Departure Decisions and Movement Behavior of Migratory Songbirds During Stopover
An ENR Graduate Defense Seminar will be presented by Bryant C. Dossman, Masters student in the Fisheries and Wildlife Science specialization area. His presentation will be Departure Decisions and Movement Behavior of Migratory Songbirds During Stopover. This seminar will begin at 2:00 p.m. in 333C Kottman Hall.
Billions of migratory songbirds worldwide make energetically costly migrations between their breeding and overwintering areas. Their small body size, and consequently limited fuel storage capacity, necessitate that these migrants make punctuated stops along their migratory route to rest and refuel. With arrival on the breeding grounds directly influencing their reproductive success, migratory birds exhibit a suite of behaviors during stopover that are thought to minimize the overall time spent on migration. These behaviors and the needs of migrants to rest and refuel, make the distribution and quality of stopover habitats a critical concern for bird conservation. Both endogenous (sex, age, energetic condition) and exogenous factors (habitat quality, food, geographical location) have been shown to influence stopover behaviors. I sought to identify the primary drivers of stopover departure decisions and their effect of movement behavior for two migratory passerines, the American redstart Setophaga ruticilla and the yellow-rumped (myrtle) warbler Setophaga coronata coronata within the western Lake Erie basin of both the United States (Ohio, Michigan) and adjacent Canada (southern Ontario). Through an experimental manipulation of condition, I determined that condition has a strong negative influence on stopover duration and a positive relationship to movement rates of migrants. Next, based on a broader sample of 124 radio marked birds, I demonstrated that stopover departure decisions are influenced by both condition and age, with adult (after-second-year) birds exhibiting greater probability of departure than juveniles (second-year) birds. Weather conditions also had a significant influence on stopover duration with increasing tailwinds leading to a greater probability of departure. Interestingly, wind was also an important driver of landscape level movement decisions. Individuals that departed with favorable tailwinds were shown to take a more direct route across the lake that resulted in increases in energetic and temporal efficiencies, which could to have cumulative effects across the entire migratory period. Stopover departure decisions and movement behavior are shown to be behaviorally complex, and governed by a variety of endogenous and exogenous factors. Ultimately, individual level responses are likely driven by the constraints imposed on them. Given the ultimate importance of time-minimization, individuals are likely making behavioral decisions that facilitate a more rapid and timely migration. Condition upon arrival was shown to promote early departure (shorter stopover duration), but departure under ideal weather conditions might have substantially larger implications on the overall rate of migration. As a consequence, individuals that are better able to make ‘optimal’ decisions (adults) are likely able to realize shorter stopovers and arrive earlier on the breeding grounds. Ultimately, my study demonstrated that stopover habitat isn’t the only primary driver of stopover duration but also highlights the importance of weather at the time of departure. With changing climate, increasing weather variability, and rapid land-use development, it will be imperative to gain a holistic understanding on how these drivers influence the timing of migration and ultimately reproductive success on the breeding grounds