Scott H. Stoleson

Hatching Asynchrony and the Onset of Incubation in Birds, Revisited

In most animals, offspring from a reproductive bout usually hatch, emerge, or are born within a relatively short time of each other compared to the time required for their development. Thus, hatching or birthing in most animals is synchronous. This is especially likely to be true for animals with internal fertilization and development, where the birth of alll offspring occurs simultaneously (e.g., some fihes, snakes, and most mammals). Synchronous reproduction also occurs in animals with external fertilization or development when all zygotes are subject to the same environmental conditions (e.g., many insects, anurans, and fishes). Thus, in most the behavior of parents has little effect on the time between the emergence of their first and last young.

SURVIVAL RATES OF A NEOTROPICAL PARROT: IMPLICATIONS FOR LATITUDINAL COMPARISONS OF AVIAN DEMOGRAPHY

Latitudinal variation in avian demography played an important early role in the development of life history theory, especially in the idea of a cost of reproduction. Recent attempts to determine the survivorship of tropical birds with mark-recapture sta- tistics have proved controversial. Here, we use a small neotropical bird, the Green-rumped Parrotlet (Forpus passerinus), as a model system for investigating sources of heterogeneity that might bias interspecific comparisons. Mark-resighting data were collected on 1334 adult parrotlets over a decade. We expected adult survival to be low because this parrot lays a large clutch (mean 5 7 eggs), is a cavity nester, and breeds in a highly seasonal environment. A two-age-class term in local survival was nonsignificant, indicating that an age or transience effect was unimportant. Local survival of males did not vary annually, but 19.3% of the yearly variation in female survival was explained by rates of nest loss during stages when females were incubating or brooding young. The overall local survival rate of parrotlets ( f5 0.565) was identical to temperate hole-nesting species of the same body size but was lower than that of tropical birds that lay smaller clutches. However, we also detected considerable heterogeneity in parrotlet survival. Females and males that were sighted but did not breed comprised a mean 23.5% and 52.9% of our population, respec- tively. Using multistate models, we found that breeders had significantly higher probabilities of local survival ( f5 0.678 vs. 0.486), of retaining their status as breeders ( c5 0.719 vs. 0.279), and of detection ( p 5 0.997 vs. 0.375) than did nonbreeders. Overall, males and females had comparable local survival rates (breeders f5 0.698 vs. 0.658, nonbreeders f5 0.536 vs. 0.436). Our estimates of local survival could be affected by breeding dispersal, but site fidelity of parrotlets was strong: 95% of adults moved ,500 m in consecutive years. A literature review for tropical birds showed that mark-resighting studies usually report return rates based on resightings of breeding or territorial adults, whereas mist net studies rely on recaptures and pool birds of different age and social status in their calcu- lations of local survival. Future studies should attempt to compare subsets of avian pop- ulations that are similar in demography. Because rates of site fidelity and social system may differ among species, these factors must also be considered in interspecific comparisons of avian life histories.

Prescribing regeneration treatments for mixed-oak forests in the Mid-Atlantic region

Includes guidelines for using the SILVAH decision-support system to perpetuate oak forests in the Mid-Atlantic region. Six chapters provide information on values of oak forests, inventory methods, key decision variables, decision charts, and silvicultural prescriptions, as well as guidance on fostering young stands. Sample tally sheets and SILVAH computer printouts are included in the Appendix.

Legacy of top‐down herbivore pressure ricochets back up multiple trophic levels in forest canopies over 30 years

Removal of top-down control on herbivores can result in a trophic cascade where herbivore pressure on plants results in changes in plant communities. These altered plant communities are hypothesized to exert bottom-up control on subsequent herbivory via changes in plant quality or productivity. But it remains untested whether top-down perturbation causes long term changes in plants that ricochet back up the new food chain that depends on them. In a large-scale, 30-yr controlled field experiment, we show that 10 yr of top-down control of an ungulate herbivore (white-tailed deer, Odocoileus virginianus) created contrasting forest tree communities exerting bottom-up effects that ricochet back up 3 trophic levels 20–30 yr later. Higher ungulate densities during stand initiation caused significant reductions in tree species diversity, canopy foliage density, canopy insect density, and bird density in young (ca. 30 yr old) forests. Because recruitment of trees from seedlings to the canopy occurs over a relatively brief period (ca. 10 yr), with membership in the canopy lasting an order of magnitude longer, our results show that even short-term perturbations in ungulate density may cause centuries-long disruptions to forest ecosystem structure and function. In documenting this five-step trophic ricochet, we unite key concepts of trophic theory with the extensive literature on effects of ungulate overabundance. As predators decline and ungulate herbivores increase worldwide, similar impacts may result that persist long after herbivore density becomes effectively managed.

