The biggest problem for wrens in winter is keeping warm, writes Dick Warner
I WAS staring idly out of the window when I spotted a movement out of the corner of my eye. I focussed on a pile of brushwood, left over from some autumn pruning, but it was a while before I spotted the wren.
It was methodically working its way through the pile, using its relatively long legs to hop from branch to branch.
A little, round ball of russet brown feathers with a cocked-up tail and a faint white stripe through its eye.
Most of our resident small birds adapt to the lack of insects in winter by changing to a vegetarian diet of seeds and berries.
Wrens are different, they stick to the animal protein.
It’s not easy to find but it does exist.
Some winged insects over-winter as pupae, ready to emerge in the spring.
These pupae, stuck to twigs or hidden in crevices in walls, are one source of food.
Another is small spiders, which are present all the year round.
And sometimes wrens abandon this form of foraging and search on the ground, working their way along hedge bottoms, turning over the leaf litter with their beaks and discovering tiny beetles, slugs and other invertebrates.
Wrens only weigh about 10g so they don’t require many of these diminutive items of prey to survive.
They are our second smallest bird, after the goldcrest, and although they weigh slightly more than goldcrests they’re actually shorter in length.
They forage in heavy cover, are not interested in birdfeeders and are rather shy so they’re not seen that often. However they are quite often heard.
Their song, which they produce throughout the winter, is surprisingly loud and complex rather than melodic.
However, although they’re not that obvious they are remarkably common and widespread.
It’s estimated that there are about six million wrens in Ireland, which means they slightly outnumber people, and they are among the top 20 in BirdWatch Ireland’s garden bird survey.
Apart from gardens, rural and urban, they inhabit practically every possible habitat type in the country, including mountains, farmland, offshore islands, raised bogs and reed beds.
The biggest problem for wrens in winter is keeping warm.
The smaller a bird is the quicker it succumbs to hypothermia on long, cold winter nights.
To a small extent wrens migrate to combat this threat.
Birds will move from mountains down into warmer valleys in cold weather and there is some international migration.
However, the stay-at-home birds have another tactic for keeping warm which is called communal roosting.
Although they’re quite territorial for most of the year in cold weather wrens from a large area will congregate at dusk to sleep together.
By cuddling up closely they manage to turn the heat loss of a very small bird into the much reduced heat loss of a large one.
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