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Great Spotted Cuckoo Chick
Image credit: Eran Finkle

A study has found that it may not be so bad for crow chicks who have to share their nest with an uninvited guest such as a young cuckoo.

For one, they can sit back and wait for food to arrive while the cuckoo chick does all the begging.

When great spotted cuckoos parasitize magpie nests they don’t evict the host’s young from the nest but instead compete with the magpie chicks for food, a battle which they often win leading to the magpie chicks’ deaths.

However, when greater spotted cuckoos take over larger carrion crows’ nests laying up to three eggs in it, both species are often raised together successfully with the young crows ultimately growing bigger than the cuckoos.

The study was carried out by a team from the University of Valladolid in Spain at the pros and cons associated with the parasitic relationship of the great spotted cuckoo and the carrion crow. The findings have been published in the journal Behavioral Ecology and Sociobiology.

Diana Bolopo led the team who filmed seven parasitized crow nests and six uninvaded ones in Northern Spain during the 2004 to 2007 breeding seasons.

The watched and listened to how intensely the various chicks begged for food and how adult carrion crows responded to these hunger cries when deciding which chick to feed first. The sampled nests contained between one and five crow chicks as well as one cuckoo chick.

Great spotted cuckoo chicks that were raised alongside carrion crow chicks were not able to monopolize the food brought to the nest because the crow parents preferred to feed crow nestlings over cuckoo nestlings. However, because cuckoo chicks begged more intensely than crow chicks over time things were evened out and each species received an equal amount of food.

The researchers found that cuckoo chicks begged more intensely than the host chicks, no matter how large the whole brood was or how many caregivers were around.

Crow chicks that were raised alongside a cuckoo chick begged less intensely than those in nests without any unrelated broods present but still managed to survive and thrive.

Bolopo said, "Despite a higher begging intensity, great spotted cuckoos do not out-compete bigger carrion crow nestlings," speculating that the cuckoo’s begging strategies are part of how it has evolved and adapted to a parasitic life in which it has to compete with similar or larger-sized nest mates.

She added, "It might actually be advantageous to crow chicks to share the nest with a cuckoo, because the crow chicks do not have to waste so much energy on begging intensely for food on their own. This advantage might balance out the costs paid for being raised together with a parasitic invader, such as loss of siblings in earlier stages."

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