Overwintering ecology, migration strategies and demography of migratory birds

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Populations of migratory birds may be limited by events in geographically separate habitats occupied at different stages of their annual cycle. Although events during the breeding season may drive the population dynamics of some species climatic conditions and anthropogenic impacts on winter and en-route habitats can also influence the distribution and survival of migrants, and conditions experienced during the non-breeding season can carryover and influence survival and productivity on the breeding grounds. Climate change and the loss or degradation of winter or en-route habitat is therefore likely to influence the overwintering ecology of migrants, alter the costs and benefits of migration, and influence the distribution and persistence of bird populations. Recognition of the connections between seasons, and investigation of the factors that influence seasonal vital rates are critical in evaluating climatic and human impacts on migratory birds.We propose to investigate climatic and anthropogenic impacts on wintering and migratory strategies, seasonal vital rates, and population dynamics of two birds that can be studied throughout their annual cycle: a neotropical migrant, the Yellow Warbler, and a partial migrant, the Black Oystercatcher. Specifically, we will 1) ask how the use of natural and modified winter habitats influence territoriality and winter survival of Yellow Warblers and investigate the sensitivity of breeding populations from different latitudes to winter habitat alteration; 2) examine whether non-breeding season events that impact vital rates scale-up and predict population trends of Yellow Warblers at a larger geographic scale; 3) evaluate hypotheses explaining variation in the migratory strategies of Black Oystercatchers; and 4) determine whether anthropogenic change influences the relative costs and benefits of migration and the predicted number of migratory and sedentary Black Oystercatchers at different latitudes.We study Yellow Warblers on the breeding grounds in B.C. and on wintering grounds in Mexico where they occupy natural and modified (agricultural) habitats. Stable isotope analysis of feather tissues can be used to infer the breeding origins of birds in Mexico; radiotransmitters and mark-resight data allow investigation of breeding origin, sex/age, climate and habitat effects on territoriality and over-winter survival. Population models can then be used to assess how season-specific vital rates contribute to population growth. Regionally specific breeding bird survey data can be used to test the generality of climatic and human impacts on populations. Black Oystercatchers are partial migrants that can also be studied on breeding grounds, wintering grounds and on migration. In Alaska migrants and residents breed together but overwinter apart, whereas in southern B.C. migrants and residents overwinter together and breed apart. Radiotelemetry and light-sensitive geolocators provide tools to determine migratory strategies and migration distances of individuals. The monitoring of resident and migratory oystercatchers from multiple sites in Alaska and British Columbia allow assessment of the causes and fitness consequences of variation in migratory strategies. The proposed research will elucidate the role of events at different stages of the annual cycle for population dynamics of migratory birds, evaluate hypotheses for differential migration by assessing the fitness consequences of alternative migratory strategies, and determine how environmental change influences the demography of neotropical and partial migrants. Consequently, the results of the proposed research will aid in the development of effective conservation strategies for migratory birds.