Brommer Jon E, Karell Patrik, Pihlaja Tuomo, Painter Jodie N, Primmer Craig R, Pietiäinen Hannu
Department of Ecology and Systematics, Bird Ecology Unit, University of Helsinki, Viikinkaari 1, P.O. Box 65, 00014 Helsinki, Finland.
Oecologia. 2003 Sep;137(1):140-7. doi: 10.1007/s00442-003-1317-1. Epub 2003 Jun 26.
Parents are expected to overproduce the less costly sex under poor food conditions. The previously regular 3-year cycle in the abundance of voles, the main prey of the Ural owl, Strix uralensis, temporarily disappeared in 1999-2001. We studied Ural owls' parental feeding investment and sex allocation during these poor-quality years. We sexed hatchlings and embryos in unhatched eggs of all 131 broods produced during these years. Population wide, the owls produced significantly more males (56%). The parental food investment in the brood was estimated by sorting out the prey remains in the bottom of nest boxes. Food delivered to 83 broods without chick mortality showed no clear sex-specific investment. Nestling mortality was equal in both sexes. Thus, evidence for an investment-driven sex allocation is weak. Neither laying date, brood size nor the female's condition correlated with offspring sex ratios. In these poor years, parents provided less food per chick and the fledgling weight of daughters was reduced more than the weight of sons compared with years of high food abundance (1983 and 1986). We discuss, in relation to published studies, the possibility of a sex-allocation scenario where, under poor food conditions, a daughter's long-term fitness is reduced more than a son's.
在食物条件较差的情况下，预计父母会更多地产出成本较低的性别。作为乌林鸮（Strix uralensis）主要猎物的田鼠数量此前有规律的三年周期，在1999 - 2001年暂时消失了。我们研究了在这些质量较差年份里乌林鸮亲代的喂食投入和性别分配情况。我们对这些年份所产出的全部131窝雏鸟以及未孵化卵中的胚胎进行了性别鉴定。在整个种群范围内，这些猫头鹰产出的雄性明显更多（56%）。通过整理巢箱底部的猎物残骸来估算亲代对一窝雏鸟的食物投入。提供给83窝没有雏鸟死亡情况的食物，未显示出明显的性别特异性投入。雏鸟死亡率在两性中是相等的。因此，由投入驱动的性别分配的证据很薄弱。产卵日期、窝雏数以及雌鸟的身体状况均与后代性别比例无关。在这些质量较差的年份里，与食物丰富的年份（1983年和1986年）相比，亲代给每只雏鸟提供的食物减少，并且雌性雏鸟离巢时的体重比雄性雏鸟的体重下降得更多。我们结合已发表的研究，讨论了在食物条件较差的情况下，女儿的长期适应性比儿子下降得更多的性别分配情形的可能性。
