Chick recognition and acceptance: a weakness in magpies exploited by the parasitic great spotted cuckoo

Abstract

Hosts of brood parasites have evolved the ability to discriminate non-mimetic and even mimetic eggs, but not non-mimetic chicks. Here we demonstrate that the great spotted cuckoo Clarnator glandarius does not provide its magpie Pica pica host with a supernormal stimulus that helps to avoid recognition, because single cuckoo chicks introduced into otherwise unparasitized magpie nests are not fed at a higher frequency than single magpie chicks introduced to parasitized magpie nests. Another series of experiments demonstrated that magpies have the ability to discriminate cuckoo chicks, mainly when these are introduced at the end of the nestling period, and especially when the cuckoo chick together with a magpie chick is presented to adult magpies outside the nest. This supports the idea that cuckoos exploit the obligatory reaction of magpies to feed all young that have been hatched in their nests and whose "signatures" they have learnt. Furthermore, the experimental cuckoo chicks in parasitized magpie nests were more likely to be accepted than they were in non-parasitized nests. This supports the hypothesis that magpies may learn to recognise their own nestlings as those present in the nest and may indicate that a comparison between cuckoo and magpie nestlings is the basis of discrimination.

The Adaptiveness of Defence Strategies Against Cuckoo Parasitism

“…There has been a long debate whether the observed lack of chick rejection (and also the variation in egg rejection in different host species) in avian brood parasitism is due to an evolutionary lag (Dawkins and Krebs, 1979;Zahavi, 1979;Lotem, 1993;Soler et al, 1995) or whether the present situation is one of evolutionary equilibrium (Davies and Brooke, 1988;Rothstein, 1990). We will argue that the model captures both ideas, and by choosing discrimination costs appropriately, we will see that the model is in agreement with both of these views.…”

Nestling discrimination without recognition: a possible defence mechanism for hosts towards cuckoo parasitism?

“…Observations that host behaviour, under natural conditions, can lead to parasitic chicks' death are very rarethey are reported only for three host-parasite systems (Fraga 1998;Lichtenstein 2001;Langmore et al 2003). All other cases of nestling discrimination in parasitic birds were elicited under unnatural experimental conditions (Redondo 1993;Soler et al 1995), or are indirectly inferred from the similarity between parasitic and host nestlings (reviewed in Redondo 1993). In other cases hosts attacked parasitic fledglings, but these successfully prevented hosts from discrimination by intense begging (see Redondo 1993).…”

Neuronal recruitment in adult zebra finch brain during a reproductive cycle

“…Unlike in mammals, in which parent-offspring recognition relies on various combinations of visual (Ferreira et al, 2000), olfactory (Maletinska et al, 2002;Dobson and Jouventin, 2003;Phillips, 2003) and auditory (Illmann et al, 2002;Terrazas et al, 2003;Mathevon et al, 2004) cues, avian parents seem to recognize their offspring by their voices (Saino and Fasola, 1996;Jouventin and Aubin, 2002;Insley et al, 2003); no visual or olfactory cues are known to play a role in this recognition. Hence, parental care after fledging requires that parents learn and remember the distinctive vocalizations of their nestlings while the latter are still in the nest, and that they maintain or update these memories for as long as parental care is given (Soler et al, 1995;Lefevre et al, 1998;Insley et al, 2003). Species like the zebra finch (Taeniopygia gutatta), which produce more than one clutch per breeding season (Zann, 1996), have to go through this learning process more frequently than single clutch breeders.…”