Ganter Barbara, Cooke Fred
Department of Biology, Queen's University, Kingston, Ontario, Canada.
Oecologia. 1996 Apr;106(2):153-165. doi: 10.1007/BF00328594.
The potential contribution of early spring feeding conditions in the Arctic to clutch size variation was examined in a population of Lesser Snow Geese Anser caerulescens caerulescens. Behavioural observations were combined with energetic analyses of food material to derive an estimate of the energy budgets of pre-laying and laying females. Food intake of females between arrival on the breeding grounds and incubation was considerable; estimated energy gains in this period were in the same magnitude as the cost of one or several eggs. The pre-laying period spent on the breeding grounds can thus be energetically beneficial rather than costly. Accumulation of resources for reproduction in Snow Geese is a continual process including the breeding grounds, and nutrient limitation after arrival in the Arctic cannot sufficiently explain the environmental component of clutch size variation. The timing of migration and follicle development is such that clutch size decisions are sometimes made during the late stages of migration and some-times after arrival. In the latter case food conditions on the breeding grounds may greatly influence clutch size; in the former case they may still influence readjustments of clutch size after the initial decision. The universal negative correlation between clutch size and laying date in Snow Geese can be explained by negative fitness consequences of late hatching, which outweigh the benefits of delayed laying and further nutrient accumulation. Food shortage on the breeding grounds may sometimes be a secondary factor contributing to seasonal clutch size decline.
在小雪雁（Anser caerulescens caerulescens）种群中，研究了北极地区早春的觅食条件对窝卵数变化的潜在影响。行为观察与食物材料的能量分析相结合，以估算产卵前和产卵期雌雁的能量收支。雌雁从抵达繁殖地到开始孵化期间的食物摄入量相当可观；在此期间估计获得的能量与一枚或数枚卵的成本相当。因此，在繁殖地度过的产卵前期在能量方面是有益的，而非代价高昂。雪雁繁殖资源的积累是一个包括繁殖地在内的持续过程，到达北极后营养物质的限制不足以解释窝卵数变化的环境因素。迁徙和卵泡发育的时间安排使得窝卵数的决定有时在迁徙后期做出，有时在到达后做出。在后一种情况下，繁殖地的食物条件可能会极大地影响窝卵数；在前一种情况下，它们仍可能影响最初决定后的窝卵数调整。雪雁窝卵数与产卵日期之间普遍存在的负相关关系，可以通过晚孵化带来的负面适应性后果来解释，这种后果超过了延迟产卵和进一步积累营养物质的好处。繁殖地的食物短缺有时可能是导致季节性窝卵数下降的次要因素。
