Breeding parameters of great cormorants (Phalacrocorax carbo carbo) at mixed species colonies on Prince Edward Island, Canada

摘要

Breeding parameters of Great Cormorants (PkaZac/iOCOfiCLX CCUibo dCUtbo) andDouble-crested Cormorants (P. CLU/uXuA CMJhLtllb) were examined at two mixedspecies colonies at Cape Tryon and Durell Point, Prince Edward Island from1976 to 1978. Differential access to nests at the two colony sites resultedin more complete demographic data for P. CCUibo than for P. CLUJiituA.In 1911j P. CCtfibo was present at both colonies by 21 March, whereasP. auAAJtuA did not return until 1 April and 16 April at Cape Tryon andDurell Point, respectively. Differences in the arrival chronology byindividuals of each species and differences in the time of nest siteoccupation according to age, are suggested as factors influencing the nestsite distribution of P. CXUtbo and P. aiVtituA at Cape Tryon.Forty-eight P. dOJtbo chicks banded at the Durell Point colony between19 74 and 19 76 returned there to nest as two- to four-year olds in 19 77 and19 78. Unmarked individuals with clutch-starts in April were likely greaterthan four years old as all marked two to four-year olds (with one possibleexception) in 19 77 and 1978 had clutch-starts in May and June.Seasonal variation in the breeding success of P. dOJibo individuals wasexamined at Durell Point in 1977. Mean clutch-size, hatching success andfledging success exhibited a seasonal decline. Four- and 5-egg clutchesrepresented the majority (75%) of all P. CCUibo clutches at Durell Point in1977 and had the highest reproductive success (0.48 and 0.43 chicks fledgedper egg laid respectively). Smaller clutches produced small broods withsignificantly higher chick mortality while larger clutches suffered highegg loss prior to clutch completion.