by Mike Dilger
Fed on a constant stream of fish, the Puffling will have grown considerably since it hatched around a month ago and will also have managed to shed much of its down to reveal a sleek plumage not dissimilar to its parents. Its upper surface should by now be a matt black, with a clean white underside, and charcoal-coloured cheeks topped off by a thin, dark bill. It will also have upped its exercise regime in preparation for its life at sea, as countless hours will now be devoted to preening, scratching and flapping. When close to fledging the Pufflings will suddenly begin venturing to the burrow’s entrance in the evening to exercise their wings and learn the visual cues they will need if and when they return as adults. On these brief forays which will take them to the very threshold of the big, wide world they need to be incredibly wary of any lurking predators keen for an easy, defenceless meal, and so look almost nervous before disappearing back down below to the sanctuary of the burrow.
It’s not just the Pufflings that need to be careful, as the adults returning with food also risk being attacked by other seabirds, which either specialise in stealing food, or killing and eating the Puffins themselves. Great Black-backed Gulls and Great Skuas (or Bonxies), for example, are easily capable of overpowering and killing any Puffin they can catch. When out at sea the Puffins are relatively safe as they’re able to escape most dangers by diving below the surface, but returning to the colony presents a much higher risk. While Bonxies use their agile nature to catch Puffins in mid-air, most gulls’ techniques seem to consist of little more than catching them unaware as they enter or leave their burrows. At some seabird colonies, the local breeding pair of Peregrine Falcons may also be partial to a Puffin or two when the opportunity arises. The commonest thieves of the food being carried back by the Puffins to feed their chicks tend to be Arctic Skuas, Herring Gulls and Lesser Black-backed Gulls, but at many of the northern colonies it is the Arctic Skua that has kleptoparasitism down to a fine art. Being sleek and streamlined, with long pointed wings and a lightweight body, the Arctic Skua has become perfectly evolved for chasing fish-laden Puffins. Able to roll, turn and dive at great speed, the skuas can change both their height in a split second, and direction on a sixpence, as they harass any returning Puffins into dropping their load. Once spilt, the ill-gotten gains are then acrobatically caught before either being lost in the water below or intercepted by less manoeuvrable predators keen for an easy meal.
The best way for the Puffins to reduce this risk of attack is to join forces with other fish-carrying birds. Linking up to form aerial flocks out at sea, the final assault on to land can then be made in the safety of numbers. Puffin wheels can also be deployed in an attempt to confuse any predators from fastening on to any one target from amongst the swirling flock, thus helping the Puffins to get to and from the burrows in a safe and highly synchronised manner. From studies carried out at different puffinries the amount of food lost to skuas and gulls is rarely disastrous. For example, on the island of Foula, off Shetland, fewer than 1% of the Puffins were chased, with only one in five forced to drop their fish, while on the Isle of May, off the east coast of Scotland, 5% of adults lost their food to gulls. Irrespective of the levels of theft, providing there are healthy stocks of Sandeels, the adult Puffins should be able to ride the occasional loss without their chick going unduly hungry.
Back at the Peregrine’s nest site, the parents will be doing their level best to ensure their adolescent young are kept well fed while learning the necessary skills to fend for themselves later in the year. The young will have been conducting mock attacks on other bird species flying past the nest site for at least a few weeks, and at some point these start to get serious as the juveniles attempt to make a kill. If their targets are skilful flyers, such as pigeons, the young Peregrines may well be repeatedly unsuccessful, but at some point they will strike it lucky by both catching and dispatching their very first meal.
Having done very little apart from avoiding being predated and constantly harassing their parents for food, the Tawny Owl chicks will soon be staring into the abyss of venturing out on their own without the life support system of their parents to keep them fed and safe. With just a few flecks of down still around their faces, the youngsters should be looking pretty similar to their parents by now, and Tawny Owl expert Dave Culley believes any siblings that branched together will at this stage still be spending most of their time in each other’s company. Dave believes, certainly for his suburban Tawny Owls, that slugs form a substantial part of the diet at this time of year and has observed youngsters watching their parents catch them on the ground. Technique duly noted, the juveniles may then proceed to copy the same foraging behaviour as they take their first tentative steps towards self-sufficiency.
Reaching the point of independence somewhat earlier than both Peregrine and Tawny Owl young, as the Swallow juveniles from first broods are now able to feed themselves completely unaided, this seems to precipitate a movement away from the site where they were reared. Still vulnerable to predation from birds such as Hobbies, the young often tend to scatter into the surrounding countryside, doubtless to find good feeding areas and familiarise themselves with any local landmarks, in preparation for a return the following spring. With the young just as likely to go north as south at this stage, this dispersal does seem to be more a case of random wandering than the beginning of a defined migration to South Africa, which isn’t likely to begin in earnest for at least another couple of months.
