by Mike Dilger
Both the spring and autumn migratory routes and the overwintering destinations of British-breeding Cuckoos in Africa.
Further north our intrepid Swallows will have just crossed the semi-arid habitat of the Sahel, a region that straddles the entire continent in a broad band between Senegal in the east and Ethiopia in the west. So by mid-March they should be girding their loins in preparation for taking on the largest hot desert in the world. Extending over nine million square kilometres, and covering a quarter of the entire African continent, the huge landforms of the Sahara Desert are shaped by both the wind and rainfall from a more fertile era. Consisting of sand dunes, sand seas, stone plateaus, dry valleys, dry lakes and salt flats, the Sahara Desert has to be one of the most inhospitable places on Earth. It is also believed to he too much of a detour for the Swallows to follow the return route of the more westerly-wintering Nightingales, meaning they will have no choice other than to engage the desert head on if they’re to reach the insect-rich summer of northern Europe. Having fed the whole way since leaving South Africa a month before, it’s highly likely that the lack of vegetation, relentless sun and strong winds will mean that invertebrates over the desert are few and far between. So as the Swallows pass through Mali and Niger and on to the huge desert country of Algeria, they will just have to trust that their limited fat reserves will see them through beyond the sand to the rich coastal crescent of North Africa.
While the Sahara Desert and the Mediterranean Sea are reached much earlier during the southbound migration in autumn, the return spring journey is a different story. Travelling north, the two immovable obstacles of sand and sea will come much later in the journey, and only after the birds have already flown several thousand kilometres across Africa. Doubtless the passage across this hugely inhospitable terrain must be physically very stressful, with innumerable Swallows perishing in the sand before the stronger and more experienced birds finally straggle into the coastal feeding areas of Algeria, Tunisia and Morocco.
There are few recorded sightings of Swallows in the Sahara itself and the 1,500km distance across the desert expanse will surely be the most gruelling five or six days of their year. Possibly flying for up to 14 or 16 hours a day, the Swallows must presumably roost wherever they are able, before the breeding imperative drives them on at dawn the following day.
Of the total of 35 Waxwings caught and ringed while overwintering in Britain only to then be subsequently recovered abroad, 27 were found across Denmark, Norway, Sweden and Finland. The fact that these birds were found in a diverse array of locations across Norway, Sweden and Finland is perhaps no surprise, as these will almost certainly be records of birds either close to, or at their breeding grounds, but the six from Denmark is in many ways more revealing. Waxwing as a species doesn’t breed in Denmark, so this would suggest that any British-ringed birds observed must be en route, thereby revealing the main route that returning birds will take on their way to northern Scandinavia and the Russia Federation. With many Waxwings already having left it’s perhaps surprising, even in a poor year, how a number will still be happily to feeding in Britain late into April. These late leavers must then presumably make a much quicker return to their breeding grounds than those that left earlier in the year.
From now on, Britain should be a Bewick’s free zone until the first birds begin returning in the autumn. Having reached Denmark, Germany, Poland and southern Sweden in one hop it seems that many of our Bewick’s are in no hurry to reach the Russian maritime tundra, which will certainly still be frozen over at this time of year. With seemingly plenty of food still available in northern Europe, satellite tracking data from the WWT indicate that some of the Bewick’s Swans will not have moved far from their first arrival point. Other birds, however, will have begun to slowly spread out along the Baltic coast, passing through Poland, Lithuania and Latvia on their way to internationally important stopover locations in Estonia.
Late March
Finally emerging from the Sahara, only to then hit the Atlas Mountains, extending some 2,500km in a south-westerly to north-easterly direction through Morocco, Algeria and Tunisia, conditions for the Swallows should suddenly begin improving as they catch sight of the Mediterranean Sea way off in the distance. As the birds drop down towards the coast, the Aleppo Pines and Evergreen Oaks of the mountain forests will soon give way to Mediterranean-type scrub, called maquis, and a welcome change of climate. For those Swallows that haven’t either perished in dust storms, or fallen from the sky due to exhaustion or a lack of water, the cooler temperatures and higher rainfall encountered all along Africa’s north coast will not have come a moment too soon.
