The buttercups currently laying eggs in Finnish birdhouses spent the winter popping insects in tropical Africa.
They also feed their chicks with insects, which are presumably found more easily in warm summers than in colts.
Surprisingly, however, winter conditions in Africa and Central Europe affect the number of airy chicks produced more than the summer weather in Finland, researchers at the University of Turku report in the journal Oecologia.
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They obtained their results by comparing nesting statistics for as many as 77 years with weather statistics for the same period.
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A cooler-than-usual season during the wintering season in West Africa knew worse chick yields the following summer. At the time of nesting in Finland, only simultaneous coolness and rainfall weakened the result.
Oddly enough, chick production was most affected by the conditions of the migration route when the catches were not present. The result of the following summer deteriorated most markedly when the wintering area was particularly rainy just before the birds arrived or when a warmer-than-usual winter occurred in Central Europe during their African period.
Hunger and disease can make birds tired
Exactly how the weather effect of the migration route and the wintering area is transmitted to the fry yield should be determined separately. In their report, the researchers try to tentatively consider what it might be about.
Warblers are small birds whose migration distances across Europe, the Mediterranean and the Sahara are long and strenuous. Both during and after the move, they need to find enough insects to feed in order to stay fit and healthy and to cope effectively with their nests.
In West Africa, toothpicks settle in moist areas of open forests and savannas. Apparently excessive rainfall there just before the birds arrive worsens the feeding situation or predisposes to disease.
Correspondingly, the coolness after the arrival of the birds is likely to be affected.
In Central Europe, a warm winter is known to impair the survival of plant-eating insects. Maybe the next spring, the migrating captors will then be harmfully hungry.
Source: Tiede by www.tiede.fi.
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