AMoveE 2014: Rachel Bolus
Channel: Movebank
Date: 2014-05-20

This talk was presented by Rachel Bolus on 5 May 2014 as part of the Symposium on Animal Movement and the Environment, held at the North Carolina Museum of Natural Sciences in Raleigh.

Bolus RT, Bohrer G, Deppe JL, Diehl RH, Moore FR, Schofield L, Ward MP, Zenzal TJ Jr, 2014, "Do migrating birds respond to altitudinal variation in winds during long, over-water flights?"

Abstract: Each fall in North America, migrating birds accumulate along the northern coast of the Gulf of Mexico. Many of these migrants take advantage of supportive weather conditions to fly the more direct route to their wintering grounds across the Gulf, which shortens their overall migration distance. We hypothesize that birds are able to further optimize their flights by identifying altitudes with the most supportive wind conditions and navigating among these altitudes. By both minimizing migration distance and flight energy, the net energetic benefits of crossing the Gulf should outweigh the risks of these long, non-stop flights. One known over-water route is between coastal Alabama and the Yucatan Peninsula, which has a crossing distance of approximately 950 km. Using automated receiving unit (ARU) towers on the Alabama and Yucatan coasts, we monitored radio-tagged migrants and identified departure times, departure directions, arrival times, and over-water flight durations. We used these data and modeled environmental data provided by the Env-DATA system (movebank.org) from the NCEP North American Regional Reanalysis (NARR) to develop individual based models that test different hypotheses for migratory birds' responses to altitudinal differences in favorable winds. Using the actual departure and arrival data of migrating individuals to constrain the model results in a more precise, more biologically likely solution space. Simulated tracks that match both flight duration and arrival location reveal to what extent birds are able to respond optimally to favorable winds over water. The decisions Trans-Gulf migrants make en route likely impact their energy expenditure, which has carryover effects on overwinter survival probability and reproductive success.