Inherited biases reveal call-type-specific conspecific alarm responses in tits

Eavesdropping on heterospecific alarm signals provides critical predator information, yet whether recognition is driven by innate phylogenetic biases or learning and ecology remains unclear. We hypothesize that decoding strategies arise from interactions between evolutionarily inherited perceptual biases and current ecological adaptations. To test this, we chose Asian Tits (Parus cinereus minor) as an “information hub species”, along with the Green-backed Tits (P. monticolus) and the Coal Tits (Periparus ater), forming a phylogenetic gradient. Playbacks used three call types: territorial song, ground alarm calls (hereafter “alarms”), and aerial alarms. Results demonstrated that Asian Tits exhibited a strong conspecific bias exclusively for ground alarms: fleeing probability in response to conspecific ground alarms (79.3%) was significantly higher than to heterospecific ground alarms, with no difference between the two heterospecific sources. Coal Tits were 2.89 times more likely to flee than Green-backed Tits in response to Asian Tit calls. These results support a binary conspecific-heterospecific distinction for ground threats, not a phylogenetic gradient. Decoding is call-type-specific: ground alarms elicit accuracy-driven responses, whereas aerial alarms permit more permissive decoding. Thus, heterospecific alarm decoding is shaped by signal function, a clear conspecific dichotomy and ecological niche, not by fine-scale phylogenetic distance.