Divergent Egg‐Rejection Strategies Between Laying and Incubation Periods in the Green‐Backed Tit ( <i>Parus monticolus</i> )

ABSTRACT Egg recognition and rejection constitute essential host defenses against brood parasitism, with rejection decisions reflecting evolutionary adaptations shaped by cost–benefit trade‐offs. Although long‐term studies have established correlations between egg rejection behavior and parasitism risk, it remains unclear whether hosts can dynamically adjust their defenses in response to stage‐specific parasitic threats across different breeding periods. We investigated temporal variation in egg recognition and rejection latency in the green‐backed tit ( Parus monticolus ), analyzing both seasonal patterns and stage‐specific responses within breeding cycles. Our findings reveal that while rejection behavior remained consistently precise throughout the breeding season without seasonal variation, we observed a striking stage‐dependent pattern: complete acceptance of parasitic eggs during laying followed by near‐total rejection during incubation. This biphasic response contrasts sharply with patterns reported in most other host species. We propose this unique recognition strategy stems from the tit's egg‐covering behavior during laying—an adaptation likely driven by nest predation pressure that temporarily suppresses anti‐parasitic defenses. These results demonstrate that green‐backed tits have evolved independent adaptive responses to distinct selective pressures: nest predation during egg‐laying and brood parasitism during incubation. This study provides new insights into the plasticity of host defenses and suggests that species with egg‐covering behaviors may develop specialized anti‐parasitic strategies. Our findings offer important implications for understanding the evolutionary dynamics of host–parasite interactions and establish a framework for investigating recognition behaviors in other cavity‐nesting hosts.