by Mike Dilger
September
While the last wave of insects emerge and migrant moths and butterflies take their final fix of nectar before the frosts set in, the first official month of autumn will bring a feeling of change as the slow descent to winter begins in earnest. Bursting forth with nectar and foliage in spring and summer, our trees and shrubs will suddenly become laden with seductive seeds and fleshy fruits. This annual bonanza will have come just at the right time for dormice preparing for hibernation, squirrels stashing for winter and our resident birds looking to lay down fat for the lean times ahead, but too late for the vast majority of our summer visitors, which should by now be busily crossing continents. It’s not all one-way traffic though as the relatively mild climate and abundant food offered here will draw a whole new cast of characters keen to spend the winter in Britain.
Early September
Despite a steady stream of continental Lapwings arriving here from as early as May or June, it is not until September that the proper autumn passage of British Lapwings to their winter quarters will begin in any numbers. Continuing right the way through to winter, the movement of Lapwings that breed here is considered to be complex, but by analysing the data from ringing recoveries, Graham Appleton from the BTO seems to have uncovered a few general patterns. Some Lapwings, it seems, are only partially migratory and where possible will winter close to their breeding grounds, while other birds patently favour moving much further in preparation for the coldest months of the year. Furthermore, amongst those birds that do prefer to migrate, where they decide to spend the winter seems at least partly to depend on the location where they originally bred.
Records of both British and Irish-ringed Lapwings recovered abroad and also foreign-ringed Lapwings subsequently found in Britain and Ireland.
Many of the Lapwings breeding in the south-east of England, for example, tend to move south to principally coastal locations in France, where the warming effect of the Gulf Steam makes frosts a rare phenomenon, and also to a lesser extent the Mediterranean climate offered down on the Iberian Peninsula. While many of the breeding Lapwings from south-west Britain will also spend the winter on the near continent, a larger proportion of this population seems to prefer crossing the Irish Sea instead to spend the winter in Ireland. For those Lapwings breeding in northern Britain, however, an even larger majority seem to prefer Ireland’s winter sun, with few birds believed to prefer crossing to the near continent.
As the Lapwings relocate to their wintering grounds, the Swallows will also begin leaving their breeding sites, with those birds from eastern Britain thought to travel down the eastern side, as opposed to those breeding in the west following the western coastline. Migrating by day, at night the Swallows will coalesce at a number of roosts across the country as they opt for a safety in numbers strategy prior to crossing the English Channel. Some of these roosts, such as Icklesham in Sussex and Slapton in Devon, are well known and regularly used each autumn, but other smaller inland sites tend to be transitory and can often shift location from year to year. The roosting habitats of choice are usually wetland sites, with reedbeds offering the Swallows the benefit of protection from any predators unhappy about getting their feet wet. Gathering at their roost of choice before sunset, the birds initially seem to fly around aimlessly, only changing their behaviour when dusk is rapidly approaching. As the light level drops below a critical level, the Swallows suddenly become galvanised into tighter flocks, which then wheel over the reedbed before small groups can be seen peeling off into the vegetation below. Incessantly twittering to each other in flight, it is only when the birds have settled down for the night that a hush finally descends over the reedbed. Quickly leaving the roost in a series of waves at sunrise, the Swallows will then disperse into the surrounding countryside to take advantage of the year’s last flush of insects. These southern roosts may well play host to Swallows for anywhere from a few nights to a couple of weeks, until the shortening days and colder temperatures finally force them to delay their migration no longer.
Keen themselves to escape the increasingly inclement weather in the Arctic, those Bewick’s Swans without young still to fledge should be leaving the tundra by early September. The first leg of their journey will often consist of little more than a hop, as the swans slowly gather on traditional pre-migratory staging sites, such as the shallow coastal waters, large lakes and river estuaries close to their breeding grounds. Two of the most important mustering sites are thought to be the Pechora Delta and Korovinskaya Bay in the Nenets Autonomous Region of the Russian Federation, with combined counts of up to 15,000 swans in some years. Both of these sites are located adjacent to the Pechora Sea, and crucially should still be ice-free at this time of year, offering the birds a last safe feeding opportunity before worsening conditions force them in a westerly direction along the coast.
In those winters when large numbers of Waxwings reach Britain, an early sign will be the sheer number of birds seen moving into northern Sweden, from Finland and the adjacent Republic of Karelia in the Russian Federation as early as September. Presumably this extraordinary influx of birds must soon strip out the entire berry supply, forcing a continued push west and south to find as yet untapped sources.
As autumn arrives in northern Europe and the Waxwings are driven on by their stomachs, it should be a very different setting for the adult Cuckoos currently still enjoying Chadian or Nigerian hospitality. In three out of the four years that Chris the Cuckoo was tracked by the BTO, he revealed remarkable fidelity to the wooded savannas of southern Chad at this time of the year, and also relatively little inclination to move around much after his arrival. With the feeding here patently good, the data collected from the transmitters of a number of the birds have shown that most of the Cuckoos are content to stay settled here for at least a few weeks before finally moving towards the Congo Basin. Back in Britain and having jettisoned their foster parents way back in July, the juvenile Cuckoos may well be busily fuelling before preparing to depart on their long and lonely migration to Africa.
