AbstractBackgroundBrood parasitic birds such as cuckoos (Cuculusspp.) can reduce their host’s reproductive success. Such selection pressure on the hosts has driven the evolution of defense behaviors such as egg rejection against cuckoo parasitism. Studies have shown that Cinereous Tits (Parus cinereus) in China have a good ability for recognizing foreign eggs. However, it is unclear whether egg spots play a role in egg recognition. The aims of our study were to investigate the egg recognition ability of two Cinereous Tit populations in China and to explore the role of spots in egg recognition.MethodsTo test the effect of eggshell spots on egg recognition, pure white eggs of the White-rumped Munia (Lonchura striata) and eggs of White-rumped Munia painted with red brown spots were used to simulate experimental parasitism.ResultsEgg experiments showed that Cinereous Tits rejected 51.5% of pure white eggs of the White-rumped Munia, but only 14.3% of spotted eggs of the White-rumped Munia. There was a significant difference in egg recognition and rejection rate between the two egg types.ConclusionsWe conclude that eggshell spots on Cinereous Tit eggs had a signaling function and may be essential to tits for recognizing and rejecting parasitic eggs.