Great Spotted Cuckoo Fledglings Often Receive Feedings from Other Magpie Adults than Their Foster Parents: Which Magpies Accept to Feed Foreign Cuckoo Fledglings?

Abstract

Natural selection penalizes individuals that provide costly parental care to non-relatives. However, feedings to brood-parasitic fledglings by individuals other than their foster parents, although anecdotic, have been commonly observed, also in the great spotted cuckoo (Clamator glandarius) – magpie (Pica pica) system, but this behaviour has never been studied in depth. In a first experiment, we here show that great spotted cuckoo fledglings that were translocated to a distant territory managed to survive. This implies that obtaining food from foreign magpies is a frequent and efficient strategy used by great spotted cuckoo fledglings. A second experiment, in which we presented a stuffed-cuckoo fledgling in magpie territories, showed that adult magpies caring for magpie fledglings responded aggressively in most of the trials and never tried to feed the stuffed cuckoo, whereas magpies that were caring for cuckoo fledglings reacted rarely with aggressive behavior and were sometimes disposed to feed the stuffed cuckoo. In a third experiment we observed feedings to post-fledgling cuckoos by marked adult magpies belonging to four different possibilities with respect to breeding status (i.e. composition of the brood: only cuckoos, only magpies, mixed, or failed breeding attempt). All non-parental feeding events to cuckoos were provided by magpies that were caring only for cuckoo fledglings. These results strongly support the conclusion that cuckoo fledglings that abandon their foster parents get fed by other adult magpies that are currently caring for other cuckoo fledglings. These findings are crucial to understand the co-evolutionary arms race between brood parasites and their hosts because they show that the presence of the host's own nestlings for comparison is likely a key clue to favour the evolution of fledgling discrimination and provide new insights on several relevant points such as learning mechanisms and multiparasitism.

Non-mimetic shiny cowbird nestlings escape discrimination by baywings in absence of host nest mates

“…They demonstrated that this could be because cuckoo fledglings that went undernourished left their foster parents and joined other cuckoo fledglings to look for new caregivers (Soler et al 2014a). Cuckoo fledglings translocated away from their natal area were able to obtain feedings from adult magpies that were already caring for parasitic young, suggesting that looking for non-parental feedings is a co-evolved strategy to overcome host discrimination (Soler et al 2014b). Feeding of shiny cowbird fledglings by individuals other than their foster parents sometimes occurs, but available data suggest that death is the most likely outcome of baywing discrimination against shiny cowbird fledglings from mixed broods (Fraga 1998;De Mársico et al 2012;this study).…”

Brood parasitism, provisioning rates and breeding phenology of male and female magpie hosts

“…Thus, the delay in laying date in the subsequent season of magpies suffering parasitism would be a consequence of an extra cost of parasitism that seems to be independent of the nest provisioning rates. This effect of parasitism on future reproduction might be related to other stages of the parental care period that we have not considered in this study, such as the post‐fledgling stage: Soler et al (, ) found that great spotted cuckoo fledglings are frequently fed by magpies other than their foster parents that had also reared cuckoo chicks that season. Feeding a greater number of cuckoo fledglings than those reared in the nest and maybe, other aspects of the post‐fledgling caring period may raise the costs of parental care even further and have cumulative carry over effects that may not affect magpies' apparent survival but their breeding phenology in the future.…”

Territoriality and variation in home range size through the entire annual range of migratory great spotted cuckoos (Clamator glandarius)

“…Large home ranges increase the costs of defense 16 and it has been suggested that this is the case in the great spotted cuckoo 24 given that they select the nests to parasitize based on the host quality 46 . On the other hand, the relatively low cost of multiparasitism for great spotted cuckoo chicks’ survival 47 and the benefits that it provides during the fledgling stage 48,49 could prevent the evolution of territoriality in this species. This cost could determine whether brood parasites might evolve territoriality and could explain why some evictor species like the Horsfield’s bronze cuckoo defend territories 21 .…”

“…1,000 m a.s.l.) with extensive non-cultivated areas, cereal crops (especially barley), some areas with dispersed holm-oak trees ( Quercus rotundifolia ) and groves of almond trees ( Prunus dulcis ) and pines ( Pinus halepensis and P. pinaster ) 48 . Magpies are the main hosts of great spotted cuckoos in this area 50 .…”