Temporal and environmental factors associated with owl calling in the Selva El Ocote Reserve, Chiapas, Mexico

Abstract

Owls are difficult to see in dark tropical forests so their calls or vocalizations are used to detect and study them. However, vocalizations may vary during the night in association with environmental factors. We evaluated variations in owl calling at night and environmental variables associated with them for the Vermiculated Screech-Owl (Megascops guatemalae), the Ridgway’s Pygmy-Owl (Glaucidium ridgwayi) and the Mexican Wood-Owl (Strix squamulata) in the Biosphere Reserve of Selva El Ocote, Chiapas, Mexico. Field surveys were carried out along 4 transects during 12 nights per month at 3 different time periods, recording environmental conditions (moon position, cloudiness, environmental lighting, moon phase and moon lighting). The frequency of calls of Megascops guatemalae and Glaucidium ridgwayi differed between time periods and was higher in the twilight of dawn. Environmental variables were associated with the frequency of calls although its intensity varied among species. The frequency of calls was explained by moon position and environmental lighting in Megascops guatemalae and Strix squamulata, and by moon position and lighting in Glaucidium ridgwayi. Time periods and environmental conditions associated with call frequency constitute basic information to understand the relationships between owl species and the environment, but also to improve sampling design in ecological studies on nocturnal raptors.