Recognition and utilization of egg maculation signals by two sympatric host species

Egg color polymorphism and egg mimicry are important adaptations in the game process between hosts and brood parasites at the egg stage. The ability of hosts to recognize and reject parasitic eggs based on effective egg characteristics is a crucial factor in determining the outcome of this arms race. The evolution of linear markings on eggs has been identified in several parasitic systems of common cuckoos Cuculus canorus, yet little is known about the functional adaptation of this egg characteristic. Here, we examined the recognition and utilization methods of maculation signals of eggs in the common cuckoo hosts, south rock bunting Emberiza yunnanensis, which lays eggs with linear mimetic spots, and yellow-throated bunting Emberiza elegans, which lays eggs with dotted mimetic spots. The results demonstrated that both species of bunting hosts show moderate recognition and rejection levels towards interspecific eggs (spotted versus streaked). Moreover, during recognition, they utilized the contrast between the maculation and the egg background rather than the contrast between the maculations themselves. Our study is the first to demonstrate that two species of open-nesting buntings use achromatic contrast (not chromatic contrast) between pattern features and egg background color to identify and reject foreign eggs. However, whether other differences in pattern features, such as pattern density, distribution, and proportion are utilized by the hosts requires further verification.