When you’re an altricial baby bird, life is either great or over. If it isn’t over—that is, assuming you aren’t eaten by a mouse, chipmunk, snake, slug, coyote, etc.—then your life is sitting still in the warm and having food shoved in your face. Excellent.
But that doesn’t last. After you fledge, your parents keep feeding you, but soon they start feeding you less. You can follow them around begging, but soon even that doesn’t do any good. You have to face it: you need to learn how to catch your own food. But that food flies and crawls and runs away!
We tend to think of wild animals as “instinctually” being able to do everything they do, but in fact, a lot of those skills have to be learned and practiced. Two of my favorite scientific papers looked at how fledgling birds developed their foraging skills. As adults, they were the expert bug-catchers you see all the time; but as fledglings, they did—well, about as well as the four-year-old child of a champion fisherman would do, the first time you handed her the fishing rod.
Davies & Green (1976) raised Reed Warbler chicks by hand, feeding them on “small balls of minced meat rubbed in cod-liver oil and dipped into a homogenized powder consisting of three measures of Saval puppy food, one of Bemax wheat germ, one of chick meal, and one of Lowe’s cat meat… supplemented with crushed flies.” Mmm! When the birds fledged, their wing feathers were only half grown, so for locomotion they relied heavily on their fully-developed legs. They were good at clinging to the vertical bars of their cage, probably because they were reminiscent of the reeds of the birds’ natural habitat; on horizontal perches they “tended to overbalance and sometimes fell off while preening or being fed.”
Adult Reed Warblers eat insects, often leaping or hovering to pick them off. After fledging, the captive birds began to peck speculatively at things – “each other, their perches, the cage wall” and even their own feces. In their defense, though, it only took them one day to learn not to try to eat their own poop. Good job, I guess…
They watched blowflies that were introduced to the cage, tracking the movement of the insects with their heads. If the flies flew nearby, the chicks gaped at them hopefully. The chicks also chased the flies, hopping toward them, but “the flies always flew off well before the bird arrived.”
As their wings and bills grew toward adult size, however, the young Reed Warblers got better and better, first catching some flies only to drop them, then successfully catching and eating them. As soon as they managed to swallow a fly, they stopped pecking at random objects and fixated on the insects. By 22 days old, they were regularly catching their own flies.
Juan Moreno (1984) followed four broods of Northern Wheatears in the wild in Sweden. In the first days after fledging, the chicks stayed close to rock piles where they could quickly hide, and passed the time begging, preening, and “manipulating only inedible objects like pieces of grass and moss, small stones, and flowers.” Soon, however, they began hopping along in the grass and pecking. As time went on they began to attempt catching prey on the wing, although they had the most success catching bugs as they flew past close to where the birds sat, probably because the young birds weren’t very good fliers yet. Eventually they too transitioned to adult foraging techniques.
I love these papers for their insight into the development of a behavior in young birds; for their now-old-fashioned-seeming attention to carefully describing behaviors (rather than, say, immediately generating sequence data in order to find the gene for foraging); and for the mental image of prominent scientists, years before I was born, watching young birds toss food balls around their cages and then sitting down to clackety-clack out on their typewriters phrases like “individuals ignored their own faeces after 1 day’s handling experience.”
P.S. If you like scientific papers describing young birds behaving in amusing ways, you might like this post from a while ago.
Davies NB, Green RE. 1976. The development and ecological significance of feeding techniques in the reed warbler (Acrocephalus scirpaceus). Animal Behaviour 24:213-229.
Moreno J. 1984. Parental care of fledged young, division of labor, and the development of foraging techniques in the Northern Wheatear (Oenanthe oenanthe L.). The Auk 101(4):741-752.