by Mike Dilger
By early March most Bewick’s Swans will have left Britain for the near continent on the first leg of their epic spring migration. Flying at speeds of between 46 and 70km per hour, depending on the prevailing weather conditions, they are not thought to fly at particularly high altitudes when migrating. It is also assumed that individual birds or family parties may well use the same staging sites each year where possible, with several locations being incredibly important for refuelling along the way. It has been calculated from energetic studies that large birds like Bewick’s Swans may only be able to fly an estimated 1,500km before needing to refuel for the next stage of their journey. Because the breeding sites are 3,000 to 3,500km away, the swans are thought to make at least a couple of stops during spring migration, and possibly even more if they encounter severe weather conditions along the way, or the adults are still accompanied by their offspring.
Satellite tracking of Bewick’s Swans has recently been initiated by scientists at the WWT. Eighteen swans were caught between 2012 and 2014 at Slimbridge and the Ouse Washes to have transmitters attached in the form of collars around their necks. Already the data the swans are sending back to the team is revelatory, proving that upon leaving Britain, the majority of tagged birds immediately relocate to Denmark. This research has also revealed that a proportion of these tagged birds (and therefore presumably a proportion of the population), will then continue either south and inland, into Germany, or further east into Poland. It’s thought the birds staying in Denmark may well be feeding in agricultural fields, such as maize stubble, in contrast to the birds visiting Germany that are feeding in wetlands, swans in Poland which have been seen feeding around fish ponds.
Unfortunately there isn’t the same level of detailed knowledge about the movement of Waxwings, but in a good Waxwing winter, both the number of birds and flocks will by now have begun to reduce as birds commence crossing back over the North Sea en route to their breeding grounds in northern Scandinavia and the Russian Federation. With spring arriving late in the boreal forests, it is reasonable to suggest that the Waxwings may well cover the 2,000km return journey at a leisurely pace, feeding along the way. Even in winters with relatively few Waxwings visiting Britain, it is still highly likely that early March will see a scattering of Waxwing records, principally along our eastern seaboard.
Of our four summer visitors, the species undoubtedly closest to its breeding grounds in early March will be the Puffin. Arrival dates tend to vary widely from year to year at the same breeding location and also between different colonies, but if each of the major British breeding sites is represented as the hub of a bicycle wheel, then the freshly-moulted adult Puffins will currently be arrowing in, like the wheel’s spokes, from all directions. It is highly likely that the Puffins will also be pausing for regular feeding bouts along the way, and having spent the winter probably feeding alone, will undoubtedly have begun to meet other Puffins returning to the same colony. These encounters out at sea after a long winter of solitude should to some extent prepare them for what will be a very intense social experience ahead.
The Nightingale has a shorter distance to cover between its wintering grounds and breeding site than either the Cuckoo or Swallow, so it’s perhaps no surprise that they will be the last birds to leave their final wintering destination. So, come early March they will still not have embarked on the first leg of their 5,000km journey, which will ultimately see them arriving in south-east England in mid-April. Capable of covering a huge distance in their first long hop, British Nightingales will currently be busily laying down fat stores, only too aware that running out of reserves while circumventing the Sahara Desert could be a death sentence for a bird weighing little more than 20g.
Finally deciding that they can’t delay any longer, early March will see our British-breeding Cuckoos at last leaving the Congo region. Data from the BTO’s work tracking Cuckoos by satellite seems to indicate that come early March most tagged birds will start heading north. What factors make them suddenly up sticks and leave behind the sanctuary of their wintering quarters is anyone’s guess, as day length and temperature don’t vary much throughout the year close to the Equator. The cues, however, may include changes in rainfall patterns, which will have a knock-on effect on the prey they’ve been consuming. Leaving the massive Congo forests behind, the general trend sees the Cuckoos pitching up in a wide belt of land consisting of mostly woodland savanna between the Central African Republic and Cameroon. After little more than a few days’ rest, the majority of tagged Cuckoos will then quickly move west through Nigeria, Togo and Benin as they head towards Ghana.
In contrast to the Cuckoo’s long hops with rests for feeding up in between, the Swallows will be continuing their migratory routine of travelling anywhere between 200 and 300km during daylight hours, before then finding a safe spot to roost each night. Working their way steadily north, early March may well see the Swallows approaching the Congo forests that the Cuckoos have only just left. It’s thought that the Swallows may well take a more westerly route than where the Cuckoos overwintered, as continuous forest cover is probably a more difficult habitat for them to feed over than the lowland wetlands and farmland found closer to the coast. As mid-March arrives many British-bound Swallows will be steaming across the Equator and arriving in the unattractively nicknamed ‘armpit of Africa’ as they cut the corner of the Gulf of Guinea into Cameroon and Nigeria.
