Bird Feeder Refill Frequency Calculator

Bird feeder consumption depends on feeder capacity, the number of birds visiting per day, and what those birds eat per visit. The math is simple division, but the per-bird seed numbers vary more than people realize, and that is what trips up most planning.

days_per_refill = feeder_capacity_grams / (birds_per_day × grams_per_bird_per_day)

Per-bird seed consumption from Cornell Lab of Ornithology and species-specific surveys (per visit, with most birds making 2-4 visits per day):

• Chickadee: 2-3 grams per day total
• Goldfinch: 4-6 grams (and they hog the niger feeder for hours)
• House finch: 5-8 grams
• Cardinal: 8-12 grams
• Blue jay: 12-20 grams
• Mourning dove: 15-25 grams (forages on the ground under feeder)
• Squirrel (uninvited): 30-60 grams

A worked example. A 5 lb (2,270 g) tube feeder, 30 birds visiting per day, mostly mixed songbirds averaging 6 g per day each. That is 180 g per day, so the feeder lasts 12.6 days. In practice, that estimate gets hit by squirrels and weather: a single rainy week can spoil seed before the birds finish it, and a single squirrel that figures out how to defeat the baffle can empty a feeder in two afternoons.

Seed type matters too. Black oil sunflower is the universal favorite, since almost every backyard species eats it and it has the highest energy density per pound. Niger (thistle) is finch-only, and a niger feeder lasts much longer because nothing else touches it. Striped sunflower is heavy and slow because some birds can’t crack it. Mixed seed marketed as “wild bird mix” includes a lot of milo and red millet that most birds throw out, so 25 percent of the bag ends up on the ground feeding starlings and house sparrows.

Seasonal patterns, and the multipliers this calculator uses. Take spring and fall as the baseline of 1.0:

Winter against summer is therefore exactly double, which matches the figure the annual seed cost calculator uses. If you have seen a bigger swing than that in your own yard it is usually squirrels rather than birds, and the squirrel field below is there for exactly that reason.

Migration weeks (mid-April and mid-October in most of North America) bring sudden visitor spikes that can empty a feeder in a day or two, so keep extra seed on hand if you watch the spring warbler push.

Cleaning. Standard advice is to clean feeders every two weeks with a 10 percent bleach solution, more often in wet weather. A neglected feeder is a vector for trichomoniasis and salmonella, which kill more songbirds in some years than predators do. If the calculator says your feeder lasts longer than two weeks, you are buying a smaller feeder, not getting longer between refills.