Impaired flight ability prior to egg‐laying: a cost of being a capital breeder

Summary To investigate flight ability in captive Zebra Finches during reproduction we compared change in escape take‐off ability and wing load of reproducing females with their mates and non‐reproducing females when attacked by a model raptor. Initially females had 18% higher wing load than males. Non‐reproducing females and females that had started egg‐laying flew slower than males. Reproducing females reduced wing load during egg‐laying and flew faster when the clutch was completed. Non‐breeding females remained on high wing load and flow slower than breeding females that had completed their clutch. The increase in flight speed of breeding females was explained by a reduction in wing load during egg‐laying. Zebra Finches use accumulated reserves to produce eggs and pay a cost in terms of reduced flight ability, but then regain flight performance when the clutch is laid, probably demonstrating a predation cost of capital breeding in birds.