Eggshell strength of an obligate brood parasite: a test of the puncture resistance hypothesis |
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Authors: | Anton Antonov Bård G Stokke Arne Moksnes Oddmund Kleven Marcel Honza Eivin Røskaft |
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Institution: | (1) University of Bulgaria, Kozloduy 3320, bl. 64, ent. A, ap. 14, Kozloduy, Bulgaria;(2) Department of Biology, Norwegian University of Science and Technology (NTNU), Realfagbygget, 7491 Trondheim, Norway;(3) Natural History Museum, University of Oslo, P.O. Box 1172, 0318 Blindern, Oslo, Norway;(4) Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Kvetna 8, 60365 Brno, Czech Republic |
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Abstract: | Eggs of several brood parasites have thicker and stronger shells than expected for their size. The present study evaluated
the puncture resistance hypothesis for the occurrence of thick-shelled eggs in common cuckoos Cuculus canorus by investigating costs of cuckoo egg ejection in four Acrocephalus warblers—the great reed warbler A. arundinaceus, reed warbler A. scirpaceus, marsh warbler A. palustris and sedge warbler A. schoenobaenus. The three latter species all suffered ejection costs, while ejection was not costly in the larger great reed warbler. The
occurrence of ejection costs was negatively related to host bill size. In the marsh warbler, we compared ejection costs in
naturally parasitized nests and two experimental treatments, in which broods were parasitized artificially with great reed
warbler and conspecific eggs. Hosts damaged their own eggs significantly more often when ejecting the thick-shelled cuckoo
eggs than when ejecting the similarly sized but thinner-shelled great reed warbler eggs, providing some support for the puncture
resistance hypothesis. Ejection of conspecific eggs did not involve any costs. Furthermore, contrary to predictions derived
from the laying damage hypothesis, there was no evidence that egg damage was associated with cuckoo egg laying. Hosts damaging
their own eggs during ejection were more likely to subsequently desert their clutches than those that did not. The frequency
of clutches smeared with the contents of the ejected egg were positively related to the hypothesized difficulty of foreign
egg puncturing. Potential advantages of thicker shells in common cuckoo eggs are discussed. |
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Keywords: | Brood parasitism Eggshell thickness Puncture resistance Acrocephalus Cuckoo |
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