|The extra-large chick in this nest is a Brown-headed Cowbird. Females of this species lay an egg in several open-cup nests of other songbirds, whose chicks are usually smaller; the strategy is called brood parasitism. Creative Commons photo.|
Brood Parasitism. Even before hatching, a baby bird has to break out of a sealed shell (exhausting) and immediately establish itself in the order-of-peck with nest mates. When eyes open and vision clears, it’s bad luck to look across the cup and see a youngster that’s twice as big (photo above right), because that bully will probably push you out. That would be a Brown-headed Cowbird, a species that lays a large egg in the nest of others, usually to the detriment of the host. The likelihood that the nestlings will be taken by cats, corvids, ants, or snakes always looms, too.
Raptors. Most raptors (hawks and owls) practice what is known as the “graduated clutch strategy.” That is, they start to incubate each egg as soon as it appears, and they lay their eggs at two- to three-day intervals. In a clutch of three, the first egg and resulting chick is perhaps six days older than the third, so the young are graduated in size and in their ability to grab food brought to the nest by adults. If prey is abundant, all the young should fledge; if not, the younger, smaller birds will starve or be nudged overboard.
Golden Eagle eaglets commit siblicide (a term used even before the current favorite field guide). That is, the oldest and largest chick kills its sibling or siblings, and only the one bird fledges. The parents do not intervene.
|Mallards. Photo by Peter LaTourrette / www.birdphotography.com.|
Clutch Size. Galliformes (quail, grouse, etc.), rails, and dabbling ducks produce large clutches of eggs. The chicks are precocial (they can see and walk right after hatching) and terrestrial. Young birds in these groups are flightless and on the ground, a combination that invites predation. The parent(s) are usually nearby but, except for vocal commands like “crouch and freeze,” are nearly helpless to defend their chicks. Perhaps 15 baby birds at hatching are often reduced to few or none within a few days. Even after making it to the relative safety of water, unaware ducklings may become nourishment for an otter, heron, bullfrog, or bass. The mother, leading the parade may not notice.
Spring Training. Kestrels hold flight school, and soon after the young falcons emerge from their nest cavity they line up on a branch. Each, it seems in turn, flies a sortie and returns to the perch. If one shows reluctance a parent swoops in from behind and shoves that bird into space. Most will triumph but some hit the ground and are at risk.
Belted Kingfishers hatch and grow in a small earthen “room” at the end of long (up to eight feet) tunnels excavated high into a dirt cliff. Their first launch into flight is virtually their first launch into light. This is a very big day for the young royals and doesn’t always go well.
|Black-footed Albatross. Photo by Bill Bouton.|
After more than 200 days as an embryo and then a dependent chick, a young Black-footed Albatross’s urge to fly may develop more quickly than its readiness, and within seconds of initial lift-off some crash into the water and are chomped down by waiting tiger sharks.
Incredible Journeys. When only two to three months old, the young of most migratory species hurtle themselves into dark and unknown skies for the first leg of a very long trip. Many will not conclude the journey, but at least as many will. With no map, no GPS, and no guide they will arrive at their genetically wired winter homes and perhaps find comfort from the presence of others of their own kind.
The new generation of individuals that survive youth and perilous travel will be back the following spring to propagate their species.