Brood parasitism
One explanation, the mafia hypothesis, proposes that parasitic adults retaliate by destroying host nests where rejection has occurred; there is experimental evidence to support this.
This enables the parasitic parents to spend more time on other activities such as foraging and producing further offspring.
The generalist brown-headed cowbird may have evolved an egg coloration mimicking a number of their hosts.
For example, two studies of cuckoos parasiting great reed warblers reported thickness ratios of 1.02 : 0.87[4] and 1.04 : 0.81.
[7] Most avian brood parasites have very short egg incubation periods and rapid nestling growth.
Not only do these brood parasites usually differ significantly in size and appearance, but it is also highly probable that they reduce the reproductive success of their hosts.
The "mafia hypothesis" proposes that when a brood parasite discovers that its egg has been rejected, it destroys the host's nest and injures or kills the nestlings.
[19] Mafia-like behavior occurs in the brown-headed cowbird of North America, and the great spotted cuckoo of Europe.
In experiments, nests from which the parasite's egg has been removed are destroyed by the cuckoo, supporting the hypothesis.
An alternative explanation is that the destruction encourages the magpie host to build a new nest, giving the cuckoo another opportunity for parasitism.
[20] Common cuckoo females have been proposed to select hosts with similar egg characteristics to her own.
The hypothesis suggests that the female monitors a population of potential hosts and chooses nests from within this group.
[21] The hypothesis has been criticised for providing no mechanism for choosing nests, nor identifying cues by which they might be recognised.
The parasites lay their own eggs into these nests so their nestlings share the food provided by the host.
[26] In duck species such as the goldeneye, this form of cuckoldry is taken a step further, as females often lay their eggs in the nests of other individuals.
[32] The mechanisms of host selection by female cuckoos are somewhat unclear, though several hypotheses have been suggested in attempt to explain the choice.
[32][33] A mochokid catfish of Lake Tanganyika, Synodontis multipunctatus, is a brood parasite of several mouthbrooding cichlid fish.
Host males guard territories against intruders during the breeding season, creating a patch of reeds as a spawning site or "nest".
Examples of cuckoo bees are Coelioxys rufitarsis, Melecta separata, Nomada and Epeoloides.
This paper wasp has lost the ability to build its own nest, and relies on its host, P. dominula, to raise its brood.
The adult host feeds the parasite larvae directly, unlike typical kleptoparasitic insects.
[41][42] Such insect social parasites are often closely related to their hosts, an observation known as Emery's rule.
[44] Thus, the M. schencki ants bring back the P. rebeli larvae to their nests and feed them, much like the chicks of cuckoos and other brood-parasitic birds.
This is also the case for the parasitic butterfly, Niphanda fusca, and its host ant Camponotus japonicus.
