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BREEDING OF WILLOW WARBLER 2(3) but the difference is not statistically significant. The optimum clutch size is 7, and the optimum brood size is between 6 and 7. 3. The average incubation period is 13.0 days. The average nestling period is 13.2 days, and is at its shortest when clutch size is at a maximum. 4. Comparison is made with the results of other similar enquiries for passerine species in Great Britain.

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Summary Egg‐laying in Woodpigeons in central London lasts from March until September in normal years, with peak production in April and May, contrasting markedly with some rural areas in England where few clutches are completed before May and the peak months are July and August. Both appear to be determined by food supplies; London birds feed mainly on bread, supplemented by vegetable foods, which is in ample supply. so that they require much less time for feeding than rural birds in winter and early spring. They are thus able to breed over the whole period for which they are apparently physiologically capable. Breeding success in central London is almost double that in Cambridgeshire and nearly 50% above that in other rural areas, due to markedly lower predation, especially at the egg stage. The factors governing the breeding seasons of different populations of Woodpigeons are discussed.

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