The adaptive significance of co-operative breeding in the red-throated bee-eater Merops Bulocki (Vieillot) and other bee-eaters (Aves: Meropidae)

• Main Author: Dyer, M.
• Published: University of Aberdeen 1979
• Subjects: 591.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.454230

Helping at the nest was recorded at 25% of Red-throated Bee-eater nests in Nigeria. Broods attended by pairs with helpers (multiple breeding units, or MBU's) received significantly more feedings than broods attended by unassisted pairs. Higher provisioning rates resulted in improved brood growth. In broods of three raised by pairs, the growth rate constant K of nestlings N1 and N2 was significantly higher than for N3; in broods raised by MBU's, no differences in K were found for N1, N2 and N3. Brood reduction occurred in 59% of broods of three raised by pairs, but in only 18% of MBU-raised broods. MBU's fledged 2.7 young per nest, significantly higher than the 2.0 young per nest fledged by pairs. To determine possible causes of the preponderance of males in adult populations of Red-throated Bee-eaters, adult weight loss over the nestling period, and nestling sex ratios were investigated. Males and females weighed less at the end of the nestling period than they did at the beginning, but no intersexual differences were found. The nestling sex ratio was found to be 1:1. Imbalance of the sexes was attributed to a combination of greater energetic investment to reproduction by females, and the tendency for females, rather than males, to disperse from the natal colony. Comparisons of life history parameters of the Red-throated Bee-eater with those of the Carmine, Little and European Bee-eaters, indicate that bee-eater species which are both colonial and migratory are more likely to be co-operative breeders than solitary-nesting, sedentary species. Since helpers are almost always offspring of the breeding pair they assist, helping behaviour is considered a strategy, through kin-selection, to minimise lose of individual and inclusive fitness.