by Steve Westerman

Wharfedale Naturalists Society

AS I mentioned in a previous Nature Notes, the Cuckoos (Cuculus canorous) that frequent Ilkley Moor are back. They travel from sub-Saharan Africa – and spend more of the year in Africa than they do here. So, these are temporary visitors from abroad - but this is definitely not a holiday for them! Cuckoos are ‘obligate brood parasites’. This means that they lay all their eggs in host birds’ nests, where they will be incubated, and their young will be raised. This will be at the expense of the host’s own brood. The female Cuckoo removes one (or more) of the hosts’ eggs when she lays her own (and swallows it), and the Cuckoo chick ejects the rest – either as eggs or as nestlings.

Each Cuckoo specialises in parasitising a particular host species – possibly the one that reared the female. Her eggs resemble those of the host (to help avoid rejection). In the case of the Ilkley Moor Cuckoos I think the hosts are Meadow Pipits (one of the most common host species).

Sometimes, the male Cuckoo will perch fairly prominently in the branches of a tree (often in one of the established wooded areas) and make the familiar ‘cuckoo’ call that can be heard echoing over the moor. However, Cuckoos are generally rather shy and not easily seen. The female is particularly secretive – often perching deep in the branches of a tree, from where she can survey nearby nests of Meadow Pipits. The female(s) that I have seen on Ilkley Moor is typical in that it can be distinguished from the male by a slight brown colouring in parts, particularly around the throat/upper breast. However, a rarer variant of female Cuckoo also exists that is generally more rufous in colour. One hypothesis is that the appearance of Cuckoos has evolved to mimic birds of prey (Sparrowhawks - or Kestrels in the case of rufous females). This, it has been argued, may deter approach by smaller birds. However, if this is the purpose, it doesn’t seem to work very well as, on a number of occasions I’ve seen the Cuckoos getting ‘mobbed’ by Meadow Pipits and other small birds, and driven from perch to perch. Even though they don’t make nests or raise young, life isn’t always easy for Cuckoos.

In not so many weeks the adult Cuckoos will be gone – leaving their offspring behind. Their young – who never meet their parents - follow shortly after. They will make their own incredible, genetically programmed, journey to Africa – before returning next year.