One site where over a million Swallows bed down for the night on their journeys both north in the spring and south in the autumn is close to the village of Ebok-Boje, of the Cross River forest region in south-eastern Nigeria. Roosting on hill slopes covered in three-metre-high elephant grass, huge numbers descend at dusk, only to leave at sunrise the following morning. This roost was unknown to the outside world until 1987, and quickly made the headlines as local communities were thought to be regularly trapping and eating as many as 200,000 birds each year. Since this discovery, considerable work has been put in by conservation agencies keen to initially reduce and ultimately prevent the industrial slaughter of the Swallows roosting here. Any Swallows escaping the liming sticks of Ebok-Boje will continue their journey north only too aware that an even bigger potential death trap, the Sahara Desert, will soon be looming very large on their horizon.
Mid-March
After spectacular aerial displays, a whole array of ritualised courtship and a fair amount of copulation, mid-March will see British Peregrines begin to start laying. The famous naturalist Derek Ratcliffe, in his peerless monograph The Peregrine Falcon in 1993, wrote that the earliest date he could find in the literature relating to when Peregrines laid their first egg was 23 March. However, the BTO has suggested that Peregrines are now laying on average nine days earlier than when Ratcliffe carried out his research. Ratcliffe also scarcely mentioned urban-nesting Peregrines in his book, as this is a phenomenon that has only been widely observed in Britain over the last 15 years. It now seems that the ‘heat island effect’ commonly found in towns and cities is the main reason why populations of Peregrines in urban locations may well be breeding earlier than on the cold Cumbrian fells where Ratcliffe watched his falcons. Suffice to say, there will of course be variation between different pairs and different years, with the temperature in spring thought to be the key factor in dictating when Peregrines begin nesting.
In contrast to many birds, the Peregrine’s nest is always a relatively simple affair, consisting of little more than a shallow depression with a few pellets and feathers drawn together. With the precise nesting location key to the success of the birds, ‘Peregrine boxes’ on churches and other high buildings have proved spectacularly successful in cities such as Bath, Norwich and Chichester. Here the box often consists of little more than an open-sided rectangle, with a roof to offer shelter from the worst of the rain and pea gravel as a substrate on which to nest, with clever placement ensuring that a sudden gust of wind won’t blow the precious clutch either off a ledge or into a gutter.
The sign t
hat a female may well be just about to begin laying will see her fairly restless early in the morning, prior to the egg being produced. This egg will represent the first in a final clutch of three or four, with as many as five reported by Peregrine ringer Ed Drewitt in Bristol’s Avon Gorge in 2008, 2010 and 2011. The prevailing colour of the eggs is red-brown, with varying degrees of freckling, mottling and blotching, and an unashamedly biased Derek Ratcliffe called them ‘the most handsome laid by any species of bird’. The eggs do, however, develop a ‘shop-soiled’ look during incubation as they become dirtier and splattered with droppings. A clutch of three or four may take a week for the female to lay, with incubation not thought to start until the final egg has been laid. Up to this moment, any development of the embryos inside the eggs will remain in a state of suspended animation until the warmth from the parents kick-starts the development process.
Already a week into incubation, the female Tawny Owl will be approximately a quarter of the way through her vigil, with the only break in monotony occurring when she has to defecate, or her mate brings food to the nest site. Carefully turning the eggs regularly to ensure they are evenly warmed, she is every inch the devoted mother. At this stage, many female Tawny Owls will actively defend their clutch from what they consider to be potential predators, with a number of anecdotal reports of certain individual birds attacking mammalian intruders such as dogs and Foxes encountered too close to the nest sites. In reality, only some will attack, as many sitting females may prefer to sit tight, while others either slip away or even become the model of docility. It must of course have been a female at the aggressive end of the spectrum that caused the famous wildlife photographer Eric Hosking to lose an eye when he was attacked entering a hide close to a Tawny Owl nest in 1937.
The only other animal likely to incur the wrath of an established pair of Kingfishers during the digging stage will be an intruding member of the same species. During this key period any trespasser ‘fishing around’ will be given short shrift, particularly when caught so close to such a valuable commodity as a good nesting bank. In addition to digging, courtship feeding will by now have become a regular feature in the birds’ daily routine. With the Kingfishers still buzzing around their territory, the male will often follow up these high-speed chases with a fishy gift. Offering a recently caught fish with its head pointing out, as opposed to head-first when feeding himself, he will present his gift amid much noise and ceremony. Quivering her wings as she accepts the fish, which in many ways mimics the behaviour of hungry baby birds, she will be helping to ensure she is in the best possible body condition with the time for egg formation rapidly approaching.
Certainly in southern Britain, mid-March should see the Robin pairs putting their initial estrangement behind them and pulling together as the mating process moves to centre stage. Nest building is an activity undertaken purely by the female, and coincides with a rise in her aggression, as she backs up the male in repelling intruders of either sex attempting to disrupt their party. With material gleaned from around the territory, the nest is built mostly of moss on a foundation of leaves, which is then often lined with hair. The location slated for construction is usually on or near the ground and well concealed in any hollow, nook or cranny, such as in amongst climbing plants, tree roots, or piles of logs. Open-fronted nest boxes can also be attractive to Robins provided they’re well concealed. Robins are also well known for nesting in all kinds of unlikely locations, and renowned Robin expert David Lack collected reports of pairs having nested in letterboxes, old boots, coat pockets, under car bonnets and even inside a human skull!
