An analysis of egg-size repeatability in Barn Swallows Hirundo rustica

Published:

Volume 45(2), December 1998. Pages 183-192.

Language:

English

Keywords:

Barn Swallow, egg size, Hirundo rustica, temporal variability, within-individual variability.

Abstract:

Variation in length, breadth and volume of eggs from complete clutches of Barn Swallows Hirundo rustica was studied in central Poland in 1978-1981 and 1994-1995. The main idea of this paper is that temporal variation in the environment may affect traits differently and that repeatability may be a good reverse indicator of environmental sensitivity. The egg traits (length, breadth and volume) were analysed using one-way and nested ANOVAs. Significant within-clutch repeatabilies of all traits were revealed, ranging from 0.60 to 0.85. Clutch mean values of dimensions of the eggs laid by particular females both in different clutches within a breeding season and in different seasons were similar, resulting in a high repeatability of ca. 0.7. In nested ANOVAs, among-female variance components as measured by intraclass correlation coefficients were 0.62-0.66 with respect to different clutches within breeding seasons, and 0.50-0.60 with respect to different breeding seasons. Interclutch differentiation of eggs within females was low, although significant. Interyear repeatability was also analysed for the sample of males that were mated to different females in subsequent years. Repeatabilities of clutch averages ranged from the insignificant value of 0.16 for egg breadth to 0.53 for egg length, the values being on average much lower than those for females. Female Swallows, showing much interindividual variation, are considerably consistent with respect to the characteristics of their eggs, which means that sensitivity to environmental impacts does not generate a large variation in egg size. The consistent interindividual variation in egg size may have some condition-dependent component.