Snake mimicry by birds

Hole-nesting tits belonging to the family Paridae produce a hissing display that resembles the exhalatory hiss of a snake. When a predatory animal enters the nest hole of a tit, tits often hiss vigorously, while lunging their head forward and shaking their wings and tail, until the intruder retreats (https://youtu.be/ymeZSeckYqc). 

We assessed the acoustic similarity between such hiss calls from 6 species of tits (example above), snake hisses (example below), and tit syllables used in alarm vocalizations, as well as white noise as a control. Tit hiss calls showed a high degree of similarity with snake hisses from 3 different snake families. Tit hisses had lower similarity to syllable alarm calls, suggesting convergence of tit hisses in their spectral structure.

Hiss calls would only be effective in protecting nest boxes if nest predators responded to these calls. In order to test this hypothesis, we trained individual squirrels to feed at feeders in proximity to nest boxes. Squirrels showed a higher degree of avoidance of feeders when hiss calls were played back than when white noise was presented. 

In conclusion, our study suggests that hole-nesting birds have evolved convergent snake-like hiss calls, and that predators avoid to prey on the contents of nest boxes from which snake-like hisses emerge. This study was conducted in collaboration with Anders Møller (Paris-Sud University, France) and Liang Wei (Hainan Normal University, China).

Diego Gil