Abstract

Parents of many bird species produce alarm calls when they approach and deter a nest predator in order to defend their offspring. Alarm calls have been shown to warn nestlings about predatory threats, but parents also face a similar risk of predation when incubating eggs in their nests. Here, I show that incubating female Japanese great tits, Parus minor, assess predation risk by conspecific alarm calls given outside the nest cavity. Tits produce acoustically discrete alarm calls for different nest predators: “jar” calls for snakes and “chicka” calls for other predators such as crows and martens. Playback experiments revealed that incubating females responded to “jar” calls by leaving their nest, whereas they responded to “chicka” calls by looking out of the nest entrance. Since snakes invade the nest cavity, escaping from the nest helps females avoid snake predation. In contrast, “chicka” calls are used for a variety of predator types, and therefore, looking out of the nest entrance helps females gather information about the type and location of approaching predators. These results show that incubating females derive information about predator type from different types of alarm calls, providing a novel example of functionally referential communication.

Highlights

  • Males often produce alarm calls in response to nest predators during the incubation stage[9,16], which may allow the incubating females to use alarm calls to assess the type of nest predator outside the nest cavities

  • Previous studies have shown that Japanese great tits produce functionally referential alarm calls for different nest predators, i.e., “jar” calls for Japanese rat snakes, Elaphe climacophora, and “chicka” calls for other predators such as jungle crows, Corvus macrorhynchos, and Japanese martens, Martes melampus[10,11,20] (Fig. 1)

  • I previously showed that seventeen-day-old nestlings, which respond to the two types of alarm calls with adaptive behaviours to avoid predation, jump out of the nest cavity in response to “jar” calls and crouch down inside the cavity in response to “chicka” calls[11]

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Summary

Introduction

Males often produce alarm calls in response to nest predators during the incubation stage[9,16], which may allow the incubating females to use alarm calls to assess the type of nest predator outside the nest cavities. Incubating females may show distinct anti-predator responses to the two types of alarm calls, since snakes and other predators use different methods to access eggs and nests; snakes invade the nest cavity, whereas crows and martens attack the nestlings from outside the nest entrance using their beaks or forelimbs[21,22]. I hypothesized that incubating female Japanese great tits assess predation risk by deriving referential information from conspecific alarm calls given outside the nest cavity. I conducted a playback experiment that examined the response of incubating females to the two types of alarm calls in the absence of actual predators. All three treatments were tested in each female and the order of trials was counter-balanced

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