Dissertational Improvement: Ecological Pressures Selecting for Dietary Plasticity During Migration in Two Neotropical Migratory Passerine Genera

在过去的十年中，许多新热带迁徙鸣禽种群的减少引发了对这些物种在温带繁殖地和热带越冬地区的生物学研究。尽管在这一过渡时期，移民的能量需求和行为非常不同，但他们对过渡时期的关注要少得多。在迁徙期间，许多鸣禽的繁殖季节行为多样化，以选择不同的栖息地，使用更多的觅食行为，并且比一年中其他时候更多样化的饮食类型。这种行为可塑性演变背后的生态因素以及这些不同行为的生态和保护意义仍然是推测性的。这项研究将从秋季迁徙鸣禽行为多样化的一个方面——从吃昆虫到吃水果的饮食转变——来调查这些问题。在罗德岛布洛克岛的初步研究表明，迁徙中转站资源丰富程度的不可预测性和迁徙期间饮食增加的能量摄入导致了鸣禽的行为可塑性。这项研究将在1994年和1995年秋季期间继续监测中途停留地点的昆虫和水果丰度，以监测这两种资源的不同程度的可预测性。此外，迁徙者将被喂食含有不同程度水果的实验性饮食，以确定他们在扩大的饮食中可以增肥的程度，从而验证摄入食物类型多样化是迁徙过程中选择最大化能量摄入的结果这一假设。最后，实验将允许评估（通过双标签水技术）候鸟在不同的饮食中节省的能量。这些技术可以估计鸟类的能量消耗，这可以在鸟类有单一和多样化的饮食的情况下进行跟踪。这些研究将为行为可塑性的进化压力以及迁徙鸣禽的生物学提供重要信息。反过来，这将有助于对这些数量下降的物种做出更好的保护决定。＊＊＊

9411650 Morse The decline of many populations of Neotropical migratory songbirds has triggered much research over the last decade into the biology of these species on their temperate breeding grounds and their tropical wintering areas. The interim migration period has received much less attention, despite the extreme energetic demands and the very divergent behavior of migrants during this transient period. During migration, many songbirds diversify their breeding-season behaviors to select different habitats, use more foraging behaviors, and feed on more varied diet types than at other times of the year. The ecological factors behind the evolution of such behavioral plasticity and the ecological and conservation implications these divergent behaviors remain speculative. The proposed research will investigate these questions in one aspect of behavioral diversification in autumn migrating songbirds - the shift in diet from eating insects to one of eating fruit. Preliminary research on Block Island, Rhode Island suggests that unpredictability in resource abundance at migratory stopover sites and increased energy intake on expanded diets during the demanding migration period have led to behavioral plasticity in songbirds. This research will be furthered with continued monitoring of insect and fruit abundance at stopover sites to monitor different degrees of predictability of the two resources during Autumn, 1994 and 1995. Furthermore, migrants will be fed experimental diets with varying degrees of fruit to determine the extent they can fatten on expanded diets, thus testing the hypothesis that diversification of ingested food types has resulted from selection to maximize energy intake during migration. Finally, experiments will allow evaluation (through doubly-labeled water techniques) of the amount of energy saved by migrant birds in feeding on diverse diets. These techniques allow estimation of the energy expenditure of birds which can be follow ed under situations where birds have monotypic and diverse diets available to them. These studies will provide insight into the evolutionary pressures for behavioral plasticity as well as important information about the biology of migrating songbirds. This in turn will allow better conservation decisions to be made regarding these declining populations. ***