Harmony and Conflict in the Living World - Alexander F. Skutch [17]
Incidentally, the strong intersexual selection associated with this mating system has given us many of our most beautiful birds, from dainty, glittering hummingbirds and ornate manakins and cotingas to lavishly adorned birds of paradise. Moreover, males in these assemblies appear to be safer from predation than they would be if they courted in solitude. Although the groups of performing, calling birds certainly attract attention, males would in any case need to make themselves conspicuous to be noticed by females, and by displaying in assemblies they gain the advantage of many vigilant eyes, as in flocks of all kinds. In courtship assemblies, a few dominant males, probably most often senior birds, win most of the females, while the younger members on the outskirts practice displays that may take time to perfect, becoming more successful as they grow older. Since only exceptionally do assembly members fight furiously together, they may live long.
Individuals also benefit their species by adopting young. Although not unknown among fish, mammals, and altricial birds, adoption is most frequent and spectacular among precocial birds that pick
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up their own food while following an adult. A parent of nidifugous chicks, who need only guidance, protection, and brooding, can attend in this manner to many more young than it can hatch; whereas parents of altricial and semialtricial young, who must be given food brought from a distance and placed in their mouths, are often unable adequately to nourish additional dependents. As they lead their families to good foraging, birds as diverse as Ostriches, rheas, grouse, sandpipers, stilts, avocets, and plovers are often joined by lost, orphaned, or abandoned chicks unrelated to them. Similarly, parent geese accumulate goslings, ducks pick up ducklings not their own. Such mixed flocks of dependents, guarded by one or a few faithful adults, can become very large, occasionally, as has been recorded of Ostriches and Shelducks, containing over one hundred young of different ages. Many nidifugous juveniles owe their lives to foster parents.
Semialtricial chicks, who leave their nests while still flightlesscolonial-nesting penguins, pelicans, flamingos, and certain ternsgather in nurseries or crèches, guarded by a few adults, while their parents forage afar and bring their meals. By voice, appearance, or both, parents and young recognize each other individually; each parent feeds its own offspring, an arrangement that ensures a more equitable distribution than would result if a returning adult delivered its food to the first claimant. By this system, weak or ailing chicks, who would be pushed aside by more vigorous young if feeding were indiscriminate, are assured meals. Among nidicolous birds, a parent that has lost its mate is sometimes joined by an unattached individual of the opposite sex, who helps the bereaved parent to feed its young (Skutch 1987). Stepparents are too infrequent, or too seldom detected and reported, to affect importantly populations of abundant, strongly established species, but by even slightly increasing the reproduction of a declining species, they may help save it from extinction.
Finally, the individual dies for the good of its species. If successful in escaping all the hazards that prematurely destroy so many free animals, it grows feeble and expires from internal causes. When we recall the great recuperative power of organisms, their ability
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to heal wounds, recover from diseases, and restore wasted tissues, senile decay is the greatest of paradoxes. Why should animals not continue to live and reproduce indefinitely? Do they die to make room for their progeny and avoid