During the winter, many species of birds rely on seeds and fruits. Seeds can be hard to see and identify unless the bird is sitting on the food plant, such as a wild sunflower. Fruit, on the other hand, can be obvious because the items are usually relatively large. Fruit contains seeds, but let’s leave that little complication for now.
One of the classic principles about food types is that fruits can be plentiful and easy to get. But they tend to be low in protein and fat. Very few species, e.g., oilbirds, can live on fruit alone. And even serious frugivores in places like the Neotropics typically need some protein to feed growing young.
Around the Treasure Valley in winter, we enjoy watching many different species consume fruit. These include cedar and Bohemian waxwings, American robins, Townsend’s solitaires, hermit thrushes, northern flickers, white-crowned and song sparrows, and waterfowl such as mallards and wood ducks.
The fruit available to a given species depends partly on the size. Small fruits like those of the honeysuckle are available even to sparrows. But rose hips and Russian olive fruits are accessible only to larger species, although smaller birds can sometimes nibble on these rather than swallow them whole. You can also watch smaller species take larger fruit and then pound them with their beaks until the fruit becomes soft or fragmented enough to swallow.
Some of the more common winter fruits around here are rose hips, hawthorn, juniper, mountain ash, dogwood, privet, Boston ivy, honeysuckle and Russian olive. Note the last four of these are introduced species. Higher in the mountains we also have serviceberry and chokecherry, both native species.
I would add Oregon grape and snowberry, but I’ve never seen a bird eating those, despite their abundance. Oregon grape also helps illustrate how the distinction between “native” and “introduced” is not that distinct. Oregon grape — aka creeping hollygrape and grape holly — is native where it originally occurred in the Pacific Northwest. But it has been introduced into other regions as an ornamental shrub. In some places, it is now considered introduced.
It’s also a good time to make a distinction between exotic species and invasive exotics. The latter spread relentlessly and rapidly once they get a foothold in some area. Many invasive exotics are grasses, such as cheatgrass, or forbs, like Canada thistle. Check Idaho’s Noxious Weeds (10th edition, 2022) for a full list. The introduced fruit-bearing shrubs of interest here are not noxious weeds in Idaho.
If you’ve ever nibbled on a rose hip (the outside becomes sweet in late winter) or looked at a hawthorn berry, you see they are dry and full of seeds. Or consider the dense flesh and sharp flavor of a juniper berry. If you’ve never bitten into one, try it. If you don’t trust me, buy some rose hip tea, a bottle of juniper berries or a bag of hawthorn berries.
Juniper berries are a minor, but I bet, distinctive item in Norwegian pork ribs and one version of garlic potatoes. Hawthorn berries are farther out on the fringe, being used in teas, jams and chutneys. The only thing I’ve had from this group is rose hip tea. But I’m now intrigued by these new possibilities.
In the wild, these fruits seem nearly inedible, and yet robins and waxwings will gobble them down in numbers. What nutrition is in these fruits to make them worth fooling with? The evolutionary perspective is that all those seeds get passed through the birds and are the plant’s way of distributing its seeds across the landscape.
Rose hips contain high levels of polyphenols, carotenoids and vitamins C and E, all of which are antioxidants. I assume antioxidants are good for birds too, but it’s probably the high concentrations of vitamin C that are most valuable. As with humans, vitamin C strengthens immune systems, especially during stressful periods like winter. There is also fiber and calories in the red coating.
Hawthorn berries contain vitamins A, B1, B2 and C, as well as calcium, iron, potassium and phosphorus. They also contain flavonoids and phenolic acids, yet other types of antioxidants. Hawthorn (genus Crataegus) is also in the rose family.
Ripe juniper berries contain protein, fat, fiber, vitamin C and carbohydrates. With a whopping 16% lipids and 46% carbohydrates, it’s little wonder birds eat these with enthusiasm. Plus, it gives them that fresh juniper breath without the aftereffects of gin.
Mountain ash berries are rich in vitamins A and C. They’re bitter to human taste buds due to their tannin (like chokecherries) and sorbic acid content so they don’t show up in many modern recipes. In the old days, they were taken on long sea voyages to prevent scurvy. Until the role of vitamin C was discovered, countless explorations by ship were devastated by scurvy. Lime juice and tomatoes were more often the preventative.
Dogwood berries contain calcium, iron, potassium, vitamins A and C, protein, fat and antioxidants. Like most of these fruits, they can be used to make tea and jam once processed in various ways. Sugar seems to help them all for the human palate. Birds do have a sense of taste, although it is much less sensitive and sophisticated than that of humans.
Looking at the other plants named above, Boston ivy berries are high in fat.
Honeysuckle berries are low in nutrients and fat but high in carbohydrates. They’re also toxic to mammals, so no tasting! Russian olive fruit contains vitamins A, B, C, and E, potassium, calcium, chromium, other trace minerals, and both fructose and glucose, hence the fruit’s sweet taste. You have nibbled on them, right? I sure have — more than once.
The only loser in all of these are privet berries, as they are low in nutrients. I have watched white-crowned sparrows eating these berries with what I would call a lack of enthusiasm. But low in nutrients doesn’t mean no nutrients at all.
What we have across these fruiting species is a variety of nutrients in various combinations. That may be why we often see fruit-eating birds eat just a few fruits off one plant and then move on to another. I suspect their bodies tell them what they need, just as happens with humans. “I’ve had enough vitamin C, time for some carbohydrates.”
Right now, my body is signaling that I need espresso and ice cream. We survive winter as best we can.