Nightingales in November (31 page)

In the Blue Tit nests of southern Britain, late May should see the nest activity reach fever pitch as the chicks' insatiable appetite increases the demand on their beleaguered parents. As the chicks are less likely to need brooding by now, both mother and father will be press-ganged into working from dawn to dusk to ensure enough food is collected, with a brood of ten chicks estimated to dispose of close to 1,000 caterpillars a day! Feeding at a rate of possibly a visit every 90 seconds will soon see the adults' plumage looking pretty ragged, or effectively like they've just been dragged through a hedge backwards – which in many ways they have! The items and quantity of food brought in to feed the chicks
will vary according to where the nest is sited, with brood sizes in farmland and gardens often being lower than for those pairs nesting in prime deciduous woodland habitat. For any pairs rearing chicks in or close to mature trees, the caterpillars of the Winter Moth and Green Oak Tortrix are thought to provide a substantial component of all the food brought in to the chicks. In some years the sheer number of all the caterpillars munching away in the canopy is so high that the sound of the larvae's frass (or excrement) falling to the ground can almost sound like rain. With each oak tree thought to be capable of holding as many as 100,000 caterpillars, the first flush of foliage can even be completely stripped on some occasions. Once the Winter Moth caterpillar reaches full size on a diet of fresh young leaves, it will then lower itself down on a single gossamer thread to pupate on or below ground. This contrasts with the Green oak Tortrix moth, which always pupates in a rolled-up oak leaf.

In the years when both caterpillars are abundant and the Blue Tits have timed the hatching of their broods to perfection, many of these caterpillars will not make it to the pupal stage, as their development becomes rudely interrupted by being plucked off a leaf and subsequently rammed down a hungry Blue Tit's throat! So important is this brief annual harvest for Blue Tits that in years when numbers of caterpillars are lower, or the birds' timing is a touch out, many chicks will simply starve in the nest. In those broods receiving plenty of food the young will quickly feather up, with the nest quickly beginning to look like it's about to burst at the seams and decidedly unfit for purpose. There will also be plenty of stretching and whirring of wings at this stage as the young Blue Tits dispense with the last of the down and build up their flight muscles. Knowing full well where the entrance (and exit) hole is due to constantly watching the comings and goings of their parents, after just a couple of weeks the chicks won't be able to resist jumping
up for their first views of the world beyond the confines of their nestsite or nest box.

Finally, some 3,500km away from the nearest British Blue Tits ready to fledge, the Bewick's Swans will at last have begun to arrive at their remote Arctic breeding grounds. Until recently, very little was known about the Bewick's Swan's summer haunts, as the Nenets Autonomous Region has only recently opened up to western ornithologists, and even for Russian scientists, the vast, sparsely populated terrain makes visits for any length of time difficult. Those Bewick's Swans overwintering in Britain are, in essence, thought to breed in a broad strip along the Barents Sea coast, anywhere from the Malozemelskaya tundra in the west, right through the Bolshezemelskaya tundra and as far as the Yugorsky Peninsula some 950km further east. This huge expanse of
land entirely confined within the Arctic Circle mostly consists of maritime tundra and low-lying marsh that is riddled with pools and lakes, criss-crossed by river channels and dominated by a mosaic of moss, lichens and sedges.

The known breeding, moulting and pre-migratory sites of Bewick's Swans in the Arctic region of the Russian Federation.

Any offspring reared during previous breeding seasons, and which spent the winter alongside mum and dad, will by now have already dispersed giving the parents the opportunity to breed unencumbered. One crucial factor which strongly determines individual nesting success in this harsh, unforgiving climate will be the age and experience of the birds. As most pair-bonds don't even become established until at least three or four years of age, it's distinctly possible that many pairs will not even attempt to breed for the first time until even older than this. Researcher Eileen Rees from the WWT has made a study of Bewick's Swans on their summering grounds and believes only between 20% and 64% of established pairs will nest each season, with the climate ultimately dictating collective breeding success. In those years when spring arrives later and the summer ends up being colder than average, clutch sizes will additionally tend to be smaller. In fact, upon arrival, a number of pairs may decide an attempt is not even worthwhile and will not even bother holding a territory, but will instead join up with those birds still too young and inexperienced to form gregarious non-breeding flocks on shallow lakes and marshland nearby.

However, those pairs keen for their journey not to have been wasted will suddenly begin actively shunning the company of other swans, as the most experienced pairs return to locations that led to successful breeding attempts in previous years. Invariably they will arrive to find their old territories still covered in snow and ice, but these conditions won't stop them marking out the boundaries and actively defending their reacquired real estate from any swans they perceive to be either trespassing on the ground or using their airspace. Mating is thought to occur close to, or on the breeding grounds, and the displays prior to copulation include subtle ritualised head-dipping, followed by the birds rising out of the
water with their wings extended, while calling vigorously. With so many predators roaming the tundra, their next job of deciding the specific location for the nest will be crucial, as the brief Arctic summer will not afford many second chances to those pairs with either chilled or predated clutches.

Like the Bewick's Swans, the sparsely populated areas where Waxwings nest means the breeding ecology of this species is also little known. In locations with plenty of suitable habitat, there seems to be a colonial element to their breeding, with the distinctive sociability that is normally such a feature of this bird in its winter quarters, not breaking down completely when nesting commences. In studies of captive Waxwings, the male was observed to select the nest location and the few observations of wild birds made suggests they favour old, stunted and lichen-festooned conifers, choosing anywhere from three to 15 metres above the ground to rear their young. As many of the birds will have already paired up before reaching the breeding grounds, the male will waste little time in declaring his territory from a tree-top close to the nest with his simple high-pitched trill. This statement of intent may also serve to encourage the female to cement their bond by joining him for a duet.

Mating is thought to occur both close to and on the breeding grounds, with the male continuing to feed his mate a combination of fruit and insects to ensure she will be in good enough condition to produce her clutch. Built by both the sexes, the female is believed to assume the larger role in nest construction as the base is built up with a cup of thin twigs, before being lined with Reindeer Lichen, moss and fine grasses. The period between when nest-building is finished and incubation is initiated is thought to be the only time when the normally placid males show aggression towards their neighbouring rivals. During this
window any intruder perceived to be interrupting business at will be sent packing by a combination of bill-gaping or snapping, as the incumbent male presses home his advantage without having to resort to physical violence.

For any Cuckoo chick that has successfully evaded detection in its foster parents' nest throughout incubation, violence will quickly become order of the day upon hatching. Weighing in at little more than 3g, the Cuckoo's egg has been carefully sculpted by evolution to mimic both the size and pattern of the chosen host species' eggs as closely as possible. Incubated in amongst the host bird's clutch, the alien chick will also be blessed with a head-start over the rest of its host's brood. Having been laid with a partially developed embryo, means the Cuckoo chick could hatch in a remarkably quick 12 days after its mother's clandestine deposition. Hatching earlier brings considerable advantages to the Cuckoo chick, as the host's own clutch of eggs, or very young chicks, are certainly much easier to eject from the nest than, say, older host chicks, which may have already put on a substantial amount of weight.

The credit for the first detailed description of Cuckoo chicks ejecting host eggs, or young, remarkably goes to Edward Jenner, the celebrated scientist who effectively invented vaccination. Before his seminal work on smallpox, he published a paper on the Cuckoo's nesting habits in 1788, which led directly to his election to the prestigious Royal Society the following year. At the time his assertions were met with widespread disbelief and initially rejected; however, as other naturalists subsequently backed up Jenner's observations he was quickly vindicated. What Jenner first recorded must surely go down as one of the greatest Machiavellian feats in the natural world.