Over the course of the summer, very different types of chicks hatch under different mother birds. Sparrows, like the titmouse, are nest dwellers. They hatch from the egg blind and naked and stay fed in the nest for a long time. Waders, such as the red-footed vulture, are evacuees. They pop out covered in down and see and are ready to waddle after their mother right away.
A different autumn awaits them. The grebe stays as a local bird to winter in its birthplace. As a migratory bird, the red-footed warbler heads further south.
The researchers discovered for the first time that differences can be seen in the egg yolk of different types of birds already at the beginning of incubation. Chicks of migratory birds and fledgling species get more thyroid hormones from it than chicks of local birds and nesting species.
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It is known that thyroid hormones are essential for chick growth and that in adult birds they regulate migration, among other things. In the egg, the chick initially does not know how to prepare them by itself, but is dependent on the portion left by the mother in the yolk.
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The differences were visible in a comparison of 34 bird species, says an international group of researchers, which included Finns, in the Journal of Animal Ecology. Compared to the red tit, the red-footed wagtail literally bathes in thyroid hormones, their concentration is up to a hundredfold in the yolk. Eggs usually have an average amount of hormones in species with “opposite” characteristics, such as the migratory finch that stays at the nest and the partridge that escapes from the nest.
Published in Science in Nature 5/2022.
Source: Tiede by www.tiede.fi.
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