Parasitic egg phenotypes induce short-term imprinting effects on host egg recognition

This study was conducted from March to August in the years 2022–2024 in the Liuzhi Special District (22°13′ N, 106°42′ E) of Guizhou Province, southwestern China, at an elevation of 1,070–1,657 m. The study area is characterized by a karst landscape, comprising a mosaic of villages, farmland, shrubland, and barren slopes. The preservation of traditional agricultural practices and architecture may play an important role in influencing the distribution and reproductive success of bird species in the area (Zhong et al. 2023).Here, the grey bushchat (Saxicola ferreus), a bird host of the common cuckoo (Cuculus canorus), was used to investigate whether learned memory of foreign egg phenotypes influences host egg rejection decisions. Results indicated that: (1) the grey bushchat uses maculation patterns (spotty and linear markings) as key recognition cues for foreign eggs; (2) short-term learning and memory, acquired through the rejection of foreign eggs, increased the likelihood of rejecting conspecific eggs that bore similar maculation patterns; and (3) in cognitive tests of rejection choice, grey bushchats showed significantly reduced rejection of test eggs (spotty or linear-marked own eggs) in the absence of foreign egg cue signals. The grey bushchat responded preferentially to spotty signals when exposed to conventional foreign egg features (background color or spotty maculation), but showed increased rejection of linear-marked conspecific eggs when presented with distinct cues (linear markings). Our field experiments provide the first direct evidence that parasitic egg phenotypes can induce imprinting effects on the host, suggesting a potential decision-making trade-off between imprinting on parasitic versus own-egg templates during recognition of foreign eggs. This study offers a new perspective on the evolution of host egg recognition and highlights the crucial role of host learning and memory of parasitic egg templates in shaping cognitive adaptations against brood parasitism.