Orell Markku, Koivula Kari, Rytkönen Seppo, Lihti Kimmo
Department of Zoology, University of Oulu, FIN-90570, Oulu, Finland.
Oecologia. 1994 Dec;100(3):339-346. doi: 10.1007/BF00316963.
Causes and consequences of non-breeding in willow tits were studied in northern Finland during 1986-1992. The breeding status was sex and age biased; males and yearling birds were in excess among the non-reproducers. Due to sex bias in the population it appeared detrimental for males to lose a mate, especially shortly before breeding. Lack of a mate was a important factor for males not reproducing (37% of non-breeding males) than for females (14%). Most of the non-breeding birds maintained a pair bond which only rarely broke up for the next breeding season (divorce rate 5.5%). This implies that parental incompatibility is not a possible explanation for pairs not reproducing. Males that did not breed tended to survive better than reproducing ones, whereas such a relationship was not found for females. It is possible that this sex-related difference in survival cost is attributable to quality differences among non-breeding individuals. It was especially low-quality yearling females, with low survival prospects, that were responsible for the discrepancy. The proportion of non-breeding females in the population correlated highly with clutch size and subsequent juvenile survival. It is therefore suggested that for most of these females non-breeding is a phenotypic response to low offspring value in the prevailing circumstances (inter-generational tradeoff). However, it is uncertain whether willow tits in a northern population can use breeding density as an indicator of changing survival prospects of their descendants, as suggested by Ekman and Askenmo (1986) for southern Sweden.
1986年至1992年期间，在芬兰北部对长尾山雀不繁殖的原因及后果进行了研究。繁殖状况存在性别和年龄偏差；在不繁殖的鸟中，雄性和一岁鸟占比过高。由于种群中的性别偏差，对雄性来说失去配偶似乎是有害的，尤其是在繁殖前不久。没有配偶是雄性不繁殖的一个重要因素（37%的不繁殖雄性），而对雌性来说这一比例为14%。大多数不繁殖的鸟维持着配偶关系，这种关系在接下来的繁殖季节很少破裂（离婚率为5.5%）。这意味着亲代不相容不是配偶不繁殖的可能原因。不繁殖的雄性往往比繁殖的雄性生存得更好，而雌性则没有发现这种关系。这种生存成本方面与性别相关的差异可能归因于不繁殖个体之间的质量差异。导致这种差异的主要是一岁的低质量雌性，它们的生存前景不佳。种群中不繁殖雌性的比例与窝卵数和随后的幼鸟存活率高度相关。因此，有人认为，对于大多数这些雌性来说，不繁殖是在当前环境下对低后代价值的一种表型反应（代际权衡）。然而，尚不确定北方种群的长尾山雀是否能像埃克曼和阿斯肯莫（1986年）对瑞典南部所建议的那样，将繁殖密度作为其后代生存前景变化的指标。
