ROOK 289 



taking a turn on the eggs has been recorded (Nethersole-Thompson and 

 Musselwhite, 1940). The Rev. F. C. R. Jourdain (1938), from whom 

 some of the above details are also quoted, states that the incubation 

 period is 16-18 days. Not all the nests are built at once; a few may 

 go on being added far into April, perhaps by young birds coming into 

 breeding condition for the first time. 



Eggs. — The eggs are of the usual Corvus type, but rather small. 

 The following condensed description is given by the Rev. F, C. R. 

 Jourdain in the work already quoted: 



"Usually 3-5, sometimes 6, rarely 7; 8 and 9 recorded: vary much 

 as Crow's: ground-colour from light bluish-green to green and greyish- 

 green but never so blue, and rarely show much of ground-colour, being 

 more uniformly marked with shades of ashy-grey and brown. Erythristic 

 varieties have occurred abroad and also Northern Ireland (H. T. 

 Malcomson). Average size of 100 British eggs, 40.0 x 28.3, Max.: 

 47.1 X 26.2 and 39.5 x 30.5, Min.: 35.1 x 27.1 and 44.2 x 25.8 mm., 

 averaging smaller than Crow's." r'j tnji 



Young. — The fledging period of the young is given by S. E. Brock 

 (1910) as 29 to 30 days. Yeates (1934) found that for the first 9 or 10 

 days the male collects all the food, but after this the female also takes 

 a share in the work. The food is brought in the capacious pouch under 

 the tongue, which produces a prominent swelling under the chin, con- 

 spicuous in birds coming into the rookery after a foraging excursion. 

 When the time c.omes for fledging the young birds, according to Yeates's 

 observations, are enticed out of the nest by the female, who refuses 

 to bring food to the nest but waits with it in the branches, calling 

 to the chicks until they venture out. They remain for some time in 

 the branches until their wings are strong enough to support them and 

 finally join the old birds in the fields, where the parents continue to 

 feed them at first. Mortality before leaving the nest is severe. Four 

 young hatched may be taken as a fair average, but counts quoted by 

 Yeates show that on an average at most only two chicks to a nest are 

 fledged. Only one brood is normally reared, but cases of breeding in fall 

 and even as late as November have been recorded. 



Plumages. — The plumages and molts are fully described by H. F. 

 Witherby in the Handbook of British Birds (1938). 



Food. — The food of the rook is thus summarized by Jourdain (1938) : 

 "In agricultural areas c.om is staple food, but potatoes, roots, fruit, 

 acorns, walnuts, peas, berries, and seeds also recorded. Animal food 

 includes insects: Coleoptera (many injurious species), also larvae, 

 larvae of Lepidoptera, Dermaptera, Orthoptera, Hymenoptera, Hemip- 

 tera, Diptera, and larvae, etc.: also earthworms, Mollusca (snails and 



