Heterospecific territorial defense in tit species varies according to breeding habitat overlap

The coexistence of species within the same guild is promoted by ecological and behavioral mechanisms, particularly niche differentiation. When niches overlap, coexistence may be maintained through spatial segregation, achieved through interspecific territoriality. Most research has focused on pairs of species, with little attention given to complex multispecies guilds. This study investigates the role of interspecific territoriality in promoting the coexistence of 5 sympatric tit species during the breeding season in northern Italy. These species are commonly grouped into "broadleaf" (great tit, blue tit, marsh tit) and "conifer species" (crested tit, coal tit), based on their habitat preferences. Indeed, in the study area, previous observations have shown that their breeding territories are spatially segregated. We experimentally tested whether aggressive territorial behaviors occurred in response to heterospecific playback stimuli, and if they were more intense against heterospecific intruders sharing the same, rather than a different habitat. Our findings revealed that this was the case for all "broadleaf species," indicating convergent adaptative heterospecific song recognition driven by competition for shared resources. In contrast, "conifer species" did not show such patterns, suggesting possible resource partitioning at a microhabitat scale or differences in breeding territory densities among habitats. This study enhances our understanding of intra-guild interactions and of the mechanisms facilitating coexistence in ecological communities.