Photo by Alex Brown.

There is a progression of fruit eaten by birds as they move through the upper midwest. We are all aware of the summer fruits, the ones we enjoy, those that ripen and spoil within a few days. Think of strawberries, juneberries, raspberries, blueberries, blackberries among others, these are all quite palatable and for the most part familiar to our palates. They are high in sugars and fats and disappear quickly as they ripen. Yet there is another class of fruits that don’t attract our attention, at least not in a gastronomic sense.

There are nannyberries, arrowwood, northern holly, high bush cranberries, mountain ash, and sumac to name a few. Now if you have ever eaten any of these berries directly from the bush you know they are far from toothsome. The cranberries can be made edible with cooking and added sugar, and sumac makes a passable tea, but straight off the bush none of these berries would make a tasty snack.

White throated sparrow. Photo by Gilles Gonthier

Birds, whose sense of taste is greatly diminished when compared to humans, eat these berries in a regular progression. In the early fall the nannyberries, and arrowwood attract many of the migratory birds. Robins, yellow-rumped warblers, and white throated sparrows are among the diners as they sweep through to warmer climes. The nannyberry and arrowwood if not eaten will whither and fall from the bushes by late October. Left behind are the northern holly, high bush cranberries and sumac. These fruits remain on the bush deeper into the winter.

In the past two years the berry crop on the northern holly have been quite heavy. Deer hunters have encountered patches of the bright scarlet berries. The shocking red color acts as a sign post to migrating birds. And the winterberry, as it is sometimes called, is ready. Throughout the early fall the berries contain a chemical that makes them distasteful even to the repressed palate of birds. Now the plant is advertising its fruit to encourage the birds to eat it and spread the seeds. There is a limit to the availability of these berries because around the first of December  they begin to fall from the plant. If a roaming flock of waxwings, or some laggardly robins should find them they will quickly eat them.

Still left behind are the cranberries, mountain ash, and sumac. The cranberries look delectable and I have often wondered why they are not quickly eaten. At least part of the answer lies in the fruit itself. Those fruits that are eaten first contain the highest amounts of food value. They are loaded with sugars and fats, but these same characteristics cause the fruits to rot more quickly. The sugars and especially the fats cause microbes to act upon them and promote their spoilage. So low fat and sugar along with high acidity and limited water preserve the berries. Cranberries, mountain ash, and most particularly sumac berries are at the extreme end of the spectrum.

At some point this winter in late January or early February a flock of bohemian, or cedar waxwings will descend upon the cranberries, and mountain ash and wipe them out. It is as if the other birds knew to leave them alone for the survival of the waxwings. These fruit eating birds almost always travel in flocks. The “many eyes” hypothesis proposes that birds in a flock benefit by early detection of danger, but it is also true that these same eyes might detect food bonanzas like the cranberries just as easily. I heard of one enterprising robin that had joined with a flock of waxwings one winter. No doubt profiting from the flock and its ability to spot food.

That leaves only the sumac, and when it comes to food value they must rank dead last among the fruits. They will remain on the plant up to eight months and will only be consumed late in the spring as the migratory birds are returning to the northland. I have witnessed crows eating sumac berries late in February and on into March and beyond. The sumac are at the extreme for they seem little more than a fuzzy skin covering a large seed. There must be some small reward for eating them. Perhaps it is a bit like eating the winter tomatoes from the supermarket. They are selected for long shelf life as opposed to flavor and they certainly meet that challenge.

Tags: berries, birds, cranberry, ecology, holly, John Latimer, KAXE, latimer, Minnesota, mountain-ash, nannyberry, northern Minnesota, Phenology, radio, sumac, survival, winter