Some passerines incorporate aromatic plants in their nest cups, and several hypotheses have been formulated to explain this behaviour. One of those, the Drug Hypothesis, states that aromatic plants present in nests have positive effects on nestlings’ development through increased immune function. In this study, we aimed to examine if experimental addition of aromatic plants had positive effects on reproductive performance (the number of fledglings produced and nestling survival rate) and nestling development (weight and tarsus length). In addition, we study whether those potential effects were more noticeable in different brood sizes–small and large–through an observational approach. We expect that large broods, due to increased resource competition between nestlings, will benefit more from aromatic plant incorporation, as compared to small broods. Nestlings were significantly heavier in 2015 as compared to 2016 and 2017 and in small broods. No effect of treatment was observed in nestling weight. Although there was no overall effect of treatment on nestling tarsus length, nestlings from aromatic nests had significantly longer tarsi as compared to nestlings from control nests, in large broods.

中文翻译：

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雏鸟蓝山雀 (Cyanistes caeruleus) 的发育受实验性添加芳香植物的影响

一些雀形目在它们的巢杯中加入了芳香植物，并且已经制定了几个假设来解释这种行为。其中之一，药物假说，指出巢中存在的芳香植物通过增加免疫功能对雏鸟的发育产生积极影响。在这项研究中，我们旨在检查实验性添加芳香植物是否对繁殖性能（产生的雏鸟数量和雏鸟存活率）和雏鸟发育（重量和跗骨长度）产生积极影响。此外，我们通过观察方法研究了这些潜在影响是否在不同的育雏规模（大小）中更加明显。我们预计，与小型育雏相比，由于雏鸟之间的资源竞争加剧，大型育雏将从加入芳香植物中获益更多。与 2016 年和 2017 年相比，2015 年的雏鸟和小雏鸟的体重明显更重。未观察到处理对雏鸟体重的影响。尽管处理对雏鸟跗骨长度没有整体影响，但与来自对照巢的雏鸟相比，来自芳香巢的雏鸟的跗骨明显更长，在大型育雏中。