Ritual displays by a parasitic cuckoo: nuptial gifts or territorial warnings?

In the sexual selection framework, nuptial gifts are materials a donor provides to a receiver that can increase the donor's fitness. In specific cases, sharing crucial information may be a nonmaterial nuptial gift. To investigate this hypothesis, we focused on the common cuckoo, Cuculus canorus, an obligate avian brood parasite whose reproduction costs of females are mainly related to finding host nests needed to lay their eggs. Nest searching is assumed to be conducted only by females. We hypothesized that males could contribute by transferring information on nest locations to females as a nonmaterial nuptial gift. Here, we show the results of a first step in this direction, in which we identified any behaviour potentially conveying information on nest abundance in the surrounding area, that is, behaviours whose frequency varied with host nest density. We conducted our investigation in a marshland area within the Po Plain (Italy), where we recorded both visual displays of cuckoos at perching sites, by using camera traps, and nest abundance of two of the most parasitized cuckoo host species, the reed warbler, Acrocephalus scirpaceus, and great reed warbler, Acrocephalus arundinaceus, by systematic nest monitoring. We found that male cuckoos adopted a certain posture, wing drooping, and tended to keep their tails up more frequently in areas with the highest versus lowest host nest densities. This is consistent with these behaviours acting as potential signals codifying information on nest abundance in the area. We finally discuss the implications of our findings for the mating choices of female cuckoos and the study directions warranted to reveal whether these displays and information transfer may be included as new elements of the sexual selection framework. (c) 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).