 14 transects (47.2 km) that we surveyed repeatedly to assess factors that affected response rates. We challenged 17 adults and 23 juveniles that were radiomarked, adults attending 50 occupied nests, and adults attending 6 groups of radiomarked juveniles to respond to broadcasted calls to assess factors that affected detectability. Across Sonora, response time averaged 2.6 ± 0.1 minutes (x̄ ± SE, n = 520), with 99 ± 0.4% of owls detected in
• Hall, D. H., & Steidl, R. J. (2007). Movements, activity, and spacing of Sonoran Mud Turtles (Kinosternon sonoriense) in interrupted mountain streams. Copeia, 403-412.
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  Abstract: We quantified movements, spacing, and activity of Sonoran Mud Turtles (Kinosternon sonoriense) in interrupted mountain streams of southern Arizona over an 18-year period using capture-recapture sampling and radiotelemetry. Movement and activity patterns of turtles depended on water availability and varied by their sex and size. Although considered almost entirely aquatic in Arizona, mud turtles estivated terrestrially during periods of extreme drought. After the onset of summer rains, turtles increased the frequency with which they moved between pools and to nesting sites. Movements (average distance moved [AvD] ± SE) of all turtles were shorter during drought years (males = 26 ± 1.3 m, females = 19 ± 1.3 m) than non-drought years (males = 153 ± 1.2 m; females = 41 ± 1.2 m). Adult male turtles made longer movements (93 ± 1.2) and had longer home-range lengths (206 ± 1.2 m) than did adult females (AvD = 38 ± 1.2; home range = 40 ± 1.2 m). Younger adult females (carapace length [CL] 100-118 mm) made longer movements (52 ± 1.2 m) and had longer home ranges (80 ± 1.9 m) than did older females (>118 CL mm; AvD = 38 ± 1.2 m; home range = 26 ± 2.2 m). Males made movements >500 m more frequently (8%) than females (2%) and moved as far as 7.2 km as measured along drainage bottoms. Large turtles used pools exclusively, only rarely sharing pools with other large individuals of the same sex. Degradation and losses of interior wetlands in the southwestern U.S. have reduced the potential for long-distance movements of turtles among disjunct, remnant populations, which has consequences for conservation of turtles and other aquatic species in the region. © 2007 by the American Society of Ichthyologists and Herpetologists.
• Steidl, R. J. (2007). Limits of data analysis in scientific inference: Reply to Sleep et al.. Journal of Wildlife Management, 71(7), 2122-2124.
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  Abstract: Statistical inference is an important element of science, but these inferences are constrained within the framework established by the objectives and design of a study. The choice of approach to data analysis, while important, has far less consequence on scientific inference than claimed by Sleep et al. (2007). Their principal assertion - that when model selection is used as the approach to data analysis, all studies provide a reliable foundation for distinguishing among mechanistic explanatory hypotheses - is incorrect and encourages faulty inferences. Sleep et al. (2007) overlook the critical distinction between inferences that result from studies designed a priori to discriminate among a set of candidate explanations versus inferences that result from exploring data post hoc from studies designed originally to meet pattern-based objectives. No approach to data analysis, including model selection, has the power to overcome fundamental limitations on inferences imposed by study design. The comments by Sleep et al. (2007) reinforce the need for scientists to understand clearly the inferential basis for their scientific claims, including the roles and limitations of data analysis.
• Flesch, A. D., & Steidl, R. J. (2006). Population trends and implications for monitoring cactus ferruginous pygmy owls in Northern Mexico. Journal of Wildlife Management, 70(3), 867-871.
• Steidl, R. J. (2006). Model selection, hypothesis testing, and risks of condemning analytical tools. Journal of Wildlife Management, 70(6), 1497-1498.
• Ober, H. K., Steidl, R. J., & Dalton, V. M. (2005). Resource and spatial-use patterns of an endangered vertebrate pollinator, the lesser long-nosed bat. Journal of Wildlife Management, 69(4), 1615-1622.
