ABSTRACT Density dependence is a conceptual cornerstone of avian population biology and, in territorial songbirds, past research has emphasized interactions among food limitation, density, and reproduction. Documenting the importance of density effects is central to understanding how selective forces shape life histories and population dynamics. During the 2008–2011 breeding seasons, we nearly doubled overall conspecific breeding densities on study sites, and manipulated nest box spacing to increase local breeding densities (defined as the number of pairs breeding within 200 m of a pair's nest) of a secondary cavity-nesting songbird, the Prothonotary Warbler (Protonotaria citrea). Our primary objective was to test for effects of food limitation, as mediated by conspecific local densities, on measures of productivity. We monitored breeding pairs and recorded the total number of fledglings produced along with several components of reproductive output (clutch size, hatching success, nestling survival, and probability of attempting a second brood), rates of nestling provisioning, and nestling body condition prior to fledging. We predicted that if the availability of food were affected by local densities, then one or more of these parameters measuring reproduction would be affected negatively. We did not detect an effect of local density on total reproductive output or its components despite our vast range of local densities (1–27 pairs; i.e. 0.16–2.23 pairs ha–1). Further, we also did not detect differences in nestling provisioning rates and nestling body condition relative to local density. By breeding in a productive ecosystem rich in food resources, these warblers appear to avoid reduced reproductive output when breeding in high densities. Whereas density-dependent food limitation may commonly reduce reproductive output in many species, the ecological circumstances underlying when it does not occur merit further investigation and may provide new insights into what is driving territoriality and what are the primary factors affecting individual fitness.

中文翻译：

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局部同种密度不影响二级腔巢鸣禽的生殖产量

摘要 密度依赖性是鸟类种群生物学的概念基石，在领地鸣禽中，过去的研究强调了食物限制、密度和繁殖之间的相互作用。记录密度效应的重要性对于理解选择性力量如何塑造生命史和种群动态至关重要。在 2008-2011 年的繁殖季节，我们将研究地点的整体同种繁殖密度几乎翻了一番，并操纵巢箱间距以增加次要巢穴的局部繁殖密度（定义为一对巢穴 200 米内繁殖的对数） -筑巢鸣禽，原声鸣鸟 (Protonotaria citrea)。我们的主要目标是测试食物限制对生产力测量的影响，由同种局部密度介导。我们监测了繁殖对并记录了所产生的雏鸟总数以及繁殖输出的几个组成部分（离合器大小、孵化成功率、雏鸟存活率和尝试第二次育雏的概率）、雏鸟供应率和雏鸟出生前的身体状况. 我们预测，如果食物的供应受到当地密度的影响，那么衡量繁殖的这些参数中的一个或多个将受到负面影响。尽管我们的局部密度范围很广（1-27 对；即 0.16-2.23 对 ha-1），但我们没有检测到局部密度对总繁殖产量或其组成部分的影响。此外，我们也没有发现雏鸟供应率和雏鸟身体状况相对于当地密度的差异。通过在富含食物资源的生产生态系统中繁殖，这些莺在高密度繁殖时似乎避免了繁殖量的减少。尽管密度依赖的食物限制通常可能会降低许多物种的繁殖产量，但不发生时的潜在生态环境值得进一步调查，并可能为驱动领土性的因素以及影响个体健康的主要因素提供新的见解。