Investigating factors influencing blue-winged teal movements and habitat selection during the nonbreeding season
Abstract
[EMBARGOED UNTIL 08/01/2026] Migration is an important life history strategy used by waterfowl to access seasonally available resources. However, migratory events in both autumn and spring are energetically demanding and migration strategies that minimize energy expenditure could offer opportunities for increased fitness. Although waterfowl may initiate seasonal migrations based on a range of favorable environmental factors that minimize energy expenditure, risk of mortality, and maintain or improve body condition, most studies have investigated these relationships at the population level using abundance and occupancy metrics. In this study, we used data from individual GPS/GSM-tracked blue-winged teal (Spatula discors) to evaluate the environmental drivers of autumn and spring migration phenology during 2020 -- 2023 (n = 321 migratory movements) at a continental scale. We modeled departure probabilities of blue-winged teal using logistic exposure models to evaluate how environmental factors influence autumn and spring migration initiation dates as well as subsequent departures from migration stopover sites. We developed candidate models to predict probability of departure, conditional on environmental covariates (e.g., photoperiod, wind bearing and speed, atmospheric pressure, precipitation, visibility, temperature, soil temperature, and low cloud cover) measured at a 32 km2 resolution. Additionally, we evaluated models that included a binary harvest season covariate in our autumn migration analyses to test if departure probabilities were conditional on hunting season (e.g., open vs closed). Departure probabilities in spring and autumn were most influenced by photoperiod although the effect was greatest for spring migration initiation movements. Departure probabilities increased with favorable wind conditions (i.e., tailwinds); however, the effect was greatest for subsequent migratory movements in spring. Autumn departure probabilities of subsequent migratory movements increased with accumulated precipitation, suggesting that blue-winged teal may respond rapidly to proximate wetland conditions. Blue-winged teal are likely to initiate migratory movements based on photoperiod, but may use proximate, local environmental cues (e.g., favorable wind conditions) to time subsequent migratory movements. Importantly, our results indicated hunting season was not associated with autumn migration departure probabilities. Our findings provide some of the first insights into the individual responses of blue-winged teal to environmental factors during autumn and spring migrations which may help inform management decisions from both a harvest and habitat management perspective.
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Degree
M.S.