Reproductive Ecology of Ospreys and Peregrine Falcons

Because ospreys (Pandion haliaetus) nesting along Delaware Bay have retained low productivity and little population growth since the mid-1970s, during 1987 and 1988 we compared reproductive dynamics of Bay ospreys with a recovering colony nesting along the Atlantic Coast. Productivity of Delaware Bay ospreys remains low because 48% of nests initiated along the Bay failed, compared to only 23% of nests along the Atlantic Coast. Only 49% of eggs laid in the Bay colony hatched, compared to 66% along the Atlantic, and 25% of those young successfully hatched near the Bay were preyed upon by great horned owls (Bubo virginianus). Higher frequence of unhatched eggs and thinner eggshells indicate that Bay ospreys may still be affected by environmental contaminants present in the Delaware estuary. Many factors may affect differential rates of growth within a species, including food supply, weather, and parental ability. We examined growth rate and brood reduction of ospreys nesting in an area supporting abundant, available prey along the Mid-Atlantic Coast. Growth of ospreys from this area was best explained by a logistic growth curve (k = 0.173). We found little difference in growth related to year, clutch size, and brood reduction, although brood reduction occurred most often in larger broods, probably because of large disparities in within-brood size of nestlings. We believe large geographic differences in osprey growth are a function of food availability, while smaller differences -- reflected in brood reduction -- may be a function of a male\u27s age, experience, or ability to supply food. Reestablishment of peregrine falcons (Falco peregrinus) as breeding birds in the eastern United States has been a highlight in endangered species management and recovery. To assess this reestablished population in New Jersey, we examined numbers, reproductive success, and eggshell thinning of peregrines during 1979-1988. From several pairs studied intensively during 1987 and 1988, we describe regional differences in reproductive success, nestling behaviors, and prey of these falcons. Although productivity compares favorably with stable populations, eggshells of New Jersey peregrines are thinning with time. This decrease in statewide-eggshell thinning and low hatching success of eggs along Delaware Bay indicates continued exposure to environmental contaminants, probably from their migratory prey

Flush responses of Mexican spotted owls to recreationists

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 = O. I 7) 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

Woody plant encroachment restructures bird communities in semiarid grasslands

The abundance and distribution of woody plants have increased in grassland ecosystems worldwide. Robust generalizations about the consequences of this transformative process on animal communities have been elusive, especially in semiarid regions where populations of many species have declined. We evaluated how distributions and species richness of breeding birds responded to woody plant encroachment by using spatial variation in woody cover as a proxy for the temporal process by which grasslands transform into shrub savannas. Specifically, we surveyed breeding birds and vegetation on 140 10-ha plots in semiarid grasslands that spanned the gradient of cover by Prosopis (mesquite), a genus of shrubs that has proliferated in semiarid grasslands worldwide. We used a multispecies occupancy model to characterize distributions of breeding bird species along the encroachment gradient. Distributions of 29 of 35 species changed markedly in response to encroachment, with distributions of most obligate grassland species contracting and most facultative grassland species expanding. Species richness increased sharply as cover of woody plants increased and peaked at ∼22% cover; this increase was driven by recruitment of generalist and shrub-associated species, many of which are common at regional scales. Lastly, we identified thresholds of woody cover where distributions contracted or expanded markedly, which provide targets for conservation and restoration efforts. Our results highlight the importance of understanding species-specific responses to woody plant encroachment as the basis for explaining community-level patterns because increases in diversity at local scales might ultimately reduce diversity at broader scales as grassland specialists are displaced.24 month embargo; published online: 14 November 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Plant invasions alter settlement patterns of breeding grassland birds

Animals have evolved strategies to identify areas that provide the resources and environmental conditions they need to survive and reproduce. To explore how invasions by nonnative plants might disrupt this fundamental process, we evaluated settlement patterns of migratory birds that breed in grasslands being invaded by two structurally different congeneric grasses. We established 40, 2.25-ha plots across an area where the composition of each nonnative grass ranged from 0% to nearly 100% of total grass cover, which provided individuals with the full range of alternatives in species composition. We then used the temporal sequence by which birds established territories to infer their habitat preferences. We evaluated responses of the most common species that settled the area, two confamilial sparrows that differed markedly in habitat breadth. The species with narrower habitat breadth, the grasshopper sparrow (Ammodramus savannarum ammolegus), first established territories in areas dominated by native grasses, where grass height and cover were substantially lower than in areas dominated by the nonnative grasses. As the settlement period progressed, they increasingly established territories in areas dominated by the smaller nonnative grass (Eragrostis lehmanniana), but never established territories in areas dominated by the larger grass (E. curvula). In contrast, the species with broader habitat breadth, the Botteri's sparrow (Peucaea botterii arizonae), established territories without regard to grass composition, likely because both nonnative grasses were within the structural range of native grasses used by this grassland generalist. Our results demonstrate that in areas invaded by nonnative plants, changes in habitat use by animals can reflect the interaction between their habitat breadth and the amount of structural contrast between invading plants and the native plant species that are displaced. This interaction provides a mechanism to explain the variation in responses among species to invasions by nonnative plants, which has consequences for broad-scale changes in the geographic distribution of many species.U.S. Bureau of Land ManagementOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Simulation process for ‘Power to detect trends in abundance within a distance sampling framework’ (Journal of Applied Ecology)

