Morphological variation in bills and claws in relation to Prey type in Southern African Birds of Prey (Orders Falconiformes and Strigiformes)

Abstract

Bill and claw morphological characteristics were measured to establish the extent of functional similarities in the hunting and feeding apparatus among Southern African birds of prey (orders Falconiformes and Strigiformes) sharing the same prey type. MANOVA (Multivariate Analysis of Variance) was used to indicate the significance of differences at prey category level among the species. Student’s T test was used to assess for significant differences between sexes in their bill and claw morphological characteristics. Regression analysis indicated significant relationships between the morphological characteristics in birds of prey. In both the Falconiformes and Strigiformes orders significant differences were observed among the prey categories in the entire three claw morphological characteristics measured (claw shape, total claw length and hind claw length). In both orders all species except for carrion feeders showed significant variation in claw lengths with increase in mean body mass and wing length. Claws of carrion feeders were the least curved and shortest relative to their body masses and wing lengths among the raptors. In both orders, beak sizes and shapes showed some overlap among the prey categories. No significant differences were observed in bill shapes and bill volumes among the prey categories of both orders. However, in both orders the prey categories showed significant differences in bill lengths and culmen lengths. Except in carrion feeders, culmen length varied significantly with increase in mean body mass and wing length in all prey categories of both orders. Reversed sexual size dimorphism was also observed in the bill and claw sizes in most species in the two orders. However, no significant differences in the hind claw shape and bill shape were observed between sexes in most species of both orders. Degree of sexual size dimorphism varied among the species. In most species the females had larger hunting and feeding appendages compared to their male counterparts. In the order Falconiformes the genus Accipiter comprising mainly of bird feeders was the most dimorphic. In the order Strigiformes insect and other arthropod feeders were the most dimorphic.