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  Abstract: Understanding how the distribution and abundance of food resources influence space use of organisms is an important element of successful conservation and recovery strategies for endangered species. We investigated interrelationships between space use, activity patterns, and food resources for lesser long-nosed bats (Leptonycteris curasoae), an endangered nectar-feeding bat, during an energetically demanding phase of its annual life cycle. We estimated the size of home ranges (95% kernel areas) and core use-areas (50% kernel areas) of bats and estimated density of their forage plant (Agave palmeri) in and near these use areas. Density (x- ± SE plants/ha) of flowering agaves within home ranges (3.6 ± 1.04) exceeded that which was available on the landscape (1.8 ± 0.36), indicating that bats selected areas with high food abundance. Although density of agaves within home ranges of bats differed in successive years (1998: 3.6 ± 1.04; 1999: 0.8 ± 0.15), sizes of home ranges and core use-areas of adult bats were similar between years, suggesting that the relationship between home-range size and density of food resources was mediated by other factors. Differences in activity budgets of bats between years suggest that bats altered their behavior in response to changes in food abundance, allocating more time to foraging the year fewer flowering plants were present. Consequently, reductions in agave density could increase energy demands of foraging bats and reduce the chances of successful recovery of lesser long-nosed bat populations.
• Ober, H. K., & Steidl, R. J. (2004). Foraging rates of Leptonycteris curasoae vary with characteristics of Agave palmeri. Southwestern Naturalist, 49(1), 68-74.
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  Abstract: We examined factors influencing foraging behavior of lesser long-nosed bats, Leptonycteris curasoae, in southeastern Arizona. When L. curasoae are present in this region, their diet is restricted to nectar and pollen from 1 species, Agave palmeri, which has heightened conservation concerns for the plant as forage for this endangered bat. We found that visitation rates of L. curasoae to individual A. palmeri near a roost were high (mean = 273 ± 17 visits per plant per hour) and varied with the spatial distribution and morphological characteristics of individual plants. Specifically, visitation rates varied with time of night, distance and orientation from the bat roost, and number and relative vertical position of flowers along the inflorescence. We suggest that both spatial distribution and temporal variation in flowering chronology be considered when developing strategies to manage A. palmeri to support L. curasoae.
• C., E., & Steidl, R. J. (2003). Experimental effects of hiking on breeding Mexican spotted owls. Conservation Biology, 17(1), 307-315.
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  Abstract: On the Colorado Plateau, some environments occupied by Mexican Spotted Owls (Strix occidentalis lucida) receive a great deal of recreational use. To assess the effects of hikers on breeding owls, we quantified changes in the activity budgets of owls at nests in response to a controlled amount of hiking in canyons of southern Utah in 1997 and 1998. We examined differences in the duration and frequency of eight behaviors as well as in the type and frequency of owl vocalizations between hiking and control treatments. In general, activity budgets of owls did not change markedly when hikers were near nests, although during hiking treatments, females decreased the amount of time they handled prey by 57% and decreased the amount of time they performed daytime maintenance behaviors by 30%. Further, hikers caused both females and males to increase the frequency of contact vocalizations by 58% and 534%, respectively. The order in which we applied treatments at nests (control-hiking or hiking-control) also influenced owl responses to hiking treatments, suggesting that observers near nests may have affected owl behavior. We concluded that the cumulative effects of high levels of short-duration recreational hiking near nests may be detrimental to Mexican Spotted Owls. Given current levels of visitation rates to most remote canyons occupied by owls, however, owl populations on the Colorado Plateau are not likely threatened by hiking. Notable exceptions are those canyons that receive use by ≥50 hikers per day. We recommend monitoring of owl occupancy, nest success, and hiking intensity in these high-use canyons.
• Mann, S. L., Steidl, R. J., & Dalton, V. M. (2002). Effects of cave tours on breeding Myotis velifer. Journal of Wildlife Management, 66(3), 618-624.
