Nightingales in November

by Mike Dilger

  Upon the flock’s arrival at a rich feeding site, it will then be down to each individual Lapwing to forage for itself. Lapwings have large eyes relative to their bill size and tend to hunt primarily by sight. The feeding technique most frequently adopted is known as ‘pause/travel feeding’ and consists of a few steps, followed by a pause, a scan, and then a move forward to either stoop for a prey item, or to repeat the process if nothing is spotted. Despite this being considered an effective method, not all scans locate prey and not all strikes are successful. When found, the prey will then be prized from the soil by the Lapwing’s short bill. In contrast to many of the long-billed waders, such as curlews and godwits, the Lapwing’s bill doesn’t have a sensitive tip capable of locating food by touch, but is instead hard and horny for grasping and holding the prey. Most of their diet seems to consist of carabid and staphylinid beetles, millipedes, slugs, leatherjackets and earthworms, with the food taken varying seasonally according to the annual life cycles of prey organism. Also the weather conditions will affect the state of the soil, with earthworms, for example, travelling deeper and in the process becoming far more inaccessible in the dry heat of the summer and autumn sun.

  Another advantage of flocking, in addition to sourcing patchily distributed food, means that there will be many more pairs of eyes looking out for predators, but one obvious downside to sharing a ‘dining table’ with so many others means that squabbles between individual birds in too close a proximity will often become inevitable. In denser flocks, aggressive interactions are recorded more regularly, resulting in territorial displays perhaps more commonly associated with breeding grounds also being observed on the Lapwings’ winter territories. Two evenly matched birds arguing over a feeding spot will often resort to parallel walking along an invisible boundary as they size each other up. If the dispute isn’t quickly settled by the equivalent of this staring match, then it can quickly escalate into hunched or crouched running, jumping up at each other and ultimately fighting.

  Continuing to arrive at their traditional overwintering sites such as Slimbridge in Gloucestershire, the Bewick’s Swans will also find that a rapidly increasing flock density will initially cause a huge amount of consternation in the ranks until a pecking order finally becomes established. Containing all social groups, the wintering flocks of Bewick’s Swans will include families, pairs without cygnets, single adults and yearling birds. When it comes to forming the dominance hierarchy, numbers and experience will count for everything. Disagreements will initially be addressed by ritualised behaviour, but can quickly escalate if neither side is willing to back down. The first sign of a dispute may consist of nothing more than a head lowered in threat, or a well-placed peck, but if these are ignored, then the Swans will enter a well-choreographed and established routine which increases in intensity with each step. The male is invariably the most common protagonist in these aggressive encounters, and after starting with neck stretching and head pumping, he will quickly move through the gears in his threatening repertoire. Starting with extending his wings to a half open position, he will then ramp up the threat to progressively higher levels, to include wings being half open and flapping, wings then fully extended and flapping and finally wings fully extended and still. If by this stage his opponent is still not willing to concede defeat, then the behaviour may quickly descend into a fight with the aggressor biting while beating his wings, in the full knowledge that his family will be noisily lending support in the wings.

  As subordinate single swans will tend simply to give way to the more dominant birds or family groups within the flock, this final ‘nuclear option’ is generally only reached when opposing parties are well matched. Submissive behaviour will usually resolve the matter and involves the defeated bird turning away with its bill tilted up so it can clearly guard its rear while beating a hasty retreat. Any successful aggressive encounters are usually followed up with ‘triumph’ displays, in which the winning swan will return to his mate and cygnets, before displaying with a neck stretching, wing flapping and loud honking routine as his family enthusiastically joins in the celebrations. By always keeping no more than just a couple of wingbeats apart when in amongst the wintering flock, the dominant families will always have muscle on hand to take the pick of the best foraging and roosting spots for the entire duration of the winter. In fact at locations like Slimbridge, where many of the swans will return each winter, this hierarchy can become so entrenched that dominance will frequently be held from year to year.

