Wellicome Troy I
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Oecologia. 2005 Jan;142(2):326-34. doi: 10.1007/s00442-004-1727-8. Epub 2004 Oct 9.
In most animals, siblings from a given reproductive event emerge over a very short period of time. In contrast, many species of birds hatch their young asynchronously over a period of days or weeks, handicapping last-hatched chicks with an age and size disadvantage. Numerous studies have examined the adaptive significance of this atypical hatching pattern, but few have attempted to explain the considerable intrapopulation variation that exists in hatching asynchrony. I explored proximate determinants of hatching asynchrony by monitoring 112 Burrowing Owl (Athene cunicularia) nests in the grasslands of southern Saskatchewan, Canada, over 4 years. Age disparities between first- and last-hatched siblings (i.e., hatching spans) varied considerably, ranging between 1 and 7 days (mode = 4 days). These hatching spans increased with increased hatching success. Hatching spans also increased with larger clutches, but the increase was less than predicted given the increased time required to lay more eggs. Hatching span was unrelated to number of prey cached in the nest during egg laying (an index of food availability), and was unaltered by a year of super-abundant prey. Furthermore, pairs given extra food during laying had hatching spans equal to those of unsupplemented control pairs. These results were inconsistent with both the energy constraint and facultative manipulation hypotheses, which predict that hatching asynchrony should vary with the level of food during laying, when incubation onset is determined. Burrowing Owls were apparently free of food limitation early in breeding, yet may not have been able to optimize hatching spans because food conditions during laying were largely unrelated to food conditions during brooding. Thus, one of the premises for facultative manipulation of hatching asynchrony-that laying females are able to forecast post-hatch food conditions-may not have been met for this population of Burrowing Owls.
在大多数动物中，同一繁殖事件产生的同胞后代会在很短的时间内相继出生。相比之下，许多鸟类会在数天或数周的时间里异步孵化幼雏，这使得最后孵化出的雏鸟在年龄和体型上处于劣势。众多研究探讨了这种非典型孵化模式的适应性意义，但很少有人尝试解释孵化异步现象中存在的显著种群内变异。我通过在4年时间里监测加拿大萨斯喀彻温省南部草原上的112个穴小鸮（穴小鸮属）巢穴，探究了孵化异步现象的近因决定因素。最先孵化和最后孵化的同胞之间的年龄差距（即孵化跨度）差异很大，在1到7天之间（众数为4天）。这些孵化跨度随着孵化成功率的提高而增加。孵化跨度也随着窝卵数的增加而增加，但增加幅度小于预期，因为产下更多的卵需要更多时间。孵化跨度与产卵期间巢穴中储存的猎物数量（食物可获得性的一个指标）无关，并且在猎物极为丰富的年份也没有改变。此外，产卵期间给予额外食物的配对的孵化跨度与未补充食物的对照配对的孵化跨度相同。这些结果与能量限制假说和兼性操纵假说均不一致，这两个假说预测，在确定孵化开始时，孵化异步现象应随产卵期间的食物水平而变化。穴小鸮在繁殖早期显然没有受到食物限制，但可能无法优化孵化跨度，因为产卵期间的食物条件与育雏期间的食物条件基本无关。因此，对于穴小鸮种群来说，兼性操纵孵化异步现象的一个前提条件——即产卵雌鸟能够预测孵化后食物条件——可能并未得到满足。
