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FIELD GUIDE

Autumn is a berry good time for the birds

An American robin ate a crabapple fruit at the Arnold Arboretum in Boston in late November.
An American robin ate a crabapple fruit at the Arnold Arboretum in Boston in late November.(Samuel Roberts)

New England is world renowned for its brilliant fall foliage. But there’s a lot more to see — if you know where to look — in the form of berries and other wild fruits that ripen in fall.

From the dark purple berries of pokeweed to the bright reds of winterberry to the yellow and orange of oriental bittersweet, the wild fruits of autumn are as colorful as the changing leaves.

And while most of these wild fruits are not edible for people, they do provide a bounty for wildlife, such as birds and mammals.

“Bittersweet and burning bush have the same trait of the fruit opening up to reveal a bright orange coating, [called an] aril, around the seed,” Scott Shumway, chairman of the biology department at Wheaton College, said in an e-mail. “That color says to the birds, ‘eat me!’”

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Fleshy-fruited plants have evolved a mutually beneficial relationship with birds and other animals, said Amanda Gallinat, who completed her doctorate in biology at Boston University this year and is now a researcher at Utah State University.

“Plants package up nutrients into brightly colored fruits and after animals eat and digest the fruits, they deposit the seeds across the landscape” in their droppings, Gallinat explained in an e-mail. “Birds have excellent vision, particularly for color, so it is likely that many fruits are brightly colored so they can be more easily spotted by birds.”

Gallinat said some birds seem to prefer red and orange fruits, many of which get their color from carotenoid pigments, while others prefer blue and purple fruits that are high in anthocyanin pigments.

Oriental bittersweet berries. The bright orange coating, called an aril, appears in autumn and attracts birds which feed on the berries.
Oriental bittersweet berries. The bright orange coating, called an aril, appears in autumn and attracts birds which feed on the berries. (Garry Kessler)

Even dark-colored fruits can be spotted by birds, said Richard Primack, a biology professor at Boston University and Gallinat’s former adviser.

“Birds can find fruits by color, and the dark fruits will contrast with vegetation,” Primack said. “For example, black berries against green vegetation.”

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When a fruit changes from green to blue or red it signals to the bird that it’s ripe, Primack said.

Shumway said it’s no accident that unripe fruits are green and blend in with the background foliage.

“Fruits are rewards given in exchange for dispersal of seeds,” said Shumway. “A fruit consumed before it and the seeds inside are ripe is a failure. The future offspring represented by the seeds will never come into existence.”

Pokeweed berries ripen in autumn, and their dark purple color stands out against the green leaves, which helps birds to find them.
Pokeweed berries ripen in autumn, and their dark purple color stands out against the green leaves, which helps birds to find them.(Garry Kessler)

Gallinat said that aside from just making fruits visible, colors also can signal the presence of certain nutrients that are beneficial to birds.

“For instance, the rich purple fruits of arrowwood shrubs contain antioxidants that may help birds avoid physical stress during migration,” Gallinat said.

Most birds migrate through Massachusetts between early September and late October, she said, and by November the last of the late-migrating birds are still trickling through. Gallinat said birds such as thrushes, catbirds, and cedar waxwings eat lots of wild fruits.

Mammals such as squirrels, chipmunks, opossums, and raccoons probably consume a number of wild fruits as well, Primack said.

But, surprisingly, even some brightly colored fruits go uneaten.

“Bird fruit preferences are complex,” said Gallinat. “So just because the fruits are advertising, it doesn’t mean the birds are buying!”

Primack said the bird species in our area don’t like to eat a lot of non-native species, such as bittersweet, multiflora rose, and buckthorn, and only eat them during the winter as a last resort.

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Local birds also don’t seem to like some native plant species, such as winterberry, which ripens in fall but typically remains uneaten well into winter. Primack speculates that’s because it’s probably low in nutrients, but said that hasn’t been investigated yet.

“Birds probably correlate taste with nutrition — sweet, fatty, protein,” said Primack. “We have that ability, presumably birds do, too. If they taste sweet or fatty or meaty, birds will continue to eat. If fruit tastes bitter or rotten, they’ll stop eating and go find something else.”

Staghorn sumac, for example, has small, dried fruit with a fuzzy red coating, and a slightly sour taste.

“Sumac probably has a low nutritional value,” said Primack. “Birds will only eat it in winter when there’s nothing else to eat.”

Staghorn sumac has small, dried fruit with a fuzzy red coating, and a slightly sour taste. Birds typically eat it in winter when there’s nothing else to eat.
Staghorn sumac has small, dried fruit with a fuzzy red coating, and a slightly sour taste. Birds typically eat it in winter when there’s nothing else to eat. (Garry Kessler)
Winterberry ripens in fall, but typically remains uneaten well into winter, possibly because of low nutritional value to birds and other animals.
Winterberry ripens in fall, but typically remains uneaten well into winter, possibly because of low nutritional value to birds and other animals.(Don Lyman)

Don Lyman is a biologist, freelance science journalist, and hospital pharmacist who lives in the suburbs north of Boston. Send your questions about nature and wildlife in the suburbs to donlyman@ix.netcom.com.