White-throated Sparrows (Zonotrichia albicollis)
Experimental manipulation of energetic condition affects orientation during fall and spring migration near a geographic water barrier
Presenters: Jennalee A. Holzschuh (SUNY College at Brockport, New York) and Mark E. Deutschlander (Hobart and William Smith Colleges, New York)
Previous research on a variety of migratory passerines from different regions has shown that orientation at ecological barriers can be correlated with condition; migrants in poor condition often re-orient in seasonally unexpected directions, and migrants in good condition show seasonally appropriate orientation. However, few studies have shown directly that individual orientation changes with energetic condition. We conducted a repeated-measures experiment on captive White-throated Sparrows (Zonotrichia albicollis) along the south shore of Lake Ontario to determine if energetic condition directly affects individual orientation. During fall and spring, sparrows were maintained on a semi-synthetic diet to manipulate mass gain or loss, and tested for orientation three times: in their original condition (e.g., fat), after their condition changed on a manipulated diet (e.g., to lean from fat), and then again after individuals were restored to their original condition (e.g., from lean to fat). Sparrows in good energetic condition oriented bimodally along a northwest-southeast axis in both seasons and showed high levels of migratory restlessness, similar to other studies of sparrows in captivity. In contrast, sparrows in lean energetic condition were not well-oriented and showed lower levels of migratory restlessness in both seasons. Analysis of individual orientation showed that most birds changed their orientation significantly when energetic condition was altered, but returned to their original orientation when energetic condition was restored. Our results demonstrate a direct effect of food availability and energetic condition on individual orientation and migratory restlessness.