Heterospecific eavesdropping on an anti-parasitic referential alarm call

Shelby L Lawson,Janice K Enos,Mark E Hauber,Niko C Mendes,Sharon A Gill

doi:10.1038/s42003-020-0875-7

Shelby L Lawson, Janice K Enos + Show 3 more

Open Access

https://doi.org/10.1038/s42003-020-0875-7

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Abstract

Referential alarm calls occur across taxa to warn of specific predator types. However, referential calls may also denote other types of dangers. Yellow warblers (Setophaga petechia) produce “seet” calls specifically to warn conspecifics of obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the warblers’ and other species’ nests. Sympatric hosts of cowbirds that do not have referential alarm calls may eavesdrop on the yellow warbler’s seet call as a warning system for brood parasites. Using playback presentations, we found that red-winged blackbirds (Agelaius phoeniceus) eavesdrop on seet calls of yellow warblers, and respond as much to seet calls as to cowbird chatters and predator calls. Red-winged blackbirds appear to eavesdrop on seets as warning system to boost frontline defenses on their territories, although they do not seem to perceive the warblers’ seets as a cue for parasitism per se, but rather for general danger to the nest.

Highlights

Referential alarm calls occur across taxa to warn of specific predator types
To assess whether redwings use yellow warbler seet calls as a frontline defense against cowbird parasitism, we report on three analyses from two playback experiments
Our results demonstrate a series of patterns in which (1) both male and female redwings respond to the seet call as to other signals for danger to their nests, (2) both sexes of redwings show response equivalency between cowbird chatters and seet calls, (3) male redwings respond to anti-parasitic yellow warbler calls to cowbird chatters, but not to yellow warblers chip calls, and (4) male redwings respond more to cowbird chatters and seet calls coming from closer yellow warbler neighbors

Summary

Introduction

Referential alarm calls occur across taxa to warn of specific predator types. referential calls may denote other types of dangers. Red-winged blackbirds appear to eavesdrop on seets as warning system to boost frontline defenses on their territories, they do not seem to perceive the warblers’ seets as a cue for parasitism per se, but rather for general danger to the nest. Heterospecific eavesdropping on vocal signals is common across many species of birds and mammals[3], and can provide benefits such as the earlier detection of predators, increased foraging opportunities, and better informed decision-making for habitat selection or predator avoidance[3,4,5]. Eavesdropping on heterospecific alarm calls, or vocalizations that alert others of nearby predation risk[8], has been detected across diverse lineages of birds and mammals[3], and provides eavesdroppers with general information about predatory threats. To protect the nest from these threats, many species act aggressively toward both predatory and parasitic intruders within their territories/near their nests[26,27,28,29]

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