Unlike the Cuckoo chicks, the Nightingale young will probably migrate at the same time and along a similar route to their parents, but having severed the family ties back in Britain, the assumption is that it will very much be a case of each Nightingale to their own. From the limited data gleaned by geolocators, it seems that most British Nightingales will spend early September in the very same dry, uncultivated land that the adults themselves will have passed through during their spring migration earlier in the year. Keeping a low profile as they hop around the mosaic of dry scrub and wooded Mediterranean groves, their simple mission will be to put on as much weight as possible before departing from Europe for Africa at the end of the month.
With the Puffins continuing to disperse far and wide from their breeding grounds, those young Peregrines moving away from their parents’ territory will now be joining a floating population of birds with a nomadic existence. Being both too inexperienced to hold a territory and still not ready to breed for at least the first couple of years, their only aims will be to find enough food to eat and a safe place to roost without ruffling the feathers of any incumbent Peregrines they may meet on their travels. Peregrine expert Ed Drewitt reported, for example, that at least five different Peregrines were identified using one particular church in the town of Aylesbury, Buckinghamshire during the autumn of 2010, a number of which will certainly have been itinerant birds merely passing through. Due to the difficulties of separating individuals purely on plumage, this will probably have been an underestimate of the real number of Peregrines visiting the town, as some may have been present for little more than a few hours or just a day before then moving on.
Any young Tawny Owls that left their parents’ territory earlier in the summer will also be in a similar position to those immature Peregrine Falcons, in that finding a place to feed and safely roost while not alerting any established territory-holding pairs as to their presence will be of the highest priority. With the odds seemin
gly stacked against the young Tawnies surviving at this stage they have a couple of factors working in their favour. First, autumn is considered to be the peak period of abundance for many of the Tawny Owls’ main prey items – mice and voles. The Wood Mouse, for example, is capable of producing litters of four to seven young in successive pregnancies from March to October, leading mammal expert Stephen Harris to estimate that a pre-breeding population of around 38,000,000 could easily rise to about 114,000,000 by autumn. This super-abundance of prey should therefore make it straightforward for even the most inexperienced of young Tawny Owls to catch enough to sustain life while honing their technique. Second, as the adults are still actively moulting in early September, they will not feel the need to put as much energy into fiercely guarding their territories as they would later in the year, meaning any young trespassing Tawnies could temporarily be given more latitude than might normally be expected from such a territorial bird.
Crucial to any Kingfisher’s survival through to the following breeding season will be the maintenance of a territory in which the sitting tenant has exclusive fishing rights. Now should be the time when many of these territories are actively being secured, with many males taking possession of exactly the same stretch of river they will have held with their mate during the summer. Unceremoniously booted out, the frequently socially subordinate females have little choice other than to hold a piece of river-front that abuts their old territory, or if this is not possible, a stretch of waterside property reasonably close by. In the world of Kingfisher politics, however, adult females should still be above juveniles in the pecking order, with any youngsters making it through to September forced to take whatever half-decent habitat they can hold without being chased away.
The famous ornithologist and Robin expert David Lack, in his wonderful monograph The Life of the Robin wrote: ‘From September onwards till May, the woodlands, parks, gardens and hedgerows of England are parcelled out into a great series of small-holdings, each owned by an individual or by a pair of robins.’ Finishing their moult before the adults, those Robins that hatched earlier in the year will by now be sporting their first red breast and so should already have been practising the fine art of territory acquisition for a few weeks. However, by early September they will suddenly find the competition increases once more as freshly moulted adults also enter the fray. Recently voted the nation’s favourite bird, maybe not as many people would have voted for the Robin if they had been made more aware of this bird’s huge propensity for violence!
When not feeding or sleeping, Lack believed a large proportion of a Robin’s life is taken up with either singing or fighting. After an uncertain couple of weeks while becoming accustomed to the plumage which puts them at least visually on a level playing field with the adults, the juveniles will have suddenly begun limiting both their singing and aggression to one particular area from which all other Robins will be excluded. To combat the adults’ experience, the juveniles will often resort to violence much more readily, and although physical, any ensuing fight will rarely result in the Robins being seriously hurt. This fighting is not just confined to the males either, with some of the females keen to acquire a territory being equally pugnacious in keeping all other Robins at bay. Less inclined to fight than those youngsters busily proving themselves, the adult Robins more commonly rely on singing and posturing, with their red breast prominent, as the main means of securing and holding a territory. As individual battles become settled, the countryside will slowly but surely be carved up into a whole series of interlocking Robin dominions.