Breeding Bird Use of and Nesting Success in Exotic Russian Olive in New Mexico

Abstract The exotic tree, Russian olive (Elaeagnus angustifolia), has invaded riparian zones throughout much of the western Unites States. Although promoted as a useful species for wildlife because of its abundant edible fruit, evidence for its value to breeding birds remains sparse. We compared relative rates of usage, nest success, and cowbird parasitism of birds breeding in Russian olive versus native tree species at a site where Russian olive is a minor component. Some species, such as the Mourning Dove (Zenaida macroura) and Yellow-breasted Chat (Icteria virens), preferentially placed their nests in Russian olive. Nest success was similar for nests in Russian olive and native species. During 1997, nests of the Willow Flycatcher (Empidonax traillii) were significantly more likely to be parasitized by Brown-headed Cowbirds (Molothrus ater) when placed in Russian olive than in native species, although nest success was not significantly different. Our results may not apply to areas where Russian olive is common.

Status, ecology, and conservation of the southwestern willow flycatcher.

This publication was prepared in response to a need expressed by southwestern agencies and organizations for a comprehensive assessment of the population status, history, biology, ecology, habitats, threats, and conservation of the southwestern willow flycatcher (Empidonax traillii extimus). The southwestern willow flycatcher was federally listed as an Endangered subspecies in 1995. A team of flycatcher experts from multiple agencies and organizations identified components of the publication, wrote chapters, and cooperatively assembled management recommendations and research needs. We hope this publication will be useful in conserving populations and habitats of the southwestern willow flycatcher. Financial assistance for preparing this report was provided by the Southwest Region and Rocky Mountain Research Stations Rio Grande Ecosystem Program of the U.S. Forest Service.This publication was prepared in response to a need expressed by southwestern agencies and organizations for a comprehensive assessment of the population status, history, biology, ecology, habitats, threats, and conservation of the southwestern willow flycatcher (Empidonax traillii extimus). The southwestern willow flycatcher was federally listed as an Endangered subspecies in 1995. A team of flycatcher experts from multiple agencies and organizations identified components of the publication , wrote chapters, and cooperatively assembled management recommendations and research needs. We hope this publication will be useful in conserving populations and habitats of the southwestern willow flycatcher.

DOES RISK OF NEST FAILURE OR ADULT PREDATION INFLUENCE HATCHING PATTERNS OF THE GREEN-RUMPED PARROTLET?

Abstract Parent birds may adjust the onset of incubation to minimize periods of high risk of nest failure due to predation (the Nest Failure Hypothesis) or of mortality to adult birds (the Adult Predation Hypothesis). We examine temporal patterns of risk of nest failure and predation on adult females in a population of Green-rumped Parrotlets (Forpus passerinus) to determine whether those patterns explain observed patterns of incubation. Over one-third of nests (38.6%) failed completely, and an additional 2.2% failed after fledging one or more young. Most nests failed due to predation and infanticide. Because parrotlets begin incubation on the first egg, we examined a range of hypothetical failure rates for the period prior to the onset of incubation. Daily survival probabilities for nests were higher during the nestling stage than during incubation or fledging. Survival of adult females varied little through the nesting cycle, but was highest while attending nestlings. Model predictions were highly dependent on assumptions made about survival rates during the pre-incubation period. When empirically based values were used for this period, maximum productivity was achieved with first-egg incubation, consistent with observed patterns. Models were most sensitive to those parameters most difficult to estimate. This study represents the first test of the Nest Failure model with a nonpasserine or tropical species, and the first assessment of the Adult Predation model using field data.

