La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	Using net sacks to examine the relationship between egg size and young size in Common Pochards
Auteurs :	David Hořák, Auteur ; Tomáš Albrecht, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (78(3) SEP 2007)
Article en page(s) :	334-339
Langues:	Anglais
Résumé :	Investigators studying the relationship between egg size and young size often face difficulties in assigning particular young to particular eggs. We present a new method based on the use of separate net sacks for each egg that allowed us to study this phenomenon in Common Pochards (Aythya ferina) without excessive disturbance of breeding birds. We found a positive isometric relationship between duckling body mass and estimated fresh egg mass (P 0.29). In addition, we found a weak positive relationship between estimated egg mass and the size of ducklings (P= 0.049). Greater hatchling mass typically means a larger yolk supply, and more yolk may provide energy crucial for survival during the first few days after hatching. In addition, ducklings with longer tarsi may be better swimmers and better at finding food and escaping from predators. Although our method has certain limitations and investigators should consider risks when applying it in over-water nests or in nests with large clutches, we believe it is a reliable way to assign young to particular eggs in waterfowl and possibly other bird species.

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