When the howling winter wind is piling snow drifts across your driveway, you might find it therapeutic to think about that iconic sign of the eventual change of seasons, the first robin of spring. In that case, I have some good news for you - the robins are already here!
The truth is, the “first robin of spring” is a bit of a myth, and has more to do with a seasonal change in robin feeding behavior than with migration.
In reality, there may be just as many American robins on Cape Cod in the winter as during the summer. The difference is that in winter, robins undergo a pretty serious lifestyle change in which they abandon our suburban lawns and flock up to become wandering frugivores. A frugivore is anything that eats primarily fruit. And that’s one natural bird food that we are loaded with here on the Cape. Enough fruit to support the more than 85,000 robins that were counted in a single flock on the Mid-Cape Christmas Bird Count back in 2008. And there’s often a winter robin roost in Barnstable where counts exceed 30,000 birds.
In recent weeks I have noticed a big influx of American robins to the area, with flocks of up to a couple hundred birds becoming more common. These are not the robins that bred here last summer, but more likely Canadian birds that wandered south in search of fruit. So what are they eating? The viburnums, plums, and cherries of summer are long gone, so our wintering frugivores depend on the hardy, persistent fruits of native trees and shrubs like red cedar, winterberry and even greenbriar. They’re especially fond of the ornamental crabapples so common in our suburban yards. Hungry birds in freezing weather can’t afford to pass up an easy meal, so they have no problem gorging also on the fruits of nasty invasive plants like multiflora rose and Asiatic bittersweet, which they help distribute across the landscape via their patented pre-fertilized, air-drop seeding method.
Robins aren’t the only flocking frugivore patrolling our bleak winter landscape—look for Cedar Waxwings, Yellow-rumped Warblers, and even Eastern Bluebirds among the flocks. And if you’re really lucky, you might find one or even a whole flock of Bohemian Waxwings, that big, rare northern cousin of our Cedar Waxwings. A few of these handsome birds of boreal forest turn up on the Cape every winter, so keep an eye on that crabapple. Northern Mockingbirds are also fruit connoisseurs, but are more sedentary than the robins, and you can often see them violently defending their patch of fruiting shrubs against an invading robin horde.
One aspect of the fruit-eating bird’s lifestyle that may surprise you is a proclivity for drunkenness. Winter fruits can ferment as a result of freezing and thawing cycles, and it’s not uncommon for robins and other birds to get staggering, rip-roaring drunk after overindulging. Physiological studies have demonstrated that fruit eating birds actually have larger livers than other species, presumably to help them handle their liquor. It occurred to me that with our winters getting warmer on average, we can expect more fermented fruits. Which brings me to the serious climate change problem no one is talking about—drunk robins.