Brood parasitism is the practice of laying your eggs in someone else’s nest and letting them raise your young. This freeloading behaviour is a byproduct of the Curse on nature following mankind’s sin (Genesis 3:17–18; Romans 8:19–22).
Birds that are obligate brood parasites—those that do it as a way of life—include one duck (Anatidae); about 53 species of cuckoos (Cuculidae); 17 honey-guides (Indicatoridae); 20 wydahs and indigo birds (weaverbirds, Viduidae); and 5 cowbirds (New World blackbirds, Icterinae). Others occasionally practise the behaviour (facultative brood parasites), but we do not consider them here.
With 12,000 species of birds, this figure represents less than one percent of all, yet the effects are widespread. The number of species parasitized by the Common Cuckoo (Cuculus canorus) is over 100,1 while over 220 have been reported for the Brownheaded Cowbird (Molothrus ater) of North America.2
The female cuckoo lurks among the foliage of a tree, quietly observing potential host species building a nest. She may have several hosts under surveillance at once. She has a fully-formed egg in her oviduct, giving it perhaps a day’s ‘head start’ to incubation. At the right moment, when the host has laid some of its own eggs and left the nest, she flies in silently, eats one or more of the host’s eggs, deposits one of her own, and leaves. It’s done in a few seconds.
In addition to this stealth, the parasite also lays mimetic (‘imitating’) eggs (fig. 1) which match those of the host accurately. Within the Common Cuckoo population, there is a variety of types of egg pattern and colour which are genetically determined. Females are accordingly classed in various ‘tribes’ or gentes based on this egg appearance. Each female knows the appearance of her own eggs before she lays them, and seeks hosts with matching patterns.
Many brood parasites lay eggs smaller than predicted for the size of adults—meaning that an egg that is a similar size to the host’s eggs will have a hatchling that grows to a larger size than its fellows in the nest. They have relatively thick shells for protection, and hatch sooner than those of hosts. Young parasites comprise two groups: host-tolerant where they coexist with the chicks of the host species and host-intolerant where they evict any host eggs and hatchlings.
Of the latter type, the young parasite is hatched naked and blind with a concavity in its back into which it manoeuvres the host, either egg or chick, as into a basket (fig. 4). It uses its well-developed feet and rudimentary wings to lift itself and its load to the edge of the nest so as to flip it out.
The honeyguides, which almost exclusively parasitize hole-nesting barbets, are hatched with deciduous (temporary) hooks on each jaw (fig. 2). They use them to lacerate and kill the chicks or break the eggs, then manoeuvre the remains up the sides of the nest chamber and out the front door. This is termination with extreme prejudice!
The hosts are not defenceless. They mob and drive away the parasites, puncture and throw out the alien egg, build an extra layer over the first eggs and lay a second clutch, or abandon the nest and try again elsewhere. Curiously, though, once the parasite hatches, the hosts seem to tolerate it (fig. 3).
Some host species are programmed to know the length of time it takes their own young to reach the fledging stage. If the parasite requires longer to grow fully, the hosts may simply lose interest in feeding it and abandon it to starve.
Most brood parasites are polygamous, with females mating with as many males as possible. Some that show monogamy do so for the purpose of deception. Males will fly near a potential host nest, drawing the attention of both the parent birds who mob it. Meanwhile the female slips in and quickly lays her egg.
Evolutionists have no idea of the origin of brood parasitism. Their speculations and ‘just-so stories’ simply do not make a plausible account. The negative effects of brood parasitism vary among species and locality. Figures for losses of host young in a species range from less than 10% of all the eggs laid to over 70%, with an average of around 44%. It is another manifestation of ‘thorns and thistles’ in a world that nonetheless still reflects the beauty and design of the original creation before it was ruined by sin.
References and notes
- Cramp, S. (Ed.), Handbook of the Birds of Europe, the Middle East and North Africa. The Birds of the Western Palearctic, Oxford University Press, Oxford, UK, Vol 4, p. 413, 1993. Return to text.
- Lowther, P.E. Brown-headed Cowbird (Molothrus ater). In The Birds of North America, No. 47 (A. Poole and F. Gill, Eds.), The Academy of Natural Sciences, Philadelphia, Pennsylvania; The American Ornithologists’ Union, Washington, D.C., 1993. Return to text.