Diet Analysis of Two Sympatric Owls to Assess Small Mammals Population Change in Nairobi Suburbs and Tsavo East National Park, Kenya

Abstract

Owls are nocturnal raptors that feed on small vertebrate animals and regurgitate undigested food remains in form of oval-shaped pellets. The pellets contain diverse species of small vertebrates and analysis of this pellets can reveal the more cryptic species that may not be trapped using the conventional live trapping methods. To address that knowledge gap, this study sought to conduct diet analysis of Spotted Eagle Owl (Bubo africanus Temminck, 1821) and Barn Owl (Tyto alba Scopoli 1769) in an urban environment in Nairobi metropolis and in natural habitats of Tsavo East National Park (TENP). The study compared prey composition, seasonal change in diet and its variation between the two owl species as well as compare prey species diversity in owl pellets and in live traps set in the two study areas. A total of 483 pellets were retrieved from Nairobi Metropolis, 371 Barn Owl pellets were collected from Ondiri Swamp and 112 pellets from Spotted Eagle Owl in Alliance Girls School. Further 424 pellets were collected from four Barn Owl nest sites in Tsavo East National, Park but no Spotted Eagle Owl pellets were available from this area. Standard live trapping was conducted across owl foraging areas in all habitats surrounding the nest sites. Data were collected during dry and wet season from December 2020 to August 2021. Small mammals formed the principal prey for all owls across habitats studied. Other species formed the least prey items. Results from ANOVA confirmed Barn Owl diet composition varied significantly in the two sites (F1,40= 93.57, P<0.05). There was no significant seasonal variation in the diet of Barn Owl in the two study sites (F3, 12=0.042, p˃0.05). Results obtained from ANOVA revealed significant statistical difference in Spotted Eagle Owl diet for the two seasons (F 1, 32= 4.9891, p<0.05). Analysis of Barn owl pellets and trapping results showed significant differences in prey species across habitats (F2, 14=2.68, p<0.05). However, spotted eagle owl diet composition and trapping did not differ significantly (t2, 9=1.44, P>0.05).