A Multifactor Study of Clutch Size Determination in the Eastern Kingbird

目前，许多生物的数量出现了令人震惊的下降。在鸟类中，建造开杯巢、在北美繁殖和冬季在新大陆热带(新热带)繁殖的鸟类数量下降最快。下降的原因尚不清楚。为了了解种群遭受痛苦的原因，有必要记录(A)成虫、(B)巢和(C)独立幼鸟的生存模式。此外，我们必须了解控制和/或限制生殖的因素。窝大小(每个巢的卵数)是鸟类的主要繁殖变量，在其他条件相同的情况下，产卵最多、产下最多幼鸟的个体应该占主导地位。因此，很难理解为什么某些鸟类的窝卵数小于最多产的雏鸟数(每窝产仔数)。了解这一现象很重要，因为生殖过程对种群动态有直接影响，因此对保护做法也有直接影响。这个项目提出了五个假设，用来解释为什么产卵量最大的雏鸟通常要小一些。东方帝王鸟(Tyrannus Tyrannus)是一种长途迁徙，在亚马逊地区过冬，通常只产三个蛋，但可以生育4个甚至5个幼鸟。将进行实验，以确定王鸟的小窝点是否与(A)食物可获得性低，(B)对巢的捕食压力高，(C)与父母生存的权衡(即，饲养许多幼鸟增加成年死亡率)，(D)与后代存活率的权衡(即，从大窝中孵化出来的幼鸟体型较小，存活率较低)，或者(E)由于种内寄生(即不同的雌性将卵添加到一个完整的巢中)而导致的窝卵数量的不可预测的增加。这项研究的结果将有助于解开“次最大”繁殖之谜，并为东方帝王鸟的生存、繁殖成功和种群稳定提供具体的信息。

Many organisms are currently showing alarming decline in abundance. Among birds, species that build open-cup nests, breed in North America and winter in the New World tropics (Neotropics) are showing the sharpest declines. The reasons for the declines are not known. To understand why populations are suffering it is necessary to document survival patterns of (a) adults, (b) nests, and, (c) independent young. In addition, it is crucial that we understand what factors control and/or limit reproduction. Clutch size (number of eggs/nest) is the primary reproductive variable among birds, and all else being equal, individuals that lay the largest clutches and produce the most young should dominate. It is therefore hard to understand why clutch size in some species of birds is smaller than the most productive brood size (number of young/nest). Understanding this phenomenon is important because reproductive processes have a direct impact on population dynamics, and therefore conservation practices. This project proposes to examine five hypotheses that have been put forth to explain why clutch sizes are often smaller than the most productive brood sizes. The Eastern Kingbird (Tyrannus tyrannus), a long distance migrant that winters in Amazonia, typically lays just three eggs but can raise 4 and sometimes 5 young. Experiments will be conducted to determine if small clutch size in kingbirds is related to (a) low food availability, (b) high predation pressure on nests, (c) trade-offs with parental survival (i.e., raising many young increases adult mortality), (d) trade-offs with offspring survival (i.e., young fledged from large broods are smaller and have lower survival rates), or, (e) unpredictable increases in clutch size due intraspecific brood parasitism (i.e., the addition of eggs to a completed nest by a different female). The results of this study should help to clarify the puzzle of "submaximal" reproduction and also provide specific information on survival, reproductive success and population stability in the Eastern Kingbird.