The believed spring and autumn migratory routes of Swallows between their breeding grounds in Britain and north Africa.
Exhausted from their efforts, and with many Swallows having lost a third of their body weight, they will need to feed up quickly before then crossing the Mediterranean Sea and arriving in Europe along a broad front, anywhere from the eastern coast of Spain to western Italian shores. Finally back over dry land, for those birds that took the more westerly route, sites such as the Ebro Delta, situated between Valencia and Barcelona, will represent an important refuelling station. Quickly moving on towards the Pyrenees, these Swallows will then begin streaming across the autonomous community of Aragon in the north-east of Spain. With Aragon’s northern boundary forming the border with France, and positioned in the middle of the mountain chain, the Aragonese say that ‘the Swallow is the bird that melts the snow’, as the birds work their way east to west, through mountain valleys flushed with melt water. By the time they reach the Bay of Biscay and the French coast, the Swallows should be spurred on in the knowledge that they’re on the home straight.
Able to help themselves to ‘in-flight food’ the Swallows are in the fortunate position of being able to press on, but any Nightingale having passed through West Africa and over the Mediterranean in one non-stop flight will need to feed quickly upon reaching land, before its fat reserves run critically low. The dry, uncultivated land in southern Portugal and Spain, which consists of a mosaic of scrub and wooded groves of Cork and Holm Oak, is thought to be the main pit stop where most of our Nightingales will then spend a while fattening up before ultimately leaving for England in mid-April.
The only one of our chosen migrants still overwintering in Africa by this stage, will be the Cuckoo. Satellite telemetry seems to indicate that most British-tagged Cuckoos by the end of March will have worked their way steadily west to reach countries such as the Ivory Coast. Traditionally very heavily forested, particularly in the lowland Guinean forests along the coast, there has been much recent concern about the rapid rate of deforestation in this old French colony, sometimes cited as the highest in the world. Certainly ‘Cuckoo Chris’ has spent two of his three pre-Saharan stopover points in March feeding up in the eastern part of the country. Fortunately the area Chris and the other Cuckoos seem to favour is in and around the forest-savanna mosaic, a belt extending across the centre of the country, and to the north of the most heavily deforested areas. Once the Cuckoos do leave this habitat in early April, they will in all likelihood not touch down again until they arrive in southern Europe. In the meantime, the only question vexing the Cuckoos as they prepare to traverse the huge arid zones further north is which route to plump for when they cross the Sahara Desert.
By late March, most inshore waters around the major colonies will have begun to turn into a Puffin-thronged melee. Emboldened by their numbers, it seems surprising that the Puffins don’t immediately pour on to the breeding colony, but instead appear reluctant to leave the sea. During the first few days back around the colony, the Puffins will use this time to join up in rafts with those birds that have become close neighbours during previous breeding seasons. These ‘clan’ gatherings at sea often tend to become aligned adjacent to the sections of the colony with which they’re most familiar, and small flocks will then quickly coalesce into much larger rafts of possibly several thousand
Puffins as more arrive back. Suddenly amid much excitement, a large number of Puffins will then begin taking off together before heading for land. Flying towards the puffinry, the Puffins will then circle over the area where they intend to breed, before looping back over the sea. This ‘circuit’ is flown a number of times, with the number of birds rapidly increasing all the time until the flock becomes a ring of fast-moving Puffins called a ‘wheel’. The different ‘sub-colonies’ within the puffinry will often have ‘wheels’ in different locations, enabling the birds to check out familiar terrain while in a large, speedy flock.
This important event in the life of the Puffin is much more than just a convenient way to travel from sea to land, as it also provides an ingenious method of checking for predators close to where they intend to nest. It’s also far more difficult for any predators, such as Great Black-backed Gulls, Peregrines or Great Skuas, to pick out just a single bird to target for attack from amongst a rapidly swirling flock. Eventually a few brave Puffins will peel away from the wheel before touching down on terra firma for the first time in over seven months, which in turn gives others confidence to join them on dry land. It’s only when this ‘touchdown’ has occured that the Puffins’ breeding season could be said to have well and truly started.
