The majority of bird species studied to date have molt schedules that are not concurrent with other energy demanding life history stages, an outcome assumed to arise from energetic trade-offs. Empirical studies reveal that molt is one of the most energetically demanding and perplexingly inefficient growth processes measured. Furthermore, small birds, which have the highest mass-specific basal metabolic rates (BMRm), have the highest costs of molt per gram of feathers produced. However, many small passerines, including white-plumed honeyeaters (WPHE; Lichenostomus penicillatus), breed in response to resource availability at any time of year, and do so without interrupting their annual molt. We examined the energetic cost of molt in WPHE by quantifying weekly changes in minimum resting metabolic rate (RMRmin) during a natural-molt period in 7 wild-caught birds. We also measured the energetic cost of feather replacement in a second group of WPHEs that we forced to replace an additional 25% of their plumage at the start of their natural molt period. Energy expenditure during natural molt revealed an energy conversion efficiency of just 6.9% (±0.57) close to values reported for similar-sized birds from more predictable north-temperate environments. Maximum increases in RMRmin during the molt of WPHE, at 82% (±5.59) above individual pre-molt levels, were some of the highest yet reported. Yet RMRmin maxima during molt were not coincident with the peak period of feather replacement in naturally molting or plucked birds. Given the tight relationship between molt efficiency and mass-specific metabolic rate in all species studied to date, regardless of life-history pattern (Efficiency (%) = 35.720•10−0.494BMRm; r2 = 0.944; p = <0.0001), there appears to be concomitant physiological costs entrained in the molt period that is not directly due to feather replacement. Despite these high total expenditures, the protracted molt period of WPHE significantly reduces these added costs on a daily basis.
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机译：迄今为止，研究的大多数鸟类的蜕皮计划与其他对能量的要求很高的生活史阶段没有同时进行，这被认为是出于精力充沛的取舍。实证研究表明，蜕皮是最耗费精力且效率最高的增长过程之一。此外，具有最高质量比基础代谢率（BMRm）的小鸟，每克羽毛产生的蜕皮成本最高。但是，许多小型雀形目，包括白羽蜜糖（WPHE;地衣青霉）会在一年中的任何时候根据资源的可利用性进行繁殖，并且这样做不会中断其每年的蜕皮。我们通过量化7只野禽在自然蜕皮期的最低静息代谢率（RMRmin）的每周变化，研究了WPHE中蜕皮的能量消耗。我们还测量了第二组WPHE中替换羽毛的能源成本，我们在自然换羽期开始时强制替换其羽毛的25％。天然蜕皮过程中的能量消耗显示能量转化效率仅为6.9％（±0.57），与从更可预测的北温带环境相似大小的鸟类报道的值接近。 WPHE蜕皮过程中RMRmin的最大增加，比各个蜕皮前水平高82％（±5.59），是迄今报道的最高值。然而，蜕皮过程中的RMRmin最大值与自然蜕皮或采摘的鸟类的羽毛替换高峰期并不吻合。鉴于迄今研究的所有物种的蜕皮效率与特定代谢率之间的紧密关系，而与生活史模式无关（效率（％））= 35.720•10 -0.494BMRm ; r 2 = 0.944； p = <0.0001），在蜕皮期似乎伴随着生理成本的增加，这不是直接由于羽毛的替换造成的。尽管总支出如此之高，但WPHE的长期换毛期每天都显着减少了这些增加的成本。
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