Effects of breeding density on the behaviour and reproductive success of cavity nesting birds

许多鸟类和哺乳动物用树洞筑巢。次级洞穴使用者竞争由被称为主洞穴挖掘者的啄木鸟等挖掘者创造的筑巢洞。不同种类的巢巢鸟所使用的资源类型（树木基质）和巢腔特征已经得到了很好的描述。然而，对于巢址的种内和种间竞争如何影响森林洞穴筑巢鸟类的定居模式、景观上的巢距和繁殖成功率，人们知之甚少。研究繁殖密度的后果很重要，因为许多栖息地正变得更加破碎，例如由于森林采伐。因此，在剩余的栖息地斑块中，密度可能会增加，鸟类可能被迫更多地相互作用。***我研究的主要目的是研究繁殖密度和筑巢地点竞争对腔巢鸟类行为和繁殖成功率的影响。我将使用在不列颠哥伦比亚省Riske Creek使用天然树洞的不同穴居群体的数据来寻找巢穴间距和繁殖成功率之间的相关性。然而，我将重点关注两种常见的洞穴筑巢物种：山青鸟和树燕，它们相互竞争筑巢地点，并随时使用巢箱。通过控制巢穴密度，我将研究在保护巢穴和觅食以及最终繁殖成功之间是否存在行为和生理上的权衡。高密度的潜在竞争对手可能会增加繁殖成本，但也可能有好处，比如共同攻击捕食者。通过对燕子和蓝知更鸟的巢箱进行巢穴密度和捕食者（模型猫头鹰和松鼠）的实验操作，我将测试相同或其他物种的邻居是否有助于群体袭击。具体来说，我将验证一个假设，即成群的巢穴比孤立的巢穴更安全。总之，我的研究将增加我们对鸟类在破碎化影响日益严重的景观中所经历的繁殖挑战和利益的理解，并可能有助于制定森林采伐模式，减少鸟类繁殖的压力

*** Many species of birds and mammals use tree holes for nesting. Secondary cavity users compete for nesting holes created by excavators such as woodpeckers which are the called the primary cavity excavators. The types of resources (tree substrates) and characteristics of cavities used by different species of cavity-nesters have been well described. However, there is a poor understanding of how intra- and inter-specific competition for nest sites influence the settlement patterns, nest spacing on the landscape, and the reproductive success of cavity-nesting birds in forests. Studying the consequences of breeding density is important because many habitats are becoming more fragmented, for example as a result of forest harvesting. As a result, densities may increase in the remaining habitat patches, and birds may be forced to interact more with one another. *** The main objective of my research is to study the effects of breeding density and competition for nesting sites on the behaviour and reproductive success of cavity-nesting birds. I will use data from a diverse community of cavity-nesters using natural tree holes at Riske Creek, B.C to search for correlations between nest spacing and reproductive success. However, I will focus on field experiments involving two common cavity-nesting species: Mountain Bluebirds and Tree Swallows which compete with each other for nesting sites and readily use nest boxes. By manipulating nest density, I will study whether there are behavioural and physiological trade-offs between defending a nest site and foraging, and ultimately reproductive success. *** High densities of potential nest competitors may increase reproductive costs but there may also be benefits such as communal mobbing of predators. Using experimental manipulations of nest density and presentation of predators (model owls and squirrels) at the nest boxes of swallow and bluebird pairs, I will test whether neighbours of the same, or of other species, contribute to group mobbing. Specifically, I will test the hypothesis that clumped nests are safer from predators than isolated nests. In sum, my research will increase our understanding of reproductive challenges and benefits experienced by birds in a landscape increasingly affected by fragmentation, and may aid in developing forest harvest patterns that reduce the stress for breeding birds.**