Receivers matter: the meaning of alarm calls and competition for nest sites in a bird community
Animal communities may constitute information networks where individuals gain information on predation risk by eavesdropping on alarm calls of other species. However, communities include species in different trophic levels, and it is not yet known how the trophic level of the receiver influences the informative value of a call. Furthermore, no empirical study has yet tested how increased competition may influence the value of alarm calls for distinct receivers. Here, we identify the importance of alarm calls emitted by a small owl, the little owl (Athene noctua), on the structure of a cavity-nesting bird community including mesopredators and primary prey under variable levels of competition for nest holes. Competitors sharing top predators with the callers and prey of the callers interpreted alarm and non-alarm calls differently. Competitors chose preferentially alarm and non-alarm patches over control patches to breed, while prey selected alarm patches. In contrast, competition for nest sites affected habitat selection of prey species more than that of competitors of the callers. This study provides support for a changing value of alarm calls and competition for nest sites for distinct receivers related to niche overlapping among callers and eavesdroppers, therefore, calling attention to possible cascading effects by the use of information in natural communities.
KeywordsAnimal communities Information networks Interspecific competition Predation risk Receivers
We are grateful to Jukka Forsman and Mikko Mokkönen for constructive and helpful comments on an earlier version of the manuscript. This study was funded by the Spanish Ministries of Education and Science/FEDER and of Economy and Competitiveness, respectively, through the projects CGL2011-27561/BOS, CGL2014-56769-P and by the Government of Extremadura through the contract TA13002 to DP.
Author contribution statement
DP and JMA designed the study. DP, JMA and MEG collected field data. DP carried out the statistical analyses and wrote a first version of the manuscript that was discussed, revised and approved for all the authors. MEG makes the drawings of Fig. 1.
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