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  Abstract: Human activity in caves can affect bats adversely, especially bats that assemble in maternity colonies where appropriate roosts are restricted to areas with a narrow range of microclimates necessary to raise young. We assessed behavioral responses of a maternity colony of about 1,000 cave myotis (Myotis velifer) to experimental cave tours by manipulating 3 factors: size of tour groups, whether tour groups talked, and a combination of light intensity and color used to illuminate trails. We also considered the effects of distances between bat roosts and the tour group as well as season. We measured 4 behavioral responses of bats: number of takeoffs, number of landings, activity level, and vocalization intensity. Light intensity affected bat behavior most; all bat responses were highest in trials with high-intensity white light and lowest in trials with no light. When tour groups talked, takeoffs, landings, and activity level increased. Size of tour groups and treatment interactions did not affect bat behaviors. When bats roosted near the tour route, takeoffs and activity level increased. In addition, all behavioral responses increased as the maternity season progressed. Designing cave tours to minimize short-term effects on bats will require careful consideration of cave lighting and tour frequency, route location, and noise levels.
• Powell, B. F., & Steidl, R. J. (2002). Habitat selection by riparian songbirds breeding in southern Arizona. Journal of Wildlife Management, 66(4), 1096-1103.
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  Abstract: Identifying habitat characteristics that influence selection of nest sites can provide information necessary for understanding and managing songbird populations. We quantified patterns of nest-site selection of 7 species in a riparian songbird community (n = 162 nests) at 2 spatial scales in southeastern Arizona, USA: Bell's vireo (Vireo bellii), verdin (Auriparus flaviceps), phainopepla (Phainopepla nitens), summer tanager (Piranga rubra), northern cardinal (Cardinalis cardinalis), blue grosbeak (Guiraca caerulea), and hooded oriole (Icterus cucullatus). We compared vegetation characteristics at nests to points chosen at random both near each nest (nest-patch scale) and within the entire study area (canyon scale). At the nest-patch scale, riparian vegetation - particularly Arizona sycamore (Platanus wrightii) and netleaf hackberry (Celtis reticulata) - was selected strongly by most species. At the canyon scale, most species nested in areas with higher vegetation density and volume than available at random. Managing riparian areas to foster high vegetation density and key structural components, such as sycamore and hackberry trees, is essential for meeting the habitat requirements necessary to maintain abundant and diverse songbird communities in the arid southwestern United States and adjacent Mexico.
• Swarthout, E. C., & Steidl, R. J. (2001). Flush responses of Mexican spotted owls to recreationists. Journal of Wildlife Management, 65(2), 312-317.
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  Abstract: Mexican spotted owls (Strix occidentalis lucida) occupy narrow canyons on the Colorado Plateau, some of which are subject to high levels of recreational activity. These activities represent a potential threat to owls, yet due to the confines of canyon walls, spatial restrictions on recreational activities would likely eliminate all activity within these canyons. We assessed factors that influenced flush responses (flush or no flush), flush distances, distances of avoidance flights, and behavioral changes of owls in response to a single hiker that approached roosting owls. Increased perch height decreased the likelihood that adults (odds ratio = 0.09) and juveniles (odds ratio = 0.17) would flush in response to the presence of a hiker; having flushed previously the same day increased the likelihood of adults flushing on subsequent approaches (odds ratio = 6.83). Juveniles and adults were unlikely to flush at distances ≥12 m and ≥24 m from hikers, respectively, and neither age class was likely to alter its behavior in response to the presence of a hiker at distances ≥55 m. Based on these response thresholds, placing a 55-m buffer zone around roosting sites would eliminate virtually all behavioral responses of owls to hikers, but would restrict hiker access to 80% of canyons occupied by owls. A less conservative 12-m buffer zone would eliminate 95% of juvenile and 80% of adult flush responses, and restrict hiker access to 25% of canyons occupied by owls.
• Tull, J. C., Krausman, P. R., & Steidl, R. J. (2001). Bed-site selection by desert mule deer in Southern Arizona. Southwestern Naturalist, 46(3), 354-357.
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  Abstract: We compared bed sites selected by desert mule deer (Odocoileus hemionus eremicus) to nearby random sites to assess bed site features. Thermal cover of bed sites (i.e., vegetation ≥75 cm high that provided shade for a deer) was highest in summer (X̄ = 43.7% ± 4.1 SE) compared to spring (29.7% ± 4.4), winter (33.5% ± 3.1), and autumn (39.8% ± 4.0); however, selection for bed sites with thermal cover that differed most from that available randomly was highest in spring (X̄ difference between bed and random sites = 14.8% ± 5.2) compared to summer (8.3% ± 4.1), winter (6.6% ± 3.5), and autumn (8.6% ± 3.5). Thermal cover is likely important as a contribution to thermoregulation, escape cover, protection of fawns, and fawn survival.
