Don't put all eggs in one nest - spread them and cut time at risk

In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are debated. Using mathematical modelling and field observations we analyse an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, a parasitic female by spreading her eggs can reduce offspring time in the vulnerable nest, at risk of predation or other destruction. The model suggests that she can achieve much of this benefit already by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a much larger than average clutch, without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproduct...