by Mike Dilger
Remarkably the Cuckoos are still not the most southerly of our twelve birds, with British Swallows having flown down to winter some 2,800km even further south. For centuries, after Barn Swallows disappeared from Britain in the autumn, they were believed to spend the winter in rock or tree crevices, or even buried in mud. It was not until the early nineteenth century that observations of birds over the English Channel, in the Mediterranean and off West Africa, supported the alternative, and at the time controversial, view that they migrated. Only in 1912 was definitive confirmation of the British Swallows’ winter home produced, when a female Swallow ringed in Staffordshire by a James Masefield in May 1911 was recovered in Natal on 23 December 1912.
From the BTO’s ringing records, it seems that most British Barn Swallows winter in South Africa, with a large number of records predominating from the Western Cape Province, an astonishing distance of around 9,600km from south-east England. Roosting by night in reedbeds or other wetland vegetation, sunrises in early January, representing high summer in the Western Cape, will see the Swallows leaving in waves to fan across the South African countryside to feed. In Britain, the airspace around cattle and horses is often a productive feeding ground as their dung attracts insects and the livestock also flush invertebrates from the vegetation as they walk. In South Africa, herds of game may well offer similar feeding opportunities. A British Swallow swooping to catch a dung fly from beneath an elephant’s legs?… not as far-fetched as it sounds!
Our final iconic bird, the Puffin, may well be somewhat more difficult to track down in early January. Having left their breeding colonies by mid-August at the latest, current research by Mike Harris and his team working on the Isle of May, Firth of Forth, eastern Scotland suggests that most of their Puffins immediately move out into the North Sea. Using geolocators attached to the Puffins, the team found that after then flying around north Scotland to spend the autumn and early winter in the north-east Atlantic, many will have already returned to the North Sea by the turn of the year. Recoveries of Puffins from colonies elsewhere in Britain suggest they disperse widely, with recoveries of birds seeing them turn up from Brittany in France to the Canaries, and a few adventurous juveniles even making it as far as Newfoundland and Greenland.
Mid-January
With Bewick’s Swans firmly settled on their wintering grounds for more than a couple of months, and dominance hierarchies mostly established, aggressive encounters between birds should now be far fewer than earlier in winter. Top of the ‘pecking order’ will be the families, consisting of a pair of experienced adults and their juveniles which were successfully raised during the previous breeding season. Sticking close together at all times, a family of two adults and three offspring represents a formidable fighting force that is easily able to bully those swans with fewer allies away from the best feeding locations and roosting sites.
Nowhere is this hierarchy more noticeable than at the WWT Slimbridge reserve in Gloucestershire. With the swans fed daily by the wardens, the families will use their superior numbers to barge their way to the front of the queue, and help themselves to far more than their fair share of the grain being handed out. Aware of the fact that numbers equate to dominance, yearlings (swans experiencing their second winter), will often rejoin their parents on the wintering grounds to boost both their own social position and that of their parents within the flock. Any trios consisting of parents and a yearling, although often not able to compete with larger families, will still be able to exert influence over those pairs of swans without any young at all to back them up. Below the established pairs without any young, and even lower down the pecking order, are those adults that have either lost a mate or have been unsuccessful in managing to secure one. And finally, the birds that will struggle the most during feeding and roosting will be those yearlings battling the unfortunate combination of a solitary existence and huge inexperience.
Compared to the highly strung Bewick’s Swans, there generally seems far less aggression amongst the socially gregarious Waxwings. By mid-January in a good ‘Waxwing winter’, the overwintering population may by now have fanned right across the southern part of the UK, with some hungry birds even braving a second sea crossing to sample the delights of Ireland’s berries. Staying in flocks is initially an asset to Waxwings, as it enables them to use their numbers to dominate prime feeding positions, in the process keeping territorial Mistle Thrushes, for example, away from the berries. However, as the fruit resource becomes far more depleted at this time of year, any larger flocks may well be forced to break up into smaller, nomadic groups. These compact, mobile flocks will then need to range far and wide to ensure they can find enough food to see them through those nights when the temperature dips below zero.
For many of our resident birds that have chosen to stay at home rather than taking a long winter break in warmer climes, extended cold periods can present a very real and imminent threat to their survival. Both Kingfisher and Lapwing from our chosen twelve will struggle to find enough food if the water and soil surface stay frozen for any length of time. According to the BTO, as many as four out of every five Kingfishers that fledge won’t see even their first birthday, with a large proportion perishing during periods of severe weather. Struggling to find unoccupied riverine territories, many young birds are pushed in the autumn to spend the winter at the coast to feed in estuaries or even in the sea itself. Although these habitats will rarely, if ever, freeze, the feeding around the coast will always be far more demanding than, say, a quiet chalk stream in Hampshire.
