The common cuckoo Cuculus canorus and its cavity nesting host, the redstart Phoenicurus phoenicurus: a peculiar cuckoo‐host system?

Abstract

We examined redstart Phoenicurus phoenicurus populations over a period of fifteen years to study interactions between the cuckoo Cuculus canorus and its cavity‐nesting host. Over 380 redstart nests were checked and more than 100 cuckoo eggs were found during the study period. The average parasitism rate was 20%. The cuckoos’ breeding success was extremely low, only 18 chicks surviving to the fledgling stage. When redstarts were parasitized experimentally with artificial cuckoo eggs, they rejected eight percent of mimetic eggs and 44% of non‐mimetic eggs. We were not able to record any rejection of the real cuckoo eggs. However, about 30% of the real cuckoo eggs were found outside the redstart's nest cup. This could be the result of laying failures by the cuckoo, rather than of a strong rejection behaviour by the redstart. We suggest that redstarts’ cavity nesting itself was a factor that reduced the cost of the parasitism dramatically. Firstly, it makes it difficult for the female cuckoo to lay her egg correctly in the nest and secondly, it is more difficult for the cuckoo chick to evict the host's eggs or nestlings effectively from the nest. Only 54% of the cuckoo chicks were able to evict all the host eggs or chicks from the nest. When reared in mixed broods, cuckoo chicks survived only in every second case to fledgling age, while at least one redstart chick from every brood managed to leave the nest.

Is brood parasitism related to host nestling diet and nutrition?

“…We cross-fostered randomly selected cuckoo eggs, and some of the cuckoo nestlings did not successfully evict all host progeny. This was not a result of cross-fostering because mixed broods were similarly frequent among naturally (9 out of 31) and experimentally parasitized nests (9 out of 51; Pearson's v 2 ¼ 1.46, P ¼ 0.23), reflecting the natural situation in this cuckoo-host system (Rutila et al 2002, Thomson et al 2016). This resulted in 64 ''solitary'' cuckoo broods (nests with 1 cuckoo that successfully evicted all host progeny; Grim et al 2009a), 70 unparasitized host redstart broods, and 18 ''mixed'' broods that included 17 cuckooredstart broods (nests with 1 cuckoo that did not evict all host progeny and both species were raised jointly; see Grim et al 2009a) and 1 brood of 2 cuckoo nestlings that both survived to fledging.…”

“…Unlike all other cuckoo hosts, this species is the only known regular cavity-nester (Rutila et al 2002, Thomson et al 2016. Redstarts often breed in ground cavities (Glutz von Blotzheim et al 2001, T. Grim, Z. Tyller, and P. Samaš personal observations) and, in contrast to other common cuckoo hosts (such as Acrocephalus species; Grim and Honza 1996), redstarts regularly collect food from the ground surface (Glutz von Blotzheim et al 2001).…”

Egg colour mimicry in the common cuckooCuculus canorusas revealed by modelling host retinal function

“…In Finland, cuckoo eggs found parasitizing redstart nests invariably correspond with the Phoenicurus gens ( Wasenius 1936;Rutila et al 2002), while pied wagtail nests have been frequently parasitized by Sylvia, Anthus and Fringilla cuckoo females besides Motacilla cuckoo females ( Wasenius 1936;. Furthermore, evidence suggests that redstarts may have problems in discriminating natural cuckoo eggs in their nests, even though they readily eject non-mimetic cuckoo eggs (Avilés et al 2005).…”

A host-race of the cuckooCuculus canoruswith nestlings attuned to the parental alarm calls of the host species

“…(d) Redstart-cuckoos This host-race, which lays plain blue eggs, was studied in 2004 in South Karelia, eastern Finland, near Taipalsaari (Rutila et al 2002). We tested six cuckoo nestlings at 6-8 days old in the playback experiment (above), with four playback treatments given in random order (alarms of redstart, reed warbler and dunnock and the chaffinch control).…”