Nest sanitation elicits egg discrimination in cuckoo hosts
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Nest sanitation is a nearly universal behavior in birds, while egg discrimination is a more specific adaptation that has evolved to counter brood parasitism. These two behaviors are closely related with nest sanitation being the ancestral behavior, and it has been hypothesized to constitute a preadaptation for egg discrimination. However, previous studies found little evidence to support this hypothesis. Here, we conducted an empirical test of the association between nest sanitation and egg discrimination in the barn swallow (Hirundo rustica) by inserting a single non-mimetic model egg or a non-mimetic model egg plus half a peanut shell into host nests. Compared to the rejection rate of single model eggs, barn swallows significantly increased egg rejection frequency if a half peanut shell was simultaneously introduced. Our result for the first time shows the impact of nest sanitation on egg discrimination and demonstrates that nest sanitation can elicit egg discrimination in hosts of brood parasites. This study provided evidence for nest sanitation being a preadaptation to egg discrimination by facilitating egg rejection, thereby significantly advancing our understanding of avian cognition of foreign objects. Furthermore, we suggest that egg discrimination behavior in many accepters and intermediate rejecters may be lost or diluted. Such egg discrimination can be elicited and restored after nest sanitation, implying a sensitive and rapid phenotypic response to increased risk of parasitism. Our study offers a novel perspective for investigating the role of so-called intermediate rejecter individuals or species in the long-term coevolutionary cycle between brood parasites and their hosts.
KeywordsEgg rejection Evolutionary lag Hirundo rustica Intermediate rejecter Nest cleaning
We would like to thank Jianhua Ma for assistance with fieldwork and Zhalong National Nature Reserve for their support and help. This work was supported by the National Natural Science Foundation of China (Nos. 31260514 to CY, 31272328 and 31472013 to WL) and Program for New Century Excellent Talents in University (NCET-13-0761 to CY). The authors declare that they have no conflict of interest.
Compliance with Ethical Standards
The experiments comply with the current laws of China, where they were performed. Fieldwork was carried out under the permission from Zhalong National Nature Reserve.
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