The female is very discreet while constructing the nest and will only build for around four hours each day. At this stage and during laying, the birds are very sensitive to any disturbance and will readily desert the nest if they think it’s been discovered. So unless the birds are particularly accustomed to people, it’s best to stay away from the immediate vicinity of a Robin’s nest until the female has begun incubation. During the nest-building stage the pair may also fleetingly display to one another as a prelude to sex. During this courtship the female will suddenly remain still before lowering her head and causing the body to hunch. The male will then occasionally sway before briefly mounting her. Sex amongst Robins seems to be nothing more than perfunctory and is only performed a few times a day during nest building and egg laying.
With most Robins aiming for two broods, and possibly even a third in good years, it is in their interests to begin the breeding season as soon as the weather permits. However, as Blue Tits will aim for just one large brood in all but the most extraordinary circumstances, timing is everything. With invertebrate prey still relatively scarce for a few weeks yet, the Blue Tits certainly in southern Britain may well be holding off nest building until the end of this month. With spring arriving first in the south-west of Britain, before then proceeding at walking pace across the country in a north-easterly direction, it’s no surprise that northern Blue Tits may well delay their nesting attempts by as much as a month compared to their southern cousins. As with the female Robins, it’s vital that the female Blue Tits remain fit and strong in preparation for the prodigious toll egg laying will exact on their bodies. Begging regularly from her mate at this stage, the female will indicate her desire to be fed by fluffing out her feathers, lowering her head and fluttering her outstretched wings, behaviour that will carry right through until when the chicks hatch.
As the female Blue Tits eat almost enough for two, the last unpaired Lapwing females should now be making their final selection of mate and territory. The females won’t just be admiring the males’ dazzling displays, but will also be running a keen eye over the quality of their real estate. The best territories have features that help camouflage their nest, such as broken or cryptic backgrounds, and are placed well away from trees and field boundaries so as to deter perching predators. Ideal locations will also be sited close to good feeding or chick-rearing areas, such as tilled land or wet areas, and additionally contain some short vegetation or bare ground on which to nest. Once the females have moved into the territory of choice the next step will be to cement their pair bond with courtship displays.
For the Puffins returning to their nesting colonies, renewing acquaintances will be a high priority before they even think of putting a foot on dry land. The first records of Puffins arriving back in spring are always of small numbers of birds on the water close to the colonies. Different colonies tend to receive the Puffins back at slightly different times, but the pattern of events at sites such as Skomer Island, the Farne Islands and St Kilda is always similar. The first birds arriving back will do little apart from float around in small groups facing into the wind and waves, but as numbers steadily build up, and established pairs meet up again after a winter in all probability spent apart, they will renew their wedding vows and pick up from where they left off last August. The most frequent early demonstration of an established pairing is ‘billing’, where the Puffins will rapidly and noisily knock their bills together, with the male invariably being the one to instigate this wooing. It is not until substantial numbers of birds build up on the water that an element of ‘safety in numbers’ will find Puffins comfortable enough to leave the sanctuary of the sea.
Until very recently, the details of not just where Nightingales overwintered in Africa, but also when and from where they left to return to northern Europe, was still largely unknown. However, thanks to the use of tiny geolocators by the BTO, these mysteries are slowly being revealed. The first Nightingale to successfully bring a geolocator back to Britain with meaningful data, imaginatively entitled OAD, revealed the path down to West Africa, but the equipment frustratingly failed around February. This meant that the return journey was still pretty much guesswork until other Nightingales successfully returned to England with fully functioning equipment in subsequent years. Five Nightingales with geolocators attached in Orlestone Forest in Kent in 2012 successfully made it down to Africa and the data from the
recovered tags revealed they all began their return migration the following spring between 11 March and 19 March.
The most remarkable of these five birds was ‘Nightingale 098’, which after leaving Sierra Leone took just three days to travel, in what must have been non-stop flight, all the way to southern Portugal, an astonishing distance of around 3,300km. Flying at a scarcely believable 45km per hour, and so almost certainly aided by a tailwind, the bird is thought to have taken the coastal route, passing through Senegambia, Mauritania, Western Sahara and Morocco, before crossing the Mediterranean into southern Portugal. Migrating along this route means that Nightingales are believed to circumvent the Sahara Desert, arriving in southern Europe just before their fat reserves run critically low – all in all, a pretty impressive feat of both physical endurance and navigational ability!
While our Nightingales are busy leapfrogging their way to southern Europe, mid-March sees most British-breeding Cuckoos resting and feeding up at a diverse range of locations centred around Ghana. A number of the satellite-tagged birds, including ‘Cuckoo Chris’ have at some point dropped in to Digya National Park, situated in the east of the country, but on the west bank of Lake Volta, the largest reservoir in the world. Digya is the second largest national park in Ghana, and situated on a lowland peninsula that mostly consists of transitional habitat between forest and savanna. So having spent the winter possibly feeding alongside gorillas, the Cuckoos will now be fattening up close to elephants as they prepare to negotiate North Africa and the mighty Sahara.