Monday 24 July 2017

Cuckoo Valedictory 23rd July 2017

By now the majority of Common Cuckoos in Britain will be on their way back to spend the winter in tropical Africa and we will see no more of them until next year. The earliest departure date recorded is the 3rd of June and over 50% will have departed by the end of June. However the eggs the females have laid in other bird's nests will have produced young and these can still be seen after they have left the nest, often being fed by their foster parents, up to the end of August or the beginning of September.  Eventually the young Cuckoos will abandon their host parents and embark on a long and hazardous five to seven thousand mile southward migration, unguided except by inherent genetics. It is yet another example of the incredible wonders of our natural world that it is all too easy to take for granted.

Sadly, as with many migrant birds, the Common Cuckoo is in a long term decline as a breeding bird in Britain although its distribution covers all of Europe and Asia. Globally it is estimated there are between 25-100 million individuals, while in Europe the population is between 12.6-25.8 million. However, in Britain the situation is not good and we have lost over 50% of our Cuckoos in the last two decades.

Until 2011 little was known about the Cuckoo's migration routes to and from Britain  but in that year the BTO (British Trust for Ornithology) embarked on a programme of satellite tagging male Cuckoos that were breeding in East Anglia and since then males from other areas of Britain have also been tagged. This has revealed that Cuckoos take two distinct routes south to their wintering areas in Africa. Birds either went southwest via Spain and Morocco (the west route) or southeast via Italy or the Balkans (the east route) before converging in the rain forests of Congo  in central Africa, the main wintering area for Common Cuckoos migrating from Britain.

Birds taking the west route left on average eight days later than those taking the east route but were more likely to die before completing the crossing of the Sahara even though their route was shorter at this point than those from the east. There was no difference in survival for the two routes during the rest of the southward migration or the return northwards in the following year. Despite the formidable obstacle of crossing The Sahara and its inherent dangers most mortality of migrating Cuckoos took place in Europe suggesting that adverse conditions at the Cuckoo's stopover sites were responsible for the deaths. A combination of large scale habitat change degrading the areas where the Cuckoo needed to refuel its energy reserves and localised adverse events such as severe drought, and wildfires as has happened in Spain since 2011 and now currently in southern France, have all contributed to the detriment of the Cuckoo's survival chances. 

Even declines in the caterpillars of large moths, the main food source of Cuckoos on their breeding grounds here, and that use the west route, may result in the Cuckoo commencing its migration underweight and ill prepared to cope with any undue adversity it meets further south in Europe, let alone coping with the crossing of The Sahara. So hazardous is its migration that the maximum lifespan recorded for a Common Cuckoo is only six years and eleven months. 

I for one will regard the Cuckoo with both a renewed respect and increased anxiety about its long term prospects when I see and hear it next year, knowing now the hazards it faces in order to return to us. 

Common Cuckoos spend remarkably little time in Britain, around eight to ten weeks only. We regard them as our bird but really we should consider them as an African species that comes to us to breed. One male Cuckoo from Norfolk was satellite tagged and named Chris in honour of Chris Packham, the well known naturalist, TV presenter and campaigner against illegal killing of birds of prey such as the Hen Harrier. The information gained from this particular tagged Cuckoo revealed it spent 47% of its time in its winter quarters in Angola in southern Africa, 38% of its time on migration and only 15% of its time in Britain!

After the Nightingale and Swallow, the Common Cuckoo has probably engendered more literature in the form of writing, poems, prose and song than any other British bird and it has acquired a mystique greater than even the two aforementioned species based on its extraordinary life.

Despite their unique and unmistakeable call they are essentially secretive birds, more often heard than seen, especially the females that will sit for long periods concealed in a tree or bush watching their particular host species building a nest and waiting until the time is right to deposit an egg in the nest. The three commonest species parasitised in Britain are Reed Warblers, Dunnocks and Meadow Pipits although more than one hundred and twenty species have been recorded as being parasitised by Common Cuckoos throughout Europe.

It is not easy to get close to a Common Cuckoo without elaborate preparations to conceal oneself in a hide and even then it is no guarantee of success but this year I was fortunate to be able to travel to see a remarkably confiding male Common Cuckoo in Surrey which had lost all fear of humankind and would come to within feet, even inches, of anyone willing to stand still and be patient (see my blog Close Encounters of the Cuckoo Kind  June 4th 2017

The unusual behaviour exhibited by this individual only added to the mystique and folklore of Cuckoos in general and my ongoing fascination with them. Seeing it so uniquely close had an almost mesmeric effect, or at least it did on  me, as it swung about on its perch, its tail hanging loose, wings drooped and expressionless staring yellow eye drawing you into its world.

Male Common Cuckoo at Thursley Common Surrey
I can also still clearly recall seeing my first ever Common Cuckoo, in the garden of my then home in suburban Surrey, more than fifty years ago, when undoubtedly they were a much more common bird than they are now. It was a fully fledged juvenile although still dependent on its foster parents which in this case were Dunnocks. Since then I have encountered Cuckoos in many places throughout Britain and when living in Sussex found two Reed Warbler's nests, each with a young Cuckoo, situated in reedy wet ditches on a farm adjacent to the sea. One of these survived to fledge but the other grew too large for the nest which could hardly bear its weight and subsequently, after a rain storm, the nest collapsed resulting in the young Cuckoo falling into the water below the nest and drowning. A sad end.

Another male Common Cuckoo two years ago, at the back of Farmoor Reservoir by the River Thames towpath allowed me to get close to it and again this was memorable because it was so unusual. Normally whenever I see one it is only as a bird flying or perched distantly in a tree.

Male Common Cuckoo at Farmoor Reservoir Oxfordshire
On Otmoor, my local RSPB reserve here in Oxfordshire, it has been an exceptionally good year for Common Cuckoo's with up to six calling males present, and even a very rare hepatic female in which the grey feathering is replaced by reddish brown.

In Spring in England, Cuckoos arrive in mid April, the average date being the 18th of April but in northwest Scotland the first birds arrive as late as early May. The earliest record of a Cuckoo in the last fifty years in Britain was a bird seen and heard on the 20th of February 1953 at Farnham in Surrey although an adult was shot at Delamere in Cheshire on the 26th of December 1897 or 1898 but this was a bird that apparently had been unable to migrate south to Africa due to injury.

In southern Africa there is also the resident African Cuckoo, a separate species which is virtually identical to the Common Cuckoo, the only discernible difference being it has more orange yellow on its bill. I can recall on a visit to a farm in Zimbabwe, when the huge shade trees in the garden were infested with caterpillars with no less than seven species of cuckoo feasting on them and trying with little success to sort out the difference between the African and Common Cuckoos, as both species were in the garden. It was not easy and to this day I feel I probably got it wrong more times than I got it right.

So farewell to our Cuckoos and here's hoping that some will survive to return again next year to give me as much pleasure as they did this year.

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