Laboratorio Ecotono, INIBIOMA (CONICET-Universidad Nacional del Comahue), Bariloche, Argentina.
PLoS One. 2012;7(9):e46347. doi: 10.1371/journal.pone.0046347. Epub 2012 Sep 27.
Age-dependent skewed sex ratios have been observed in bird populations, with adult males generally outnumbering females. This trend is mainly driven by higher female mortality, sometimes associated with anthropogenic factors. Despite the large amount of work on bird sex ratios, research examining the spatial stability of adult sex ratios is extremely scarce. The Andean condor (Vultur gryphus) is the only bird of prey with strong sexual dimorphism favouring males (males are 30% heavier than females). By examining data from most of its South-American range, we show that while the juvenile sex ratio is balanced, or even female-skewed, the sex ratio becomes increasing male-skewed with age, with adult males outnumbering females by >20%, and, in some cases by four times more. This result is consistent across regions and independent of the nature of field data. Reasons for this are unknown but it can be hypothesized that the progressive disappearance of females may be associated with mortality caused by anthropogenic factors. This idea is supported by the asymmetric habitat use by the two sexes, with females scavenging in more humanized areas. Whatever the cause, male-skewed adult sex ratios imply that populations of this endangered scavenger face higher risks of extinction than previously believed.
在鸟类种群中观察到了与年龄相关的性别比例偏斜，成年雄性通常多于雌性。这种趋势主要是由较高的雌性死亡率驱动的，有时与人为因素有关。尽管对鸟类性别比例进行了大量研究，但研究成年性别比例的空间稳定性的研究却极为罕见。安第斯神鹰（Vultur gryphus）是唯一一种具有强烈性别二态性的猛禽，雄性（雄性比雌性重 30%）占优势。通过检查其大部分南美的分布数据，我们发现，虽然幼鸟的性别比例是平衡的，甚至是雌性偏斜的，但随着年龄的增长，性别比例变得越来越偏向雄性，成年雄性的数量超过雌性超过 20%，在某些情况下，甚至超过四倍。这一结果在各地区都是一致的，与实地数据的性质无关。造成这种情况的原因尚不清楚，但可以假设，雌性的逐渐消失可能与人为因素造成的死亡率有关。这种情况得到了两性不对称的栖息地利用的支持，雌性在更有人化的地区觅食。无论原因是什么，雄性偏斜的成年性别比例意味着这种濒危食腐动物的种群面临着比以前认为的更高的灭绝风险。
