Black-capped chickadees, like this one at Gisland Farm in Falmouth, are not reliant on the food we provide. Just be sure to keep that feeder clean to prevent spread of disease, and watch out for those raptors. Brianna Soukup/Staff Photographer

To feed or not to feed? The widespread practice of bird feeding has advocates and opponents. We’ll review the pros and cons of providing handouts.

Much of the research on the effects of bird feeding has been done on black-capped chickadees in several states and provinces during the fall and winter. In every case, supplemental food in the form of black oil sunflower seeds increases survivorship. We have no reason to doubt that other common feeder birds also benefit by feasting on the food we offer them.

A feeding station does what it is supposed to do; it causes birds to aggregate where we can see them. A surprising number of birds use your feeders. I did a study of bird feeder use in the woods east of Flagstaff Lake. At each of my banding stations, I caught and color-banded chickadees in November so I could recognize individuals. I counted the visits and checked the identities of chickadees as they came to the feeder to claim a seed. At first, most of the birds were color-banded. By March, I was seeing mostly unbanded birds. A mathematical model allowed me to determine that around 120 different chickadees were visiting the feeder each day in March, although I would only see a dozen or so at a time.

Two negative effects can occur by concentrating birds.

First, the spread of avian diseases can be facilitated.

In 1994, many house finches in the east were afflicted with avian conjunctivitis. The disease causes swelled, crusty eyes. In extreme cases, the birds are virtually blind. It’s easy to see how the disease could by spread quickly among such gregarious birds. Afflicted birds are likely to stay close to a feeder, infecting healthy birds. The disease caused massive mortality and house finches have still not returned to pre-1994 levels.

What can you do? All people who feed birds should clean their feeders regularly. If you see a bird at your feeder that is sluggish or weak or has abnormal eyes, take your feeder down immediately.

Bird feeders can become a different type of feeding station. A sharp-shinned hawk or other raptor may decide to stay in the vicinity of an active feeding station. If raptor predation becomes a problem, take your feeders down for a few days (and give them a good cleaning while you are it).

Some people who feed birds worry about being away from their feeders for part of a winter (those were the days!) and thus depriving birds of a food source. The good news is that research has clearly shown that black-capped chickadees do not become dependent on our bird seed. Birds seek food in many places so that if one food source is depleted, food can be found elsewhere.

A recent paper by Rachael Mady and colleagues in the journal Behavioral Ecology extends this research. They wanted to know if three common feeder birds (black-capped chickadees, tufted titmice and white-breasted nuthatches) stayed closer to feeders that constantly had food versus those with intermittent food or no food at all.

The researchers began their experiment in August by putting out constantly stocked feeders in a forest. Then in late October, they assigned each feeder to one of three protocols (constant food, pulsed food – three days with food followed by four days without – and no food).

Over the winter, the authors did regular five-minute counts of the birds from points 10 meters from the feeder and 200 meters from the feeder. Few birds were in the vicinity of empty feeders. Feeders with constant food anchored the birds; they were more abundant within 10 meters of the feeder compared to points 200 meters away. But the birds in the pulsed treatment were anchored near a feeder when food was available but spread farther away when food was removed. These birds nimbly changed their foraging strategy based on the reliability of food in the feeders.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]du


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