现场工作很难。这很难，因为您必须提早起床，在燃烧的阳光或倾盆大雨中长时间工作，但最困难的是您无法预测会发生什么。In 2013, when we went to the Biological Station of Queen’s University near Kingston, Canada to work on wild tree swallows, we didn’t know that the experiment that we had carefully designed and had discussed over and over would ultimately fail miserably because of forces much greater than us.
Mother Nature decided not to approve our study, but instead, to teach us something else. And although we still regret that our plans didn’t work out, we think we might have been lucky to learn something about the life of these birds that we wouldn’t have otherwise.
我们研究的物种
Tree swallows are small (~20g) birds that live in socially monogamous pairs and (like many other passerine birds) work very hard to raise their kids that grow very fast: usually 4-6 chicks hatch from tiny eggs smaller than a penny and grow to adult size within three weeks.
结果，小鸡总是饿了，父母需要四处飞走，以捕捉足够的苍蝇来喂养饥饿的小鸡。那么，什么使他们能够做到这一点？
One hypothesis is that the glucocorticoid hormone, corticosterone, fuels the increased energetic demands during reproduction. A previous study in the same population found that when the number of chicks was experimentally increased, the mothers also increased their corticosterone levels, probably as a response to the increased demand.
However, corticosterone is also known as a ‘stress hormone’; therefore, high levels of this hormone will cause parents to abandon reproduction completely and divert energy to themselves. Thus, animals need a careful, internal balance that also responds to outside conditions.
我们做了什么？
为了测试皮质酮是否与父母努力的强度有因果关系，我们增加了皮质酮的雌性燕子的水平，这些雌性燕子的小鸡已经四天了。为此，我们在皮肤下植入了一个微小的含激素的可生物降解沉淀。我们的目标是看看他们是否会改变生殖工作。因此，这就是计划，但实际上是被雨水冲走了。
简而言之，2013年夏天在加拿大很糟糕。温度低于季节平均值，下雨了很多，当我们在繁殖季节中间看到一些雪花时，我们知道燕子很难。
树燕子专门以飞行的昆虫为食，因此您可以想象到这些鸟类最糟糕的天气是最糟糕的天气。在这种天气中，没有飞行的昆虫，即使父母正在竭尽全力找到一些昆虫，婴儿也留在巢中，他们的冷却很快。
那我们发现了什么？
毫不奇怪，重复的，寒冷的温度和大雨导致我们人口中的大多数鸟类放弃了繁殖。
毫不奇怪，重复的，寒冷的温度和大雨导致我们人口中的大多数鸟类放弃了繁殖。这些日子里，我们研究人群中几乎所有雏鸟都死亡，导致人口范围的死亡率达到90％以上。
但是，这些冷战使我们有机会测试环境条件如何与激素治疗相互作用以影响年轻人的生存。我们发现，当天气特别寒冷和多雨时，经过治疗和对照处理的巢的皮质酮的生存率相似。
However, when the weather was better, corticosterone treatment hastened brood mortality. In fact, control treated nests’ survival followed the weather patterns exactly, whereas corticosterone treated nests showed a mismatch with environmental conditions.
In the graph above, the black lines show the brood mortality and the blue dotted line shows the temperature (note that the scale is reversed on the right axis, so the highest peaks show the lowest temperatures). The brood mortality in the control group follows the temperature closely, whereas the corticosterone implanted group (solid black line) is mainly disconnected from the weather. In cold weather, the lines of the two groups overlap, whereas in warm weather they are more distinct.
此外，我们发现，在植入之前，有多少父母以一种有趣且出乎意料的方式对他们的后代进行了重要的投资。植入前的女性喂养率高意味着育雏的生存时间更长。
Surprisingly, however, even though we only manipulated females, males also responded to their partners’ altered states. High male feeding rates prior to implantation increased survival only in the control group, the reverse was found in the males whose partners received the hormone treatment.
It seems that males that were investing the most effort early on are more sensitive to changes in weather, and less able to persist with their high level of investment after their partner was hormone-implanted.
Adapting to challenging conditions
随着气候变化不可预测的天气的发生可能会增加，受干扰的人口可能无法适应更具挑战性的条件。
这些结果表明，激素水平对生殖成功的影响取决于上下文。尽管我们无法测试皮质酮的增加是否会使父母更加努力，但似乎在环境反对他们时，他们变得更容易失去小鸡。提高皮质酮水平以提高父母的努力可能是一个冒险的游戏。
Tree swallows are declining rapidly in the area where we studied them. As the occurrence of unpredictable weather is likely to increase with climate change, disturbed populations, with individuals that are already undergoing many stressors and have higher levels of glucocorticoids, may not be able to respond adaptively to even more challenging conditions.
注释