by Mike Dilger
Cuckoo expert Nick Davies from Cambridge University has watched Cuckoos parasitise Reed Warbler nests on a number of occasions: ‘Before laying, the female remains motionless and hidden in a tree, up to 100 metres away from the host nest. Then, after a period of anywhere between 30 minutes and two and a half hours, she glides down to the nest and lands on the rim before bowing into the cup; a few seconds later she lifts her head, holding one of the warbler’s eggs in her bill, and then moves to sit on the nest. Her abdomen moves down as she lays her own egg, then without even a single glance into the nest, she flies off, still carrying the warbler’s egg in her bill. She lands in the bushes 30 metres away, swallows the egg whole and then utters a strange bubbling call as if in triumph.’ Both Nick Davies and Edgar Chance reported that in each case the female usually conducted the whole process of stealing a host egg and then replacing it with one of her own in less than ten seconds.
The total number of eggs the female is able to lay in a season will be limited by the number and state of host nests available, but some Cuckoos are able to maximise the number of eggs they can deposit by manipulating their hosts. By predating any clutches that are at too advanced a stage for parasitism, thereby causing the hosts to re-lay, this should enable her to take advantage of these nests the second time round. By manipulating the Meadow Pipit clutches himself, Edgar Chance observed one female laying an incredible 25 eggs in a single breeding season. However, this was equalled, without human interference, by a female Cuckoo studied by ornithologist Mike Bayliss in Oxfordshire in 1988, who recorded one female working over a population of 36 Reed Warbler nests, resulting in 24 pairs being successfully parasitised, including one poor pair twice! These records aside, it’s thought more likely that the number of nests parasitised by most females will be around eight, with subordinate females at some locations often prevented from laying any more than just a couple of eggs.
Laying her clutch in the far more conventional manner, most female Nightingales should be sitting on a full clutch by the middle of May. Even though the male will occasionally feed his mate while she incubates, the pair are thought to find their own food, with the male using his courtship song to summon her off the nest as and when the coast is clear. However, should the male spot a potential predator, he will also give her a warning whistle to sit tight in the nest. Hoping not to be spotted is her best form of defence, but she will never sacrifice her own well-being just for the sake of a clutch, and so will always slip away at the last moment if she feels in mortal danger herself. The male tends to sing less during the laying period, but will then strike up his song briefly again as his partner begins to sit. Due to the warmer summers in continental Europe, many of the Nightingales are double-brooded, meaning the male will need to hold his territory for much longer, but as English Nightingales are right at the edge of the species’ range, it is almost certain that our birds will only ever rear one brood. One unfortunate knock-on effect of the shorter British breeding season is that with the male’s beautiful song having already fulfilled its purpose it will be heard far less often as the month of June progresses.
As most Puffin burrows are either on islands or at sites that rats have been unable to colonise, such as Bempton Cliffs RSPB Reserve in East Yorkshire, predation of any of the subterranean eggs is considered to be minimal at most puffinries. The reasonably constant temperature underground means the sitting bird shouldn’t need to warm the egg continuously, leaving them free to take short breaks above ground for a preen and a stretch. Changeovers between the parents generally occur in the morning or evening, with the period just before dusk also seemingly the key time when most Puffins socialise above ground with their peers. These ‘socials’ are thought to fulfil an important function within the colony, and are used by each pair to maintain close and regular contact with their neighbours. When both parents are present during this fraternising hour, their agenda will include checking up on the progress of pairs close by and peering down adjacent burrows. As night falls, the slopes will become deserted, as the birds either fly out to roost on the sea or retire underground for a night’s egg-warming.
For those Swallows that have chosen to nest as part of a loose colony, such as favoured sites on dairy farms, it pays to be very wary of your neighbours around nesting time. On the surface, Swallows seem socially monogamous, but in reality male Swallows will, if given the chance, be promiscuous with neighbouring females. In fact so intense is their desire to father as many offspring as possible that some males are even capable of infanticide of a neighbouring brood of chicks if they think it will force the female into being receptive again. Copulating either at the nest, on a nearby roof, or on overhead wires, established pairs of Swallows will mate frequently during the small window that the female is fertile, which generally only lasts from five days before the first egg is laid until the day before the clutch is completed. Any male attempting to mate with a next-door neighbour, known as ‘extra-pair copulation’, will most likely only try this devious strategy once his own mate has laid her own clutch and so past her fertile period. To counter this cuckoldry, many males will guard their females during their fertile period, but in reality are unable to be present by her side the entire time. Of course any male keen to engage in extra-pair copulation will only be successful if the neighbouring female permits this behaviour to happen, and to add an interesting twist, those females that initially chose mates with a short tail will often permit a male with longer tail-streamers to mate with her. In fact most female Swallows seem to find the males with longer tail-streamers more attractive, with the result that well-endowed males are far more likely to father chicks in nests other than their own.
