August time, with lovely wild flowers still shining in our Norfolk roadsides and hedgerows but one of our best loved summer sounds, the call of the Cuckoo, has come to an end, now. Adults started leaving for their winter quarters in Africa as early as June and by now most will be gone; the young will follow in a month or so. In the last twenty years we have lost half the number of our cuckoos and in 2011 the British Trust for Ornithology tagged a number of birds, five from Norfolk, to try to find out what is happening to them. They are being tracked by satellite as they make their way to Africa and back again to Britain. The Cuckoo is a bird more heard than seen, the distinctive call carries for quite a way across the countryside. This is the male bird declaring his territory, usually from the top of a post or tree; the female makes a gurgling, bubbling sound. The male and female are similar in appearance being slatey-grey with a white belly banded in dark grey or black, although the female usually has a rufous tinge to her chest; occasionally a brown type of female will occur and the juveniles are also reddish-brown; in flight, because of their shape and colouration, Cuckoos are often mistaken for raptors. Everyone knows that Cuckoos are not good parents, in fact they leave the job of bringing up their children to other birds.
The female will watch the nest of the target bird, often a Dunnock, Robin, Meadow pipit or one of the warblers, and when the owner leaves she will quickly fly in, remove one of the eggs and put her own in its place. She may lay a dozen or more in this way, each in a different nest and, although they will be larger, the colour and pattern will closely resemble those of the host bird fooling her into thinking that it is one of her own. Interestingly Cuckoos are genetically programmed to lay in the nests of the same species of bird by which they themselves were reared and therefore Cuckoo eggs vary greatly. When the young Cuckoo hatches its first job is to get rid of the eggs and young of the host bird. Amazingly, this newly hatched, naked little interloper has enough strength to push them up the side of the nest and tip them over the edge. It will eventually grow to be much bigger than its foster parent which will often have to stand on the chick’s back to be able to deposit food into the gaping mouth. The young Cuckoo also imitates the begging call of the host chicks; this is purely instinctive as it has never had a chance to hear this sound.
Cuckoos are insectivorous birds and consume a great many caterpillars, even hairy ones which other birds reject because of the toxins they contain; the Cuckoo’s digestive system is adapted to cope with this. Last year a young one found its way into one of our raised vegetable beds and was feasting on the succulent caterpillars of the Large white butterfly that were busy consuming our cabbages. Who needs sprays when we have one of nature’s pest controllers ready to do the job!
Of course, the Large white is only considered a pest if it doesn’t leave any cabbages for ourselves and it too has its place in the world, even if it is only to provide tasty snacks for Cuckoos. The butterflies lay their skittle shaped eggs in clusters on the leaves of the plant and there are usually two broods a year, sometimes a third; the hatching caterpillars will become brightly coloured as they grow, a warning to birds that they contain harmful poisons. This, however, does not bother the Cuckoo nor a type of parasitic wasp which will lay an egg into the body of the caterpillar.
The larva of the wasp feeds on its victim, avoiding vital organs so as to keep its lunch alive until it has finished eating and is ready to pupate. The Large white is one of our best known and most widespread butterflies; the female has two black spots on each forewing and the male just has the dark tips.
Advertising that they are not good to eat by bright colouration is just one way that animals have of defending themselves. Some insects, like the Green shield bug we talked about last month, give out a nasty smell. A Grass snake also produces an evil smelling liquid from its vent and will, by flopping on to its back, with an open mouth, play dead.Toads release a fluid from their skin which will cause a burning sensation in the mouth of a would-be predator and, like frogs, can change colour to blend in with their surroundings.
Some butterflies and moths, like the Peacock and Emperor, have ‘eye spots’ on their wings which will either scare off a predator or confuse it into thinking that this is the place to attack, thereby avoiding damage to the vulnerable head and body. The tiny communally living caterpillars of the Small tortoiseshell butterfly use another method of confusion. When feeding outside their protective web, if they are disturbed they stand up and wave!
Other insects use imitation as defence, like harmless hover flies which send out an ‘I am dangerous’ message by looking like bees and wasps with their black and yellow bands. Young Caddis flies, which live underwater when at this larval stage, build themselves a mobile home. They collect tiny stones, or pieces of vegetation, and create little tubes to live in. This provides protection from fellow residents, such as dragon fly larvae which are voracious hunters.
The tiny nymph of the Froghopper produces its own protective covering; it secretes a white foam with which to surround itself. We know this as cuckoo spit and you will see it on a great variety of plants.
Many female birds are quite dull in colour and therefore not as visible when sitting on their nests, a vulnerable time for them, as they would be if they were as brightly feathered as their mates. This is particularly true of ground nesting birds such as pheasants and ducks; the young of these are also usually well camouflaged to match their surroundings.
These tactics are all part of the process of natural selection. Those that did not evolve a method of protection died out, leaving those that defended themselves in these ways able to survive, breed and pass on the abilities with their genes. It is thought by some that this process has ceased to exist as far as humans are concerned because, by the way of science, we are able to extend life and prevent death. But our existence is just a blink in the eye of time and maybe our very interference in the course of nature is all part of the natural selection process. (Enough philosophy, Sheila, on with what we can do this month while we’re all still here!)
- Butterfly day – meet at Northrepps
- Whale & Dolphin watch – Overstrand on 2nd August 9 – 4pm.
Contact www.wildlifetoursandeducation.co.uk or 01263 576995.
- Crickets & Grasshoppers, Bugs & Beetles – Sheringham Park.
www.nnns.org.uk or Tony Leech 01263 722282.
- Marine Mayhem, Tern Tuesday & many others – Cley Marshes.
- Rambling & Dyke Dabbling – Ranworth Broad.
www.norfolkwildkifetrust.org.uk or 01603 625540.
© Sheila Sims 2015. Email: firstname.lastname@example.org