Abstract

The effects of urbanization on woodland insectivorous mixed-species flocks have been little studied, and no seasonal studies have been conducted. This study aimed to describe the structure and seasonal dynamics of insectivorous mixed flocks in urban green areas of Buenos Aires City, Argentina. A total of 82 visits were conducted from April 2025 to March 2026. The potential effects of temperature, precipitation, humidity, and Julian day on flock occurrence were analyzed. The most frequent and abundant bird species in flocks were the White-crested Tyrannulet (Serpophaga subcristata), the Greyish Baywing (Agelaioides badius), the Masked Gnatcatcher (Polioptila dumicola), and the Tropical Parula (Setophaga pitiayumi). Serpophaga subcristata, Polioptila dumicola, and Setophaga pitiayumi tended to occur together in flocks. Flocks were observed in both native and exotic tree species. Flock occurrence was significantly associated with Julian day and peaked in autumn and during the early winter, coinciding with the non-breeding season. These results align with other studies conducted in subtropical and temperate regions. The significant relationship between flock occurrence and Julian day during the non-breeding season suggests that mixed flocking behavior helps individuals and pairs of different bird species by likely improving access to food and reducing predation risk as they move outside their breeding territories. A better understanding of the effects of urbanization on mixed flocks would be gained by comparing the spatial and temporal dynamics of flocking behavior in insectivorous birds in urban green areas with those in the region’s native woodlands.

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