Choosing suitable hosts: common cuckoos Cuculus canorus parasitize great reed warblers Acrocephalus arundinaceus of high quality

Abstract

We investigated the hypothesis that the common cuckoo Cuculus canorus selects host pairs of good phenotypic quality. As there is some evidence that cuckoos may select hosts within a population non-randomly based on external cues reflecting their foster abilities, we predicted that great reed warbler Acrocephalus arundinaceus pairs parasitized by the cuckoo would exhibit higher quality than unparasitized ones. To test this assumption, we evaluated two different parameters indicating host quality: body condition and characteristics of host eggs. We found that parasitized females showed significantly better body condition than unparasitized ones, and the model showed that the probability of being parasitized by the cuckoos increased with increasing body condition. Moreover, the likelihood of being parasitized by a cuckoo within the great reed warbler population increased with decreasing colour variability within clutches: parasitized females allocated costly blue pigments to eggshells more equally compared with unparasitized ones. Our study revealed that cuckoos parasitize great reed warbler females of higher quality, as reflected in host body condition and egg colour characteristics. In highly mimetic systems, cuckoos may choose to parasitize hosts with eggs displaying low intraclutch variation, both because this leads to reduced rejection and because these hosts are of high quality.

Is brood parasitism related to host nestling diet and nutrition?

“…This model took into account the fact that provisioning rate in relation to nestling age differed across broods. Further, nestling growth performance and fledging success may vary because of cohabitation (Grim et al 2009a) and individual host quality (Polačiková et al 2009). Therefore, we additionally tested for the potential confounding effects of ''brood type'' (categorical variable: mixed or not) and ''parasitism status'' (categorical variable: nest originally parasitized by a cuckoo female or not).…”

Unusual diet of brood parasitic nestlings and its fitness consequences

“…This suggests that cuckoos do not target host pairs that bring more suitable food (invertebrates) or do not avoid host pairs that bring less suitable diet items (fruits, vertebrates; cf. Grim 2002, Polačiková et al 2009). …”

“…The quality of parents could differ between naturally parasitized and naturally unparasitized nests: Female cuckoos may target hosts of higher quality (Polačiková et al 2009) or may disproportionally parasitize host individuals of lower quality due to structural habitat constraints (Grim 2002). In either case, such nonrandom host targeting might confound dietary comparisons if individual host quality covaries with individual host prey selection.…”

“…Theoretically, poorer fledging parameters of cuckoos fed with unusual dietary items could be a by-product of individual host pair selection by cuckoos, that is pair quality (Grim 2002, Polačiková et al 2009). We excluded this potential confounding factor experimentally by crossfostering randomly selected cuckoo eggs between naturally parasitized and unparasitized nests (see Methods).…”

Factors influencing host nest use by the brood parasitic Asian Koel (Eudynamys scolopacea)

“…This may indicate that larger nests, which are easier to find for parasites, have been parasitized at a higher frequency and hence such species have evolved egg rejection due to stronger selection imposed from parasites. Second, there may be more host activity around a large nest because it requires more building activity (Øien et al 1996;Antonov et al 2007), and third, large nests may be preferred by parasites because the nest owners may be high quality birds that offer better parental care to the parasite nestling (Polaciková et al 2009). It was demonstrated by Soler et al (1995) that Great Spotted Cuckoos (Clamator glandarius) preferentially parasitized Magpie (Pica pica) pairs with larger nests, which were an indicator of territory quality.…”