• Powell, B. F., & Steidl, R. J. (2000). Nesting habitat and reproductive success of southwestern riparian birds. Condor, 102(4), 823-831.
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  Abstract: Vegetation structure and floristic composition strongly influence the structure of bird communities. To assess the influence of vegetation and other environmental characteristics on songbirds, we quantified nest-site characteristics and reproductive success of a riparian songbird community in Arizona. Although we found interspecific variation in characteristics associated with nest sites, we identified two suites of species that chose sites with similar characteristics. These 'nest groups' were explained largely by nest height and characteristics of nest trees. Overall, nest success was low for songbirds in this community, and averaged 23%. The most common cause of nest failure was predation (81%), although brood parasitism by Brown-headed Cowbirds (Molothrus ater) was highest at nests of Bell's Vireos (Vireo bellii) (29%). No vegetation or environmental features were associated with the likelihood of cowbird parasitism for any species; nest success for Bell's Vireos was negatively associated with the amount of netleaf hackberry (Celtis reticulata) in the understory. Arizona sycamore (Platanus wrightii) and netleaf hackberry trees contained 41% and 17% of all nests, respectively, and therefore provide critically important nesting substrates for birds in this rare yet diverse vegetation community.
• Steidl, R. J., & Anthony, R. G. (2000). Experimental effects of human activity on breeding bald eagles. Ecological Applications, 10(1), 258-268.
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  Abstract: To assess the consequences of increased recreational activity in wilderness areas, we studied the effects of human activity on breeding behavior of Bald Eagles (Haliaeetus leucocephalus) in interior Alaska. Activity budgets of breeding eagles changed considerably when humans were camped for 24 h at a distance of 100 m from nests (treatment) compared to when they were camped 500 m from nests (control) (P = 0.0036). With humans near nests, adult eagles decreased the time they preened (percentage change from control to treatment = -53%), slept (-56%), maintained nests (-50%), and fed themselves and their nestlings (-30%) and increased the time they brooded nestlings (+14%). Further, overall activity (total number of behaviors performed by adults at nests per day) decreased by 27% with humans near nests, as did the amount of prey adults consumed (-26%) and fed to nestlings (-29%). In contrast, nest attendance did not change with humans near nests (percentage change = 0.3%, P = 0.9); however, the time adults were absent from the nest area (≥200 m from nests) increased by 24% with humans near nests (P = 0.013). Throughout 24-h treatments, eagle responses to nearby humans diminished, suggesting that eagles habituated to the disturbance. During the last 4 h of treatment, however, adults still vocalized twice as frequently as controls, indicating continued agitation. Human activity near nests caused clear and consistent changes in behaviors of breeding eagles, suggesting that frequent human activities near nests could adversely affect nestling survival, and therefore reproductive success.
• Daw, S. K., DeStefano, S., & Steidl, R. J. (1998). Does survey method bias the description of northern goshawk nest-site structure?. Journal of Wildlife Management, 62(4), 1379-1384.
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  Abstract: Past studies on the nesting habitat of northern goshawks (Accipiter gentilis) often relied on nests found opportunistically, either during timber-sale operations, by searching apparently 'good' goshawk habitat, or by other search methods where areas were preselected based on known forest conditions. Therefore, a bias in the characterization of habitat surrounding northern goshawk nest sites may exist toward late-forest structure (large trees, high canopy closure). This potential problem has confounded interpretation of data on nesting habitat of northern goshawks and added to uncertainty in the review process to consider the species for federal listing as threatened or endangered. Systematic survey methods, which strive for complete coverage of an area and often use broadcasts of conspecific calls, have been developed to overcome these potential biases, but no study has compared habitat characteristics around nests found opportunistically with those found systematically. We compared habitat characteristics in a 0.4-ha area around nests found systematically (n = 27) versus those found opportunistically (n = 22) on 3 national forests in eastern Oregon. We found that both density of large trees (systematic: x̄ = 16.4 ± 3.1 trees/ha; x̄ ± SE; opportunistic: x̄ = 21.3 ± 3.2; P = 0.56) and canopy closure (systematic: x̄ = 72 ± 2%; opportunistic: x̄ = 70 ± 2%; P = 0.61) were similar around nests found with either search method. Our results diminish concern that past survey methods mischaracterized northern goshawk nest-site structure. However, because northern goshawks nest in a variety of forest cover types with a wide range of structural characteristics, these results do not decrease the value of systematic survey methods in determining the most representative habitat descriptions for northern goshawks. Rigorous survey protocols allow repeatability and comparability of monitoring efforts and results over time.
