Data from: Phenotype-limited distributions: short-billed birds move away during times that prey bury deeply

In our seasonal world, animals face a variety of environmental conditions in the course of the year. To cope with such seasonality, animals may be phenotypically flexible, but some phenotypic traits are fixed. If fixed phenotypic traits are functionally linked to resource use, then animals should redistribute in response to seasonally changing resources, leading to a ‘phenotype-limited’ distribution. Here, we examine this possibility for a shorebird, the bar-tailed godwit (Limosa lapponica; a long-billed and sexually dimorphic shorebird), that has to reach buried prey with a probing bill of fixed length. The main prey of female bar-tailed godwits is buried deeper in winter than in summer. Using sightings of individually marked females, we found that in winter only longer-billed individuals remained in the Dutch Wadden Sea, while the shorter-billed individuals moved away to an estuary with a more benign climate such as the Wash. Although longer-billed individuals have the widest range of options in winter and could therefore be selected for, counterselection may occur during the breeding season on the tundra, where surface-living prey may be captured more easily with shorter bills. Phenotype-limited distributions could be a widespread phenomenon and, when associated with assortative migration and mating, it may act as a precursor of phenotypic evolution.在我们所处的季节性世界中，动物在全年的生命周期内会面临多样的环境条件。为应对这类季节性变化，动物可表现出表型可塑性（phenotypic flexibility），但部分表型性状（phenotypic trait）是固定的。若固定表型性状与资源利用存在功能关联，则动物应随季节性变化的资源重新分布，进而形成"表型受限"的分布格局。本研究以滨鸟（shorebird）类群中的斑尾塍鹬（Limosa lapponica，一种长喙且具有性二态性的滨鸟）为研究对象，这类鸟类需依靠固定长度的探喙获取埋藏于地下的猎物。雌性斑尾塍鹬的主要猎物在冬季的埋藏深度较夏季更深。通过对佩戴个体标记的雌性斑尾塍鹬的观测记录，我们发现冬季仅长喙个体仍栖息于荷兰瓦登海（Dutch Wadden Sea），短喙个体则迁徙至气候更为温和的沃什湾（Wash）等河口区域。尽管长喙个体在冬季拥有更广泛的觅食选择，因此可能受到正向选择，但在苔原（tundra）的繁殖季可能会出现反向选择：此时短喙更易捕捉地表活动的猎物。表型受限的分布格局可能是一种广泛存在的现象，若其与选型迁徙（assortative migration）和选型交配（assortative mating）相关联，则可能成为表型进化的前驱过程。