Double nesting of the Red-legged Partridge Alectoris rufa.

Some Red-legged Partridge females lay two clutches in separate nests, one immediately after the other, which are incubated separately by the male and female of the pair. Pairs remained together during the laying of both clutches so that there were delays between the end of laying and incubation at the first nests. Incubation of the two nests began at approximately the same time but discrepancies of up to ten days occurred. Males incubated first clutches and females usually the second, but probably the first if the second was destroyed during laying. The proportion of surviving eggs which hatched was similar in first and second clutches but declined if the delay between laying and hatching was exceptionally long.

Yearling females began laying late and few seemed to attempt two clutches compared with older females of which 60–80% showed the double nesting habit. A model predicting reproductive success for both sexes in relation to the rate of nest predation during laying, suggested that attempting two clutches rather than one would be disadvantageous at high predation rates. Females would produce more young if their mates incubated their first clutch immediately it was complete rather than accompanying them during the laying of the second. However, males may benefit by this delay, even though it exposes the nest to predators for a longer time, because they are able to guard their mate and prevent other males from mating with her and fertilizing eggs of her second clutch.