Sumer is icumen in

. . .lhude sing cuccu. Forgotten the words? Here they are in the sumptuous and now fully digitised Harley MS 978 a hand-lettered manuscript dating from about 1260 and now in the British Museum (this is nearly 200 years before the first book was printed in Europe):

all the words and a translation here.  Go on - sing it! Í heard our first 2014 cuckoo on the air at 0545hrs yesterday morning.  The unexpected benefits of having to wake through the night and run up to see if either of the last two ewes are ringing delivery bells is that I was first in family to catch the harbinger of Summer . . . and to see the gibbous waning moon suspended over an eerily yellow Cullentra ridge on the other side of the valley. Our cuckoo arrival records are even more desultory than those for the swallows:

2007	19 Apr	2010	20 Apr
2009	02 May	2011	18 Apr

Cuckoos Cuculus canorus are infinitely interesting to an evolutionary biologist (meeeeee!).  Apart from the distinctive cuck-koo call (that's the males advertising their wonderfulness), the only thing most people know about cuckoos is that they are brood parasites.  Not that Joe Public or Sean Gnáth would use that term for laying your eggs in someone else's nest and expecting your offspring to be raised by a deluded bird-brain like the meadow pipit Anthus pratensis.  It's not only meadow pipits that are so deluded, lots of other small birds serve as unwitting hosts; Cuckoos, although they are all the same species (fully inter-fertile) have formed themselves into behavioural sub-species, called gentes by Latinate ornithologists. Each gens preferentially lays eggs in the nest of a particular species and hen-cuckoos of each gens lay eggs with a pattern that more or less closely resembles that of the host species while looking nothing like the eggs of cuckoos who belong to a different gens.  It's one of the best examples of adaptive mimicry that you're like to see in Europe unless you're mad about orchids.  The hen-cuckoo seizes an opportunity (mother pipit off down the boozer getting a small port and lemon) to lay a single egg in a nest and tumble one of the existing eggs out onto the ground below - it all takes about 10 seconds.  Lots of person-years research has gone into working out how much the male and female parent contribute to the genetic determination of mimicry.  Some of the gentes have evolved a far better match to the eggs of the host species, possibly because those species have been parasitised longer and have evolved discriminatory counter-measures.

When the chick hatches it uses a special hollow in its back to finish the job that its mother began and heave-ho: the other eggs and/or hatchlings go over the edge.  That gets it the exclusive attention of one or both foster-parents.  The behaviour of birds is generally much more genetically hard-wired than those of mammals.  Parent birds are programmed to sick up a crop full of food into any gaping red maw.  There is some evidence that they respond more strongly if the mouth is redder, bigger or gapinger; all of which dances to the cuckoo's tune. But other evidence ties the rate of feeding by the parents to the number of open mouths, in which case the solitary cuckoo-chick is at a disadvantage. The observation that the chicks contribute more to the murder than the hen-cuckoo was first made by Edward Jenner, whom we've met before inoculating people against smallpox.

The small fostering birds - more than 100 species have been documented as hosts - have not taken this all lying down.  Some of them are clearly better at discriminating the unwelcome visitor.  They have also generalised a behaviour called 'mobbing' which is used against avian predators like hawks and owls, but is also applied to cuckoos. When these hoodlums appear in the neighbourhood, lots of small potential prey consort to dive-bomb and harass it until it goes elsewhere.  Cuckoos with barred breast-feathers which more closely resemble sparrowhawks Accipiter nisus are less likely to be mobbed - so here is another possible adaptation in cuckoos to secure more time to lay-and-go.  It's also a good idea to nest far from the places that cuckoos habitually perch although that might be difficult if you have make your nest before t'buggers come back from over-wintering in Africa.

Those who are interested in the socio-geological landscape will know all about the Gowk Stanes which litter the Scots countryside.  These are standing stones or glacial erratics which may serve as cuckoo-perches: gowk is Scots for Cuculus like gøg (.dk); gjøk (.no).  These stones also serve a variety of other purposes - directional, boundary, social and religious.

Finally, if you want proof that the Germans didn't learn anything between 1936 and 1972 about the desirability of putting young people into uniforms and making them march about singing, checkout the Den Olympischenjugend singing the cuckoo song.