How do cuckoos find their hosts? The role of habitat imprinting.

Although a number of hypotheses have been proposed for how European cuckoo, Cuculus canorus, females may find hosts belonging to their foster parents' species, clear evidence is lacking for any of them. Here, we propose 'habitat imprinting' as an alternative mechanism for host selection and provide evidence that cuckoos are able to remember acquired information about a familiar habitat. We hand-reared seven cuckoos in one of five different artificial habitats and tested them as adults in habitat choice experiments. In each test habitat, a pair of zebra finches, Taeniopygia guttuta, was presented as 'hosts'. We tested cuckoos of both sexes because the genotype of males may influence egg colour, and therefore egg mimicry; alternatively, habitat imprinting may be a general mechanism existing in both sexes but affecting egg mimicry only via females. Test cuckoos spent significantly more time looking at their respective familiar habitats than at other habitats in 1 of 2 test years. How long cuckoos were reared in the artificial habitats correlated positively with how long they spent in this habitat during the choice experiments. Additionally, test cuckoos remained longer with zebra finches that showed more nest-building behaviour but had lower levels of general activity, and they also observed these 'hosts' more frequently. If cuckoos choose to breed in habitats resembling those on which they were imprinted and search randomly for hosts in these habitats, they would increase their probability of parasitizing nests of their foster species. We propose that host specificity would be strengthened, however, if cuckoos use a sequence of several mechanisms, rather than just one, to find their hosts. (c) 1998 The Association for the Study of Animal Behaviour.