Abstract
Vertebrates obtain social information about predation risk by eavesdropping on the alarm calls of sympatric species. In the Holarctic, birds in the family Paridae function as sentinel species; however, factors shaping eavesdroppers' reliance on their alarm calls are unknown. We compared three hypothesized drivers of eavesdropper reliance: (a) foraging ecology, (b) degree of sociality, and (c) call relevance (caller‐to‐eavesdropper body‐size difference). In a rigorous causal‐comparative design, we presented Tufted Titmouse (Baeolophus bicolor) alarm calls to 242 individuals of 31 ecologically diverse bird species in Florida forests and recorded presence/absence and type (diving for cover or freezing in place) of response. Playback response was near universal, as individuals responded to 87% of presentations (N = 211). As an exception to this trend, the sit‐and‐wait flycatcher Eastern Phoebe (Sayornis phoebe) represented 48% of the nonresponses. We tested 12 predictor variables representing measures relevant to the three hypothesized drivers, distance to playback speaker, and vulnerability at time of playback (eavesdropper's microhabitat when alarm call is detected). Using model‐averaged generalized linear models, we determined that foraging ecology best predicted playback response, with aerial foragers responding less often. Foraging ecology (distance from trunk) and microhabitat occupied during playback (distance to escape cover) best predicted escape behavior type. We encountered a sparsity of sit‐and‐wait flycatchers (3 spp.), yet their contrasting responses relative to other foraging behaviors clearly identified foraging ecology as a driver of species‐specific antipredator escape behavior. Our findings align well with known links between the exceptional visual acuity and other phenotypic traits of flycatchers that allow them to rely more heavily on personal rather than social information while foraging. Our results suggest that foraging ecology drives species‐specific antipredator behavior based on the availability and type of escape cover.
Highlights
Species with similar foraging behav‐ iors convergently evolve similar morphological and physiological structures known as ecomorphs (Botero‐Delgadillo & Bayly, 2012; Corbin, 2008); for instance, eye morphology differs significantly be‐ tween bird species in different foraging guilds (Lisney et al, 2013; Moore, Doppler, Young, & Fernández‐Juricic, 2013). These suites of physiological adaptations to foraging behaviors may result in similar physiological limitations on detection capability, and similar degrees of reliance on social information
We conduct a comparative test of the role of three species‐level ecological hypotheses in determining the degree of reliance on eavesdrop‐ ping, while controlling for local microhabitat effects
In order to include a greater diversity of species in our analy‐ sis of playback response, we ran (3) a second generalized linear model (GLM) model of response in which we included all species that received playbacks (N = 31 species, 238 playbacks), and a greater diversity of forag‐ ing behaviors and body masses
Summary
Vertebrates must constantly seek information about their surround‐ ings to reduce uncertainty and make adaptive behavioral choices (Dall, Giraldeau, Olsson, McNamara, & Stephens, 2005; Danchin, Giraldeau, Valone, & Wagner, 2004; Schmidt, Dall, & van Gils, 2010; Seppänen, Forsman, Mönkkönen, & Thomson, 2007). Species with similar foraging behav‐ iors convergently evolve similar morphological and physiological structures known as ecomorphs (Botero‐Delgadillo & Bayly, 2012; Corbin, 2008); for instance, eye morphology differs significantly be‐ tween bird species in different foraging guilds (Lisney et al, 2013; Moore, Doppler, Young, & Fernández‐Juricic, 2013) These suites of physiological adaptations to foraging behaviors may result in similar physiological limitations on detection capability, and similar degrees of reliance on social information. Social species employ complex vigilance behaviors such as the sentinel systems which can accurately assess ambient preda‐ tion risk through alarm calls (Ridley & Raihani, 2007; Ridley, Raihani, & Bell, 2010) Both birds and social primates only make use of het‐ erospecific social information when in small conspecific groups, switching to conspecific social information in larger groups (Bshary & Noë, 1997; Ridley & Raihani, 2007). We conduct a comparative test of the role of three species‐level ecological hypotheses (foraging ecology, sociality, and call relevance) in determining the degree of reliance on eavesdrop‐ ping, while controlling for local microhabitat effects
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