Confining their territorial behaviour to just the period around when their chicks were reared means there should be little need for any aggression amongst the hordes of Blue Tits roaming local woodlands and gardens in their mixed feeding flocks at this time of year. Having started their moult as early as June, the adult Blue Tits in the southern half of Britain should by now be completing their moult, which will see the males looking particularly dapper in their electric blue caps. Retaining the vast majority of their flight feathers, the juvenile Blue Tits will still not begin to resemble their parents until their body moult is completed later in the autumn.
Mid-September
As autumn unfolds Robin activity will move centre stage, as the experienced adults enter the fray to compete with those birds barely four months old for that all-important territory which could mean the difference between life and death. For beauty and complexity the Robin’s song is often considered to play second fiddle to that of the Nightingale’s, but while the latter’s song is confined to just south-east England and only heard for a brief period between mid-April and the first days of June, the Robin not only geographically serenades most of Britain, but is also heard for most of the calendar year too. When attempting to describe the Robin’s song it has been invariably described as ‘a distinctive, cheerful and varied warble’, but scientists studying the song are discovering its structure has a surprising level of complexity.
When singing, the Robin utters its song in a series of short bursts, with each burst lasting little more than two or three seconds before being interspersed with a short pause. A bout of singing can often last a few minutes and may often consist of dozens of different bursts of song, each of which can be further broken down into around four to six phrases that last, on average, around half a second each. The French ornithologist Jean-Claude Brémond, who has specialised in bio-acoustics, documented the Robins he was studying as having a repertoire of more than 1,300 different phrases, which when placed together in a constantly varying sequence were theoretically able to create an astronomical number of permutations. By experimentally manipulating pre-recorded Robin song, Brémond also discovered that the different phrases tended to alternate between high and low pitch, and despite the birds being potentially able to produce endlessly variable songs, it is highly likely that all the local Robins become familiar with the basic characteristics of the songs of all the birds in their immediate neighbourhood. Recognising a neighbour’s voice will mean that a territory-holding Robin need not waste any time and energy on an aggressive response, saving it instead for when a ‘new’ voice is heard. Any unfamiliar song suddenly heard in a familiar place, which may represent a newcomer threatening to upset the status quo, will then instantly trigger a call to arms for those territory owners within earshot.
In addition to the song’s complexity, volume also plays a key part in helping to convey meaning for the Robins at this crucial time of year. Encroaching birds intent on securing a territory will often begin with a cautiously uttered song from low down in the bushes. Only when no opposition is encountered will the newcomer then gradually ratchet up the volume to a level where the song can be belted out from the tree-tops as it attempts to claim the territory for itself. In those territories already occupied, possession frequently seems to be ‘nine-tenths of the law’, meaning the owner is usually able to drive the interloper from the premises. So clearly marked are these Robin territories that if a bird suddenly disappears, the surrounding neighbours will quickly extend their boundaries to fill the vacant lot, so that the ground will often be fully occupied again within just 24 hours. At this stage the plaintive and wistful ‘winter song’ is the warble of choice and will be heard right the way through until they change their tune back to the full-blooded spring song around Christmas. Regardless of the seemingly more laid-back tone to the winter song, it is still primarily concerned with conveying one simple message: ‘back off… this is my territory’.
Now unshackled from the needs of their youngsters, the adult Tawny Owls will be quietly left to their own devices at this time of year. Sporting fresh flight feathers, the adult Tawnies will need until at least early December before their entire annual moult is finally completed. Remaining on territory for the duration, and needing only to find sufficient food for themselves, it will still be a few weeks before the pair begins reasserting possession of their dominion. Most Tawny Owls are considered to be a model of monogamy from
year to year, with a Finnish study revealing that 67% of females only bred with one male during their reproductive lifetimes. It is also likely that a high proportion of the remaining 33% were only forced to find other partners upon the disappearance of their original mate, making it very much a case of ‘till death us do part’ for many Tawny Owl relationships.
For those established and experienced Tawny Owls, it will be highly unlikely that their territorial boundaries will change much after the breeding season, contrasting with the far more fluid state of Kingfishers’ real estate. Antisocial by nature, Kingfishers usually undergo a post-breeding ‘divorce’, leading to their territories sometimes being split as each individual bird settles for a more modest-sized piece of waterfront throughout the winter months. Unsurprisingly for a bird with a typical lifespan of little more than two years, it probably pays not to put too much investment into a partner that may not even see out the winter. So by using mostly a core area within their domain, each Kingfisher will hope to spend most of the rest of the year quietly concealed amongst bank-side vegetation, only revealing itself either to feed or to chase away any Kingfishers caught trespassing.
With any semblance of territoriality dropped when their young fledged, adult Blue Tits, along with the small percentage of juveniles still alive, will by now be roaming the countryside for food in their mixed species flocks, a practice that will last right the way through until early spring the following year.
