Wild Things: Road Birds (The Nitty Gritty)

The red crossbill. CONTRIBUTED PHOTO

By ED KANZE 

Why in winter do we see songbirds, sometimes in flocks of dozens, hopping along snowy or slush-covered roads after the sand truck has gone by? The answer seems to lie largely in grit.

A great many birds have a modified part of the stomach known as the gizzard. It’s a place for grinding. The gizzard is wrapped in sturdy, powerful muscles that push and shove and twist. To break up tough food items such as seeds and insects with sturdy exoskeletons, birds need help in the form of abrasives. 

We mammals grind food, too, but we tend to do it with something birds lack: teeth.

When you want to grind the surface of something, you’ll likely rummage in a cellar drawer or pop out to the hardware store. There you may seek sandpaper. You’ll choose a grit matched to the degree of abrading you want to do. Fine sandpaper is covered with fine grit, coarse sandpaper with — well, you get the idea.

For songbirds in need of mini-millstones for grinding, the hardware store is often a dirty road. The more dirt the better. If a sand truck has just gone by, spewing a wide range of grain sizes, mobs of birds may descend to shop for the stuff.

Recently at our house, my wife, Debbie, and I were out for our morning constitutional when we saw, quite far away, two chunky songbirds leave the road and fly into a tree. Fortunately we had binoculars. Debbie raised her Vortex and I my Swarovski, and lo and behold we found ourselves admiring a pair of red crossbills. The female was yellow-green, the male red and black. Both sported the underbite-overbite combo that gives crossbills their name.

In a moment, the birds dropped back to the road. They were discerning shoppers. I was amazed how many tiny stones and sand grains each bird nibbled on before one seemed to pass the test and disappear down its finder’s throat. The crossbills lingered nearly an hour, carefully picking and choosing.

Crossbills are more often seen in the Adirondacks than in more southerly parts of New York, but I’ve seen both red crossbills and their cousin white-winged crossbills “gritting” (as ornithologists and birdwatchers call the acquiring of small gizzard stones) on roads in Westchester, not far from New York City. The behavior is fun to watch and interesting to contemplate. It’s also a reason to drive slowly when approaching birds on the road. Recently we had a pine siskin (a small, stripy, yellow-tinged finch of northern forests) flattened by a speeding car, right in front of our house.

Sometimes, the hunt for gizzard stones gets birds in trouble without vehicular involvement. Ducks and geese rifle through pond, lake, and stream bottoms, looking for stones to aid their grinding. Unfortunately, the small round fishing sinkers known as split-shot may interest them. Digestive juices dissolve some of the lead, and the birds may sicken or die. Lead-free sinkers are widely available these days, so this sort of harm is easily avoided.

I’ve always wondered if the birds I see gritting on roads are exclusively in search of grit. Might they also be feeding? Well, in one sense they already are. Minerals in grit may enrich a bird’s diet. But I suspect that sometimes there is more to it.

Once, when I saw a flock of winter finches lift off a quiet country and retreat to nearby trees, I got down on my hands and knees. I slipped on my reading glasses (not being as young as I used to be) and studied the surface of the road. I found grit, to be sure. But that wasn’t all. The road was generously scattered with the small winged seeds of the pines and spruces that grew thereabouts. Which inclines me to think that what we bird lovers tend to call gritting may in fact be a more complex behavior.

Ed Kanze is a Westchester-born author, naturalist and licensed guide who lives in the Adirondack Mountains. His latest book, “The Nature of the Place,” will be published in March 2025.