Climate change and migration
Species may differ in how they adjust to climate change, and one factor that likely constrains rapid adjustment is migratory behavior. Because long-distant migrants winter thousands of kilometers away from their breeding grounds, they likely have difficulties to anticipate on year-to-year changes in the optimal phenology of their breeding grounds.
Pied flycatchers are long-distance migrants. They spend most of their life in West Africa, arrive in April at their European breeding grounds and depart again in early August. This life style makes optimal use of the spring burst of insects in temperate habitats, while retracting to the benign winters of subtropical regions. We study their migratory behavior using geolocation loggers, which gives indications where they winter, when they leave the breeding grounds in the fall, and when they leave Africa in spring. The first results show that these birds take on average 40 days to migrate to the wintering grounds in West Africa, and only 20 days in spring. Since they arrive only shortly before breeding, they have little flexibility to anticipate to the ongoing advance in spring migration, and especially not to the year-to-year variation in spring phenology.
Whereas flycatchers cannot easily adjust with flexibility, we observe that many species of long-distance migrants, including flycatchers, now arrive earlier at their breeding grounds than 20 years ago. How have they managed? Is this a result of ongoing evolutionary change, or is there an unknown mechanism of phenotypic flexibility, that may contribute to this ongoing change over the generations. We study this by building up a pedigree of ringed individuals for which arrival dates are known for many years, so we can look at inheritance of arrival time and its fitness consequences. Furthermore, we experimentally study how ontogeny may affect timing decisions later in life.
Understanding timing of the annual cycle also requires knowledge of ecological conditions at the African wintering sites. Are there important ecological factors that constrain their departure date, either now or in the future with ongoing environmental change? We have been doing some work on wintering pied flycatchers in Ghana, and hope to continue this in the near future. New tracking opportunities will also arise, which may allow a better identification of the environmental conditions that make some individuals to migrate early and others late.
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- Knudsen E et al (2011). Biol. Rev. 86:928–946
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