佛罗里达大学（University of Florida）的科学家们发现，在动物界，一种生物的灭绝可能会波及其它动物，例如2万年前多种大型哺乳动物的绝灭殃及了一种北美燕八哥。相关文章发表在《古地理学，古气候学，古生态学》（Palaeo-3）杂志上。
“对陆地生态系统来说，最大的打击莫过于失去大型哺乳动物；同样，海洋生态系统若失去鲨鱼、金枪鱼和其它顶级捕食者，也会面临灾难，”研究的承担者之一，佛罗里达自然博物馆鸟类部馆长D.Steadman说。“我们发现非洲部分地区狮群和象群正在减少，佛罗里达的美洲豹种群也渐渐走向衰落，这些现象会引起一连串不利的多米诺效应。”
佛罗里达自然历史博物馆的鸟类学家们对墨西哥北部的8种鸣禽类化石进行了研究，其中一种来自Térapa 遗址区，名叫Pandanaris convexa的燕八哥是当地的常见种，生活在热带环境。2万年前，当地的大型哺乳动物迁徙路线呈南北方向。
燕八哥依靠草原和这些哺乳动物为生，此二者有内在联系。大型哺乳动物来回地踩踏和取食，使草原不被树木占据。而燕八哥不但吃草籽，还捕食哺乳动物体表的昆虫，这形成了一种互利互惠的种间关系。
当时生活在墨西哥北部的远古哺乳动物有地懒、猛犸、马、貘、骆驼和野牛。2万年前它们尽数灭绝，食腐动物秃鹫、秃鹰和燕八哥也随之消失了。集群灭绝可能撼动整个生态系统的基础，并从根本上改变物种分布。所有物种都不能孤立生存，当整体中的一小部分遭遇灭绝，很难推测会引起怎样的连锁反应。
科学家们认为，大型哺乳动物灭绝所引发的涓滴效应（trickle-down effect）会影响其它物种，2万年前的故事警示我们应当谨慎地开发自然资源。
墨西哥北部的遗址区曾是一片多沼泽和河流的稀树草原，生活有多种爬行动物、哺乳动物和30多种鸟类，还不包括鸣禽。虽然鸣禽在鸟类物种中占据了50%以上，但化石却发现得不多，特别是中美洲和南美洲。该研究还为墨西哥鸣禽化石记录作出了贡献。（生物谷Bioon.com）
生物谷推荐原文出处：
Palaeogeography, Palaeoclimatology, Palaeoecology doi:10.1016/j.palaeo.2010.12.020
Late pleistocene passerine birds from Sonora, Mexico
Jessica A. Oswald, a, and David W. Steadmana
Abstract
Songbirds (Passeriformes) have a very limited fossil record in spite of making up more than one-half of the world's 10,000 living species of birds. From the late Pleistocene fossil site of Térapa in east-central Sonora, Mexico, the identifiable fossils of songbirds consist exclusively of species of Icteridae. The seven extant species (Red-winged Blackbird Agelaius phoeniceus, Yellow-headed Blackbird Xanthocephalus xanthocephalus, Brewer's Blackbird Euphagus cyanocephalus, Great-tailed Grackle Quiscalus mexicanus, Bronzed Cowbird Molothrus aeneus, Brown-headed Cowbird M. ater, and Orchard Oriole Icterus spurius) still occur in Sonora, either as residents or migrants. The eighth fossil icterid from Térapa is an extinct genus and species of cowbird, Pandanaris convexa. The genus Pandanaris was known formerly only from late Pleistocene sites in southern California (P. convexa A. H. Miller) and Florida (P. floridana Brodkorb). We synonymize P. floridana with P. convexa because their supposed differences either cannot be substantiated or can be attributed to sexual dimorphism in size within a single species. Among the few Pleistocene sites from Mexico or the United States with well-studied and substantial assemblages of fossil passerines, Térapa is unique in its dominance of icterids (which may be common elsewhere but not dominant) and in its absence of corvids. Today, tropical “foothills thornscrub” is the vegetation type at Térapa except for riparian forest along the río Moctezuma. The icterid fossils are compatible with previous evidence (from plant, invertebrate, and other vertebrate fossils) that tropical/subtropical marsh, savanna, and riparian forest existed at Térapa during the late Pleistocene. Just as the two extant species of cowbirds associate today with large grazing mammals, the extinct Pandanaris convexa may have foraged in association with Pleistocene mammals whose extinction led to the demise of P. convexa as well.
Keywords: Late Pleistocene bird communities; Icteridae; Pandanaris; Megafaunal extinctions; Historical biogeography; Quaternary vegetation change
