THE BREEDING AND FEEDING OF JACKDAWS AND ROOKS WITH NOTES ON CARRION CROWS AND OTHER CORVIDAE.

摘要: Summary. 1 The nestling food and breeding of Jackdaws, Rooks, to a lesser extent Carrion Crows were studied at Oxford from 1952 1954. 2 The average clutch-size in the Jackdaw is 4–4 Rook 4–3. Late clutches are significantly lower than early but not Jackdaw. Annual variation small. 3 In both survival nestlings decreases as brood-size increases. Predation, disease, nest-site unimportant producing this mortality; food-shortage very important. 4 In Jackdaws Rooks eggs hatch asynchronously an adaptation variable food-supply; by speedy elimination small young brood when short, brought into closer correspondence with food-supply. 5 In which effectively produces most lies between four five. This corresponds clutch. 6 Rooks typically probe grassland where they obtain earthworms form bulk nestlings. April on best month for obtaining (or suitable alternative food) nest. feed surface open grassy places have their nest many varied invertebrates habitat abundantly available. partly woods grassland. The fed mainly earthworms, birds mammals. 7 The season varies little year year. food-supply unlikely be major factor initiating ovulation since its abundance variable.