Vigilance against predators induced by eavesdropping on heterospecific alarm calls in a non-vocal lizard Oplurus cuvieri cuvieri (Reptilia: Iguania)

Abstract

Prey animals can reduce their risk of predation by detecting potential predators before encounters occur. Some animals gain information about nearby predators by eavesdropping on heterospecific alarm calls. Despite having well-developed ears, most lizards do not use vocal information for intraspecific communication, and few studies have shown practical use of the ears in wild lizards. Here, we show that the Madagascan spiny-tailed iguana (Oplurus cuvieri cuvieri) obtains auditory signals for predator detection. The Madagascan spiny-tailed iguana and the Madagascar paradise flycatcher (Terpsiphone mutata) are syntopic inhabitants of the Ampijoroa dry deciduous forest of Madagascar. The iguana and the flycatcher have neither a predator-prey relationship nor resource competition, but they have shared predators such as raptors and snakes. Using playback experiments, we demonstrated that the iguana discriminates mobbing alarm calls of the flycatcher from its songs and then enhances its vigilance behaviour. Our results demonstrate the occurrence of an asymmetrical ecological relationship between the Madagascan spiny-tailed iguana and the paradise flycatcher through eavesdropping on information about the presence of predators. This implies that indirect interspecific interactions through information recognition may be more common than generally thought in an animal community.

Figure 1.

Mean number of active-response-exhibiting Madagascan spiny-tailed iguanas in each baseline and playback period. (a) Experiment in which alarm call was played back first and song second. (b) Experiment in which song was played back first and alarm call second. Baseline-C and baseline-S indicate periods preceding alarm call playback and song playback periods, respectively. Error bars represent 1 s.e. See text for detailed descriptions of active responses.

Figure 2.

Temporal changes in the number of individuals that exhibited the four behavioural responses: (a) head movement, (b) anterior body movement, (c) whole body movement and (d) immobility. The three active responses (a–c) are not mutually exclusive, but are collectively exclusive of the one static response (d). Dashed lines indicate the commencement of the playback of alarm call.