Cuckoo hosts fine-tune their egg rejection after experiencing a parasitism event
This study was done in Jingdong County (23°56′~24°29′ N, 100°22′~101°15′ E), where is located in the central-southern part of Yunnan, southwestern China, with a total land area of 4,532 km2 and a population of 377,000 people. The Lancang River and the Bianjiang River form two major water systems in the county, and this county is known for its rich biodiversity and abundance of endemic species, making it one of the diverse regions in terms of biological diversity in Yunnan Province (Luo et al., 2011).
To investigate whether the egg rejection behavior of host birds changes after encountering a parasitism event, we conducted egg recognition experiments in a population of the grey bushchat (Saxicola ferrea) in Yunnan, China. When a single pure white egg of the white-rumped munia (Lonchura striata) and a blue model egg were individually added to the nest of the grey bushchat, the rejection rate for the white-rumped munia eggs was as high as 93.3%, whereas the rejection rate for the blue model egg was minimal (5.56%). However, when the grey bushchat rejected the munia egg and a blue model egg was subsequently added to its nest, the rejection rate for the blue model egg significantly increased to 54.5%. The presence of the munia egg in the nest may serve as a cue of parasitism risk for the grey bushchat. After rejecting the munia egg, the grey bushchat likely became aware that it was parasitized. Consequently, the bird may intensify its inspection of nest eggs, leading to increased rejection of the previously accepted blue model eggs. Our results are consistent with the optimal acceptance threshold hypothesis, suggesting that as the predictability of parasitism risk increases, the grey bushchat adjusts its acceptance threshold for foreign eggs to become more stringent.
