The timing of the spring migration of European birds wintering in sub-Saharan Africa, depend on weather conditions in the rest area on the way home. To such conclusion researchers have come, having analysed the data about flights of six species of passerine birds from 1960 to 2014. As noted by the authors in an article for the journal PNAS, this contradicts the idea that time travel distant migrants is fixed very firmly and can not quickly enough to move in response to global climate change.
In recent years, increasingly popular among birdwatchers gaining the idea that the breeding period of birds from temperate latitudes accurately synchronized with peak availability of insects required for feeding the Chicks. This adaptation, as expected, increases the chances of successful rearing, however, requires that members of the migratory species return to the breeding grounds not later than a specified time.
Unfortunately, global climate change complicates this task. The growth temperatures peak in the number of insects shifted earlier, so the migrating birds are late to it and cope worse with the introduction of the Chicks. Although many species in response to climate change are also beginning to fly earlier, this process is not fast enough. Hardest desync affects distant migrants. A number of experts even consider it the main factor which is responsible for the reduction in the number of migratory birds.
Although the hypothesis of out of sync with the life cycles of birds and their prey seems logical, it is based on the obvious assumption that the timing of spring flights from the far migrants are determined mainly by internal biological rhythms and the length of daylight and weakly depend on the weather conditions. To verify this, a team of specialists led by Birganim Heston (Birgen Haest) of the Swiss ornithological Institute analysed data on bird migration collected from 1960 to 2014 on the German island of Helgoland.
The focus of the authors were six species of passerine birds nesting in Europe and wintering in Africa South of the Sahara: Flycatcher is a Flycatcher (Ficedula hypoleuca), spotted Flycatcher (Muscicapa striata), garden Redstart (Phoenicurus phoenicurus), the willow Warbler (Phylloscopus trochilus), common Whitethroat (Sylvia communis) and garden Warbler (S. borin). They all fit the definition of long-range migrants. In addition, the analysis included data on weather conditions, which these birds encountered during the journey from the wintering ground.
It turned out that the date of arrival of the species in different years 72-86 percent dependent on the weather in several places of rest during migration. Birds change the timing and speed of migration in response not to a specific parameter, and the combination of wind speed, air temperature and, to a lesser extent, precipitation. Particularly strong this effect was, in points situated in front of the Sahara and the Mediterranean sea, as well as immediately after them. Another important factor was the air temperature in the last section of migration in Central Europe.
So far migrants may be sensitive to weather conditions specific to the season and according to them adjust the return date to breeding grounds. This means that the flexibility of their migratory behavior was underestimated and the vulnerability to climate change, by contrast, is revalued. According to the authors, in the observed reduction in the number of migratory birds should not blame global warming, and habitat destruction in the breeding areas and wintering.
Sometimes even wintering birds can’t find enough food to feed their young. This happens, for example, in cities where the little insects. As found Hungarian ornithologists, to rectify the situation may additional dressing.