Data from: House sparrows offset the physiological trade-off between immune response and feather growth by adjusting foraging behavior

Growing feathers and mounting immune responses are both energetically costly for birds. According to the life history trade-off hypothesis, it has been posited that the costs of feather growth lead to temporal isolation between molt and other expensive activities, reproduction for example. In contrast to life cycle events, the need to mount an immune response can occur at any time, including during feather growth. Thus, we hypothesized that mounting an immune response during feather growth may divert energy and resources from feather growth and impair feather renewal. To test this hypothesis, we clipped or plucked the same feathers of male house sparrows, Passer domesticus biblicus. In the clipped group (n = 16), the feathers were absent with no regrowth; in the plucked group (n = 14), feathers were absent and regrowth was initiated. We also had an intact control group of 15 sparrows. We then initiated an inflammatory immune response by subcutaneous injection over the left breast muscle of the birds with a lipopolysaccharide (LPS) and quantified behavioral and physiological responses. We predicted that sparrows with plucked feathers would incur the highest energetic costs while mounting an immune response, and would increase their foraging effort to offset this cost. We found no difference in body mass and resting metabolic rates among sparrows subjected to the different feather and immune treatments. However, we did find that while sparrows with plucked feathers increased foraging efficiency following the immune challenge by paying fewer but longer visits to the food tray, allowing them to maintain food consumption. Foraging efficiency in sparrows with clipped feathers was reduced. We also found that quality of newly grown feathers after the immune challenge was poorer in the plucked group, suggesting that mounting an immune response competes with feather growth for resources.

对于鸟类而言，羽毛生长与免疫应答均属于高能量消耗的生理过程。根据生活史权衡假说（life history trade-off hypothesis），已有研究提出，羽毛生长的能量成本会导致换羽与其他高消耗活动（例如繁殖）在时间上出现隔离。与生命周期内的固定事件不同，免疫应答的触发时机并无固定规律，甚至可能出现在羽毛生长期间。因此我们提出假说：在羽毛生长阶段启动免疫应答，可能会分流羽毛生长所需的能量与资源，进而损伤羽毛更新效果。

为验证该假说，我们对雄性家麻雀（Passer domesticus biblicus）的同侧羽毛分别进行修剪或拔除处理。其中修剪组（n = 16）的羽毛被移除且无再生现象；拔除组（n = 14）的羽毛被移除并启动了再生过程；此外还设置了15只家麻雀作为完整对照组。随后我们通过在鸟类左侧胸肌皮下注射脂多糖（lipopolysaccharide, LPS）来诱导炎症性免疫应答，并量化其行为与生理响应。

我们推测，处于羽毛拔除再生阶段的家麻雀在启动免疫应答时将承受最高的能量成本，并会通过增加觅食投入来抵消该成本。研究结果显示，接受不同羽毛处理与免疫处理的家麻雀，其体重与静息代谢率并无显著差异。但我们观察到：处于拔除组的家麻雀在免疫刺激后，通过减少觅食频次、延长单次觅食停留时间来提升觅食效率，从而维持了食物摄入量；而修剪组家麻雀的觅食效率则出现下降。此外我们还发现，免疫刺激后新生长羽毛的质量在拔除组中更差，这表明免疫应答与羽毛生长存在资源竞争关系。