Nonrandom spatial distribution of Neotropic Cormorants (Phalacrocorax brasilianus) along a coastal highway in Lima, Peru

Abstract

Neotropic Cormorants (Phalacrocorax brasilianus) are common seabirds along the Peruvian coast. They frequently perch on trees, poles and port structures in urban areas, causing discomfort and esthetic problems due to the dropping of their feces on infrastructure and people. Hundreds of these birds rest on lighting poles and telephone cables along a 12.7 km highway in the coastal strip of the city of Lima, Peru. We hypothesized that the distribution of the cormorants along this highway is clustered and could be associated with physical features of both the coast and the adjacent marine area. Half-monthly or monthly surveys were performed from July 2018 to March 2020 in the Circuito de Playas de la Costa Verde highway. At each survey, cormorants were counted per lighting pole and adjacent telephone cables (pole-cable) at four count hours (0600 h, 1000 h, 1400 h and 1800 h). Our results revealed that daily bird numbers varied from 46 to 457 individuals and that only 17% of the total number of pole-cables (N = 651) was occupied once by at least one individual. The number of cormorants also varied between count hours within the same day (higher numbers at 1000 h and 1400 h). Birds were clustered into a maximum of five hotspots along the highway. According to the Akaikes information-theoretic approach applied to Poisson GLMM, higher numbers of cormorants on pole-cables were associated mainly to a closer distance from these structures to the shoreline and to the surf zone, suggesting that Neotropic Cormorants may select such pole-cables as optimal sites for sighting and receiving clues of prey availability. Based on the results, the use of nonlethal deterrents and the relocation of these birds to other perching structures on nearby groynes could be the most suitable and eco-friendly solution for the problems caused by their droppings.