  Freshly arrived from northern Europe, any aggression between individual Waxwings from the same flock only ever seems to be minimal as these gentle birds adopt a far more consensual approach to feeding than the obstreperous Bewick’s Swans. Where Waxwings go after their initial arrival is now more clearly understood thanks to work carried out by colour-ringing studies. By ringers using different colour combinations on the legs of each Waxwing netted, birdwatchers up and down the country are then able to report the location of different individuals without the need for their recapture. During the influx of 2010/11, for example, the Grampian and Orkney Ringing Groups managed to catch and individually colour-ring almost 500 Waxwings through late October and November in an attempt to try and track the movement of the birds as they spread across Britain. With competition for berries patently at a premium, Waxwings quickly departed both ringing locations, with one particular Orkney-ringed bird rapidly relocating to Norfolk and a number of Aberdonian-ringed Waxwings subsequently reported from Dunfermline, Lothian, Glasgow, Cumbria and Manchester. The subtleties of each Waxwing invasion will of course play out differently, but the general pattern of movement usually sees birds streaming in a southerly and westerly direction as the food becomes stripped out of their original entry points. Interestingly, one of the Waxwings caught in Aberdeen was an adult male that had been ringed in Svartbyn, a town in northern Sweden, close to the Finnish border. After having travelled 1,654km all the way to Duthie Park in Aberdeen, this bird then sadly proved to be a window casualty just a week later, but only after having served as a standard bearer to further illustrate the strong Waxwing link between Sweden and Scotland.

  The Swallow’s link between Britain and South Africa was first established over a century ago, when a female ringed in Staffordshire in 1911 was subsequently recovered from the Province of Natal in December of the following year. This was merely the first of an astonishing 447 British-ringed birds that have so far been recovered in South Africa, patently making the southern reaches of the African continent their destination of choice. It’s believed that most returning Swallows will generally be faithful to their winter quarters, although locations can vary if the weather impacts on food availability. Just as in Britain, the Swallows will forage across a wide variety of habitats, as they swoop over grassland, forest edge, cultivated fields and particularly any wet environment, before then returning each evening to their communal roosts.

  Up to 2011, not a single ringed British-breeding Nightingale had ever been reported south of the Sahara, leaving the sum total of knowledge about the location of ‘Nightingales in November’ to be collated from the information gleaned by the geolocator attached to ‘Nightingale OAD’. As geolocators have an inherent degree of inaccuracy in the tropics, where dawn and dusk vary little throughout the year, the BTO researchers interpreting the data believed OAD most likely to have been passing through Mauritania in early November. Comparable in size to Egypt, around 90% of this huge but impoverished country is categorised as ‘Sahara Desert’, with most of the population living in the south-west, which experiences a marginally higher rainfall than in the desert interior. Despite a substantial mineral wealth consisting of significant deposits of iron ore and oil, severe international sanctions following a coup d’état in 2008, a poor human rights record and corruption have all combined to ensure that Mauritania remains a desperately poor desert nation.

  The believed autumn and spring migratory routes of Nightingales between their stopover sites in southern Eur
ope and overwintering destinations in west Africa.

  The topography of the country is generally considered fairly flat, with vast arid plains broken by occasional ridges and cliff-like outcrops. To the west, between the Atlantic Ocean and the higher desert plateaus, the land alternates between clay plains and sand dunes, or ergs, some of which can become mobile during high winds. Following the Atlantic Coastal Flyway, which is considered a key route for many migratory birds moving between Europe and Africa, the Nightingales in early November are still believed to be steadily working their way along this route, represented along this particular stretch by the ‘thin green line’ of the Atlantic coastal desert. As the birds advance further south, their move into the semi-arid savanna close to the border with Senegal will bring a measure of relief for the Nightingales, as the marginally higher annual rainfall closer to the equator enables the desert scrub to become steadily replaced by wooded grassland and bushland.

  Over 4,000km to the south-east, the annual rainfall of around 180cm experienced in the Congolian swamp forests will find the Cuckoos experiencing a somewhat different climate to the Nightingales currently working their way along Mauritania’s arid coast. Undoubtedly keeping a low profile in these wet, humid forests, the Cuckoos will not be the sole British-breeding representative to spend winter in the heart of Africa, as Swifts have recently been revealed through geolocator technology to spend most of their winter in the Congo too. Adopting a somewhat higher profile - and niche - than the Cuckoos, the Swifts will spend most of the winter months sailing above the canopy as they take advantage of the abundant insect life emanating from these incredibly diverse forests.