• Steidl, R. J., Hayes, J. P., & Schauber, E. (1997). Statistical power analysis in wildlife research. Journal of Wildlife Management, 61(2), 270-279.
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  Abstract: Statistical power analysis can be used to increase the efficiency of research efforts and to clarify research results. Power analysis is most valuable in the design or planning phases of research efforts. Such prospective (a priori) power analyses can be used to guide research design and to estimate the number of samples necessary to achieve a high probability of detecting biologically significant effects. Retrospective (a posteriori) power analysis has been advocated as a method to increase information about hypothesis tests that were not rejected. However, estimating power for tests of null hypotheses that were not rejected with the effect size observed in the study is incorrect; these power estimates will always be ≤0.50 when bias adjusted and have no relation to true power. Therefore, retrospective power estimates based on the observed effect size for hypothesis tests that were not rejected are misleading; retrospective power estimates are only meaningful when based on effect sizes other than the observed effect size, such as those effect size hypothesized to be biologically significant. Retrospective power analysis can be used effectively to estimate the number of samples or effect size that would have been necessary for a completed study to have rejected a specific null hypothesis. Simply presenting confidence intervals can provide additional information about null hypotheses that were not rejected, including information about the size of the true effect and whether or not there is adequate evidence to 'accept' a null hypothesis as true. We suggest that (1) statistical power analyses be routinely incorporated into research planning efforts to increase their efficiency. (2) confidence intervals be used in lieu of retrospective power analyses for null hypotheses that were not rejected to assess the likely size of the true effect, (3) minimum biologically significant effect sizes be used for all power analyses, and (4) if retrospective power estimates are to be reported, then the β-level, effect sizes, and sample sizes used in calculation must also be reported.
• Steidl, R. J., Kozie, K. D., & Anthony, R. G. (1997). Reproductive success of bald eagles in interior Alaska. Journal of Wildlife Management, 61(4), 1313-1321.
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  Abstract: We compared productivity and nesting success of 2 adjacent populations of bald eagles (Haliaeetus leucocephalus) near the northern limits of their range in interior Alaska during 1989-94. Productivity (x̄ ± SE young fledged/occupied territory) and nesting success differed between populations; pairs in the Gulkana River basin had higher productivity (0.86 ± 0.05, n = 274) and nesting success (59%) than those in the Copper River basin (0.71 ± 0.04, 48%, n = 471; P < 0.02). Productivity varied both annually and spatially within each basin (P < 0.001). However, brood sizes of successful nests were identical for both basins (1.48 ± 0.03), suggesting that variability in productivity resulted largely from differences in nesting success. Patterns of variability in reproductive success within a territory also were similar for both populations. Pairs that were successful one year fledged more offspring, were more likely to be successful, were more likely to reoccupy the same territory, and were less likely to change nest locations the following year compared to pairs that were unsuccessful the previous year (P < 0.025 for all comparisons). Most nesting failure (92%) occurred during incubation when weather conditions tend to be most severe. However, reproductive success was not negatively correlated with severity of spring weather (temp or rainfall) or strongly correlated with prey abundance during brood rearing. We hypothesize that annual and spatial variability in reproductive success of these northern bald eagle populations may be associated with variation in prey availability, especially before and during incubation.
• Steidl, R. J., & Anthony, R. G. (1996). Responses of bald eagles to human activity during the summer in interior Alaska. Ecological Applications, 6(2), 482-491.