The two birds with a considerable distance still to cover before they even reach their breeding grounds will be our two winter visitors, Bewick’s Swan and Waxwing. Those Waxwings that have already left Britain will in all likelihood have crossed the North Sea and be currently spread out at still fairly low latitudes in a broad front across Denmark, Norway and Sweden. As they head north-east towards the northern forests surrounding the Arctic Circle, they will certainly be eating on the way. Due to the breeding season at high latitudes often being short, many Waxwings will be keen to hit the ground running the moment the weather ameliorates. This ability to quickly capitalise on conditions should give them sufficient time to successfully raise chicks before the days once again shorten and temperatures plummet.
Thanks to intense field work by researchers from the WWT and recent advances in satellite telemetry, the migration picture is currently much clearer for Bewick’s Swans than for Waxwings. As the month draws to an end, most British Bewick’s Swans will suddenly leave Denmark, Sweden, Poland and Germany to head towards their key spring staging posts – the estuaries and wetlands off the coasts of Estonia and Latvia, most of which should by now be ice-free. Matsalu Bay, and Pärnu just further south, have long been recognised for their importance for migrating Bewick’s Swans, with Matsalu being re-designated as a Ramsar site by the Estonian Government in 1994. These sites were well watched between 1992 and 1994, with Matsalu accounting for approximately 14,500 Bewick’s Swans and a further 7,000 dotted around Pärnu Bay and the Pärnu River’s watershed. When combined, this figure will have formed a very high proportion of all the Bewick’s Swans from the European flyway.
Having been sitting since early March, the embryos inside the eggs should by now be developing quickly providing the female Tawny Owl has been regularly fed by her mate. With her clutch well defended, the only issues that could prejudice the welfare of the clutch at this time is if the Owls have chosen to breed in a year when prey is scarce, or if hunting activity is reduced by prolonged poor weather. In these situations the female may have to break away from incubating to go hunting herself, which could put the eggs at risk of chilling. Dave Culley has found that his resident male Tawny can be incredibly resourceful at this time of year, and with small mammals in lower abundance in early spring, frogs frequently start to form a substantial component of the items brought in to the sitting female.
By the end of March most urban Peregrines should have been sitting on a full clutch for at least a couple of weeks. Unlike the Tawny Owl, both male and female Peregrine will incubate the eggs, although the female will invariably undertake the greater share and additionally cover the night shifts. Producing three or four eggs is an incredible investment in time and energy for the female, and so if the weather does take a turn for the worse, the incubating birds will often sit tight to ensure their precious clutch doesn’t chill. A supreme example of adult Peregrines’ devotion to their eggs occurred with an established pair nesting on Nottingham Trent University’s Newton Building in late March 2013. An unseasonably late snow flurry virtually covered both the open nest box and the female sitting on a clutch of three eggs. Despite being virtually buried until the snow melted, she didn’t abdicate her responsibility and all three chicks successfully hatched at the end of April, a testament to her dedication.
With a territory secured and one or even more females interested, the Lapwing’s breeding season will now be quickly gathering pace in the more southerly breeding sites. Having taken to the air to display the calibre of his site and his qualities as a potential partner, the male will now capitalise on his good early work to further court the female on the ground. The main ground display between the pair centres on ‘nest scraping’. Here, the female squats down, often in the location where she would like the nest scrape to be positioned. The male will then approach her while alternately flashing his orange undertail coverts and white rump. The female responds to this overt display by moving towards him, and bowing steeply as she too displays her bright undertail and rump colours. Moving back into the scrape the female then starts raking the ground while the male flicks any material close by along her flanks, and if suitably impressed she will then invite him to mate with her. Mating directly from flight, the male will need to use his wings to maintain his balance while copulation takes place.
