Life History Correlates of Alternative Migratory Strategies in American Dippers

Abstract

Partial migration is thought to be a critical step in the evolution of avian migration, but data on the life history correlates of alternative migratory strategies are extremely limited. We have studied a partially migratory population of American Dippers since 1999. This population is composed of sedentary individuals (residents) that maintain the same territory year round and altitudinal migrants that share winter grounds with residents, but move to higher elevations to breed. We used seven years of data on individually marked birds to (1) determine if individuals consistently use the same migratory strategy, (2) determine if offspring have the same strategy as their parents, and (3) estimate reproductive and survival rates of the two migratory strategies. We evaluate hypotheses for the persistence of partial migration and discuss their implication for the evolution of migration in sedentary populations. Individual American Dippers rarely switched migratory strategy (4/169 monitored more than one year). An individual's strategy, however, was not always that of its parents, indicating that, while migratory behavior may have a genetic component, environmental or social conditions probably influence the migratory strategy that an individual adopts. Sedentary dippers consistently had higher annual productivity (approximately 1.4 more fledglings/year) than migratory dippers, but mark-recapture models suggested that migratory dippers may have slightly higher survival than residents (approximately 3.4%). Migrants were estimated to have lower lifetime reproductive success than residents because their higher survival was insufficient to offset their lower productivity. Our data suggest that alternative migratory strategies in American Dippers are unlikely to be a fixed genetic dimorphism that persists because the two strategies have equal fitness, or because the relative fitness of the two strategies fluctuates over time. Migratory strategies in American Dippers are more likely to be condition dependent, and the two strategies persist because migrants "make the best of a bad job" by moving to higher elevations to breed. Because migrants obtained no fitness benefits by moving to seasonal breeding territories, our data are consistent with the hypothesis that migration could evolve in sedentary populations if competition for limited resources forces some individuals to seek breeding opportunities outside their initial range.

Sex‐ and context‐dependent migration in a pond‐breeding amphibian

“…Asymmetries are expected when partial migration is condition dependent and individuals that are in better condition or more dominant are expected to seek the better habitat (Alerstam and Hedenstrom 1998, Brodersen et al 2008, Gillis et al 2008. We expected larger newts to remain resident to take advantage of spring reproductive opportunities and a reproductive advantage over migrants.…”

Are Dutch Skylarks Partial Migrants? Ring Recovery Data and Radio-Telemetry Suggest Local Coexistence of Contrasting Migration Strategies

“…Our study population thus might consist of facultative partial migrants, where some individuals migrate in some years and not in others, depending on conditions at the time (Terril & Able 1988, Newton 2008. A switch in migratory strategy in individual birds has been shown for European Robins (Harper 1985but see Adriaensen & Dhondt 1990, rarely occurred in American Dippers Cinclus mexicanus (Gillis et al 2008), and was age and sex-dependant in Blackbirds (Schwabl & Silverin 1990).…”

Does stress response predict return rate in a migratory bird species? A study of American redstarts and their non-breeding habitat

“…and because of better environmental conditions (high-quality breeding and non-breeding territories). Therefore, their survival may not predominantly depend on their ability to react to stressors, but rather on the accumulated effects of life-history decisions made throughout the life cycle such as breeding investment (Reid et al 2003), migration and molt strategies (Barta et al 2008;Gillis et al 2008). On the contrary, the survival of birds wintering in poor habitats may very well primarily depend on their ability to react to the numerous unpredictable perturbations that they encounter during their annual life cycle.…”