Effects of Helpers on Parental Condition in Red-Throated Bee-Eaters (Merops bullocki)

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Abstract
(1) Weights of nesting red-throated bee-eaters in Nigeria were monitored using electronic weighing-perches set into a colony cliff-face: 3600 weights were obtained at two colonies over two breeding seasons. (2) Weights of individuals varied by 5% diurnally, with a maximum variation of 10.6%. Regurgitated pellets each weighed up to 2.6% of body weight (0.6 g) and faeces up to 0.8% (0.2 g). (3) All birds were heaviest just before egg-laying, and lightest at the end of the nestling period. (4) Breeding males, with and without a helper, peaked at 26.5 g then lost 8% of body mass in the week prior to egg-laying and a further 7% (down to 23.0 g) when their young fledged. The initial weight loss is ascribed to feeding their mates and guarding them. Helpers provided some assistance to males at this time. (5) Weights of helpers followed a similar seasonal pattern to those of breeding males. (6) Breeding females with helpers weighed the same as those without, at all stages of nesting. (7) Weights of only unhelped females were correlated with visiting rates to their nests: increased visiting was associated with decreased weight. (8) All bee-eaters maintained their weights despite the vagaries of the weather: showing fewer correlations than expected by chance between mean daily weights and five different weather parameters.