Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Champaign, IL, USA.
Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Champaign, IL, USA.
Proc Biol Sci. 2022 Sep 14;289(1982):20221223. doi: 10.1098/rspb.2022.1223.
Generalist brood parasites that share nests with host nestlings can optimize resource acquisition from host parents by balancing the benefits that host nest-mates provide, including attracting increased provisions to the nest, against the costs of competing with the same host young over foster parental resources. However, it is unclear how parasitic chicks cope when faced with more nest-mates than are optimal for their survival upon hatching. We suggest that, in the obligate brood parasitic brown-headed cowbird (), chicks use a niche construction strategy and reduce larger, more competitive host broods to maximize the parasites' survival to fledging. We experimentally altered brood sizes to test for Goldilocks principle patterns (i.e. a 'just right' intermediate brood size) of cowbird survival in nests of prothonotary warbler () hosts. We found that intermediate brood sizes of two host nestlings maximized cowbird fledging success relative to 0 or 4 host nest-mates at hatching. Specifically, cowbird nestlings lowered host brood sizes towards this optimum when placed in broods with more host nestlings. The results suggest that cowbirds reduce, but do not eliminate, host broods as a niche construction mechanism to improve their own probability of survival.
一般性巢寄生者与宿主雏鸟共享巢穴，可以通过平衡宿主同伴提供的利益来优化从宿主父母那里获取资源，包括吸引更多的食物到巢中，以及与同一宿主幼鸟竞争寄养父母资源的成本。然而，当寄生雏鸟面临比孵化后生存所需的最佳巢同伴更多的情况时，它们如何应对还不清楚。我们认为，在专性巢寄生的褐头牛鹂（Molothrus ater）中，雏鸟会使用生态位构建策略，减少较大、更具竞争力的宿主雏鸟数量，以最大限度地提高寄生虫的存活率，直至离巢。我们通过实验改变了窝雏数量，以测试在黄腹森莺（Protonotaria citrea）宿主的巢穴中，牛鹂生存是否存在“金发姑娘原则”模式（即“恰到好处”的中间窝雏数量）。我们发现，相对于孵化时有 0 或 4 个宿主巢同伴，两个宿主雏鸟的中等窝雏数量使牛鹂的离巢成功率最大化。具体来说，当放置在有更多宿主雏鸟的窝中时，牛鹂雏鸟会将宿主的窝雏数量降低到这个最佳水平。研究结果表明，牛鹂通过减少但不消除宿主窝雏数量，作为一种生态位构建机制，来提高自己的生存概率。
