It's around sunrise when I leave the warmth of the hut and take in the frozen world outside. The crunch of the snow under my shoes is all I hear as I walk onto the frozen lake and see white-rumped redpolls in birch trees along the shore (Acanthis hornemanii) warms itself in the orange-red glow of the rising sun.
I woke up this morning in Kaamanen, Finland, a collection of wooden houses in a rolling white landscape of birch, pine and snow-covered lakes, two hundred miles north of the Arctic Circle. Scandinavia is home to redpolls, hardy finch species with a distinctive red spot on their forehead, which are optimally adapted to life in the Arctic tundra. While many birds migrate south in autumn, the white-rumped redpolls, weighing only fifteen grams, brave the weeks of darkness of the northern winter, when nights of -40 degrees Celsius are not uncommon. Huddled in their dense winter plumage, redpolls seek shelter in snow tunnels that they dig in the dry snow during these months. By collecting up to 40 percent of their body weight in birch seeds every day in their crop – an outpouching of the esophagus – and gradually digesting them, they keep their metabolism and heat production high.
Despite these adaptations, redpolls migrate south en masse in some winters, when birch trees produce few seeds and food shortages threaten. After 1986, 2005, 2008 and 2017, we experienced another redpoll invasion this winter, with on some days not a few, as usual, but hundreds of passing redpolls being observed along our coast. This concerned all three now known redpoll species;
common, small and a few white-rumped redpolls.
In the past, the taxonomy of birds was based on external characteristics, including behavior and song (phenotypic), but DNA research (genotypic) is becoming increasingly important. The three currently known redpoll species are distinguished on the basis of color, stripe pattern and beak shape, but have many intermediate forms. They are genetically the same. But differences in appearance are due to variable expression of individual genes under the influence of external factors such as food, climate and living environment.
Unaware of all this, the white-rumped redpolls foraged for breakfast to immediately dive into the new breeding season full of energy. It is not inconceivable that their offspring will be renamed redpolls and simply look paler than their more southerly counterparts in response to longer exposure to a snowy habitat.
#winterhardy #finch #common #redpoll
