Meeting Abstract

64.3  Wednesday, Jan. 6  Effects of Nutritional Condition on Migration: Do Dark-Eyed Juncos Use Resource Availability to Keep Pace with a Changing World? BRIDGE, E. S.*; KELLY, J. F.; BJORNEN, P. E; CURRY, C. M.; CRAWFORD, P. H. C.; PARITTE, J. M.; University of Oklahoma Center for Spatial Analysis; Oklahoma Biological Survey; Oklahoma Biological Survey; University of Oklahoma Department of Zoology; Oklahoma Biological Survey; University of Oklahoma Department of Zoology brid0030@tc.umn.edu

Because of their reliance on temporally predictable resources across large spatial scales, migratory birds may be especially vulnerable to anthropogenic climate and land-use changes. Although some long-distance migrants appear unable to adjust to phenological shifts on their wintering grounds, several short- and medium-distance migrants appear to have altered the timing and/or distance of their yearly movements to compensate for the environmental effects of global warming. Which environmental cues are responsible for stimulating these adjustments is an open question, although most studies have focused on weather conditions. In this study, we present a novel field experiment that demonstrates an alternative cue, food availability, may be a critical link between local conditions on the wintering grounds and the timing of spring departure. We captured free-living Dark-eyed Juncos (Junco hyemalis) and held some individuals captive for 5 to 7 days during which they were fed either an ad libitum diet consisting of a variety of foods or a restricted diet limited to 3g of millet per day. We then released these birds and initiated daily resighting surveys to determine when individuals left the study area (i.e., began migration). Juncos given an abundant food supply demonstrated advanced spring migration, and this was especially apparent among individuals with the most pronounced increases in mass and fat stores. This finding indicates a simple mechanism by which short-distance migrants may calibrate their migration behavior such that arrival on the breeding grounds and initiation of reproduction are in sync with resource availability.