Interspecific territoriality despite vocal divergence in two sympatric Laterallus crakes

Abstract

Territoriality is a widespread behavioral phenomenon that functions for partitioning space and defending resources. Birds tend to defend territories against homospecific individuals through long-distance acoustic signals, but some species also exhibit interspecific territoriality. Two main hypotheses could explain interspecific territoriality mediated by long-distance acoustic signals: (1) misidentification of heterospecifics as homospecifics (misdirected aggression), or (2) recognition of heterospecifics as threats (purposeful aggression). The sympatric Red-and-white crake (Laterallus leucopyrrhus) and the Rufous-sided crake (L. melanophaius) are reciprocally territorial, but the mechanism underlying this interspecific territoriality is not known. We assessed the similarity of territorial long-distance acoustic signals (duet trills) between these crakes in comparison to more closely related species: Red-and-white vs. Rufous-faced crake (L. xenopterus) and Rufous-sided vs. White-throated crake (L. albigularis). Duet trills are two-parted, beginning with soft initial notes audible at close range and followed by a loud-trilled portion audible at long range. We ran univariate comparisons (Kruskal–Wallis), assessed overlap in multivariate acoustic space (PCA), and calculated vocal similarities (cluster analysis; Euclidean distances). The loud-trilled portions of the interspecifically territorial Red-and-white and Rufous-sided crakes occupied completely non-overlapping acoustic spaces, and were not grouped together by vocal similarity. Their territorial signals were more similar to those of their closest relatives, than between them. Soft initial notes of duet trills were in general very different between species, and their general structure matched the phylogenetic relationships. We found no evidence for strong character convergence and partial phylogenetic conservatism in signal explained overall similarities in vocalizations among species. The highly divergent vocalizations of Red-and-white and Rufous-sided crakes in conjunction with their interspecific territorial responses suggest that recognition of heterospecifics as threats, and not misidentification of heterospecifics as homospecifics, mediates their vocal responses. Our study adds evidence showing that interspecific territoriality represents purposeful heterospecific aggression and is not the product of misdirected homospecific aggression.