Environmental and Demographic Correlates of Intraspecific Nest Parasitism in Lesser Snow Geese Chen caerulescens caerulescens

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Abstract
(1) Intraspecific nest parasitism was the source of 5.3% .+-. 0.02 (S.D.) of the goslings hatched annually at the La Perouse Bay snow goose colony near Churchill, Manitoba [Canada], between 1969 and 1986. Yearly values ranged between 1.8 and 9.3%. (2) The rate of parasitism was low in years when nest-sites were readily available at the start of laying, and high when fewer sites were clear of snow or water. High parasitism rates did not occur in years of high nest failure during laying. This suggests that more parasitism occurs as a response to a lack of suitable nest sites than occurs as a consequence of nest failure. (3) Nest parasitism was higher at times when a higher than average proportion of young birds did not attempt to nest. (4) Nest parasitism had no measurable effect on the hatching sucess of host eggs. On average, the hatching success of parasitic eggs was lower than that of host eggs, primarily due to poor timing of laying by parasites relative to the onset of incubation. (5) Due to physiological constraints on total clutch size, enst parasitism in arctic nesting geese is largely a ''salvage'' female productive tactic, used by females that have a low likelihood of nesting successfully. This contrasts with the situation in temperate-nesting ducts and many other species of birds, where nest parasitism has the potential to be part of a mixed female reproductive strategy that may produce higher reproductive success than that obtained by laying the optimal number of eggs in a female''s own nest.