Observations on the Breeding Kittiwake

r.The history and growth of a Kittiwake colony first established on a warehouse at North Shields, Northumberland in 1949, and now containing 47 nests, are described.2. The Kittiwake colonies on the east coast of Gt.Britain within too miles radius of the colony studied have all shown an increase in the number of breeding pairs in recent years.3. The Kittiwake's incubation period was measured in four years of study, 1954 to 1957.The average incubation period of 119 eggs was 27.3 ± 1.3 days.4. The average `fledging period' of 116 chicks was found to be 42.7 ±4.4 days, the minimum period being about 36 days.There was no difference between the fledging periods of single and paired chicks.5. The mean clutch size of 149 clutches was 2.01 eggs, and clutches laid during the latter part of the season were significantly smaller than early clutches.The average brood size at hatching was 1.82 chicks (not including clutches which failed completely).6.The breeding success of the colony was 56% between egg-laying and fledging of young, 1.14 young being fledged per breeding pair.7. The average daily increase in weight of chicks between 100-300 g. was 16 g.There was no difference between the growth rates of broods of one and two chicks, and no difference between the growth rates of older and younger birds in broods of two chicks.8. Clutches and broods of three produced more fledged young per breeding pair than those of two and one, but only two broods of three were successfully fledged.The high mortality among clutches of three was brought about by two factors, (a) asynchronous hatching resulting in one chick being starved, and (b) crowding on nest sites.