Hissing Predicts Lower Tonic Immobility and Higher Nest Success in the Great Tit (Parus major)

Antipredator behavior can vary consistently among individuals, yet links between proactive nest defense and passive fear responses are rarely quantified in the wild. We tested whether hissing, a conspicuous, snake-like bluff display at the nest, predicts tonic immobility (TI) and breeding success in Great Tits (Parus major). In pine forests in southeastern Latvia (2023–2024), we presented a taxidermic Great Spotted Woodpecker (Dendrocopos major) at nest-box entrances during incubation and scored whether females hissed and how many calls they produced. The same females were later assayed for TI by brief supine restraint when nestlings were 3–4 days old. Of 141 incubating females, 105 (74.5%) hissed. TI duration differed sharply between groups: non-hissing females showed significantly longer TI than hissing females. Nest failure was significantly lower in hissing than non-hissing nests. These results reveal a strong negative association between proactive defense and passive fearfulness, and they show that hissing can translate into higher reproductive success in a Woodpecker-dominated predator environment. We conclude that defense behaviors covary within individuals along a personality axis and that predator community composition may shape selection on these strategies.