Behavioural and evolutionary ecology of avian brood parastism

专性巢寄生虫将卵产在其他鸟类的巢中，因此依赖宿主来抚养后代。由于大多数宿主产生的后代较少，成功寄生的适应会被宿主日益复杂的适应所抵消，从而最大限度地减少寄生的影响或发生寄生的可能性。我们主要关注北美的寄生牛鹂，并与旧世界的杜鹃进行比较，从寄生虫和宿主的角度研究这种相互作用。牛鹂曾经被认为会寄生在它们遇到的任何巢穴上，但现在人们知道它们会更多地使用某些宿主。这并不奇怪，因为牛鹂产的蛋比以前认为的要少。他们似乎只选择某些主机，也许是最好的主机。通过研究不同栖息地的牛鹂和宿主，我们正在探索选择性宿主使用可以提高牛鹂繁殖成功率的想法。通过实验，我们正在识别可能导致牛鹂非随机产蛋的宿主属性：（1）巢穴防御和必要行为的获得，（2）巢穴放置，（3）寄生耐受性，以及（4）宿主质量。我们正在比较影响寄主使用的物种内部和物种之间的差异，例如大小、巢的攻击性、已寄生巢的寄生性（及其保护影响）、蛋辨别能力以及接受与拒绝牛鹂蛋的成本。我们将主要关注寄主耐受性和寄主质量，这在一定程度上是基于我们 15 年前发现的一种能够排出牛鸟蛋的小型物种。实验将扩大对宿主如何看待牛鹂蛋和自己的蛋相对于它们识别外来蛋的能力的限制以及喙尺寸限制的研究，回答为什么如此多的宿主物种容忍昂贵的寄生的普遍问题。了解喷射的最低物理要求和宿主特定的接受成本对于理解平衡或滞后是否能更好地解释每个宿主物种的接受至关重要。拒绝成本可以解释某些宿主的接受性（平衡），而滞后则解释了无法识别牛鹂蛋的宿主的接受性。

Obligate brood parasites lay their eggs in nests of other species of birds, thus depending on the hosts to rear their offspring. As most hosts produce fewer young, adaptations for successful parasitism are countered by increasingly sophisticated adaptations by hosts that minimize the effects of parasitism or the likelihood that it will occur. Focusing primarily on parasitic cowbirds in North America, with comparative work on cuckoos in the old world, we are studying this interaction from the standpoints of parasite and host. Once believed to parasitize any nests they happened upon, cowbirds are now known to use some hosts more than others; this is not surprising because cowbirds lay fewer eggs than previously believed. They seem to select only certain hosts, perhaps the best ones. Studying cowbirds and hosts in different habitats, we are exploring the idea that selective host use increases a cowbird's reproductive success. With experiments, we are identifying attributes of hosts that may cause cowbirds to lay non-randomly: (1) nest defense and acquisition of requisite behaviour, (2) nest placement, (3) tolerance of parasitism, and (4) host quality. We are comparing differences within and among species that influence host use, such as size, aggressiveness at nests, parasitism of already-parasitized nests (and its conservation implications), egg-discrimination capabilities, and costs of acceptance versus rejection of cowbird eggs. We will focus mainly on host tolerance and host quality, building in part on our discovery 15 years ago of a small species that ejects cowbird eggs. Experiments will extend work on limits of how hosts see cowbird eggs and their own eggs relative to their abilities to recognize foreign eggs, and on bill-size constraints, answering the pervasive question of why so many host species tolerate costly parasitism. Knowing the minimum physical requirements for ejection and host-specific costs of acceptance is essential for understanding whether equilibrium or lag better explains acceptance in each host species. Rejection costs may explain acceptance in some hosts (equilibrium), whereas lag explains it in hosts that cannot recognize cowbird eggs.