BIRDWISE: For young birds, there are two paths to maturity
This is the time of year when most birds are either sitting on eggs or tending their young.
The timing of the hatch tends to coincide with peaks of abundance of the foods that are most important for development of the young.
In my last column, I spoke about how many species switch from a vegetarian diet to a high-protein insect diet when their young are in the early developmental stage.
Now let's take a look at the very different strategies that birds employ to get their young from hatching to fully-feathered and flying juveniles. There are two basic types: precocial and altricial.
Precocial species are those that leave the nest within a day of hatching. Examples are duck and geese, grouse, shorebirds and loons.
At hatching their eyes are open, musculature is well-developed and their down feathers enable them to self-regulate body temperature. Consider a brood of mallards. Almost as soon as they are dry, the chicks are in the water, following the mother and darting about, snatching small insects off the water surface and aquatic plants. They never return to the nest once they leave it. Chicks of species like loons and grebes are similarly precocial, but not quite as independent as ducks and geese. Because their prey are too large for them to manipulate and more difficult to catch, these chicks depend on their parents for several weeks to catch their prey and feed them as they gradually acquire these skills.
Precocial young are unable to fly for up to several weeks while their flight feathers are growing. Consequently, as they move about, they are highly vulnerable to predators like hawks, eagles and snapping turtles. The parent(s) are very attentive and give warning signals when a predator is spotted so the young can seek suitable cover.
Altricial species are naked and helpless when they hatch. All songbirds have this altricial "life style." For 10 to 14 days, young are confined to a nest, where they are totally dependent on their parents for warmth and food-provisioning. Their eyes remain closed for several days.
As nestlings they face a different array of survival challenges than precocial species. First, their survival depends upon their parents having chosen a nest location unlikely to be detected by potential predators.
Second, nests are vulnerable to infestation by mites and other pests that can kill if abundant. The risk of such infestations is minimized, however, by a remarkable adaptation. The feces of the young do not contaminate the nest because they are enclosed in a gelatin-like case (fecal sac), which enables the parent to carry them away and deposit them far from the nest.
Third, any chick in a nest is at risk of being out-competed by siblings for the food the parents bring them.
Altricial species do, however, have a big advantage over precocial species: they achieve the ability to fly and evade predators in half to a third the time needed by precocial species.