Breeding Biology of White-Fronted Bee-Eaters at Nakuru:
The Influence of Helpers on Breeder Fitness

Emlen, S.T. & Wrege, P.H. (1991). Journal of Animal Ecology, 60:309-326.

Among white-fronted bee-eaters (Merops bullockoides ) near Nakuru, Kenya, helpers dramatically increased the fitness of breeders. Using 5 years of data, we examine the relative importance of food availability, breeder attributes and group size on reproductive success. Both food availability and size of the group attending the nest had significant effects on productivity, while the characteristics of breeders (age, experience) did not. Helpers had their effect almost entirely through increased productivity per nesting attempt, each helper on average increasing the number of fledglings by 0 multiplied by 50 ( plus or minus 0 multiplied by 06 S.E.). The activities of helpers did not affect either breeder survival or the number of nesting attempts per year. The presence of helpers did not affect clutch size, had no influence on the probability of successful hatching, but dramatically increased the rate of provisioning per nestling.