[not in handout, see intranet]
Instincts in Cuckoos etc

For the task of species identification learning (e.g. via imprinting) is is an option for some species.

But in many other species there must be innate mechanisms for species identification (e.g. in Cuckoos, or other species with no parental care of the young including many fish, frogs and reptiles see Animal Thought, Chapter 6 “the survival value of intelligence”)

  • European Cuckoos when first hatched have an innate motor pattern for ejecting any other eggs from the next.

  • Their own begging call works with a wide range of hosts. They do not learn to vary their begging call structure for different hosts (Butchart et al. 2003).

  • The begging call-rate from a single cuckoo is very high — so that a single cuckoo sounds like a nest full of the host's own chicks (Kilner et al., 1999 or see Davies et al, 1998, below).

  • American cowbirds do not learn recognize the vocalizations of their hosts (Madden et al., 2005), but respond selectively to the typical “chatter” sound of their own species (Hauber et al., 2001).

  • Australian brush turkeys incubate eggs in piles of decaying vegetation, and the hatchlings do not associate with the parents, and therefore have innate visual mechanisms for recognizing conspecifics, studied by Goth and Evans (2004) by using stuffed robot chicks as choice stimuli.

Lotem (1993) points out that tiny hosts feeding a huge cuckoo nestling is a challenge if evolution is adaptive.

However cost-benefit analysis may be complicated. Hauber et al (2004)

Lotem (1993) says that learning to recognize one's own young by experience would be dangerous because of the possibility of imprinting on the wrong species, and thereafter only accepting cuckoos.

He recognizes that this does not explain why small birds don't have an innate bias against feeding cuckoos. The general argument here is that having a very strong parental instinct is on average beneficial, since there are plenty of opportunties for birds later on rearing own young. (Gleitman 1995 p. 400, 1999, p. 427)

Apart from the familiar common cuckoo, a wide range of bird species have a similar practice of laying their eggs in other birds' nests (“brood parasitism”) and many species of cuckoo always rear their own young.

Most brood parasitic species use more than one host species. In North America, the widespread brown-headed cowbird (Molothrus ater) regularly parasitizes as many as 50 host species.

On the other hand some African parasitic finches specialise in just one host.

References on brood parasitism

Davies, N. B., Kilner, R. M., & Noble, D. G. (1998). Nestling cuckoos, Cuculus canorus, exploit hosts with begging calls that mimic a brood. Proceedings of the Royal Society of London Series B-Biological Sciences, 265(1397), 673-678.

Nestling cuckoos, Cuculus canorus, eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus, as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula, or song thrush, T. philomelos, chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick's rapid begging call ('si, si, si, si...'), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.

Gibbs, H. L., Sorenson, M. D., Marchetti, K., Brooke, M. D., Davies, N. B., & Nakamura, H. (2000). Genetic evidence for female host-specific races of the common cuckoo. Nature, 407(6801), 183-186.

The common cuckoo Cuculus canorus is divided into host-specific races (gentes)(1). Females of each race lay a distinctive egg type that tends to match the host's eggs, for instance, brown and spotted for meadow pipit hosts or plain blue for redstart hosts(2-4). The puzzle is how these gentes remain distinct. Here, we provide genetic evidence that gentes are restricted to female lineages, with cross mating by males maintaining the common cuckoo genetically as one species. We show that there is differentiation between gentes in maternally inherited mitochondrial DNA, but not in microsatellite loci of nuclear DNA. This supports recent behavioural evidence that female, but not male, common cuckoos specialize on a particular host(5), and is consistent with the possibility that genes affecting cuckoo egg type are located on the female-specific W sex chromosome(6). Our results also support the ideas that common cuckoos often switched hosts during evolution(7,8), and that some gentes may have multiple, independent origins, due to colonization by separate ancestral lineages.

Kilner, R. M., Noble, D. G., & Davies, N. B. (1999). Signals of need in parent-offspring communication and their exploitation by the common cuckoo. Nature, 397(6721), 667-672.

Nestling birds present vivid gapes and produce loud calls as they solicit food, but the complexity of the display is poorly understood. Here we explain the function of reed warbler begging signals and show how they are exploited by the common cuckoo, Cuculus canorous, a brood parasite. Reed warbler parents integrate visual and vocal signals from their young to adjust their provisioning rates, and the two signals convey more accurate information about offspring need than either does alone. The cuckoo chick has a particularly striking begging display which has been suggested to be irresistible to host parents. However, we show that the cuckoo, reared alone in the nest, presents a deficient visual display, and elicits the same amount of care as a reed warbler brood only by compensating with its exaggerated vocal display. Therefore the cuckoo succeeds not through mimicry of the host brood begging signals, but by tuning into the sensory predispositions of its hosts. (PsycINFO Database Record (c) 2000 APA, all rights reserved)(journal abstract) Record 4 of 4 in PsycINFO 1999-2000/11

Lotem, A. (1993). Learning to recognize nestlings is maladaptive for cuckoo Cuculus canorus hosts. Nature, 362(6422), 743-745.

