Tufted titmice, black-crested titmice, and their hybrids occupy different types of habitat within their hybrid zone

Abstract

Tufted Titmice (Baeolophus bicolor) (TUTI) and Black-crested Titmice (Baeolophus atricristatus) (BCTI) are sister species that hybridize within a narrow east–west contact zone that extends from central Texas into southwest Oklahoma. The zone corresponds with an ecotone that transitions from closed-canopy deciduous forests in the east, occupied by TUTI, to arid and open woodlands in the west occupied by BCTI. Furthermore, the ecotone encompasses areas impacted by urban and suburban development. We tested whether landscape-level landcover characteristics found within the TUTI × BCTI hybrid zone influence the abundances of the two parent species and their hybrids. We predicted that the parent species would differ in their habitat associations and hybrids would associate with habitats intermediate between that of TUTI and BCTI and with human disturbed habitats. In ArcGIS Pro, we used a grid-based sampling design to extract estimates of six land cover variables (derived from National Landcover Database data) and TUTI, BCTI, and hybrid abundances (derived from eBird data). Partial redundancy analysis (RDA) was used to examine the habitat associations of the three titmice types. The results revealed that TUTI associated most strongly with the percentage of mixed forest cover, and BCTI with the percentage of evergreen forest cover and impervious surface cover. No single landcover variable could be identified as a definitive association for hybrids, however, hybrid individuals do appear to be more abundant in a habitat type that is intermediate between that of the two parent species. Future studies should incorporate genotypic data from titmice in the hybrid zone and analyze habitat associations at finer spatial scales to gain a more conclusive understanding of the patterns detected in this broad scale study.