Back feeding young again, the Kingfisher parents will see their second brood still some way off fledging as fish deliveries begin to rise dramatically to cope with the incessant demands of their young chicks. With the adults alternately brooding the young for at least the first week, the non-sitting bird will be delegated fishing duties, which should be none too onerous given the sheer amount of food on offer at this time of year. Irrespective of the quantity of fish available, they do still need to be caught, however, and relieving a stream, river or pond of its fish is an art that the Kingfisher has certainly mastered like no other in Britain. Their preferred technique usually begins with a period spent quietly perching on a favoured spot anywhere from a metre to three metres above the water as the bird weighs up its options. The Kingfisher is believed to have excellent eyesight and is aided by two fovea, which are highly sensitive areas on the retina where the image appears particularly sharp. Also utilising special elliptical lenses, the bird is not just able to cope with the reflection from the water’s surface, but also refraction – the phenomenon where light is deflected, or bent, when passing between air and water. In the instant before its dive, the bird is thought to instinctively make a three-dimensional calculation of its flight path based on the fish’s position.
The dive itself is remarkably quick, with the Kingfisher able to leave its perch, execute the dive and return all within little more than a second. Using its wings to increase the acceleration of the dive, the tail can provide any micro-adjustments before the bird hits the water, by which time it will have covered its eyes with a special nictitating membrane and have its bill already agape. The Kingfisher is not a deep diver, with most fish caught just below the surface, and if it does manage to grab a fish in its bill it will then quickly power out of the water on beating wings, helped by a positive buoyancy due to air trapped in its feathers. The Kingfisher is certainly not a spear fisher, and so any tiny miscalculation that results in the fish being accidentally impaled on either mandible, will usually end with the prey being dropped into the water and lost. However, any fish snaffled in the textbook manner will be quickly dispatched, as the now perching bird whacks the fish’s head on a branch, or something equally unforgiving close at hand, to immobilise it. In the case of Sticklebacks the Kingfisher must be careful of the spines, and particularly robust species, like Bullheads, may need some serious blunt force trauma to either kill the fish outright or at least render it sufficiently dazed to be swallowed without causing the birds any harm. If the fish is considered sustenance for the parent itself, it
will be quickly swivelled around in the bill before disappearing down the throat head first, but if destined for the brood, the adult will then return straight back to the nest before offering the meal head first to its chick of choice. Repeated and constant immersion in water throughout the day will mean that in addition to the pressure of finding enough food, the adults will also need to spend a large amount of time preening and oiling their feathers from an oil gland on their rump to ensure they don’t become waterlogged. Even for those pairs still rearing young, moulting may already have begun as their flight feathers are replaced in a slow, methodical fashion that will last until at least November, or even later in those cases where the breeding season may have been delayed.
With their young dispersed, those adult Robins that limited their breeding season to just two attempts will be busily keeping out of the public eye as they replace their entire plumage. It’s vital that they’re able to retain the power of flight during this period, and so the feathers will be shed and regrown in a slow, precise and controlled manner. The moult starts in the middle of each wing, with the primary feathers moulting outwards and the secondaries moulting inwards. Usually the first feather to be shed is the innermost primary, with each successive feather then being shed every four or five days, so by the time the fifth primary has been dropped the first two primaries should have completely regrown. Vital for manoeuvrability, the tail feathers are shed from the centre pair outwards and their slow replacement will also span the entire period of the wing moult. Taking around two months, by the time the flight and tail feathers will have been exchanged, the Robin will also have replaced all of its body feathers. Only then, looking immaculate in its fresh plumage, will the Robin be ready to finally show its face again as it prepares to commence battle for the all-important winter territory.
The mass feather replacement that is the annual moult won’t just be restricted to Robins at this time, as Blue Tits, Lapwings and Nightingales will also be busily shedding and regrowing feathers in preparation for either a winter spent in Britain or a more benign climate elsewhere. As the adult Blue Tits slowly continue their moult, their young will also begin to replace the hastily grown juvenile feathers for a set that will allow them to survive their first winter and last until their first breeding season. For these immature birds the most important feathers to replace will be those around the head and body, which will not just ensure better insulation but enable them to play a full and vigorous part in the mating game the following spring. This post-juvenile moult means that young Blue Tits will not actually replace their flight and tail feathers until completing a full annual moult following their first breeding season, resulting in them only becoming indistinguishable from fully adult Blue Tits at the grand old age of 17 months.
Also keen to retain the power of flight during their moult, the annual replacement of feathers will not prevent a large number of continental Lapwings from reaching Britain throughout July and August. Arriving first on the east coast, these Lapwings which will have summered on the continent will probably just slowly melt into the flocks of British-breeding Lapwings already roving the countryside. The origin of these Lapwings may vary from eastern European birds, which commonly undertake a post-breeding westerly or north-westerly movement to reach Britain, to those dispersing south-west from breeding grounds in Scandinavia.
