baby birds

"Nature Guide Journal"

25 May 2002

At first I thought it was hurt. The small, striped sparrow with a too-short tail fluttered clumsily. Failing attempts at effective flight, the fledgling finally managed to scramble to safety in the dense cedar branches.

Though I didn't see or hear it, I knew its parent was nearby. Parenthood is particularly demanding for most birds.

Birds can be divided into two broad groups, identified by how independent of their parents the freshly hatched young are. Some birds hatch as fairly developed chicks that need relatively little parenting ("precocial"); other birds hatch as less well-developed chicks that need much more help from their parents ("altricial").

In some precocial birds, such as ducks, parents simply accompany the downy, wide-eyed chicks as they leave the nest in search of food shortly after hatching. Parents in other precocial species, such as chickens, help more by demonstrating food-finding and food-catching techniques. Parents in still other precocial species, such as grebes, may actively feed their young.

In contrast, altricial birds are hatched helpless, nearly naked, with closed eyes. These are the stereotypic baby birds that linger in the nest, requiring unremitting attention from their parents for food, warmth, shelter, and protection.

Altricial nestlings require high protein food—and lots of it. Many species of bird babies eat about their weight every day; some parents must feed their young every several minutes.

What passes as "baby food" differs among species, certainly. Hawks and owls feed their young chunks of meat torn from freshly caught prey; songbirds deliver beakfuls of insects. Many birds, such as gulls, regurgitate semi-digested food from their gullets. Pigeons and doves even produce "pigeon milk" in their crops that's regurgitated for newly hatched young. (Found in many birds, the crop is a food-storage sac above the stomach.)

Sometimes the food requirements of the young differ from that of the parents. For example, the protein needs of the young of many primarily-seed-eating adults require the parents to supply large numbers of invertebrates.

In most altricial species, nestlings stretch their necks up, tip back their heads, and gape their mouths as widely (and loudly) as possible when the parent arrives with the catch-of-the-moment. Presumably, the hungrier babies are pushier. The parents thrust food down the throat of the most insistent youngster.

Some baby altricial birds demand food by pecking the bill of the parent. In a few species, the young go so far as to stick their heads into the throat of the parent in search of the meal.

Weak nestlings that fail to demand food strongly or often enough will likely starve.

After eating, of course, there are the remains to tidy up. In some nesting birds, such as hawks, the young turn tails out and eject the droppings away from the nest. Waste from songbird nestlings is usually packaged in a membrane; the parent picks up the fecal sac and either eats it, or carries it away from the nest to discard.

Altricial nestlings need protection from heat, as well as from cold and rain. They also need protection from predators. The dutiful parents warm, shade, and shelter their young; many also aggressively drive off threatening predators.

And then there's the flight training.

Indeed, the challenges of being a parent in altricial bird species have made it advantageous for parent in some species to enlist the assistance of other family members. Crow parents, for example, use the help of a previous brood member or aunt to help raise this year's offspring.

Of course, this grinding work has a biological payoff for the hidden parent of my flushed-up sparrow: with luck, the young fledgling will finally earn it's independence—and survive to rear it's own brood.

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