SGER: Dispersal Decisions and Social Reorganization of American Crows Following a West Nile Virus "Removal Experiment"

西尼罗河病毒“去除实验”后美国乌鸦的分散决策和社会重组对于大多数动物来说，成年雄性和雌性在卵子受精后不会相互联系，雌性产卵，孵化出的年轻人没有得到父母的照顾;父母和后代从不见面。某些动物的双亲或一方，例如，鸟类、哺乳动物和一些鱼类确实提供父母的照料--它们可能孵蛋、喂养和/或保护幼崽--但在大多数情况下，后代一旦独立就离开“家”;没有多少动物生活在家庭中。然而，2-3%的鸟类（和哺乳动物）物种的后代“延迟扩散”-他们与父母呆在家里很长一段时间，而不是分散自己生活-创造家庭群体。因为延迟扩散的后代往往有助于其父母随后的繁殖尝试，所以发生这种情况的物种被称为“合作繁殖”。“在合作繁殖的物种中，大多数选择推迟扩散的个体也选择了推迟繁殖，这激发了许多理论，探讨与这种看似非适应性行为策略进化相关的可能因素。成熟的个体鸟类必须评估所有行为选择的后果--扩散，试图繁殖，或不这样做--然后以最大化适应性的方式行事。个体应该在可接受的繁殖机会出现时分散，而不应该在独立繁殖的选择质量不佳时分散（独立繁殖在生态上受到“限制”），特别是如果延迟繁殖的成本通过与作为“辅助”的家庭相关的利益来补偿。“在这种情况下，合作繁殖群体应该是不稳定的;当缺乏可接受的繁殖机会时，个体应该作为辅助者，当机会开放时，它们应该分散自己繁殖。 乌鸦的社会组织在同种种群中是可变的，并且可能相当复杂;位于俄克拉荷马州斯蒂尔沃特的一群美洲乌鸦（Corvus brachyrhynchos brachyrhynchos）是已知最复杂的群体之一。这一种群中的乌鸦做出了高度可变的扩散决定，许多个体的性别都推迟了多年的扩散，许多个体在试图独立繁殖之前与其他家庭一起移动。最近的研究重点之一是试图通过标记和跟踪个体乌鸦来确定不同传播策略的各种成本和收益。2002年9月，西尼罗河病毒到达斯蒂尔沃特，在两个月内40%的人口死亡或失踪。所有年龄和地位阶层的男女个体都消失了; 9名饲养员丧偶，4个整个家庭消失了。突然之间，对于这个种群的成员来说，繁殖的机会大概是敞开的。随着2003年天气变暖，西尼罗河病毒周期再次开始，将继续提供更多的机会。记录的幸存者的扩散反应，和健身的后果，将使“生态约束”的决定，以延迟繁殖和扩散在这个人口中所发挥的作用进行检查。 在西尼罗河病毒“清除实验”之后的第一个繁殖季节，扩散决定及其后果将与过去几年的决定进行比较。检查这些决定和许多特征之间的潜在关系，已被测量为个别乌鸦（包括种群成员之间的遗传相关性），将有助于阐明进化机制的高度不寻常的社会组织所造成的高度可变的传播决策正在由乌鸦在这个人口。

Dispersal Decisions and Social Reorganization of American Crows following a West Nile Virus "Removal Experiment"Carolee CaffreyFor most animals, adult males and females do not associate with each other after egg fertilization, and females lay eggs from which young hatch that do not receive parental care; parents and offspring never meet. One or both parents in some types of animals, e.g., birds, mammals, and some fish, do provide parental care - they may incubate eggs, feed and/or guard young - but in most of these cases the offspring leave "home" as soon as they are independent; not many animals live in families. Yet the offspring of 2-3% of bird (and mammal) species "delay dispersal" - they remain home with parents for extended periods rather than disperse to live on their own - creating family groups. Because offspring that have delayed dispersal often contribute to the subsequent breeding attempts of their parents, species in which this occurs are said to "breed cooperatively." Across cooperatively breeding species, most of the individuals choosing to delay dispersal have also chosen to delay breeding, which has stimulated much theorizing as to the possible factors associated with the evolution of this seemingly nonadaptive behavioral strategy.Maturing individual birds must assess the consequences of all behavioral options - to disperse, to attempt to breed, or not - and subsequently behave in ways that maximize their fitnesses. Individuals should disperse when acceptable breeding opportunities are available, and should not disperse when options for independent reproduction are of poor quality (independent breeding is "constrained" ecologically), especially if the cost of delaying breeding is compensated via benefits associated with remaining home as an "auxiliary." Under such conditions, cooperative breeding groups should be unstable; individuals should remain as auxiliaries when acceptable breeding opportunities are lacking, and they should disperse to breed on their own as opportunities open up. Crow social organization is variable across conspecific populations and can be quite complex; that of a population of Eastern American Crows (Corvus brachyrhynchos brachyrhynchos) in Stillwater, OK, is one of the most complex known. Crows in this population have made highly variable dispersal decisions, with many individuals of both sexes delaying dispersal for years, and many individuals moving in with other families before attempting to breed independently. One focus of recent research has been attempting to identify the various costs and benefits associated with different dispersal strategies through marking and following individual crows over years.In September 2002, West Nile virus arrived in Stillwater, and within two months 40% of the population was dead or missing. Individuals of both sexes and all age and status classes are gone; nine breeders were widowed, and four entire families disappeared. All of a sudden, for the members of this population, breeding opportunities are presumably wide open. As the weather warms in 2003 and the West Nile virus cycle begins again, more opportunities will continue to become available. Documenting the dispersal responses of the survivors, and the fitness consequences thereof, will enable the role played by "ecological constraints" on decisions to delay breeding and dispersal in this population to be examined. Dispersal decisions, and their consequences, in this first breeding season following the WNV "removal experiment" will be compared to those made in past years. Examination of potential relationships between those decisions and the many characteristics that have been measured for individual crows (including genetic relatedness among population members), will help to elucidate the evolutionary mechanisms underlying the highly unusual social organization resulting from the highly variable dispersal decisions being made by crows in this population.