Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Specialization
Ecology and Ecosystem Sciences
Department
Natural Resources Science
First Advisor
Scott R. McWilliams
Abstract
Declines in young forest in eastern North America during the last century have led to declines in wildlife species that inhabit and depend on this habitat for at least some portion of their annual cycle. For example, the American woodcock (Scolopax minor), a hunted upland shorebird that inhabits early successional habitats has experienced long-term (ca. 1% annually) population declines since monitoring of singing males began in 1968. For nearly a century, woodcock research has primarily focused on males because of the difficulties associated with capturing females, thus relatively little is known about females and if factors related to their ecology may be contributing to declines. Like many shorebirds, there is also a critical need to better understand woodcock ecology during different portions of the annual cycle in order to effectively conserve this species amidst a rapidly changing environment. Recognizing the need for comprehensive knowledge across various portions of the year, we investigated three portions of the woodcock’s annual cycle (i.e., spring migration, breeding, and post-breeding periods) in Rhode Island as well as throughout eastern North America. In chapter 1, we tracked VHF-tagged male and female woodcock during the post-breeding period to assess third-order habitat selection and look for sex-specific differences in Rhode Island. Additionally, we leveraged a long-term (9-years of data collected over 11-years) male tracking dataset of 146 individually marked males in Rhode Island to identify trends in habitat selection over time and enhance forest management planning for woodcock and other early successional species in the state. Our study of 146 male woodcock represents one of the largest habitat selection studies to date for this species. Although sex-specific differences in habitat use have been observed in other shorebird species, this was the first study to examine if such differences exist between male and female woodcock. We found that males typically had smaller home ranges (35.0 ± 10.7 ha) than females (78.7 ± 46.4 ha) and that males preferred habitat mosaics that consist of forested wetlands, young forest patches, areas of deciduous forest, moist soils with gentle slopes, and riparian corridors. We detected subtle differences between males and females in selection for wetland young forest, upland young forest, percent slope, distance to upland young forest, distance to streams, and distance to moist soils. In contrast, we found that females more strongly selected areas closer to riparian corridors while males selected areas that were closer to upland young forest with flatter slopes than the available surrounding landscape. We suspect that these observed differences are related to post-breeding prospecting for future breeding sites by males and females as has been shown in some other shorebird species. Finally, we used our top-ranked habitat selection models for males and females to produce spatially explicit state-wide maps that identify low-to-high likelihood of use areas that can be used to guide forest management decisions in southern New England to maximize benefits for woodcock.
In chapter 2, we cooperated with the Eastern Woodcock Migration Research Cooperative (EWMRC; woodcockmigration.org) to answer fundamental questions about woodcock breeding behavior and nesting ecology at the range-wide scale using movement data from satellite-tagged female woodcock. This allowed us to uncover unprecedented results- female woodcock are ‘itinerant breeders’ that defy conventional life-history theory by desegregating spring migration and reproduction, an incredibly rare breeding strategy (<0.1% of extant bird species). This finding emerged from a two-step approach. First, from February to June 2021 and 2022, we engaged with EWMRC partners to field verify 26 suspected nesting attempts from satellite-tagged female woodcock exhibiting small step-lengths (i.e., < 20 m) throughout Eastern North America. We then used the recursion patterns and step-lengths from this set of field-verified nests to retroactively identify nesting attempts from a larger 4-year satellite-tagged female dataset (n < 200 females) collected by the EWMRC from 2019 to 2022. We found that most female woodcock (>80%) nested more than once (some up to 6 times) with short renest intervals, and females moved northward on average 800 km between first and second nests, and then smaller distances (ca. 200 + km) between subsequent nesting attempts. Reliance on ephemeral habitat for breeding, ground-nesting, and key aspects of life-history that reduce both the costs of reproduction and migration likely explain the prevalence of this rare phenotype in woodcock and why itinerant breeding so rarely occurs in other bird species. We think that the extreme flexibility exhibited by itinerant breeders in their choice of breeding locations may also make these species less vulnerable to environmental change, as long as some suitable habitat remains.
In chapter 3, we worked with volunteer pointing dog handlers to locate breeding females from 15 March to 15 June of 2020-2022 to assess previously unknown life-history aspects for breeding woodcock in the state (i.e., multi-scale nest-site selection and nest and brood survival) in relation to various environmental and temporal variables. To do this, we GPS marked nest sites and VHF-tagged broods so that we could monitor them and determine fate. After nest hatch or failure, we returned to nest sites to collect local-scale vegetation measurements for our assessment of multi-scale nest-site selection. At the landscape scale, we found that nesting woodcock select for early successional habitats (i.e., pastures, grasslands, or regenerating clearcuts) and areas closer to upland young forest and reverting agricultural openings. They also occupied forests and wetlands of varied species composition and age (i.e., upland young and coniferous forests as well as upland and wetland deciduous forests, and emergent wetlands). At the local scale, we found that nesting woodcock select nest sites providing visual concealment (i.e., larger percentages of herbaceous cover, canopy cover, and surrounding vegetation that is taller). Despite this multi-scale nest site selection, nest and brood survival were low (10% and 16%, respectively) and were not significantly influenced by vegetation, landscape configuration, and weather. Given that woodcock nest site selection is driven by vegetative structure and concealment, yet reproductive success was low, habitat management practices that mitigate predation and increase cover are needed especially in fragmented landscapes.
In chapter 4, we tracked VHF-tagged male woodcock from May to September to estimate post-breeding survival. Similar to chapter 1, we utilized the long-term male tracking dataset of males in Rhode Island to assess the relationship between survival and factors such as age, precipitation, habitat, and time to identify what may be contributing to ongoing population declines. Although survival estimates exist for much of the woodcock’s annual cycle, this study is one of the first long-term (i.e., nearly a decade) empirical studies of male survival (n = 200 radio-tagged individuals). Overall post-breeding survival estimates for the period from May to September were high 0.90 (95% credible intervals = 0.80, 0.98), and the four covariates that we assessed did not significantly influence daily survival rate. However, relative probability of use score had a high probability of direction (0.910) indicating a high certainty that the effect of this habitat quality metric was in a positive direction. The high post-breeding survival of male woodcock in our 11-year study period was consistent with other estimates from Maine populations. Despite moderate to high adult survival estimates throughout much of the annual cycle, American woodcock populations continue to decline. This decline seems most influenced by factors during the breeding period (i.e., low nest and brood survival rates) which means the most effective conservation and management should focus on reducing predation on nests and broods.
Recommended Citation
Slezak, Colby R., "HABITAT SELECTION AND BREEDING ECOLOGY OF AMERICAN WOODCOCK IN SOUTHERN NEW ENGLAND" (2024). Open Access Dissertations. Paper 1666.
https://digitalcommons.uri.edu/oa_diss/1666