Experimental manipulation of mixed-species flocks reveals heterospecific audience effects on calling

A community context for aggression? Multi‐species audience effects on territorial aggression in two species of Paridae

“…Therefore, the number and kind of heterospecific species/individuals, the presence of other parids, and environmental conditions all influenced the probability of territorial aggression. These findings confirm emerging insights and expectations concerning impacts of heterospecific audiences on avian social interactions (Coppinger et al., 2020; Magrath et al., 2020). However, our work is novel in detecting strong heterospecific audience effects on aggression, a pervasive social interaction within free‐living bird communities not generally considered as being connected to heterospecific influences.…”

“…Also, TUTI exhibited higher aggression overall than CACH (both intraspecific and interspecific). Given that most interspecific aggressive interactions among closely related bird species are asymmetrical and favor the larger species (Martin et al., 2017), it is clear that the larger‐bodied TUTI is the dominant species (Cimprich & Grubb, 1994; Coppinger et al., 2020).…”

“…This asymmetry is likely derived from the interspecies dominance relationship. In aviary trials involving antipredator versus control treatments in mixed flocks of TUTI and CACH, CACH vocal activity was repressed in the presence of TUTI to avoid aggression from the bigger birds in control conditions (without explicit predation risk or antipredator defense; Coppinger et al., 2020). In contrast, both TUTI and CACH called more in mixed flocks when presented with predation risk treatments, consistent with expectations under a social facilitation scenario during collective defense.…”

“…Titmice dominate chickadees at feeders and in foraging flocks in winter, yet they also interact in obtaining novel foods (Cimprich & Grubb, 1994; Freeberg et al., 2017) and share the same antipredator signaling system (Hetrick & Sieving, 2012). Moreover, both species can kill the other in direct conflicts despite a large size difference (titmice ~ 20–25 g; chickadees ~ 10–12 g) yet can also peaceably coexist in aviaries together (Coppinger et al., 2020).…”

Great tits (Parus major) adequately respond to both allopatric combinatorial mobbing calls and their isolated parts

“…For example, birds responding to each other alarm calls are more readily seen as by‐product mutualism, where the information produced is mostly directed towards conspecifics and, by chance, is also useful to heterospecifics listeners (Bradbury & Vehrencamp, 2011). However, recent studies have begun to unravel complex interactions between different species, especially in bird flocks (Carlson et al., 2020; Coppinger et al., 2020; Goodale & Kotagama, 2008). The gathering of birds of different species, either all year round in tropical environments (Goodale et al., 2015) or during the non‐breeding season in temperate environments (Dutour et al., 2019), is widespread and usually thought to be beneficial for both foraging efficiency and predator defence (Berner & Grubb, 1985).…”