Wednesday, October 19, 2016 5:14 PM
There’s a scientific term for birds that eat fruit — it is frugivore. During the summer nesting season, insects provide the bulk of a protein-rich diet that ensures healthy growth and development of nestlings. In the fall, a number of species shift their diet slightly to include more fruit as the quantity of available insect matter declines.
Female Rusty Blackbird (Photo by Don Reimer)
Generally rich in water content and carbohydrates, fruit pulp provides an excellent energy source of sugar, playing an essential role in maintaining body heat in chilly temperatures. Migrating robins, waxwings, blackbirds and brown thrashers are currently drawn to brightly colored October fruits and coastline berries. Depending on the bird species, the ripeness of the fruit and the type of fruit, birds might eat the flesh, sip the juice or do both.
By virtue of their broad travel habits, birds are effective dispersers of fruit seeds to distant locations. Interestingly, the seeds of bird-dispersed fruits are often adapted to survive digestion by frugivores. Seeds pass rapidly through birds’ digestive tract, becoming more water permeable after passage through a bird’s gut. In turn, this leads to higher seed germination rates.
I’ve noticed certain birds taking full advantage of this year’s ample apple crops. A few Rusty Blackbirds were huddled in apple trees on Monhegan Island, pecking at the ripened apples there. I’ve also witnessed several Rusties, specialized inhabitants of wet boreal forest zones from Alaska to Newfoundland, overturning decayed, water-soaked leaves in search of invertebrate prey. As their name implies, winter Rusty Blackbirds are tinged with rusty brown caps and backs. Yellow eyes and a prominent pale eyebrow are other distinguishing features.
Since the 1960s, 90% of Rusty Blackbird populations have quietly disappeared. In the past, dense single-species migratory flocks passed overhead. In these times, we must carefully scan through mixed blackbird flocks to discern a few scattered rusties. If present population trends continue, extinction of the species is possible within mere decades.
Another member of the blackbird family, most of our summering Baltimore Orioles have now migrated. Lingering groups of young orioles use fruit as a convenient fall food source. Fruit constitutes a large portion of the oriole diet on their neo-tropical wintering grounds. That is why spring arrivals so eagerly accept the halved oranges we offer here in Maine.
Fall warblers? We might consider flitting warblers as the ultimate consumers of tiny summer insects. By late fall, most warbler species have retreated far southward. Yet limited numbers of hardy Yellow-Rumped Warblers manage to overwinter along our beachfronts by feeding on, you guessed it, fruits and berries. Yellow-Rumps focus mainly on the fruits of bayberry bushes and the seeds of rugosa rose hips. These probing warblers inevitably find some bonus insect larvae hidden within the plant interiors.
Planting fruit trees, berry shrubs and other plants that produce fruit is a productive way to feed birds on a budget. These plants will help support vagrant flocks of winter waxwings and finches such as Pine Grosbeaks. And by leaving some of the windfall fruit on the ground, you will provide birds with some welcome food to sustain them through the leaner months of fall and winter.