Coexisting and competing? Relationship of urban and anthropogenic variables and House Sparrow (Passer domesticus) abundance with the abundance of native Rufous-collared Sparrow (Zonotrichia capensis) in a small Mexican town

Urbanization poses significant challenges for bird species, acting as a spatio-temporally dynamic ecological filter. Birds respond to urban environments in varied ways, resulting in classifications like urban avoiders, users, and dwellers, with some species thriving in cities. The House Sparrow (Passer domesticus), a successful invasive species originally from the Middle East, has rapidly colonized urban areas across the Americas, where its adaptability and aggressiveness has shown to have the potential to threat native birds. While its impact is well-documented in northern Mexico, less is known about its potential effects in southern Mexico, particularly its competition with the native Rufous-collared Sparrow (Zonotrichia capensis). This study addresses this gap by investigating the relationship between these species in urbanized environments of a small town in Chiapas, Mexico. Using a city-wide sampling scheme, 224 survey sites were selected, and point-counts were conducted to record the abundance of both sparrows during their breeding season. A generalized linear model (GLM) revealed a negative relationship between Rufous-collared Sparrow numbers and ambient noise. A further regression tree analysis identified ambient noise, built cover, and House Sparrow abundance as variables related toRufous-collared Sparrow abundances. Sites with higher ambient noise levels, greater built cover, and more than six House Sparrows per site showed the lowest Rufous-collared Sparrow numbers, suggesting competition and habitat pressures are driving their distribution in urban environments.