Nightingales in November (28 page)

While needing to be in the best possible condition to produce her eggs, some females must be careful not to delay the breeding process any more than is absolutely necessary, as late arrival to the party may have already resulted in them missing opportunities to parasitise the first clutches of resident breeding birds such as Dunnocks, Robins, Meadow Pipits and Pied Wagtails. However, for those Cuckoos that have evolved to specifically victimise Reed Warblers, the need to lay quickly
may be less of an issue, as Reed Warblers, like the Cuckoos, are summer visitors, meaning they will invariably be laying their first clutch later than the resident species.

Once the female Cuckoo's initial assessment of the state of the surrounding host nests has been completed, she will then be in a position to succumb to the male's overtures. Picking up on this sudden interest, the male will respond by singing excitedly, while displaying with a bowed posture, his wings drooped and his tail held, half-erect and fanned, to expose the white tips and notches. He may also rotate his body and swivel the fanned tail, as the female quietly watches – no doubt assessing his calibre. Astonishingly for a bird that doesn't make a nest, the male will often fly down and even offer her a piece of grass, leaf or twig, but courtship feeding is only believed to occur very occasionally. After the relationship is consummated, the female's next job is to continue her watching brief, as she quietly sits in any bushes or trees that afford discreet views of any host nests she may have already earmarked for an egg.

The fact that each female Cuckoo specialises on a certain host species was first discovered by the pioneering work of Edgar Chance on a Worcestershire common between 1918 and 1925. Chance noted that each Cuckoo egg tended to look remarkably similar to those of its chosen host species, and only ever appeared during the host's laying period and, crucially, before the completed clutch meant incubation had already begun. As each host is deemed suitable for parasitism for such a small window of time, consisting of no more than three or four days, Chance realised that the female Cuckoo must watch her victims very closely in order to get her timings right. He subsequently discovered that the eggs are laid into different host nests at two-day intervals, with the crime always perpetrated in the afternoon or early evening. This interval not only gives the female Cuckoo plenty of time to form another egg but also to locate her next nest, enabling the egg to be quickly introduced at the precise moment of her
choosing, when the parent hosts are least likely to be present at the nest. Ideally the Cuckoo will try to lay into those nests containing only one or two eggs, to not only minimise the chance of her own egg being rejected by the host, but also to ensure that her chick hatches as early as possible, in turn making the Cuckoo chick's job of ejecting the host's own eggs or chicks much easier.

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.