Bird's Patterns of Chick Development -- Page 5

Precocial parents need only lead the chicks to appropriate feeding habitats, keep them warm during the first days by occasional brooding, and protect them from predators This last job is especially critical. Since the chicks are moving around in open habitat, they are easily noticeable; because they are unable to fly, they are easy prey. Among shorebirds the solution is a combination of remarkable chick camouflage and energetic adult distraction displays. Baby shorebirds have special down feathers that create a finely spotted effect to break the outline of the chick, and their response to an alarm call from a parent to crouch, motionless, amid the vegetation. The parent then employs the rodent run, broken wing, or other distraction displays. The distraction displays are often so artful and insistent that the predator is drawn far away from the chick area. Afterwards, the parent circles back, giving the all-clear whistle, and gathers the brood together again.

Precocial development does, however, impose some limitations. It is well suited mainly to species that nest on the ground and feed on foods that can be taken by chicks on the ground or on water. For many songbird species that forage on insects in treetops, or for hawks and owls, which kill relatively large prey, precocial chicks would still be unable to feed themselves. Furthermore, precocial chicks must accomplish much more development than altricial chicks while still in the egg, which means that females must lay large eggs and spend more time incubating them in a vulnerable, ground nest site. Altricial birds shift more of their parental care effort into the post-hatching stage.

Precocial parents need only lead the chicks to appropriate feeding habitats, keep them warm during the first days by occasional brooding, and protect them from predators This last job is especially critical. Since the chicks are moving around in open habitat, they are easily noticeable; because they are unable to fly, they are easy prey. Among shorebirds the solution is a combination of remarkable chick camouflage and energetic adult distraction displays. Baby shorebirds have special down feathers that create a finely spotted effect to break the outline of the chick, and their response to an alarm call from a parent to crouch, motionless, amid the vegetation. The parent then employs the rodent run, broken wing, or other distraction displays. The distraction displays are often so artful and insistent that the predator is drawn far away from the chick area. Afterwards, the parent circles back, giving the all-clear whistle, and gathers the brood together again. Many precocial waterfowl chicks are even better equipped to avoid predators because they can swim almost from birth. Everyone has seen baby songbirds in the nest with eyes closed and mouths open. The adults of common backyard birds have to feed their young. Ducklings and goslings, on the other hand, hatch with their eyes open and already have feathers because they will soon have to feed themselves. Remarkably, young waterfowl spend only about a day in the nest.

Precocial development does, however, impose some limitations. It is well suited mainly to species that nest on the ground and feed on foods that can be taken by chicks on the ground or on water. For many songbird species that forage on insects in treetops, or for hawks and owls, which kill relatively large prey, precocial chicks would still be unable to feed themselves. Furthermore, precocial chicks must accomplish much more development than altricial chicks while still in the egg, which means that females must lay large eggs and spend more time incubating them in a vulnerable, ground nest site. Altricial birds shift more of their parental care effort into the post-hatching stage.

A few other differences in parental care systems arise from these differences in chick development patterns. Whereas altricial species must be stay-at-home parents, always returning with food to the same spot, precocial species are quite free to travel.

Precocial chicks' ability to care for themselves lessons the burden on parents, permitting single parenting to be more successful and more prevalent among these species. In many shorebirds one adult leaves the nesting grounds before the chicks fledge; in some the second adult may even depart when chicks are barely able to fly. In species such as Pectoral, White-rumped, or Baird's Sandpipers, the parents depart from arctic nesting areas in July and August, headed for wintering areas in southern South America. Their barely grown chicks are left behind to fend for themselves while they continue to feed for a few more weeks to build up their stores of fat. Before the early arctic winter appears, these four- to six-week-old birds begin the same several-thousand-mile flight for themselves, with no adults to guide them. It sounds impossible, but it works every year.