Ardea
Official journal of the Netherlands Ornithologists' Union

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Ryder J.P. (1972) Biology of nesting Ross's Geese. ARDEA 60 (3-4): 185-215
Breeding biology and effects of variations in timing and spacing of Ross's Goose Anser rossii nests on clutch size and the production of young were studied in 1966, 1967 and 1968 on a large island (45.9 acres) at Karrak Lake, Northwest Territories (6715'N 10015'W) in the central Canadian Arctic. In 1966 and 1967, once geese arrived, the island was searched daily for new nests until the end of egg-laying. Nests were marked with a wooden stake and a history kept from the first egg to the hatching or disappearance of all eggs. In 1968, 11 circular plots of radius 100 feet were selected on the island before geese arrived. A history was compiled for nests in the plots. .In 1966 and 1967 nest spacing was determined in the field from nearest neighbour distances and the number of contemporary nests within a 20-foot radius of each+ marked nest. In 1968 scale maps of the circular plots were used to obtain nearest neighbour distances and the number of contemporary nests within 20-foot and 40-foot radii of each marked nest. The degree to which the observed nest dispersion departed from random was calculated from nests in 10 100-foot square plots in 1966 and the 11 1968 plots. Ross's Geese were first seen at Karrak Lake on30 May 1966, 10 June 1967 and 4 June 1968. Peak arrival dates, 3 June 1966, 13 June 1967 and 8 June 1968, were within a week of the mean weekly temperatures rising above 32F. Nest habitat was available each year when geese arrived. The interval between clutch initiation and completion in the late 1967 season was 55 per cent less than in. 1966 and 1968. Each year the modal clutch size was 4. The recorded average clutch size of 3.6 1.0 eggs in 1968 was smaller (P<0.05) than the 1966 and 1967 averages of 4.0 1.1 and 3.8 0.91 eggs respectively. It is thought the smaller clutch size in 1967 resulted from the late starting nesting season and, in 1968, from a larger proportion at young geese nesting for the first time. Clutches started before the modal date of clutch initiation (early clutches) averaged 1.5 eggs more (P<0.05) than those started after (late clutches). The incubation period averaged 21.8 0.90 days for the three seasons. About 50 per cent of eggs hatched each year were from 4-egg clutches. Hatching periods were 29 June-9 July 1966, 11-18 July 1961 and 5-16 July 1968. Over 70 per cent of all clutches hatched in 1 day. Nest success varied from 88.3 per cent in 1967 to 67.6 per cent in 1968. Hatching success was 80.3 per cent in 1967 and 60.6 per cent in 1968. The lower success in 1968 is attributed to the possible increase in young geese nesting for the first time. The mean distance to closest neighbour was 15 6.0 feet. It is suggested the number of nests in high density plots was regulated finally by a minimum distance nesting pairs tolerated between each other. In low density plots the number of nests may be regulated by the amount of suitable habitat. Nests showed a more uniform than random dispersion. It was calculated the present nesting population could be doubled in occupied areas before closest neighbour distances would be decreased and densities increased to the point where behavioural interactions might affect egg and young production. Some negative effects of distance to closest neighbour, density and clutch size on nest and hatching success were noted.


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