Birds under pressure: associations of highly-, moderately-, and lowly-abundant birds with landscape and local variables in a dense Neotropical city

Urban ecological studies often emphasize the role of vegetation-related factors in promoting local biodiversity, but less attention has been given to human-related factors, especially in tropical assemblages dominated by native species. In this study, we assessed the role of landscape and local variables in bird species richness and abundance in Medellín (Colombia), based on a city-wide survey (n = 212). We recorded 87 resident bird species, 97% of which were native, including the two species categorized as highly-abundant. Highly-abundant species showed mostly positive relationships with human activities (i.e. pedestrians and motorized vehicles), though only at the abundance level. In contrast, moderately-abundant species showed mostly negative relationships with both human activities and urban infrastructure (e.g. buildings, motorized vehicles), but mostly at the species richness level. Species richness of moderately-abundant species increased particularly at sites with low to intermediate fragmentation levels and landscape proportion of green cover, where the number of vegetation layers increased. Lowly-abundant species showed the strongest negative relationships with human activities and urban infrastructure, at both the species richness and abundance levels, particularly in sites with higher green cover fragmentation and lower landscape proportion of green cover. Interestingly, highly-abundant species abundance, and lowly-abundant species richness and abundance showed significant negative relationships with distance to the city border, but only the lowly-abundant species showed substantial spatial autocorrelation within the city. Our findings suggest that in Medellín, human-related factors can strongly constrain urban bird diversity. Therefore, given the substantial management limitations found in the most intensely urbanized environments, if we aim to promote biodiversity conservation across highly dense urban landscapes, it is important to reduce human-related constraints in sites with intermediate to low urbanization levels. Additionally, we should protect green cover remnants in areas with low urbanization levels and nearby non-urban areas.