2 resultados para COLONIES
em Brock University, Canada
Resumo:
Breeding parameters of Great Cormorants (PkaZac/iOCOfiCLX CCUibo dCUtbo) and Double-crested Cormorants (P. CLU/uXuA CMJhLtllb) were examined at two mixed species colonies at Cape Tryon and Durell Point, Prince Edward Island from 1976 to 1978. Differential access to nests at the two colony sites resulted in more complete demographic data for P. CCUibo than for P. CLUJiituA. In 1911j P. CCtfibo was present at both colonies by 21 March, whereas P. auAAJtuA did not return until 1 April and 16 April at Cape Tryon and Durell Point, respectively. Differences in the arrival chronology by individuals of each species and differences in the time of nest site occupation according to age, are suggested as factors influencing the nest site distribution of P. CXUtbo and P. aiVtituA at Cape Tryon. Forty-eight P. dOJtbo chicks banded at the Durell Point colony between 19 74 and 19 76 returned there to nest as two- to four-year olds in 19 77 and 19 78. Unmarked individuals with clutch-starts in April were likely greater than four years old as all marked two to four-year olds (with one possible exception) in 19 77 and 1978 had clutch-starts in May and June. Seasonal variation in the breeding success of P. dOJibo individuals was examined at Durell Point in 1977. Mean clutch-size, hatching success and fledging success exhibited a seasonal decline. Four- and 5-egg clutches represented the majority (75%) of all P. CCUibo clutches at Durell Point in 1977 and had the highest reproductive success (0.48 and 0.43 chicks fledged per egg laid respectively). Smaller clutches produced small broods with significantly higher chick mortality while larger clutches suffered high egg loss prior to clutch completion.
Resumo:
Aspects of the breeding biology of two Lake Erie Herri ng Gull colonies were studied in 1975 and 1976. In 1976 the incubation attention given 2-egg and 3-egg clutches initiated early and late in the season was measured. Brood size at one colony was artificially increased or decreased by addition of chicks shortly after hatching. Hatching success was not consistently re~ated to clutch size but early nesters were more successful than late nes'ters. Differences in hatching success between 2-egg and 3-egg clutches were a function of the time of clutch initiation with the clutch size having the greater proportion of its nests initiated early in the season being more successful. The incubation attentiveness of parents of 2-egg and 3-ev,g , and early and late clutches was similar. Most nests were incubated greater than 95% of the time although t heir hatching success was similar ' to those incubated less than 75% of the time. Fledging success, chick growth and weight at fledging were similar among broods of one, two and three chicks and artificially increased broods of four and five chicks. Fledging success was highest for o.e chick broods reduced from two and three chick broods.