Phenology habitat choice and reproduction of the Great Crested Grebe Podiceps cristatus on a fish-farm.

On a fish-farm in The Netherlands Great Crested Grebe breeding pairs arrived in two distinct periods. We suggest this pattern reflects differences in migratory behaviour, whereby late birds are migrants. In early arriving grebes clutch size decreased with an increasing pre-laying period, whereas in late grebes clutch size decreased with arrival date. Early grebes produced larger eggs, made more breeding attempts and produced more fledglings per pair than late birds. Food availability did not influence distribution, habitat choice nor breeding activities of Great Crested Grebes, but habitat choice, distribution and hatching survival were positively influenced by the presence of reedbeds. The number of pairs per pond was related to pond surface. Clutch size and egg size decreased with laying data and, independent of laying data mean egg size was larger in successful than in unsuccessful broods. On average 0.97 young fledged per breeding pair. Hatchling mortality was about 60%, and 75% of the nests (N = 66) produced no young. Interbrood-interval, difference in clutch size and egg volume between two successive broods were correlated with the reproductive effort in the initial breeding attempt.

Ulenaers P. & Dhondt AA., ARDEA 79 (3): 395-408.