Their scientific name (Turdus migratorius) suggests that Robins are only temporary inhabitants of this harsh northland, and indeed, it would seem to be a bad idea for a fruit and insect specialist to stick around here during the coldest weather when plants and insects are inactive.
We are used to thinking of Robins as harbingers of spring, migrating back only when the ground thaws and the earthworms become active, but some Robins are hearty and savvy enough to remain here all winter, even during the coldest, and snowiest weather.
The overwintering, non-migratory Robin — see my earlier post in December 2013.
So, how do they manage to stay warm, find enough food they like, and tolerate these harsh conditions? (On a day like today, with 40 mph winds chilling the already subzero air, I have to wonder how anything tolerates living here.)
Maybe eating fruit isn’t such a bad strategy for a bird that overwinters in northern latitudes. Consider the advantages:
1) fruit is full of sugar, and some fruits have a waxy coating that is digestible, providing extra calories;
2) when you find a tree or bush with fruit, there is usually a lot of it, and a bird can “stuff its gut”, literally, in one sitting;
Frozen crabapple — what could be better on a cold day?!
3) fruit passes through the gut rather quickly, compared to the protein and fat content of seeds or insect bodies, so the bird can go back and fill its gut again and again, until its fat stores are replenished;
4) plucking enough fruits to meet the daily energy quota is much less expensive than foraging for seeds or insects, and lastly
5) fruit-eaters that harvest dense patches of food (berry bushes or crabapple trees) have a lot of down-time, when they can economize on their daily expenditures by resting in sheltered areas, away from predators and bad weather.
So the next question might be: is there enough fruit here to sustain Robins all winter? What is their diet in the winter?
A high proportion of a Robin’s winter diet is buckthorn berries, along with fruits of the dogwood, honeysuckle, holly, Viriginia creeper, and waxy fruits of bayberry, juniper, red cedar, and poison ivy.
The increasing infestation of northern forests by invasive Buckthorn seems ideal for overwintering Robins, who can feast on its fruits and return the favor by dispersing buckthorn seeds in their excreta.
As much as 85% of the buckthorn berry crop may fall directly beneath the shrub, so Robins, which like to forage at ground level anyway, have a high density food resource there as well.
So, why spend all the energy to migrate and have to compete with the locals and other migrants, when you can stay put with a nice dependable fruit crop at home and be first with the best nest site in the spring? Winter Robins are so smart.
“I am so smart..S-M-R-T”. (Homer Simpson)