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  Abstract: Along narrow rivers, spatial restriction of human use based on wildlife responses can effectively eliminate the entire river corridor from human use. Therefore, if river use by both wildlife and humans is a goal, an alternative management strategy is necessary. We measured flush response rate and flush distance of breeding and nonbreeding Bald Eagles (Haliaeetus leucocephalus) to recreational boating along the Gulkana River in interior Alaska from 1989 to 1992. Eagle responses to our nonmotorized boat were governed by the context within which human-eagle encounters occurred. Flush response rate of nonbreeding eagles decreased as perch height and its distance from the river's edge increased, increased as the season progressed and as eagle group size increased, was lower for juveniles (20%) than other age classes (49-65%), and varied with the existing level of human activity in a geographic location (P < 0.001 for all parameters). Flush distance of nonbreeding eagles increased as the distance a disturbance was first visible to a perched eagle increased, as perch height and its distance from the river's edge increased, and as the season progressed. In contrast to flush response, flush distance was strongly associated with age and was greatest for adults, least for juveniles, and intermediate for subadults. Breeding adults were much less likely to flush than nonbreeding adults, and flushed at lesser distances. We recommend that along narrow wilderness rivers, the impacts of human activity on Bald Eagle populations be regulated with temporal, rather than spatial, restrictions.
• O'Neil, T., Steidl, R. J., Edge, W. D., & Csuti, B. (1995). Using wildlife communities to improve vegetation classification for conserving biodiversity. Conservation Biology, 9(6), 1482-1491.
• Steidl, R. J., Griffin, C. R., & Niles, L. J. (1991). Contaminant levels of osprey eggs and prey reflect regional differences in reproductive success. Journal of Wildlife Management, 55(4), 601-608.
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  Abstract: Compared levels of organochlorines, mercury and lead in Pandion haliaetus eggs and potential prey from Delaware Bay to a successful population along the Atlantic Coast (
• Steidl, R. J., Griffin, C. R., & Niles, L. J. (1991). Differential reproductive success of ospreys in New Jersey. Journal of Wildlife Management, 55(2), 266-272.
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  Abstract: Productivity of Pandion haliaetus along Delaware Bay was low because 50% of all nests initiated failed, whereas only 21% of Atlantic Coast nests failed. Only 50% of all eggs laid in the Bay colony hatched, compared to 69% in the Atlantic Coast colony. Nestling mortality was similar between colonies (26 vs. 18% for Delaware Bay and Atlantic Coast, respectively) but 21% of those young hatched near the Bay were probably preyed upon by great horned owls Bubo virginianus. Although Delaware Bay ospreys spent considerably more time away from their nests, presumably foraging, adults from both colonies spent similar amounts of time feeding young, which suggests that food stress did not influence productivity. High frequency of unhatched eggs and thinner eggshells (8% below pre-DDT levels vs. 3% for Atlantic Coast eggs) of ospreys along Delaware Bay suggests possible exposure to environmental contaminants that may reduce hatching success. -from Authors
• Steidl, R. J., Griffin, C. R., Niles, L. J., & Clark, K. E. (1991). Reproductive success and eggshell thinning of a reestablished peregrine falcon population. Journal of Wildlife Management, 55(2), 294-299.
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  Abstract: Examined numbers of Falco peregrinus pairs, reproductive success, and eggshell thinning in New Jersey during 1979-88. Productivity of these falcons (mean 1.38 young fledged/pair) was comparable with that of stable populations, but productivity was lower for pairs near Delaware Bay and River (0.58 young/pair) compared to those in other regions of New Jersey (1.55 young/pair). Lower productivity and nest success of 4 pairs near Delaware Bay and River studied in both 1987 and 1988 were due to low hatching success and predation, probably by great horned owls Bubo virginianus. During 1985-88 eggshell thickness from New Jersey peregrines averaged 16.4% below pre-DDT levels and apparently has decreased steadily since 1979. This decrease in eggshell thickness statewide suggests that falcons continue to be exposed to environmental contaminants. -from Authors

Presentations

• Smalls, Z., Howery, L. D., Tuttle, S., Ruyle, G. B., & Steidl, R. J. (2018, January). Effects of Time-controlled Livestock Grazing on Habitat of Southwestern Willow Flycatchers in West-central Arizona. The International Society for Range Management ConferenceThe Society for Range Management.
