Individual dispersal among colonies of Little Egrets Egretta garzetta

Colonial waterbirds are unusual in that competition for nest‐sites or mates may occur at a scale of a few metres, whereas thousands of birds may overlap in their foraging range at a larger scale. Dispersal has been evaluated for only a few such species, and its adaptive significance remains unclear....

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Bibliographic Details
Published in:Ibis (London, England) England), 2002-04, Vol.144 (2), p.192-199
Main Authors: Fasola, Mauro, Hafner, Heinz, Kayser, Yves, Bennetts, Robert E., Cezilly, Frank
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Animals
Aves
Biological and medical sciences
Demecology
Egretta garzetta
Freshwater
Fundamental and applied biological sciences. Psychology
Vertebrata
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Summary:Colonial waterbirds are unusual in that competition for nest‐sites or mates may occur at a scale of a few metres, whereas thousands of birds may overlap in their foraging range at a larger scale. Dispersal has been evaluated for only a few such species, and its adaptive significance remains unclear. We studied Little Egret dispersal among all the colonies within the Camargue, southern France. The overall probability of dispersal between successive years was 0.45. The probability of dispersal was unaffected by a bird’s age, or by any density‐dependent effect of colony size. Juveniles dispersed at distances that would be expected if colony selection were random, while adults tended to remain within 10 km of their previous colony. We found no obvious environmental ‘trigger’ for an individual to disperse. Although our evidence is inconclusive, the short dispersal distances of adults are not consistent with foraging conditions as the primary trigger for dispersal. Little Egrets generally forage within 8 km of their colony, so birds dispersing less than 10 km would gain little advantage in response to unfavourable foraging conditions. Our data, with 75% of dispersing birds coming from decreasing colonies and 72% joining increasing colonies, suggest that individual dispersal depended on colony dynamics as a whole, i.e. (1) a social component of dispersal at the individual level, or (2) a simultaneous colony response to unfavourable environmental conditions or (3) both. Further investigation at a higher social level may be necessary to understand dispersal of this colonial nesting species.
ISSN:0019-1019
1474-919X
DOI:10.1046/j.1474-919X.2002.00060.x