Mere hours old, a comical procession of 12 downy puffs drop one by one from their nest cavity 30 feet high in a white ash snag. Scrambling to keep up with their mother, a female wood duck, they head to the nearest wetland. They plop into the water feet away from a well-concealed cup nest tightly woven among the cattails, where four naked red-winged blackbird chicks – also just out of the egg – huddle with eyes closed, awaiting a parental delivery of soft-bodied invertebrates.
Parenting in birds is a splendor of diverse chick-rearing strategies, which fundamentally relate to the maturity of young at hatching. Chick development follows two basic patterns along a spectrum. At one extreme are species that produce precocial young. These include all waterfowl, as well as ruffed grouse, wild turkeys, and kildeer. Precocial chicks hatch with eyes fully open, a covering of down feathers that enable them to immediately thermoregulate, well-developed legs, and the ability to feed within hours. Also termed nidifuges (from Latin: “nest fugitives”), precocial chicks leave their nest shortly after hatching, instantly imprinting on and closely following their parent(s).
At the other extreme, songbirds, hummingbirds, kingfishers, and woodpeckers are altricial species. Their newly hatched young are completely helpless. They lack feathers and must be brooded (usually by their mother) to maintain body heat. They’re also blind for the first week or so, and cannot move other than to raise their heads and beg for food. Also referred as nidicoles, or “nest dwellers,” altricial young remain wholly dependent on their parents until ready to fly from the nest. Fledglings stay with parents for variable periods (typically 2 to 3 weeks in songbirds), a critical stage during which the young birds gain the skills needed to survive on their own.
Between these ends of the hatchling maturity spectrum lie two intermediate categories: semi-precocial and semi-altricial. The former includes gulls and terns, whose young hatch with eyes open, downy plumage, and the ability to walk or swim, but remain in or close to the nest and are fed by their parents. Semi-altricial chicks also hatch with a full covering of down and eyes open, but cannot leave the nest and depend on parental provisioning at least until they fledge. Herons, hawks, and falcons belong to this category, as do owls, with the exception that owlets hatch with eyes closed.
Generally, the smaller the species, the shorter the period between hatching and fledging, which is when young birds first gain flight capabilities. For altricial species, fledging occurs when chicks leave the nest. Nestlings of most songbirds fledge within 2 weeks after hatching, some after only 8 or 9 days, while bald eagle nestlings take flight in 10 to 12 weeks. Open-cup nesters, including most songbirds, tend to fledge sooner than cavity nesters such as woodpeckers and kingfishers, whose nests are less vulnerable to predators.
For precocial birds, fledging times vary widely but are typically longer than those of altricial species. Spruce and ruffed grouse are exceptional in that their mobile chicks can undertake short escape flights a mere week after hatching. Killdeer young may begin flying at 3 weeks, but wood ducks need 8 to 9 weeks, and common loon chicks may not lift from their natal waters until 12 to 13 weeks of age.
These different modes of offspring development reflect evolutionary tradeoffs. Precocial species acquire abundant resources before egg laying; they must produce energy-rich eggs that support the greater prehatching development of chicks. Females of altricial species have lower nutritional demands prior to egg laying, but must be able (typically, with their mates) to find enough food for their helpless young. The entire brood is extremely vulnerable to predation, depending on nest concealment and parental defense for survival. In contrast, precocial young have the ability to feed themselves and to avoid predators, with a much smaller chance of the entire brood (as opposed to single chicks) being lost.
Whether this summer’s cohort of young birds are precocial, altricial, or somewhere in between, they require an extraordinary investment by their parents, and a remarkable array of tactics to accomplish the job!