Cuckoo eggs sometimes resemble the eggs of the host, but nestlings of the common cuckoo look very different from the young of the host. The inability of the host to discriminate against such divergent nestlings is especially puzzling as some cuckoo hosts show a finely tuned discrimination ability between eggs. This article presents a model to explain this paradox. The model shows that although learning to recognize eggs is adaptive, learning to recognize nestlings might not be. The mechanism of learned recognition, previously shown to maintain egg recognition, is unlikely to be adaptive for hosts like those of the common cuckoo, in which only the parasitic nestling remains in the nest. The reason that discrimination against parasite nestlings is not adaptive is that the cost of misimprinting (learning to recognize the parasite nestling as the parents' own) exceeds the benefit of correct learning. (PsycINFO Database Record (c) 2000 APA, all rights reserved)(unassigned)

Marchetti, K. (2000). Egg rejection in a passerine bird: Size does matter. Animal Behaviour, 59(4), 877-883.

Avian brood parasites reduce the reproductive success of their hosts, selecting for the evolution of egg discrimination by the host, and potentially creating a coevolutionary arms race between host and parasite. Host egg discrimination ability is crucial in determining whether the arms race results in extinction (of the parasite on a particular host) or stable coevolutionary equilibrium of the host- parasite pair. This study examined egg discrimination behavior in 39 nests of the yellow-browed leaf warbler, Phylloscopus humei, a presumed former host of parasitic cuckoos, to show how discrimination ability has become very strong. Field experiments using model eggs demonstrate that rejection decisions are based on the relative size of eggs in the clutch. Individuals do not learn the particular size of their own eggs, but will accept both large and small eggs as long as all eggs in the clutch are of similar size. Host rejection decisions are continuously modified based on assessment of variation in egg sizes currently in the clutch, making it a difficult strategy for a cuckoo to defeat. (PsycINFO Database Record (c) 2000 APA, all rights reserved) Record 2 of 4 in PsycINFO 1999-2000/11

Noble, D. G., Davies, N. B., Hartley, I. R., & McRae, S. B. (1999). The red gape of the nestling cuckoo (Cuculus canorus) is not a supernormal stimulus for three common hosts. Behaviour, 136(6), 759-777.

In this paper, the authors test three hosts of the common cuckoo in Britain for their nestling gape color preferences and ask whether the vivid red gape of this cuckoo's nestling can be attributed to coevolution with its hosts. Parents of the three hosts were assessed for their response to their own nestlings with artificial grapes. Little evidence was found that reed warblers, robin or dunnock parents show a preference for red nestling gapes, or that redder gapes elicit an increase in overall provisioning rates for broods of reed warblers. Although mouth color has little influence on the allocation of feeds resulting from sibling competition and begging intensity, it may have a role under certain conditions. (PsycINFO Database Record (c) 2000 APA, all rights reserved) Record 3 of 4 in PsycINFO 1999-2000/11

Payne, R. B., Payne, L. L., Woods, J. L., & Sorenson, M. D. (2000). Imprinting and the origin of parasite-host species associations in brood-parasitic indigobirds, Vidua chalybeata. Animal Behaviour, 59, 69-81. (ATHENS username and password needed for access outside the College)

Brood-parasitic village indigobirds, Vidua chalybeata, were bred in captivity and foster-reared by their normal host species, the red-billed firefinch, Lagonosticta senegala, or by an experimental foster species, the Bengalese finch, Lonchura striata. Captive-reared female indigobirds were. tested as adults for mate choice and for host choice. In tests of mate choice, female indigobirds responded preferentially towards mimicry songs of male indigobirds that were similar to those of the females' own foster parents. Females reared by Bengalese finches responded to male songs that mimicked Bengalese finch song rather than to male songs that mimicked their normal host species, the firefinch. In tests of host choice, females reared by Bengalese finches laid in the nests of Bengalese finches, and females reared by firefinches laid in the nests of firefinches. Wild-caught females showed the same behaviours as captive-bred females reared by firefinches. A female indigobird's social companions (firefinch or Bengalese) following her independence of her foster parents had no effect on her sexual response to male mimicry song or her choice of a host species in brood parasitism. The results support the predictions of a model of imprinting-like behaviour development in which young indigobirds;focus their attention on their foster parents, rather than a model of innate bias for songs and nests of their normal host species, or a null model of nonspecific brood parasitism and differential survival. The results provide experimental support for the recent origin of brood parasite-host associations and the significance of imprinting in speciation in these brood parasites. (C) 2000 The Association for the Study of Animal Behaviour.


cuckoo nestling ejecting an egg
click on image to enlarge |
view a sequence of 4 photos


   adult brush turkey

  hatchling brush turkey