Host intra-clutch variation,cuckoo egg matching and egg rejection by great reed warblers |
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Authors: | Michael I Cherry Andrew T D Bennett Csaba Moskát |
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Institution: | (1) Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa;(2) School of Biological Sciences, Bristol University, Bristol, BS8 1UG, UK;(3) Animal Ecology Research Group of the Hungarian Academy of Sciences, Hungarian Natural History Museum, Budapest, Ludovika ter 2, 1083, Hungary |
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Abstract: | Prevailing theory predicts that lower levels of intra-clutch variation in host eggs facilitate the detection of brood parasitism.
We assessed egg matching using both human vision and UV-VIS spectrophotometry and then followed the nest fate of great reed
warblers naturally parasitised by European cuckoos. Rejection was predicted by the following three variables: matching between
cuckoo and host eggs on the main chromatic variable defined by principal components analysis of the egg spectra (which has
a strong loading in the UV); the number of host eggs in the nest; and human estimates of intra-clutch variation. The first
variable is not correlated to human estimates of matching, which do not predict rejection. In line with another recent study,
rejection rates were predicted by higher levels of intra-clutch variation in the host eggs, suggesting that higher rather
than lower levels of intra-clutch variation can facilitate the discrimination of cuckoo eggs by hosts. We suggest that the
importance of intra-clutch variation is context dependent, with intra-clutch variation being important when there is good
matching between the host and the cuckoo eggs. Our results also suggest that both spectrometric and human visual assessments
of egg matching and intra-clutch variation are prudent: the former provide the best method of estimating reflectance variation,
whereas the latter include some assessment of patterns of maculation. |
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Keywords: | Cuculus canorus Acrocephalus arundinaceus Brood parasitism Spectrophotometry Human assessment Mimicry Intra-clutch variation Egg discrimination |
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