Description of simulation process for Andersen and Steidl (J. Applied Ecology

A Bayesian state-space model for seasonal growth of terrestrial vertebrates

The rate of somatic growth determines when individuals transition between life stages, which along with survival and reproduction, are principal factors governing the rate of population change. For short-lived species that inhabit seasonally dynamic environments, accounting for fluctuations in somatic growth is necessary to make reliable inferences about population dynamics. We describe a Bayesian, state-space formulation of a von Bertalanffy growth model that integrates a sinusoidal model to allow for seasonal fluctuations in growth while also accounting for individual heterogeneity and measurement error. We use this model to describe post-metamorphic growth of canyon treefrogs, Hyla arenicolor, based on capture-recapture data from 404 individuals over a two-year period. For simulated data where we assumed growth varies seasonally, our model provides unbiased estimates of growth rate, mean asymptotic length, standard deviation of individual asymptotic lengths, and date of maximum growth. For field data from canyon treefrogs, we found strong evidence of seasonal variation in growth, with maximum growth during the summer monsoon season. Growth rate of females was 19 % lower than males, although on average, females reached asymptotic lengths that were 15 % greater than males. Ignoring systematic Intra-annual variation in growth can bias inferences about population dynamics, particularly for fast-growing species that reproduce more than once per year or inhabit environments with strong seasonal signals. We present a straightforward approach for using repeated length measurements from individuals of unknown age to estimate growth while accounting for seasonality and individual heterogeneity, which are sources of variation common in many vertebrate populations.24 month embargo; published online: 12 February 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

HUMAN ACTIVITIES THAT AFFECT WILDLIFE AND THEIR HABITATS are pervasive and increasing.

Effects of these activities are manifested at all ecological scales, from short-term changes in the behavior of an individual animal through local extirpations and global extinctions (Pimm et al. 1995; Chapin et al. 2000). Consequently, understanding the effects of humans on wildlife and wildlife populations, as well as devising strategies to ameliorate these effects, is an increasing challenge for resource managers. Given the conflicting mandate to both encourage human use and to protect sensitive natural resources in national parks, developing reliable strategies for assessing and monitoring the effects of human activities on natural resources is essential to ensuring appropriate stewardship of these resources. Given the breadth of relevant human activities, the diversity of wildlife species potentially affected, and the multitude of ways they may be affected, scientists and resource managers planning to assess the effects of human activities on wildlife must wildlife interactions, be careful to state their study objective

Data from "Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival"

Avian point count, nest monitoring data, and associated vegetation data for the article 'Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival' published in Ornithological Applications, 2022. For inquiries regarding the contents of this dataset, please contact the Corresponding Author listed in the README.txt file. Administrative inquiries (e.g., removal requests, trouble downloading, etc.) can be directed to [email protected]</p

Effects of Cave Tours on Breeding Myotis velifer

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

Responses of grassland arthropods to an invasion by nonnative grasses

In grassland ecosystems, invasions by nonnative grasses typically decrease floristic diversity and structural heterogeneity in ways that alter the quantity and quality of habitat for animals. Grassland arthropods that rely directly on herbaceous plants for food, shelter, or as substrates for reproduction are especially vulnerable to these invasions because many have evolved specialized relationships with host plants that might be displaced. We evaluated how invasions by nonnative grasses affected abundance and richness of foliage-dwelling arthropods in semidesert grasslands of Arizona, USA. On 90, 3.1-ha plots established along a gradient of invasion where dominance of nonnative grasses ranged from 0 to nearly 100% of grass cover, we captured >90,000 arthropods from 11 orders during 270 surveys in 2014 and 2015. Although the invasion by nonnative grasses (primarily Eragrostis lehmanniana and secondarily E. curvula) increased the amount of herbaceous foliage available to arthropods, richness of arthropods decreased by an average of 2% and total abundance by an average of 7% for every 10% increase in nonnative-grass dominance. Responses to the plant invasion, however, varied among taxa and functional groups. As dominance of nonnative grasses increased, abundances of most predators and specialist herbivores decreased, whereas abundances of most generalist herbivores were lowest at intermediate points of the invasion gradient. The changes we observed in the arthropod community have potential to alter broad-scale ecological processes, including energy flow and nutrient cycling, and to reduce food resources for insectivores, which can have adverse, cascading effects on imperiled grassland ecosystems.U.S. Bureau of Land Management; Arizona Game and Fish Department's Heritage Program; Audubon through an Apacheria Fellowship12 month embargo; published online: 3 September 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]