Saturday, 8 March 2014

Great Spotted Cuckoos

Almost everywhere we have been this week we seem to have seen (and heard) Great Spotted Cuckoos.  At Castro Marim, around Tavira and all over the Mértola / Castro Verde area we have watched them engage in their annual battle of wits with the local Common Magpies.  In other parts of the world Great Spotted Cuckoos lay eggs in the nests of various species of corvids but in Europe, including Portugal, the Common Magpie is definitely their preferred victim.

During a season, a female Cuckoo is said to lay as many as 30 eggs, often laying more than one egg in each nest.  Frequently at least one Magpie’s egg may be damaged by the Cuckoo and that must reduce the competition for food when the chicks hatch.  However, as the young Cuckoos generally hatch several days before the Magpies, it is an uneven contest; the Cuckoos are always favourites to out-compete the young of the host species.

Common Magpie isn’t a widely distributed or particularly numerous species in the Algarve.  However, where there are Magpies we expect to find Great Spotted Cuckoos and we wonder what effect they have on the Magpie population.  In the absence of Cuckoos would there be more Magpies?  Maybe the introduction of Great Spotted Cuckoos into the UK would be a way of controlling the seemingly ever-increasing Magpie population there!


Anonymous said...

Don't young Great Spotted Cuckoo's push the eggs of a host species out of the nest like Common Cuckoo's?

Peter and June said...

No, young Great Spotted Cuckoos are able to out-compete the young Magpies, which eventually starve. They do this by hatching sooner from eggs that need a shorter incubation period than those of the host species. They get a head start!