Fight or flight: Geographic variation in antipredator defenses by cinereous tits

Abstract

In the face of death from predation, parent birds have to choose between prioritizing current versus future reproduction. Previous studies have shown that when exposed to predation risk, birds breeding in the tropics prioritize their own safety, whereas birds breeding at high latitudes prioritize the safety of future generations. However, this phenomenon has rarely been investigated among populations within a single bird species. Here, we studied the anti-predation behavior of female birds in response to a human observer of four cinereous tit (Parus cinereus) populations during their incubation period across different latitudes in China. When confronted with nest predation risk induced by the presence of a human, the probability of escape by cinereous tits decreased with increasing latitude, that is, the proportion of female birds that escaped from the nest was significantly larger in southern than in northern populations. For female birds that did not leave the nest, the proportion of individuals who produced a hissing call for nest defense was significantly lower in the southern than in the northern populations. In addition, nest defense behaviours were unrelated to nest predation rates, and clutch size in the southern cinereous tit populations was significantly smaller than that in the northern population, it was, therefore, likely that nest defense behaviours were related to clutch size. The present study confirms within a single species that under predation risk, female birds in the tropics prioritize future over current reproduction, while the birds breeding at high latitudes do the opposite.

Keywords

• Hissing call
• Life history theory
• Nest defense
• Nest predation
• Trade-off