• Zylstra, E. R., Mannan, R. W., & Steidl, R. J. (2018, November). Density dependent effects on survival in an urban-nesting population of Cooper’s hawks. Annual Meeting of the Raptor Research Foundation. Kruger National Park, South Africa: Raptor Research Foundation.
• Zylstra, E. R., Swann, D. E., & Steidl, R. J. (2018, May). Drought governs metapopulation dynamics of lowland leopard frogs in the Sky Island region. Biodiversity and Management of the Madrean Archipelago IV. Tucson, AZ: Sky Island Alliance.
• Zylstra, E. R., Swann, D. E., & Steidl, R. J. (2018, October). Drought governs extinction of an arid-land amphibian: insights from a spatially explicit occupancy model. The Wildlife Society Annual Conference. Cleveland, Ohio: The Wildlife Society.
• Smalls, Z., Howery, L. D., Ruyle, G. B., Steidl, R. J., & Tuttle, S. (2017, October). Effects of Time-controlled Livestock Grazing on Habitat of Southwestern Willow Flycatchers in West-central Arizona. The Wildlife Society Annual Conference. Albuquerque,NM.
• Tuttle, S., Smalls, Z., Ruyle, G. B., Howery, L. D., Andersen, E., & Steidl, R. J. (2017, October). Ensuring habitat for southwestern willow flycatchers through sustainable grazing. The Wildlife Society Annual Conference, Albuquerque, NM. Albuquerque, NM.
• Tuttle, S., Steidl, R. J., Ruyle, G. B., Howery, L. D., & Smalls, Z. (2017, January). Effects of Time-controlled Livestock Grazing on Habitat of Southwestern Willow Flycatchers in West-central Arizona. The International Society for Range Management Conference, St. George, UT. St. George, UT: The Society for Range Management.
• Tuttle, S., Steidl, R. J., Ruyle, G. B., Howery, L. D., & Smalls, Z. (2017, January). Effects of Time-controlled Livestock Grazing on Habitat of Southwestern Willow Flycatchers in West-central Arizona. The International Society for Range Management ConferenceThe Society for Range Management.
• Tuttle, S., Steidl, R. J., Ruyle, G. B., Howery, L. D., & Smalls, Z. (2017, October). Effects of Time-controlled Livestock Grazing on Habitat of Southwestern Willow Flycatchers in West-central Arizona. The Wildlife Society Annual Conference, Albuquerque, NM. Albuquerque, NM.
• Tuttle, S., Steidl, R. J., Smalls, Z., Andersen, E., Howery, L. D., Ruyle, G. B., Ruyle, G. B., Howery, L. D., Andersen, E., Smalls, Z., Tuttle, S., & Steidl, R. J. (2017, October). Ensuring habitat for southwestern willow flycatchers through sustainable grazing. The Wildlife Society Annual Conference. Albuquerque,NM.
• Andersen, E. M., & Steidl, R. J. (2016, August). Effects of nonnative grasses on density and nest success of birds in desert grasslands. Science on the Sonoita Plain.
• Steidl, R. J., Griffin, D. J., Howery, L. D., Ruyle, G. B., Smalls, Z., & Tuttle, S. (2016, October). Ensuring habitat for southwestern willow flycatchers through sustainable grazing. The Wildlife Society Annual Conference. Raleigh, NC: The Wildilife Society; Raleigh, North Carolina; October 18, 2016.
• Tuttle, S., Smalls, Z., Ruyle, G. B., Howery, L. D., Griffin, D. J., Steidl, R. J., Tuttle, S., Smalls, Z., Ruyle, G. B., Howery, L. D., Griffin, D. J., & Steidl, R. J. (2016, October). Ensuring habitat for southwestern willow flycatchers through sustainable grazing. The Wildlife Society Annual Conference, Raleigh, NC. Raleigh, NC: The Wildilife Society; Raleigh, North Carolina; October 18, 2016.
