Long-Term Population Fluctuations of A Burrowing Owl Population On Kirtland Air Force Base, New Mexico, USA

Western Burrowing Owls (Athene cunicularia hypugaea; hereafter, Burrowing Owls) were once widespread residents of grasslands throughout western North America, but their range has contracted, and abundance has declined in some regions. The causes of declines and geographic variation in population trends of Burrowing Owls are unclear but may be linked to changing land use and urbanization. Burrowing Owls are often found in association with airfields and airports, and their presence at such facilities is sometimes considered to be in conflict with those operations. Documenting the long-term persistence of Burrowing Owls at active airfields can help airfield managers who face decisions regarding compatibility of owls and airfield operations. We report the results of a long-term effort to monitor Burrowing Owls on Kirtland Air Force Base in New Mexico, USA, including the rapid recovery of Burrowing Owl numbers from near-extirpation and the relationships between abundance and other demographic traits. The number of breeding pairs of Burrowing Owls increased from one pair in 2013 to 28 pairs in 2019 and 2020, and the number of fledglings produced increased from one in 2013 to 84 in 2019 and 61 in 2020. The recovery was not uniform across all areas of Kirtland Air Force Base, and some formerly occupied areas remained unoccupied. We documented dispersal outside the Air Force base boundary and that the number of breeding pairs was more strongly influenced by the number of offspring produced in the prior year than the number of owls returning from prior years, which indicated that the population is part of a larger meta-population. Our results demonstrate that the maintenance of Burrowing Owl populations is not necessarily at odds with safe airfield operations, that Burrowing Owls exhibit complex population dynamics, and can rapidly recolonize previously occupied areas if habitat and nest sites remain suitable.

Urban life promotes delayed dispersal and family living in a non-social bird species

In some vertebrate species, family units are typically formed when sexually mature individuals delay dispersal and independent breeding to remain as subordinates in a breeding group. This behaviour has been intensively studied in gregarious species but has also been described in non-social species where ecological and evolutionary drivers are less known. Here, we explore factors that favour delayed dispersal and family living and potential benefits associated with this strategy in a non-social, monogamous species (the burrowing owl, Athene cunicularia) occupying urban and rural habitats. Our results show that family units arise when first-year individuals, mainly males, delay their dispersal to stay in their natal nests with their parents. This delayed dispersal, while still uncommon, was more prevalent in urban (7%) than in rural (3%) habitats, and in areas with high conspecific density and productivity. Birds delaying dispersal contributed to the genetic pool of the offspring in 25% of the families analysed, but did not increase the productivity of the nests where they remained. However, their presence was related to an improvement in the body condition of chicks, which was ultimately linked to a slightly positive effect in offspring future survival probabilities. Finally, delayed dispersers were recruited as breeders in high-quality urban territories and closer to their natal nests than individuals dispersing during their first year of life. Thus, our results suggest that delaying dispersal may be mainly related to opportunities to inheriting a good quality territory, especially for males. Our study contributes to understanding the role played by habitat quality in promoting delayed dispersal and family living, not only in social but also non-social species, highlighting its impact in the ecology and evolution of animal populations.

Hippoboscid flies (Diptera: Hippoboscidae) on birds of prey in the Atlantic Forest, Minas Gerais, Brazil

Hippoboscid flies are potential ectoparasites of several avian orders, including birds of prey, a group formed by the orders Falconiformes, Strigiformes, Cathartiformes and Accipitriformes. In this study, we evaluated 155 birds of prey that were brought to the Wildlife Rehabilitation Center of Juiz de Fora, Minas Gerais, Brazil, between the years 2016 and 2019. Two species of hippoboscid flies (Ornithoctona erythrocephala and Icosta americana) were found in five species of birds of prey (Megascops choliba, Asio stygius, Athene cunicularia, Asio clamator and Caracara plancus). The average intensity found was 1.4 hippoboscids/bird and Megascops choliba (tropical screech-owl) was the most parasitized bird. This is the first record of parasitism of Asio stygius (stygian owl) by Ornithoctona erythrocephala in Brazil and of Athene cunicularia (burrowing owl) and Asio clamator (striped owl) by Icosta americana. Ornithoctona erythrocephala is recorded here for the first time infesting birds of prey in the state of Minas Gerais, Brazil.