Berggren Asa, Armstrong Doug P, Lewis Rebecca M
Ecology Group, Massey University, Private Bag 11 222, Palmerston North, New Zealand.
Proc Biol Sci. 2004 Oct 22;271(1553):2123-30. doi: 10.1098/rspb.2004.2846.
Many bird species show delayed plumage maturation (DPM), retaining sub-adult plumage until after their first breeding season. Most explanations assume that DPM increases fitness over the breeding season. However, unless birds undergo a full moult before breeding, DPM could also be an adaptation to increase survival over the previous winter. The winter adaptation hypothesis has never been tested owing to the difficulty of measuring overwinter survival. We experimentally tested this hypothesis in North Island robins (Petroica longipes) using a closed island population where we could accurately estimate survival. The experiment involved dyeing 41 juveniles to mimic adult males, and comparing their survival with 41 control juveniles treated with the same peroxide base minus the pigment. The population was monitored with a series of resighting surveys, and mark-recapture analysis used to estimate overwinter survival. Survival probability was estimated to be 10% for dyed birds versus 61% for control birds in 2001, and 29% for dyed birds versus 40% for control birds in the winter of 2002, supporting the winter adaptation hypothesis for DPM. Access to suitable habitat is the key factor limiting juvenile survival in this population, and the locations where dyed juveniles were sighted suggest that they were often excluded from suitable areas.
许多鸟类表现出延迟换羽成熟（DPM），即保留亚成体羽毛直至其第一个繁殖季节之后。大多数解释认为，DPM会在繁殖季节提高适应性。然而，除非鸟类在繁殖前经历一次完整的换羽，否则DPM也可能是一种为提高上一个冬季的存活率而做出的适应。由于测量越冬存活率存在困难，冬季适应假说从未得到过检验。我们在北岛知更鸟（Petroica longipes）身上通过一个封闭岛屿种群进行了实验来检验这一假说，在该种群中我们能够准确估计存活率。实验包括给41只幼鸟染色以模仿成年雄鸟，并将它们的存活率与41只使用相同过氧化物基但不含色素处理的对照幼鸟进行比较。通过一系列重新观察调查对该种群进行监测，并使用标记重捕分析来估计越冬存活率。2001年，染色鸟的存活概率估计为10%，而对照鸟为61%；在2002年冬季，染色鸟的存活概率为29%，对照鸟为40%，这支持了DPM的冬季适应假说。获得适宜栖息地是限制该种群幼鸟存活的关键因素，观察到染色幼鸟的地点表明它们常常被排除在适宜区域之外。