Favoured locations for nest scrapes tend to be poor, stony areas with limited plant growth, which offer both good cryptic camouflage and yet excellent all-round visibility. With the precise spot chosen, both sexes will then enlarge the scrape and proceed to line it with whatever is close to hand. As she becomes broody, the female will then constantly add extra material to the nest as a precursor to laying the first egg in her clutch of four.
Once the nest excavation is complete, the Kingfishers should be in a position to mate. However, the female might not have always read the script and even at this stage can still prove unreceptive to his advances. In contrast to the Lapwings, where courtship seems to be key before mating, the male Kingfisher’s tactic involves bribery. Offering the gift of a fish may well help break the resistance of any females still reluctant to commit. Suitably assuaged, the submitting female will then lie prostrate, quivering her wings and suddenly changing her tune to one of encouragement. Jumping on and flapping for balance, the male will often hold his mate’s crown feathers in the tip of his bill to ensure compliance as they touch cloacas. The act itself often looks quite rough but is usually over in less than ten seconds. Unlike the Lapwings, the Kingfishers don’t collect any material to actively line their nest, but a smelly layer of fish bones and scales will frequently quickly build up to make a cup of sorts as the breeding season develops.
Even though it’s doubtful the male Robin will ever win any awards for ‘most devoted husband’, his generosity does extend to helping feed his mate as her nest building nears completion. Courtship feeding is often initiated by the female uttering a sharp call as the male approaches with food. Lowering her wings and quivering with excitement, her tune then changes to a rapidly repeating note, mimicking the call of a hungry baby bird. By constantly begging from the male in this way she will receive the vital calories necessary for the incredibly demanding task of producing a clutch amounting to two-thirds of her body weight in the space of just a few days.
As spring arrival in Britain varies according to location, and with Blue Tits keen to rear their young at a time of maximum food abundance, the dates when a pair starts nest building can vary enormously according to whether they are Blue Tits from Devon or Dundee. Generally in southern England, Blue Tits will begin construction duties in late March, with the same chore often pushed back by as much as a month in northern Scotland. In addition to this, sudden weather changes su
ch as prolonged wet periods or a warm spell can even produce variation from year to year at the same location. The job of building the nest is always carried out by the female, and so the period when March fades into April should see many female Blue Tits gathering the necessary nest construction material as they start the ball rolling on their one and only breeding attempt of the year.
April
With around six hours more daylight and average daily temperatures at least 5°C higher than the dark, cold days of January, April is the month when the natural world breaks free from the constraints of winter, and attempts to make up for lost time by forging ahead with the business of passing on its genes. As frogs and toads squabble for mating partners, hedgehogs, bats and reptiles will also have fully emerged from hibernation by now. This frenzy of activity also coincides with the buds of familiar trees such oak, Beech and Hawthorn bursting as Bluebells, Wood Anemone and Wild Garlic carpet the woodland floor below. This month will also see the majority of migrant birds pouring back into Britain, which will instantly transform the dawn chorus into a sound sensation as, depending on the habitat, birds from Blackcaps and Bitterns to Woodlarks and Willow Warblers add their voices to this glorious natural symphony. Stealing a march on these fair-weather immigrants, many of our resident birds should by now either have started to lay, or already be incubating clutches as they attempt to precisely time the hatching of their brood to match the exponential increase in food that spring brings.
Early April
Even with early migrants such as Wheatears, Sand Martins and Chiffchaffs already arriving in force by early April, for anyone even remotely interested in wildlife, the first Swallow sighting of the year is always a red-letter day. Having traversed the entire continent of Africa, crossed the Sahara Desert, flown straight over the Mediterranean Sea and travelled through Europe, the final obstacle – the English Channel – should present little problem to these international jet-setters. The first Swallows are usually recorded in south-west England, a mere five to six weeks after they leave South Africa, and as ever larger numbers begin to pour off the sea, they will then steadily fan out in a north to north-easterly direction across Britain. With the first Swallows often not recorded until early May in Scotland, any birds returning to northern breeding sites will be keen to make sure they’re not travelling ahead of spring, which is generally considered to arrive a month later than along England’s south coast. This means Scottish Swallows can afford to take their time as they feed up on the flush of invertebrates further south.