  Certainly the contrast in habitat type could not be any greater than between where Cuckoos and Puffins will choose to spend their winter. Weighing in at just under 400g, and only marginally larger than a pint pot, most British-breeding Puffins at this time of year will be at the mercy of the North Atlantic as they spend most of the daylight hours diving for dinner. How far Puffins disperse after leaving their breeding grounds was very poorly understood until Mike Harris’s team on the Isle of May began to follow the movements of 13 birds with the help of geolocators. The first revelation was that ten of the tagged Puffins, upon leaving their breeding colony on Scotland’s east coast, didn’t stay in the North Sea, but immediately travelled anti-clockwise around Scotland’s north coast to head out into the Atlantic Ocean. At some point during the winter all Puffins will spend four to five weeks with their wings effectively clipped as they moult their primaries, but this didn’t restrict one tagged individual, ‘bird 6539’, travelling an estimated 3,000km during an extensive tour of the north-east Atlantic during the winter months. Initially heading up to the waters around the Faroe Islands, this bird subsequently travelled down to the west of Ireland in early November, before then returning further north, presumably after having moulted its primaries, to spend time off St Kilda. Although many of the Puffins followed did not travel as widely as this adventurous individual, it’s likely that many birds may well be covering a much wider area of ocean during the winter months than was previously thought.

  As Puffins undertake expansive voyages out at sea, the adult Tawny Owl’s entire universe will be the territory currently being vociferously secured for the winter and the breeding season beyond. The size of territory tends to depend on the quality of the habitat, with an established pair in mature, high-quality woodland often possessing a much smaller piece of real estate compared to those Tawnies living in either open woodland, or farmland containing small isolated patches of forest. In studies made in and around the intensively researched Wytham Woods near Oxford, the Tawny Owls living in the deciduous woodland were found to occupy a territory, on average, of around 18 ha, while pairs living nearby in mixed farmland needed a territory of around double the size. Clearly, in the world of the Tawny Owl, territories are all about quality not quantity. Additionally, the boundaries between prime territories can often stay remarkably stable between years, even remaining fixed despite changes in ownerships as established birds either die of natural causes or become ousted by any young pretenders waiting in the wings.

  With Robins also considered to be strongly territorial at this time, it is perhaps a surprise that Robins have been found to roost communally at some locations. After a roost was discovered in Aberdeen, further searching revealed five more around the city, with the largest gathering holding 53 different individuals throughout the season. By netting and colour-ringing birds using these roosts, the Robins were tracked down to breeding territories in local woodlands, which were patently exchanged in the autumn for different territories in nearby housing estates. While yielding more than enough food throughout the winter, thanks primarily to the generosity of householders leaving out food, it seems these urban territories may not be in a position to provide a sufficient number of roosting sites, hence the reason for the birds grouping together. Communal roosts have also since been located in Cambridge, where it was thought that many of the participating Robins were young birds unsuccessful in securing a territory in the autumn. Using these communal roosts may enable any newcomers to get the feel of the local situation on the ground, empowering them either to stay on in the hope of ultimately gaining a territory, or simply moving on elsewhere if they considered the surrounding areas overly congested.

  Keeping rigidly on territory wherever possible, each Kingfisher will defend its patch throughout the winter as if its life depended on it, which for once is not hyperbole. Certainly in the breeding season, territories can vary from a couple of hundred metres to a few kilometres of riverbank or lake perimeter in length, but winter territories generally tend to be smaller. Within that territory, most of the birds’ activity will in fact be mostly confined to an even smaller core area, containing both good fishing spots and suitable roosting locations, as they knuckle down to the serious matter of seeing out the winter.

  More confined to a home range rather than a territory, which they’ll share with a motley band of other bird species by day, Blue Tits will normally prefer to spend their nights in a far more solitary fashion. Having such a small body mass can make surviving the long winter nights a tough ordeal, so the Blue Tits’ technique for keeping themselves warm at night involves finding accommodation in the form of sheltered nooks and crannies. Keen to conserve energy by reducing heat loss means these tight spots may well be at a premium, with the result that any Blue Tit already occupying a favoured location as dusk approaches should easily be able to drive away any other bird attempting to gatecrash this party for one.