In very harsh conditions, some Kingfishers holding inland territories may be forced to temporarily move if their established feeding areas freeze over. The cold weather movements of continental Kingfishers are well known, and particularly in Germany, where the Kingfisher’s name ‘Eisvögel’ translates into ‘ice bird’. Perhaps a technically more accurate name, although undeniably more of a mouthful, would be ‘the bird that moves ahead of the ice’!
After heavy snow, or during periods of hard frosts, many Lapwings from northern Britain tend to be either pushed towards south-west Britain or across to southern Ireland, which tends to avoid the worst excesses of winter, thanks to the warming influence of the Gulf Stream. This contrasts with the many Lapwings that have bred in the southern half of Britain, which seem to respond to freezing conditions by simply abandoning the British Isles entirely. Crossing the English Channel, most of these birds will temporarily settle anywhere from coastal France all the way down to the Atlantic coasts of Spain and Portugal, before the ‘breeding imperative’ draws them back to Britain later in the spring.
One bird that will refuse to budge from its territory, come rain, shine or even Arctic conditions, is the Tawny Owl. An established pair will rely on an intimate knowledge of their territory to eke out an existence even in the most severe of conditions. For those ‘Tawnies’ that have set up home in more urban and suburban environments, recent research suggests that they take a higher proportion of birds in their diet, meaning their choice of food may well be easier to find after a covering of snow. This contrasts with many rural Tawnies, which mostly rely on small mammals for sustenance throughout the year, with Bank Vole and Wood Mouse being the two species most commonly encountered in the owls’ pellets. Unlike many British mammals, the Bank Vole and Wood Mouse do not hibernate, but stay active all winter, with the Wood Mouse venturing out to forage mostly at night, while the Bank Vole will feed intermittently right around the clock. Snowy conditions, for example, can make hunting the owls’ prey far more difficult, as the mice and voles will still be going about their business, but out of sight under the snow. In this situation, the Tawny Owls may supplement their diet with carrion from animals that have succumbed to wintry conditions. This was clearly demonstrated in the BBC’s Winterwatch in January 2015, where the team managed to film a Tawny Owl tucking into a deer carcass each night at the Mar Lodge Estate, within the Cairngorms National Park. Tawny Owls, it seems, are not just top predators, but suprem
e opportunists as well.
Harsh British winters can exact a toll on even the hardiest and most resilient of birds, such as Robins. With insects providing the bulk of its diet for most of the year, the Robin’s ability to change to fruit and seeds during winter stands it in far better stead than birds such as Treecreepers and Dartford Warblers, which are confined to an insectivorous diet throughout the year. It will not just be the Robin’s catholic diet that helps see it through any particularly cold periods, but also its willingness to take advantage of our love of feeding garden birds. Being so confiding by nature has enabled the resident Robin to often be first in the queue when it comes to dining out on any food we leave out on bird tables up and down the land.
Unlike the Robin, the holding of a territory is not an issue for Blue Tits in the winter, resulting in large numbers of individuals continuing to move through our gardens at this time of year. Frequently accompanied by other small birds, the majority of Blue Tits passing through will be local birds that have bred in neighbouring gardens or nearby woods, with a varying number of nomadic birds added to the mix. Most British Blue Tits are not thought to move more than a few kilometres from where they hatched, but by contrast continental Blue Tits are much more inclined to migrate in winter, even crossing the North Sea in some years. So for those with gardens on the east coast, there is every possibility that some of the birds seen feeding on peanuts or fat balls could be Blue Tits of Belgian, Dutch, German, or even Norwegian descent.
While many Peregrines breeding in northern Europe, North America and Siberia will be forced to migrate south to find enough food to hunt, our comparatively mild winter climate means most British Peregrines will rarely have to move far from their nest site even when the temperatures drop. Although some upland Peregrines will move away from their breeding quarters as winter sets in, most urban pairs should be able to find enough feathered prey in and around their towns and cities to sustain them through to spring. Recent research carried out by Peregrine expert Ed Drewitt suggests that urban Peregrines might not just be hunting during the day, but are making a substantial number of kills through the night too. By examining prey remains, mostly in the form of feathers collected at well-established plucking sites, Ed has been able to reveal that Peregrines are taking a far wider range of food than just feral pigeons. Winter visitors to Britain such as Woodcock, Teal and Moorhen are also being taken at this time of year as they migrate across urban areas at night. Historically, these birds may well have formed a much smaller part of the Peregrine’s diet; however, it is thought that as the light from street lamps and buildings shines into the night sky, this light pollution is illuminating them as they pass overhead.
While Peregrines are most commonly seen catching birds during the day with the stoop dive, which involves closing their wings and dropping out of the air at immense speeds to hit and hopefully kill outright their chosen quarry, at night they employ a totally different technique. Lurking in the shadows of a church or tower block, when an urban Peregrine spots the pale belly of a bird lit up like a light bulb, it only need fly a short distance upward to take the bird unawares from below. Peregrines will also insure against any potential temporary shortages by storing excess food during times of plenty. In winter this means that any cached food will effectively be stored in the equivalent of a fridge freezer!
