The Vocal Activity of Twelve African Owl Species

Abstract

Vocalization of different species of owls carries a lot of scientific information on their distribution and diversity. There is little information on the owl vocalizations in the tropical environments. The calling of 12 African owl species was studied in Malawi 1993–1998, and in The Gambia 1998–2004. The direct listening method was used to collect some 2062+ vocal records mostly at the house gardens or sometimes on the balcony at wildlife lodges and rural hotels. Owls are normally vocal most actively especially just before breeding, but in this material, the peak months coincided very little with the given breeding times in Malawi and The Gambia. It is possible that the validity of the breeding times is not enough, but other reasons are not clear because the sampling was opportunistic rather than systematic. If vocalizations are used to estimate owl populations, it is important to identify the environmental factors affecting owl calling. Heavy rain and wind were silencing the owls or at least made it impossible to hear their voices due to the background noise. Barn Owls Tyto alba were often calling immediately after the heavy wind calmed and no precipitation was falling. The temperature is not so important if the other conditions are suitable for calling, Barn Owl and Pearl-spotted Owl Glaucidium perlatum were vocal as well in +37°C as in +15°C. Some owl species may increase vocal displays during full moonlight (like the African Barred Owlet Taenioglaux capense, Pearl-spotted Owl, and Southern White-faced Owl Ptilopsis granti) but others call less or not at all during the full moon (Barn Owl). The impact of the full moon was not that obvious as the bright sky can also activate the Pearl-spotted Owl. Barn Owl started to call actively again when the moon was diminishing to 60% of its full size and its luminosity. It was noted in The Gambia that the obvious predation risk and interference competition was altering the vocal activity of the African Scops Owl Otus senegalensis, which stopped calling when the Barn Owl was active. Barn Owl is a predator that can attack the smaller African Scops Owl. In Malawi Spotted Eagle Owl, Bubo africanus calling bouts were suspected to silence the Pearl-spotted and Southern White-faced Owls as the larger owl could prey on these smaller owls if hearing their calls.