SOUTHWESTERN WILLOW FLYCATCHERS (EMPIDONAX TRAILLII EXTIMUS) IN A GRAZED LANDSCAPE: FACTORS INFLUENCING BROOD PARASITISM

Abstract Brood parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds”) is an important factor contributing to the endangered status of the Southwestern Willow Flycatcher (Empidonax traillii extimus, hereafter “flycatcher”). We report on factors that influence brood parasitism on the flycatcher using seven seasons of nest data (n = 491 nests) collected in riparian patches comprising cottonwood (Populus fremontii), willow (Salix spp.), and boxelder (Acer negundo) along the Gila River in southwest New Mexico. We quantified habitat and landscape characteristics that might be associated with higher levels of parasitism and assessed the correlation between those and the observed incidence of nest parasitism. Given that cowbirds associate with cattle, we were particularly interested to determine whether the distance to active summer grazing would influence the frequency of brood parasitism. We found an apparent negative trend between the distance to grazing and brood parasitism, but this trend was not statistically significant. Rather, brood parasitism was more strongly correlated with characteristics of the habitat. Specifically, nests in larger patches, and nests built near the patch edge adjacent to the river, were more susceptible to parasitism, which suggests that these areas are preferred nesting habitat for cowbirds because of a potentially greater abundance of hosts. Parasitism was significantly lower within the core of large patches, but the insulating effect was not evident in small and medium-sized patches. Higher nest height was strongly correlated with lower probability of parasitism, most notably for nests in boxelders. Nests in boxelders were less susceptible to parasitism, whereas nests in willows were more susceptible to parasitism. We discuss the results in the context of other studies. We recommend that management efforts to recover the flycatcher should focus on increasing quality habitat, and we suggest that cattle management should focus on eliminating the adverse effects of grazing on riparian health as a more feasible option than removing cattle far enough from riparian corridors so as to preclude parasitism. Empidonax traillii extimus en un Paisaje con Pastoreo: Factores que Influyen sobre el Parasitismo de la Nidada

Condition Varies with Habitat Choice in Postbreeding Forest Birds

ABSTRACT. Many birds that are experiencing population declines require extensive tracts of mature forest habitat for breeding. Recent work suggests that at least some may shift their habitat use to early-successional areas after nesting but before migration. I used constant-effort mist netting in regenerating clearcuts (4–8 years postcut) and dense mature-forest understories to assess (1) whether most bird species of mature forests show habitat shifts after breeding; and (2), on the basis of several measures of condition, whether birds using early-successional habitats garnered any benefits or penalties, compared with those that remained in forests. I captured 3,845 individual birds of 46 species at four pairs of sites in mature Allegheny hardwood forests in northwestern Pennsylvania during the postbreeding periods of 2005–2008. Most, but not all, forest birds were captured at higher rates in cuts than in forests, and that pattern persisted through the postbreeding season. Using an information-theoretic approach, I found strong support for a species-habitat interactive effect on both molt progression and body condition as measured by residuals from speciesspecific regression of mass on wing chord. Some, but not all, forest birds appeared to be in better condition when captured in cuts than when in forests. I found no support for a habitat effect on presence of fat or ectoparasites. My result s reveal that habitat choice in the postbreeding season is correlated with physiological condition for a subset of forest birds, which suggests that the maintenance of such early-successional habitats in mature forest may benefit these species.

Mixed effects of geolocators on reproduction and survival of Cerulean Warblers, a canopy-dwelling, long-distance migrant

ABSTRACT Light-level geolocators, miniature devices used for tracking avian migration over the full annual cycle, are being widely deployed on small migratory passerines. However, the effects of carrying geolocators on the breeding biology of songbirds are unclear, and variable species- and guild-specific conclusions have been drawn regarding their effects on return rates (apparent annual survival). In particular, there is a lack of published information on the effects of geolocators on Nearctic–Neotropical migrant warblers and canopy-dwelling bird species, which limits our ability to determine whether this technology is appropriate for use on species within these groups. During 2014 and 2015, we deployed geolocators on 49 adult male Cerulean Warblers (Setophaga cerulea) in Pennsylvania, Missouri, and Arkansas, USA. We monitored the effects of geolocators across the full annual cycle by comparing apparent within-breeding-season survival (within-season φ), nestling provisioning rates, nest survival, and return rates between geolocator-tagged adult males and color-banded controls. We found no negative effects of geolocators during the breeding season of geolocator deployment, but the return rate of geolocator-tagged birds was lower than that of control birds (16% ± 5% vs. 35% ± 7%). We found no strong evidence that the differential return rate between the 2 groups was influenced by breeding region, body mass, bird age, year of geolocator deployment, or method of attachment. Although finding no effect of geolocators during the breeding season is encouraging, the lower return rate of geolocator-tagged birds warrants further investigation in the field. If further improvements in the design or attachment methods of geolocators are not technologically possible, the potential for increased mortality (or dispersal) of geolocator-tagged birds should be weighed against the potential conservation gains that could be made by identification of critical stopover, wintering, and breeding habitats for populations of interest.