British-breeding Puffins, come the middle of January, will still be dispersed in a wide arc between the North Sea and the north-east Atlantic. As many birds are already in winter plumage by the end of August, they are thought to undergo a complete moult between late autumn and early spring to ensure they look freshly laundered by the time they arrive back at their breeding colonies the following spring. It’s not clear exactly when the main flight feathers are replaced during the winter, but recoveries of dead Puffins either hunted or washed up ashore during this time seem to show that the moult is carried out in a synchronous fashion along each wing. While these feathers are growing the Puffins will become flightless, but despite an inability to take to the air, they are still able to dive and search for food. Presumably any Puffin still renewing its flight feathers at this stage will need to have made sure its chosen moult location will be able to provide enough food until its wings are finally ready for taking to the air as well as cutting through water.
Unlike the Puffin, which will be bobbing around out at sea like a cork for at least four to five weeks while moulting its flight feathers, our British Swallows down in South Africa will still be able to fly throughout their entire moult. Because Swallows obviously need to be able to fly efficiently in order to feed, the moult is a slow process which may take anywhere between four and a half and six and a half months. The Swallow’s body and head feathers are the first to moult, followed by those on the wings and tail. They must also moult the flight feathers in a symmetrical, ordered fashion along each wing to prevent any imbalance during flight and ensure their manoeuvrability is not impaired while feeding. With these feathers being replaced so gradually, it is quite normal for the outer primary and tail feathers to still be actively growing by the time the birds have begun their long spring migration back to Britain in around a month’s time.
Meanwhile, further north it seems from telemetry data provided by the BTO that most British-breeding Cuckoos will be in a broad belt stretching along the mighty Congo River in mid-January. The river also marks the boundary between the two Congo countries – the Republic of Congo to the west of the river and the Democratic Republic of Congo to the east. This border region is dominated by Western Congolian swamp forest which, when combined with the Eastern Congolian swamp forest, is thought to be one of the largest continuous freshwater swamp forests in the world. Known for its large numbers of Lowland Gorillas, the Western Congolian swamp forest consists of seasonally flooded forest with a high canopy, dense undergrowth and a muddy floor, which is also interspersed with grassland areas. Lush Raffia palms and low vegetation, mixed in with swamp and abundant waterholes, makes passage through this largely pristine habitat almost impossible for man.
Due to the more imprecise positioning of geolocators, when compared to the Cuckoos’ satellite transmitters, it’s difficult to pinpoint which habitat Nightingale OAD was using during its stay in Guinea. Since the original pioneering work tracking OAD, five more British Nightingales have been successfully tracked all the way to West Africa, with most seeming to spend mid-January along the coastal strip between south-west Guinea and north-west Sierra Leone. Having spent a month up to mid-December in coastal scrub further north in Senegal and The Gambia (Senegambia), Chris Hewson from the BTO thinks that as Senegambia becomes too dry at the end of the year, the Nightingales may well be moving south up a ‘moisture gradient’ to an area where the rainy season has only just finished, potentially making it easier for the birds to find food. In other words, with the start of their return journey to England just two months away, moving even further in the other direction seems to be the smartest move!
Late January
Leading the headlong charge towards the breeding season will be the Tawny Owls. Any established pair will have already been holding exclusive access to a territory throughout the winter, and the next logical step will be to select the precise nesting location in which their clutch will be laid and resultant brood reared. The end of January will see the parents visiting all the potential sites within their territory before deciding which suits their precise requirements best. The Tawny Owl is of course primarily a cavity-nesting species, often favouring large holes in deciduous trees, although they will sometimes resort to old stick nests or even sites in buildings if push comes to shove. In territories that consist mostly of coniferous woodland, with few natural cavities, they may even nest in amongst rocks or tree roots on the ground. More recently, where natural options may be scarcer, many Tawny Owls have been persuaded to use nest boxes, with a considerable degree of success. The recent advances in miniature camera technology have meant that for any box-nesting Tawnies we’re now in a position t
o learn much more about their secretive nesting behaviour.
Certainly in southern Britain, most Robin pairs will already have become established by the end of January. Pair formation is considered distinct from courtship, which is usually nothing more than a brief precursor to when nesting begins properly in the spring. Like most species of bird (and indeed most wildlife), it is ultimately the female Robin who will choose the male. So with the males already singing lustily at this time of year, the onus will be on the bachelors to entice any unpaired females into their territory. With a surplus of unmated males each year, the female can afford to be quite fussy, and will sometimes move into the territory of a single male, only to quickly reject him for the neighbouring male if she feels he has more to offer. It’s difficult to elucidate exactly how the female makes her choice, but it may well be a combination of the standard of his song, the quality of his territory, his looks and aggression.