Female song in passerine birds may be more common than traditionally assumed, but it is not well‐documented or understood, especially in migratory species. We describe the first evidence of sex‐specific songs produced by female Prothonotary Warblers, as well as the results of playback trials aimed at exploring the adaptive function (if any) of this female‐specific vocalization. Based on the behaviour of three females and our playback trials, we suggest that these unique songs are related to mate acquisition during the early stages of courtship.
Hybridization between two species typically occurs when allopatric or ecologically dissimilar species expand into areas of secondary contact or habitat transitions. However, as species' ranges shift rapidly in response to environmental change, the potential for novel types of ephemeral hybrid zones exists. Here, we document and describe the occurrence, prevalence and symmetry of a previously undocumented hybrid zone involving two sympatric, ecologically similar sister species that have been expanding their ranges eastward in the central USA: Scissor‐tailed Flycatchers Tyrannus forficatus and Western Kingbirds Tyrannus verticalis. We identified cases of hybridization and introgression using analyses of eight microsatellite DNA loci and a single mitochondrial gene. We also evaluated short‐term reproductive consequences of hybridization for both species by surveying for both species and potential hybrids at the periphery of their ranges in northeastern Arkansas and western Tennessee, USA. Genetic data revealed bi‐directional backcrossing at the periphery of the species’ ranges, including a cryptic hybrid. We also analysed DNA of putative ‘pure’ individuals from other parts of their ranges and detected two cryptic admixed individuals, suggesting backcrossed individuals from the periphery may be dispersing to breed or that hybridization events have occurred in the core. Finally, our results suggest that there are no short‐term reproductive consequences of hybridization for the two species. In total, hybrid zones that occur at the edges of expanding, sympatric ranges may be ephemeral; we suggest they play an important role in introgression and may have long‐standing impacts for sympatric sister species. Exploring the extent of hybrid zones such as this for other range‐expanding taxa will elucidate whether this type of hybrid zone is unique or a common occurrence.
We used whole-genome resequencing to estimate genetic distinctiveness in the Black-throated Green Warbler (Setophaga virens)—including S. v. waynei—a putative subspecies that occupies a narrow disjunct breeding range along the Atlantic Coastal Plain. Despite detecting low global differentiation (FST = 0.027) across the entire species, the principal components analysis of genome-wide differences shows the main axis of variation separates S. v. waynei from all other S. v. virens samples. We also estimated a low migration rate for S. v. waynei, but found them to be most similar to another disjunct population from the Piedmont of North Carolina, and detected evidence of a historical north-to-south geographic dispersal among the entire species. New World wood warblers (family: Parulidae) can exhibit strong phenotypic differences among species, particularly in song and plumage; however, within-species variation in these warblers—often designated as subspecies—is much more subtle. The existence of several isolated Black-throated Green Warbler populations across its eastern North American breeding range offers an excellent opportunity to further understand the origin, maintenance, and conservation status of subspecific populations. Our results, combined with previously documented ecological and morphological distinctiveness, support that S. v. waynei be considered a distinct and recognized subspecies worthy of targeted conservation efforts.
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