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, 5 (3), 302-5

Stopover Decision During Migration: Physiological Conditions Predict Nocturnal Restlessness in Wild Passerines

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Stopover Decision During Migration: Physiological Conditions Predict Nocturnal Restlessness in Wild Passerines

Leonida Fusani et al. Biol Lett.

Abstract

During migration, a number of bird species rely on stopover sites for resting and feeding before and after crossing ecological barriers such as deserts or seas. The duration of a stopover depends on the combined effects of environmental factors, endogenous programmes and physiological conditions. Previous studies indicated that lean birds prolong their refuelling stopover compared with fat birds; however, the quantitative relationship between physiological conditions and stopover behaviour has not been studied yet. Here, we tested in a large sample of free-living birds of three European passerines (whinchats, Saxicola rubetra, garden warblers, Sylvia borin and whitethroats, Sylvia communis) whether the amount of migratory restlessness (Zugunruhe) shown at a stopover site depends on physiological conditions. An integrated measure of condition based on body mass, amount of subcutaneous fat and thickness of pectoral muscles strongly predicted the intensity of Zugunruhe shown in recording cages in the night following capture. These results provide novel and robust quantitative evidence in support of the hypothesis that the amount of energy reserves plays a major role in determining the stopover duration in migratory birds.

Figures

Figure 1
Figure 1
Scatterplots of log-transformed Zugunruhe intensity versus the principal component CONDITION extracted from muscle score, fat score and body mass for (a) whitethroat, (b) whinchat and (c) garden warbler. In all three species, Zugunruhe and CONDITION were positively correlated.
Figure 2
Figure 2
Scatterplot of the coefficient of variation (CV) of Zugunruhe versus the fat score. The two variables were negatively correlated in all species. Squares, garden warbler; circles, whinchat; diamonds, whitethroat.

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