Nightingales in November (44 page)

Having already departed our shores well in advance of the Nightingales, the BTO has discovered that late July or early
August seems to be the prime time when many British Cuckoos will leave any established stopover locations in Spain or Italy for their journey to the heart of Africa. Followed with the help of satellite technology between spring 2011 and the summer of 2015, three out of four of Chris the Cuckoo's southerly migrations have him recorded leaving Italy in the second half of July, only to arrive in Africa a few days later. In 2011, for example, a signal from Chris's transmitter reported him to be close to the River Po in northern Italy on 22 July, only then to be picked up in northern Chad, a distance of over 2,600km away, just 55 hours later! As they power over both the Mediterranean Sea and most of the Sahara Desert in one gigantic hop, it now seems likely that Chad may well be a favoured stopover for many of the British-breeding Cuckoos in July and August. As the Cuckoos generally seem to take a more easterly route on their southward migration compared to their journeys north in spring, this would seem to indicate that many of the birds must pass directly over Libya. With a good number touching down in desertified northern Chad, it seems this arid part of the country may in fact be little more than an opportunity to draw breath before the Cuckoos then quickly move to more fertile regions further south. The richer feeding grounds surrounding Lake Chad in the south of the country represent an excellent opportunity to recover any condition lost while crossing North Africa, and mean the Cuckoos are in no hurry to leave this region until they ultimately head for the tropical forests later in the autumn.

As the summer rolls on, any young Peregrines which fledged in the spring should by now have become sleeker, faster and far more adroit at catching their own food. Having served their apprenticeship well, the loosening of the ties with their parents will probably have been initiated by the young who
now be regularly feeding well away from the nest site during the day. Still returning to the comfort blanket of their parents' territory at night, these day trips will not just be helping the young birds to find other good feeding areas, but also locate possible overwintering locations and even potential breeding territories. At those sites with an absence of breeding Peregrines, birds may well now begin turning up again at a whole host of sites that have been abandoned since late winter as the whole population becomes far less territorial and much more mobile.

Mobility will also have become a distinguishing feature in the behaviour of both British-breeding Lapwings and any immigrant birds still pouring over from the continent. Ringing records of Lapwings which were known to have bred elsewhere, before then being noted in Britain, seem to suggest that the largest influxes originate from Belgium, the Netherlands, Denmark, Germany, Sweden and Norway, but there have also been some interesting recoveries from elsewhere. In 2003, for example, a Lapwing found dead on Romney Marsh in Kent was revealed to have been ringed as a nestling in northern Lithuania in 1994, a distance of 1,724km from where it was recorded. This record is one of a handful of Lapwings known to have originated from a broad arc encompassing Estonia to the north and Poland further south, and due to the very limited number of birds ringed in these countries, these records may merely represent the tip of an iceberg. All these countries surrounding the Baltic sea have much colder continental winters than Britain, where freezing temperatures are the norm, and due to the Lapwing's inability to extricate food from frozen ground it's perhaps no surprise that a healthy number will move west to the Gulf Stream-warmed climate found in and around the UK.

August

Synonymous with school holidays and filled with the frenzied activity of families trying to enjoy what remains of the British summer, August is a time when the wildlife will be keen to complete breeding cycles before the nights start drawing in. With the bird breeding season largely over for another year, those visiting just for the summer will either have already departed or be busily stocking up on last minute provisions for the flight. Amongst those birds residing here all year, a continued moult and dispersal into the countryside will be the order of the day, giving the garden that empty feeling of a stadium just after a match has been played. Around our coasts the picture could not be more different, however, as waders like Knot, Turnstone and Sanderling exchange their Arctic breeding grounds in their droves for our mudflats - representing just the vanguard of a whole variety of bird species keen to spend the winter in Britain.

Early August

A mere three months after arriving in England, and with their main flight feathers freshly grown, by August many Nightingales will have already turned their attentions towards the continent, as the exodus takes place to southern Europe and beyond. The sum total of knowledge as to exactly when Nightingales leave Britain was, until very recently, compiled from little more than a combination of the occasional bird recorded at a host of southern English migratory hotspots and a paltry total of 13 British-ringed birds recovered from abroad. However, since the BTO has managed to attach tiny geolocators to Nightingales, the movements of this mysterious bird are now finally being revealed.

Of all the Nightingales with geolocators attached in the spring of 2009 and then crucially re-trapped to recover the equipment the following spring, only one individual was able to deliver any meaningful data. The bird, named OAD because of the letters on its device, is believed to have divulged more information in a single stroke about the movements of Nightingales than in a hundred years of ringing. The recovered data revealed that OAD was thought to have left England in early August, only then to be recorded passing west of Paris a week later. Despite a substantial layover in Spain and Portugal, the spring migration north is now believed to be conducted at a much more rapid rate than the southward journey, which appears decidedly far more leisurely by comparison. Needing neither to proclaim a breeding territory nor a mate in Africa, it seems there may not be quite the imperative for the Nightingales to migrate so quickly, thereby leaving them free to feed along the way.

Unlike the Nightingales which will have certainly moulted their flight feathers in Britain, the adult Cuckoos will only undergo the majority of their annual moult upon arrival at their long-term wintering destination. In fact moulting studies of a variety of different migratory species have shown a general pattern appearing; the further south the birds migrate, the more their moult will be delayed until later in the year.

It is only since the BTO began satellite tracking Cuckoos that the region surrounding Lake Chad was revealed to be a favoured stopover location for many of the British-breeding Cuckoos. Due to its particularly shallow nature, with the deepest recorded point being little more than ten metres, the lake's size doesn't just vary throughout the year, but has alternately shrunk and grown enormously over the centuries. Being an ‘endorheic' system, or a closed drainage basin, means the lake retains the water as there is no outflow or discharge into rivers or oceans, so its precise level tends to be dictated by the difference between any inflow and the amount escaping by evaporation. This will in turn be controlled by the prevailing climatic conditions. The lake is also situated in a region called the Sahel, a climatic zone of semi-arid habitat which runs in a narrow horizontal band across the entire African continent. Representing the transition between the Sahara Desert to the north and the wooded savanna and tropical forests further south, it is likely that this region will represent the first proper opportunity for the Cuckoos to feed since their departure from southern Europe. Using this region to slowly recuperate and recover condition after crossing the world's greatest desert, the satellite telemetry indicates that the Cuckoos will be in no great hurry to reach the Congo Basin with many staying put until around the time that autumn begins to take hold in Britain.

The plumage of the now fully-fledged Cuckoos still back in Britain can vary enormously between being predominantly grey, to decidedly rufous, with the latter coloration not dissimilar to the rare rufous or hepatic colour form of a select few adult females. These juvenile body feathers will not last long though, with many being slowly replaced soon after leaving their hosts' nests. The exception to this rule will be the the wing and tail feathers, which like the adults' plumage will not be replaced until much later in the year. While their errant biological parents rest and recuperate in the Sahel, very little is known about the movements of the juvenile Cuckoos, but it is suspected they may well stay in Britain until at least September. Until then, the young Cuckoos will continue to feed themselves on a diverse array of invertebrate food, with large hairy caterpillars probably the preferred food source. As the summer rolls on, a different suite of butterfly and moth caterpillars will in turn become available for the juvenile Cuckoos to exploit, as they hop around the ground, amongst hedges and up in trees for surely one of the most unpalatable of all meals.