Behavioural and evolutionary ecology of avian brood parastism

专性寄主在其他鸟类的巢中产卵，因此依靠寄主抚养后代。由于大多数寄主产生的后代较少，成功寄生的适应被寄主日益复杂的适应所抵消，这些适应使寄生的影响或发生寄生的可能性最小化。我们主要以北美的寄生牛鹂为研究对象，并对旧大陆的杜鹃进行了比较研究，从寄生物和寄主的角度研究了这种相互作用。曾经人们认为牛郎鸟会寄生在它们偶然发现的任何巢穴上，现在人们知道牛郎鸟会更多地使用一些宿主；这并不奇怪，因为牛椋鸟下的蛋比以前认为的要少。它们似乎只选择某些宿主，也许是最好的宿主。研究不同栖息地的牛郎鸟和寄主，我们正在探索选择性寄主使用增加牛郎鸟繁殖成功率的想法。通过实验，我们正在确定可能导致牛椋鸟非随机产卵的寄主属性：(1)巢的防御和必要行为的获得，(2)巢的放置，(3)寄生的耐受性，以及(4)寄主质量。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、巢穴的攻击性、已经寄生的巢穴的寄生（及其保护意义）、蛋的识别能力以及接受和拒绝牛鹂蛋的成本。我们将主要关注寄主的耐受性和寄主的质量，这部分是基于我们15年前发现的一种能排出牛鹂蛋的小物种。实验将扩展研究宿主如何识别牛鹂蛋和它们自己的蛋，以及它们识别外来蛋的能力，以及喙大小的限制，从而回答一个普遍存在的问题，即为什么这么多宿主物种容忍代价高昂的寄生。了解驱逐的最低物理要求和宿主接受的特定成本对于理解平衡或滞后是否更好地解释每个宿主物种的接受是必不可少的。拒绝成本可以解释某些寄主的接受（均衡），而滞后解释了无法识别牛鸟蛋的寄主的接受（均衡）。

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.