OBSERVATIONS ON THE ROOK CORVUS FRUGILEGUS IN SOUTHWEST CORNWALL

Abstract

SUMMARY Observations on the breeding behaviour of Rooks were made between 1943 and 1955. The gonads of a series of Rooks from the same area and during the same period were examined (Marshall & Coombs 1957). The autumn sexual resurgence is comparable to early spring in both gonad condition and behaviour. Display postures are described. A slow wing‐raising component, common to several postures, is very rare and perhaps absent when the testes are refractory. It might have a sexual significance. Rooks use song posts, but song is not used in the establishment or defence of territory. Copulation occurs most frequently between birds that are not paired to each other. It is usually interfered with, and in more than 90% of the incidents observed the female was incubating. Resemblances between the incubating position and the female soliciting posture may lead to this. The territory is a small area round each nest: neighbouring territories may overlap. Rooks who are active in pilfering a neighbour's nest for building material, may establish some territorial dominance over it. Nest sites are selected by both sexes and in both spring and autumn. Either sex can build a nest. Normally the male does most of the stick structure, and the female more of the cup and lining. During incubation the female is fed on the nest by the male, and after the young have hatched for as long as he can provide food for her as well as the young. Droppings are removed by both parents, partly as a response to fouling of the nest. Development of the gonads and of the behaviour of juveniles is described. A few birds reach breeding condition at one year old, the majority a year later. Expectation of life at one year old is probably four years. Some data are given on the relationship with other Corvidae in the area and with some other species.