• Zylstra, E. R., Steidl, R. J., Swann, D. E., & Hossack, B. R. (2016, July). Population dynamics and dispersal of canyon treefrogs in desert mountain canyons. Joint Meeting of Ichthyologists and Herpetologists. New Orleans, LA.
• Zylstra, E. R., Steidl, R. J., Swann, D. E., & Hossack, B. R. (2016, October). Population dynamics and dispersal of canyon treefrogs in desert mountain canyons. The Wildlife Society Annual Conference. Raleigh, NC.
• Schmidt, C. A., Steidl, R. J., & Chambers, C. (2014, Spring). Habitat use by bats and radon concentrations in uranium mines. Joint Annual Meeting of the AZ-NM Chapters of The Wildlife Society. Phoenix, AZ: TWS.
• Steidl, R. J. (2014, October). Functional Shifts in Ecological Drivers in Grassland Ecosystems. Research Insights in Semiarid Ecosystems.
• Litt, A. R., & Steidl, R. J. (2013, Oct). Restoration in light of ecological changes: Complex consequences for wildlife populations and communities.. World Conference on Ecological Restoration. Madison, WI: Society for Ecological Restoration.
• Campbell, S. P., & Steidl, R. J. (2012, Aug). A spatially-explicit population viability analysis for the desert tortoise. Ecological Society of America Annual Meeting. Portland, OR: Ecological Society of America.
• Campbell, S. P., & Steidl, R. J. (2012, Spring). A spatially-explicit population viability analysis for the desert tortoise. Joint Annual Meeting of the AZ-NM Chapters of The Wildlife Society. Phoenix, AZ: TWS.
• Gray, K. M., & Steidl, R. J. (2012, Fall). Effects of buffelgrass (Pennisetum ciliare) on Sonoran desert tortoises (Gopherus agassizii). 10th Annual Symposium on the Conservation and Biology of Tortoises and Freshwater Turtles. Tucson, AZ.
• Gray, K. M., & Steidl, R. J. (2012, Spring). Effects of a nonnative grass on condition of Sonoran desert tortoises. 37th Annual Meeting and Symposium of The Desert Tortoise Council. Las Vegas, NV.
• Gray, K. M., & Steidl, R. J. (2012, Spring). Effects of buffelgrass on habitat use of Sonoran desert tortoise. Biodiversity & Management of the Madrean Archipelago III. Tucson, AZ.
• Gray, K. M., & Steidl, R. J. (2012, Summer). Effects of a nonnative grass on condition of Sonoran desert tortoises. Joint Annual Meeting of the AZ-NM Chapters of The Wildlife Society. Phoenix, AZ: TWS.
• Steidl, R. J. (2012). Effects of grasslands restoration efforts on birds in southern Arizona. Science on the Sonoita Plains. Elgin, AZ: Science on the Sonoita Plains.
• Steidl, R. J., & Campbell, S. (2012, September). A spatially-explicit population viability analysis for the desert tortoise. Annual meeting of the Ecological Society of America. Portland, OR: Ecological Society of America.
• Steidl, R. J., & Powell, B. F. (2012, Spring). Habitat characteristics of montane riparian bird communities in southern Arizona. Biodiversity & Management of the Madrean Archipelago III. Tucson, AZ.
• Zylstra, E. R., & Steidl, R. J. (2012, Spring). Drought decreases survival of Sonoran desert tortoises. Biodiversity & Management of the Madrean Archipelago III. Tucson, AZ.
• Steidl, R. J. (2011). Effects of grasslands restoration efforts on birds in southern Arizona. NLCS Science Symposium: A Decade of Discovery. Albuquerque, NM: NLCS Science Symposium.
• Steidl, R. J. (2011, June). Responses of songbirds to restoration of shrub-invaded grasslands. Science on the Sonoita Plains.
• Steidl, R. J., & Wolf, S. (2011, February). Effect of near-infrared light on foraging behavior of nectarivorous bats. Annual meeting of the AZ/NM chapters of The Wildlife Society, Albuquerque, NM.
• Steidl, R. J., & Zylstra, E. (2011, September). Survival rates of Sonoran Desert tortoises in Arizona. Annual meeting of the Desert Tortoise Council. Las Vegas, NV: Desert Tortoise Council.