By contrast, no such advance movement will be seen from those Nightingales that successfully bred in Britain earlier in the summer as their rapid moult will see them quietly feeding away as they attempt to take on sufficient fuel to power the quick growth of their new feathers before their flight to west Africa. Like the Blue Tits, the juvenile Nightingales will also at this stage be undergoing a partial moult of primarily their body feathers and some of the coverts (the feathers covering the main flight feathers) but their primaries will not be replaced until this time next year.
By the middle of July, data collected by the BTO suggests that the male Cuckoos will have already made their choice as to the migratory route they will take into Africa, with the birds seemingly split between those Cuckoos preferring the Iberian route and those deciding to travel via Italy. Chris the Cuckoo is currently the only bird to have successfully carried a fully functioning transmitter for four years until his demise in the summer of 2015 and, interestingly, was a bird that always chose the Italian route down to Africa. It seems certain that Chris, and possibly many of the other Cuckoos too, tend to be site-faithful to a few tried and tested locations during their migratory route and undoubtedly for Chris the most important stopover in southern Europe was the huge Po Valley in northern Italy. Travelling over 600km from its source in the Cottian Alps to its mouth in the Adriatic Sea, the River Po is the longest in Italy and surrounded by an expansive, fertile flood plain, which has now largely been converted to agriculture. The delta on the Adriatic coast is considered particularly important for migratory birds with the Po Delta Regional Park designated as a World Heritage Site in 1999. Consisting of wetlands, forest, dunes and salt pans, this site must obviously be the perfect place for a British-breeding Cuckoo to spend time fattening up before traversing both the Mediterranean and the Sahara Desert in one enormous leap.
With their biological parents ready to exchange Europe for Africa, the young Cuckoos should still be feeding up in Britain prior to their own departure. After fledging there appears to be a period where the young Cuckoos will leave the location where they were reared to spread out in any direction. This seemingly random movement mostly tends to occur over a short distance, and despite British juvenile Cuckoos having been recorded as far away as Denmark and Germany, this ‘wanderlust’ shouldn’t be confused with their proper migration to Africa, which will still not be conducted for a couple of months. In many ways the young Cuckoos’ journey is even more remarkable than that of their errant parents, as they will not have been able to either learn the route from older, more experienced birds or orientate themselves with the help of familiar features in the countryside. The only conclusion to draw is that the young must follow some kind of genetically hard-wired satellite navigation system, which not only specifies both direction and distance but can also be re-calibrated for variable weather conditions or any obstacles encountered along the way. Irrespective of how this feat is achieved, their piloting skills across thousands of kilometres of utterly alien territory remains one of the great feats of the natural world!
Late July
After six weeks spent underground being waited on ‘wing and foot’ by its parents, the young Puffling should by now be finally ready to leave the confines of the burrow to make its bid for freedom. Weighing in at around 35 to 40g when hatching, the Puffling will have reached between 250 and 350g by week five, before this final week sees the bird frequently losing a little weight. This ‘slimming’ programme comes about as a result of a rapid increase in exercise from the constant flapping of its wings and also a decrease in the amount of food brought in by the parents. This crucial weight reduction will primarily ensure the young Puffin is not too obese to ‘lift off’ at the defining moment it decides to exchange the land for the sea. Despite losing around 10% of its body weight during this time, the Puffling will still have retained more than enough reserves to see it through those first few critical days out at sea while honing its foraging skills.
With so many avian predators keen to make a meal out of a naive young Puffling, the youngsters will only ever leave for the surrounding sea under the cover of darkness. Although the fledging of the youngsters across a large colony can often be spread over a few weeks, on a good night hundreds will often leave the colony within a few hours. Moving to the burrow entrance, the Puffling will often linger at the entrance to get its bearings before a last minute preen and a fluffing-up of its feathers then sees it take to the air for the first time. A good sense of direction is vital as the Puffling attempts the most important short flight it will ever make, often only staying airborne just long enough to splash down in the comparative safety of the water, no m
ore than a few hundred metres from where it was reared. Having successfully navigated away from the puffinry and any chick-hunting gulls still patrolling the burrows on a late shift, the young Puffin will take to the sea just like a duck to water. Able to swim and dive instantly and keen to capitalise on such a confident start, it will then set about distancing itself from all the predators circling the colony to reach the safer waters further offshore. Such is the youngster’s eagerness to leave its birthplace behind, by daybreak it could have already paddled several miles out to sea, perhaps even linking up with other recently fledged Pufflings or any adult birds loafing around at the surface in preparation for their post-breeding moult. The parents are thought to play no active part in encouraging the young from the burrows, to the extent that some adults may even briefly continue to bring back food to an empty burrow, seemingly unaware that their chick has already flown the coop. With their chicks having fledged there will then be little incentive for the adults to linger any longer than necessary, and a rapid desertion of the colony will quickly ensue, leaving the puffinry pretty much devoid of life by the end of the month.
