Abstract
BackgroundPrevious investigations of autumn-migrating ducks have reported weak connections between weather conditions and the decision to migrate from stopover sites. We leveraged relatively new weather surveillance radar technology to remotely detect departures of discrete groups of various species of migratory dabbling ducks (Anatidae) in autumn to more directly assess the effect of specific weather conditions on departure from discrete stopover sites.MethodsUsing radar data collected over fifteen years (1995–2009), we documented a consistent phenomenon where a single, identifiable group departed from our study area on 30% of days during the autumn study period, and no ducks departed on the other days. We gathered weather variables from nearby stations and used them to develop competing models to explain temporal patterns of departure versus non-departure to better understand the potential mechanisms associated with binomial patterns of departures.ResultsThe best approximating model of departure probability was our integrated model, which included variables accounting for wind aloft direction favorable for departure (i.e., tailwind), absence of precipitation, and a partially or completely clear sky. The integrated model accounted for all model weight in the candidate set and explained 55% of the variation in departure probability. Estimated probability of departure was 0.76 after parameterizing the best model with favorable conditions for all covariates.ConclusionsOur results contrasted those of previous studies of autumn duck migration as a small set of simplistic, extrinsic conditions substantially influenced departure decision.
Highlights
Previous investigations of autumn-migrating ducks have reported weak connections between weather conditions and the decision to migrate from stopover sites
Among the environmental factors that affect the timing of autumn migration, weather has been identified as a key factor for many avian taxa [10, 11]
Our integrated model, which included following winds aloft, no precipitation, and a less than complete cloud cover, was clearly superior among candidate models describing migratory departure in autumn-migrating dabbling ducks. This model outperformed simpler models in spite of being more parameterized. It explained over half of the variation in daily departure timing versus non-departure, which was considerably more than previous studies that sought to quantify the WINDALOFTINDEX + CLOUDCOVERINDEX + PRECIPINDEX
Summary
Previous investigations of autumn-migrating ducks have reported weak connections between weather conditions and the decision to migrate from stopover sites. Throughout the course of migration, birds, bats, and other organisms make many important decisions, including where to go, how long to stay, and when to leave. Each of these decisions affects the others and contributes to the fitness of the individual [1,2,3,4,5]. Despite the extensive study of migration and weather [12], the specific role of weather in the regulation of autumn migration remains uncertain for some major avian taxa including waterfowl guilds such as dabbling ducks (but see [13, 14]). The timing of duck migration is further complicated by hunting pressure [18] and habitat quality [19]
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