Abstract
AbstractObligate avian brood parasites lay their eggs in hosts' nests and play no role in the provisioning of the progeny. Many parasites, including Cuculus cuckoos, hatch before their hosts and the altricial chick evicts hosts eggs and nestlings. A hypothesized, but so far untested parasite adaptation is that the embryos of cuckoos develop more quickly than the hosts' because the higher porosity of the parasite's eggshell allows greater gaseous exchange, potentially supporting more rapid development. We compared the water vapour conductance (GH2O) of common cuckoo (Cuculus canorus) eggshells and those of several passerines, including various cuckoo host species, and non‐passerine species. Contrary to the prediction, the cuckoo eggs had lower GH2O than eggs of their hosts, and lower GH2O than predicted for their egg size and phylogeny. A potential advantage for the cuckoo egg of having a lower GH2O may be that the yolk is depleted at a slower rate, allowing more reserves to remain at the end of incubation, assisting the embryo with the energetically demanding tasks of hatching from a thicker eggshell, and evicting host eggs and nestmates.
Highlights
Common cuckoos (Cuculus canorus: hereafter cuckoo) are obligate avian brood parasites that exploit a range of passerine host species (Brooke & Davies, 1988)
Eggshells of the following hosts were selected, Anthus pratensis, Anthus trivialis, Erithacus rubecula (European robin) and Prunella modularis
We confirmed that cuckoo eggshells were thicker
Summary
Common cuckoos (Cuculus canorus: hereafter cuckoo) are obligate avian brood parasites that exploit a range of passerine host species (Brooke & Davies, 1988). Female cuckoos lay their eggs in host nests, and the costs of incubating the egg and rearing the chick are undertaken by the host parents (Schulze-Hagen, Stokke & Birkhead, 2009). 12-day long incubation, shorter than that of their hosts, which typically need 13+ days from laying to hatching (Davies, 2000; Schulze-Hagen et al, 2009). This fast development rate of cuckoo embryos has been attributed to:
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