Department of Biology, Western Kentucky University, Bowling Green, Kentucky, USA.
Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
J Exp Zool A Ecol Integr Physiol. 2024 Dec;341(10):1137-1146. doi: 10.1002/jez.2863. Epub 2024 Aug 16.
Arctic-breeding birds exhibit around-the-clock activity, and these activity cycles are postulated to maximize reproductive success during the short breeding season characteristic of high-latitude regions. Two closely related species of arctic-breeding songbirds, Lapland longspurs (Calcarius lapponicus; ground-nesting) and snow buntings (Plectrophenax nivalis; cavity-nesting) exhibit extended activity cycles throughout the polar day (71° N) except for 4-5 h of daily quiescence. Ground-nesting Lapland longspurs experience higher levels of nest predation than cavity-nesting snow buntings, and this difference is reflected in elevated nest vigilance in male longspurs compared with snow buntings. In this study, we examined the effect of melatonin supplementation upon male parental care, corresponding measures of nestling growth, and ability to reduce activity (and increase sleep). A pharmacological dose of melatonin in captive snow buntings dampened the amplitude of activity rhythms over the polar day with no detectable phase-shifting compared with control-implanted birds. Melatonin treatment reduced nest visits and overall time spent on the nest by male snow buntings compared with controls. There was no significant increase in time spent by female snow buntings on the nest to compensate for this, and there was no significant effect on offspring growth rates. There were no effects of melatonin supplementation on longspur adults or offspring, suggesting behavioral insensitivity to exogenous melatonin treatment. These differences in sensitivity underscore the importance of nest defense in ground-nesting longspurs compared with cavity-nesting snow buntings, which participate minimally in nest defense.
北极繁殖的鸟类表现出昼夜不停的活动，这些活动周期被假设为在高纬度地区短繁殖季节内最大限度地提高繁殖成功率。两种密切相关的北极繁殖鸣禽，即拉普兰长脚鹬（Calcarius lapponicus；地面筑巢）和雪鹀（Plectrophenax nivalis；洞穴筑巢），在极昼（71°N）期间表现出延长的活动周期，除了每天有 4-5 小时的安静时间。与洞穴筑巢的雪鹀相比，地面筑巢的拉普兰长脚鹬经历了更高水平的巢捕食，这种差异反映在雄性长脚鹬比雪鹀更高的巢警戒水平上。在这项研究中，我们研究了褪黑素补充对雄性亲代照顾、相应的雏鸟生长测量以及减少活动（和增加睡眠）的能力的影响。在圈养的雪鹀中，褪黑素的药理剂量抑制了极昼期间活动节律的幅度，与对照植入鸟类相比，没有可检测到的相位移动。褪黑素处理减少了雄性雪鹀的巢访问次数和整体在巢时间，与对照组相比。雌性雪鹀没有显著增加在巢上的时间来弥补这一点，对后代生长速度也没有显著影响。褪黑素补充对长脚鹬成鸟或后代没有影响，这表明对外源性褪黑素处理的行为不敏感。这些敏感性差异突出了在地面筑巢的长脚鹬中巢防御的重要性，与参与最小化巢防御的洞穴筑巢的雪鹀相比。