Although many male Swallows won’t have had the opportunity to mate with their neighbours in this way, a study of chick paternity through DNA analysis found that between a third and a half of all broods will contain at least one such extra-pair chick, making it a worthwhile strategy for the long-tailed males to attempt. Females also seem to prefer males that are already paired with mates, so relatively few unmated males will have success when striving to copulate with a female that already has a partner. However, those males initially unable to secure a nest site and a mate may still have one last chance of rearing a brood if they’re able to displace another male. Any unmated male able to drive an incumbent male away will then be free to destroy the vanquished male’s clutch or kill his chicks. Desperate to rear a clutch and ensure her journey all the way from South Africa was worthwhile, the resident female will then have little choice but to mate with the killer and help rear their resultant offspring. To add an extra layer of intrigue into the unprincipled nesting behaviour of the Swallow, some females engage in a process not dissimilar to the Cuckoo, called brood parasitism or ‘egg dumping’. These parasitic females will lay their own eggs in the nests of close neighbours also at the egg-laying stage, and providing the egg hasn’t been placed into a still empty nest (which will cause it to be rejected), the unsuspecting host female will just assume the introduced egg to be one of her own and rear it alongside her own clutch.
Having fed well on the sugar-rich aquatic plants along the Russian Federation’s northern coast, the Bewick’s Swans will leave the sanctuary of the White Sea around the middle of May to fly north-east into the incredibly remote Nenets Autonomous Okrug (or Region). Another of Russia’s federal subjects, despite this vast region being rich in oil and gas, its remote location means these resources are exploited by a population of little more than 40,000, around half of which reside in the provincial capital of Naryan-Mar. Playing host in the summer to a large proportion of the entire Bewick’s Swan breeding population from the European flyway, this region is mostly composed of barren Arctic tundra, with the and adjacent to the Barents Sea being the main area favoured by the swans. As the Bewick’s swans finally reach their destination, their arrival will mean that the breeding season can at last swing into action.
By mid-May, most Waxwings should have arrived at their breeding grounds in
the taiga forests. Breeding in such a remote location has resulted in few studies of Waxwings in the field, so most of the behavioural observations have come from captive birds. It’s presumed that those males already in established pairs will have already initiated courtship prior to their arrival at the breeding sites in order to hit the ground running. The courtship behaviour could never be described as extravagant, and is believed to consist of little more than the male forming a hump posture with his body and rump feathers ruffled, while depressing his tail, raising his crest and hopping around in front of his mate. A responsive female will then also ruffle her feathers and quiver her wings in return before allowing him to pass her a food item. This relationship-bonding behaviour is believed to continue right the way through nest building to the point when egg laying begins, and has certainly been observed taking place in northern Scandinavia as late as the middle of June.
For those birds not already paired up, it’s assumed that the largely sociable lifestyle of the Waxwing means that males and females should find mates with relative ease, rendering the prolonged and noisy courtship of many other bird species redundant. This is a smart move in a location such as the taiga, where the breeding season will always be far more truncated than at temperate latitudes like Britain. Certainly in the closely related, and more intensively studied, Cedar Waxwing from North America, it has been revealed that females select partners according to the number and state of the red waxy tips on their secondary feathers, which ringers now know to be an indicator of age and experience. Not all the Waxwings travelling north will breed, of course, and nomadic flocks comprising a mix of first-year and unpaired birds, can also be seen on the breeding grounds. These inexperienced and unlucky birds will use their time to learn both the lie of the land, and the tricks which should enable them to have more success on their return the following year.
Back in Britain, the speckled Robin juveniles that managed to negotiate their first traumatic week out of the nest will still need help finding enough food for another fortnight before they can consider themselves truly independent of their parents. With spring now well and truly under way, food should certainly be far easier to find, as the youngsters learn to take advantage of the exponential increase in invertebrates that the longer and warmer days will bring. When foraging, the Robin’s favoured technique is to take food from the ground while searching through the soil and leaf litter, but they will also use any lower branches of trees or bushes as observation perches, before flying down when any movement from a tasty morsel is detected. Their search image will encompass a wide and varied diet of caterpillars, beetles, flies, ants, spiders, centipedes, earthworms, slugs and snails, all of which will be bolstered by seeds and fruit as invertebrate abundance declines later in the year. As the chicks steadily become more independent, their mother should by now already be focused on clutch number two, and the completion of her second rest will see her wasting no time in proceeding to lay her second batch.
Those Lapwing chicks managing to avoid the jaws of a Stoat, the talons of a Buzzard or the beak of a Carrion Crow will see their growth quickly accelerate as they approach the grand old age of a couple of weeks. Upon hatching, their wings were little more than articulated stumps, but flight feathers will now be emerging through the down as the young go about their feeding business under the watchful eyes of their parents. Lapwing young hatch with relatively large eyes and a well-developed head, bill and legs, meaning they are well equipped to both spot and quickly dispatch a whole variety of beetles, fly larvae, earthworms, caterpillars and spiders. However, it won’t be until early June that they will be ready to fledge, and a further week after that until they would be able to stand any chance of survival without their parents’ constant support.
