Female-focused Full Annual Cycle Research (2024-present)
Funded by: USDA Forest Service – International Program, Environment and Climate Change Canada, and Forest Ecosystem and Monitoring Cooperative
Despite decades of research, much of our understanding of the demographics and movement of Bicknell’s Thrush and other migratory species has been based on data from male birds. Some of this bias stems from differences between males and females and their ease of study. First, the abundance of singing males informs many of our inferences for occupancy, abundance, and distribution in the breeding season, despite the fact that singing males can often be indicative of unpaired status. Second, much of the winter research has been conducted in higher-quality, high-elevation habitats, which harbor roughly twice as many males as females. Finally, for migratory behavior and routes, archival light-level geolocators and GPS tags have been deployed overwhelmingly on males because their response to playback makes them easier to recapture, and males are large enough to carry the heavier archival GPS tags. Our understanding of the population dynamics requires critical pieces of missing information from understudied females.
The data gap on females is particularly relevant to Bicknell’s Thrush because VCE’s breeding season monitoring shows an average population-level sex ratio bias of 2.15 males for every female. However, VCE’s long-term data shows that the male-to-female ratio varies between years, ranging from as low as 1:1 (parity) to as high as 4:1. Since data show that nestling and sex ratios are not skewed towards males, a critical question remains, where are female Bicknell’s Thrush limited (i.e. dying) in their annual cycle? Identifying where and when females are most limited will provide essential information to improve conservation actions for this species.
First, we are using the long-term banding data from both the breeding and wintering grounds to quantify relationships between climatic patterns, land use change, demographic trends, and sex-specific survival. Second, we are deploying solar-powered hybrid nanotags to track migratory patterns of individuals throughout their lifetime and estimate female survival across the annual cycle.
Linking insect and bird populations on Mansfield (2023-present)
Funded by: TBD
Birds aren’t the only organisms we study on Mansfield. We are also studying what these birds eat—which during the breeding season are mostly insect prey. In the 1990s, UVM entomologists completed a comprehensive moths and ground beetle inventory at Mount Mansfield and Underhill State Park. We are resampling these locations to see how moth and beetle community composition has changed over the elevational gradient in thirty years and to test whether low-elevation species may be shifting upslope. We are sampling moths with a special UV light trap and ground beetles with pitfall traps. We are also measuring caterpillar and other foliage arthropod abundance on trees. Moths and ground beetles are identified to species, and we measure biomass at a familial level for all other organisms.
To quantify bird diets, we take small samples of blood and fecal material from the birds we catch. This gives us a full picture of what food items are important for our focal bird species and allows us to see whether the demographic patterns we have observed in insectivorous birds are related to changes we observe in the insect community. We are currently seeking funding to expand this food web work long term, and to take advantage of archived diet samples using newer molecular techniques.