  Due to the abundant food on tap in towns and cities, many urban Peregrines will attempt to stay on their territories all year round, but certainly those Peregrines at traditional rural sites in remote Scottish or Cumbrian fells, for example, may well be forced to relocate for the duration of the winter as their prey seeks more clement conditions elsewhere. Often these tough northern birds may opt to station themselves at, or close to estuaries, where bird numbers will have been steadily building up throughout the autumn. Originating from breeding areas as diverse as Siberia, northern Europe, the Russian Federation, Iceland, Greenland and north-east Canada, literally millions of wildfowl and waders are attracted to British estuaries each winter, thanks to a combination of our mild maritime climate and large tidal ranges. Feeding on the extensive areas of mud and saltmarsh around our coasts as the tides ebb and flow, large flocks of Teal, Dunlin and Knot will need to keep their eyes peeled if they are to avoid appearing on the diet of this most ruthless of avian predators.

  Mid-November

  Having been on the move ever since exchanging Europe for Africa a couple of months earlier, British-bred Nightingales should finally be arriving at the destination that will become their home until at least Christmas. Even before the wintering location of Nightingale OAD was revealed by analysis of the data from its geolocator, it had long been suspected that British Nightingales spend at least part of the winter in the countries of Senegal and The Gambia. Both
situated in West Africa, the much larger country of Senegal is externally bounded by the Atlantic Ocean to the west, Mauritania to the north, Mali to the east and Guinea and Guinea-Bissau to the south. Senegal also almost entirely surrounds the Gambia – mainland Africa’s smallest country, which apart from a short stretch of coastline bordering the Atlantic Ocean, is a country consisting of little more than a long strip of land straddling the Gambia River.

  Both Senegal and The Gambia are considered to be politically fairly stable, with the former’s economy driven by exploiting and refining natural resources, while the latter’s is dominated by farming, fishing and tourism. The region is characterised by a tropical climate, with a mostly pleasant to stifling heat throughout the year and well-defined wet and dry seasons. The vegetation close to the coast, in both countries, mostly consists of savanna woodland, thorny scrub, gallery forest and wetland, with The Gambia being particularly well known amongst the British birdwatching community, enticed by an impressively high avian checklist for such a small country. Highlights of a trip to The Gambia in the winter will include many species never likely to be seen in north-west Europe, together with a smattering of visitors only familiar to Britain during the summer months, such as Ospreys, Sandwich Terns, Reed Warblers and of course Nightingales. Just as in their English breeding grounds, when in Senegambia the Nightingales tend to stay true to their naturally skulking behaviour, preferring to keep low down in the tangled, thorny savanna scrub typifying their accommodation at this time of year.

  Having completed most of their moult before they left British shores, any Nightingale glimpsed should be looking decidedly fresh as it settles down into a daily routine. The timing of the Nightingales’ moult is thought to contrast starkly with that of the Cuckoos, which are only believed to carry out most of their moult when well ensconced on their Congolian wintering grounds. Due to the Cuckoos’ effective disappearance from view for over 80% of the year, their moult is little understood, but it is believed that a proportion of adults may well replace at least some of their body, flight and tail feathers before crossing into Africa. With the on-board satellite tags revealing that the Cuckoos move little at this time of year, it is reasonable to suggest they will be using this settled period to actively moult their remaining flight feathers. Cuckoos possess ten primaries, with ringers identifying the innermost primary (closest to the body) as P1, while the outermost feather is P10. These ten primaries are believed to moult in two series, with feathers P1 to P4 shed in descendant fashion – or away from the body, while P5 to P10 are moulted in an ascendant manner – or towards the body. To further complicate the issue, P5 to P10 moult in alternate fashion, giving a possible replacement sequence of 9-7-5-10-8-6. This regular alternation between growing and non-growing feathers should still presumably give the Cuckoos enough lift to both evade predators and forage effectively for food.