How often do feeder birds eat? How long does it take them to digest a meal and be hungry again? And how does one know?

The answer to the last question is simple: Mark the seed with food coloring. Start the clock. Watch for colored bird poop. Stop the clock.

The small birds we see at our feeders in Orono, the chickadees, nuthatches and finches, feed briskly through the morning, returning in early afternoon. They are at the feeders sporadically as the day ages.

Cardinals, a crepuscular species, follow their own schedule, eating an early breakfast and a stylishly late dinner. They will break that schedule on very cold days.

Looking for research answers I found seven papers addressing this (SORA.com).

Small birds process their food faster than large birds. Seeds take longer to digest than soft fruit.

The number of meals per day, or times the stomach is filled daily, has been estimated by various ornithologists at eight times a day for seed-eaters, six to seven for birds on an insect diet.

A study summary said small birds do not fill their crops and stomachs and then wait until they are empty before eating. They eat from time to time.

Sparrows and starlings were fed cracked corn, raspberries and mealworms (all dipped in food coloring), to measure digestion times. The birds first were starved for two or more hours, according to a published study. All of the birds showed colored excrement in about 90 minutes.

The study pointed out that such rapid digestion means birds must actively search for food each day. That seems to be a settled question.

The experiment where birds were starved? A starling died after 48 hours. Do not try this at home.