Colisões de aves em estruturas de vidro no campus de Sorocaba da Universidade Federal de São Carlos: uma ameaça que persiste

Abstract

It is estimated that collisions with glass panes cause the death of over one billion birds annually in North America alone. These collisions mainly occur because birds struggle to perceive glass as an impassable barrier due to its reflectivity and transparency, combined with various physiological, anatomical, and behavioral factors. However, studies on this issue in Brazil are still limited, which is concerning given that the country has the second-highest bird diversity in the world. This study aimed to detect evidence of bird-glass collisions on the Sorocaba campus of the Federal University of São Carlos (UFSCar) and to identify factors contributing to the frequency of these collisions. Additionally, we sought to estimate the persistence of bird carcasses in the environment and assess the negative effects of collisions on the physical condition of the birds to complement the collision data. Data on the number of collisions were collected through regular monitoring over one year. We also gathered information on building characteristics, their surroundings, and the biological traits of the species involved. To analyze whether there are differences in the number of collisions related to seasonality, building characteristics, surroundings, and species traits, we employed mixed generalized linear models (GLMMs) and univariate statistical analyses. For experimental trials, bird carcasses from collisions were placed around campus buildings and monitored to determine their average persistence in the environment and identify the species responsible for their removal. Necropsies and X-rays were conducted to identify injuries caused by these collisions. During the monitoring period, 152 pieces of collision evidence were collected; however, no significant difference was found between the number of collisions in the rainy and dry seasons. Additionally, no morphological predictor variables could explain the variability in collision numbers among species. Nonetheless, the area of transparent glass, total glass area, and black glass area in square meters were the predictor variables that best explained the number of collisions between buildings, with a positive correlation observed between these surface areas and the number of collisions. Carcasses had an average persistence of 110.69 ± 196.06 hours in the environment. Five species were identified as responsible for carcass removal: Homo sapiens sapiens, Cariama cristata, Coragyps atratus, Canis lupus familiaris, and Caracara plancus. Necropsies and X-rays revealed that the most common injuries in birds that collided with glass were fractures, cerebral hematomas, and cranial hemorrhages. This study provides evidence of bird collisions with glass structures at UFSCar Sorocaba, indicating that it is a high-risk area for such accidents. The monitoring methods used and the detrimental effects of these collisions on bird health were discussed. Urgent preventive measures are needed to mitigate this generally fatal threat.