Despite flying well just two weeks after leaving their nesthole, the Tawny Owl youngsters, unlike the more precocious Lapwing chicks, will still be entirely dependent on their parents for all their dietary needs right the way though to at least midsummer. How many chicks successfully fledge will depend on a variety of factors: the quality of the territory, their parents’ level of experience and perhaps most importantly whether it happens to be a good or bad vole year. An extended study in Scotland found that in years with plenty of prey abundance an average Tawny Owl nest would fledge 2.6 young, in contrast to only 0.2 young per nest in years when voles were thin on the ground. For those Tawny Owl pairs nesting in urban environments, and more heavily reliant on bird prey, there is thought to be less of a cyclical element to the number of young successfully fledging each year, as few bird species exhibit such pronounced fluctuations in their population levels when compared to small mammals. Irrespective of how many chicks successfully fledge, those young that have already beaten the odds by surviving well into May will at this stage be relentlessly hectoring their parents for food, as mum and dad work hard to ensure their young are sufficiently well fed.
By the time the Peregrine chicks are around three weeks old, they will rarely be brooded by their mother unless the weather suddenly takes a severe turn for the worse. They will also have grown considerably in the short space of time since hatching, and even at this relatively early stage, the larger female chicks can often be differentiated from the smaller, lighter males. Their contour feathers (the outermost feathers providing the colour and shape of any bird), including those belonging to the wings and tail, will also be growing rapidly and should by now be visible as they emerge from the chicks’ second coat of down. Starting off looking just like light-blue pins, as the feathers emerge from the sheaths they will uncurl and straighten, with the nestlings’ heads often showing the characteristic juvenile markings quite early in thier development.
When not sleeping, the chicks will be far more active, with wing-flapping, stretching and preening all part of their daily routine as they begin preparations for life away from the ledge. At around four weeks old, the chicks will also have found their voice, and can be heard either alarm calling with their parents, or making a racket particularly when food arrives. By the time the youngsters reach a month old the female should be back actively hunting again in an attempt to keep up with their insatiable demands, and the arrival of either adult is often the cue for pandemonium to break out as the ravenous nestlings crowd around in an attempt to grab any prey brought in. Whichever chick is successful in snatching the spoils will then often use its wings to ‘mantle’ or hood the item, primeval behaviour that has evolved to enable the youngster to eat without interruption. Sometimes a tug-of-war over a prey item can ensue, but once possession has been decided, the victorious nestling is usually left to eat its ill-gotten gains in peace. The number of feeds can vary between around six to eight a day during this demanding period, with food brought in any time from before dawn to after dusk. During this time of plenty, the male may also begin to cache food whenever there is a surplus, as he prepares for the leaner times that will surely lie ahead.
Growing quickly on a constant stream of fish, the Kingfishers’ nesting chamber by now will not just reek of partly decomposed and regurgitated meals but also look a sight, as the discarded sheaths are added to the overall mess. The youngsters, when not cadging fish from their parents, will spend a lot of time preening their newly acquired feathers, and where room permits, may also be stretching and flapping their wings to build up the all-important flight muscles. As fledging approaches, the nest can often become a much quieter place as the parents slowly reduce the frequency of feeds in order to encourage the chicks out. As the middle of May slips by, the bright orange and blue youngsters will intuitively and suddenly know it’s time to leave as they trudge down the tunnel and into the light for the first time.
Due to the delayed arrival of spring further north, Scottish Blue Tits may well only just be beginning incubation, as their southern cousins see their clutches starting to hatch. Immediately upon emergence of each chick the female will step into pick up any discarded eggshell, before then jettisoning it some distance away from the nest. The entire clutch can
take anything from a few hours to a whole day to hatch, and as the tiny, blind chicks are susceptible to chilling at this stage they will need to be initially brooded for large parts of the day and all night. The clutch hatching is also the trigger that instantly sees the male pressed into action as he undertakes the first of many foraging trips for his brood. Initially tiny morsels like aphids, small caterpillars and spiders are brought back, but the young will quickly be in a position to start taking caterpillars, the staple diet of any Blue Tit chick. To keep up with the increasing demands of their ravenous youngsters, the number of visits to the nest by the male, and in good weather by his partner, will rise exponentially as the surrounding foliage is scoured for caterpillars. These prey items are then brought back to a sea of hungry gapes at the nest, with any faecal sacs taken away afterwards as the parents waste no time in departing on yet another foraging mission. If the adults have timed their broods correctly, they will be able to take advantage of the sudden huge flush of caterpillars that late spring brings, and with so much natural food on offer in the countryside, garden bird tables will often become surprisingly quiet when compared to winter and early spring. While sunflower hearts or peanuts will undoubtedly provide sufficient energy to help keep the parents busy from dawn to dusk, they’re not considered the ideal foodstuffs for the growing chicks, which given the choice will plump for a protein-rich caterpillar every time.
