Nightingales in November (53 page)

Having conquered the Sahara Desert as long ago as late July, most British-breeding adult Cuckoos will still currently be feeding up in the wooded savannas of Chad and Nigeria as their biological young back in Britain will finally be setting off for Africa. With no lead to follow, the juveniles' journey must be genetically hardwired, but as satellite technology has still not been miniaturised sufficiently for immature Cuckoos to be tracked, we can only presume that a similar route to that of their parents must be taken.

So little is also known about the dispersal of Puffins from their breeding grounds that their winter distribution must also be considered little more than educated guesswork. However, the limited research carried out suggests that those dispersing furthest are younger birds. Of the four Scottish-ringed Puffins recovered off eastern Canada during the last 50 years, for example, all were in their first year of life. Why young birds seem to have more wanderlust than their less adventurous parents can possibly be explained by the fact that most Puffins do not even attempt to breed until at least five years old. So these far-flung individuals may simply be
youngsters keen to see some of the world and enjoy a relatively care-free adolescence until responsibility kicks in a few years down the line.

Late September

Having joined forces to form mixed species flocks with Great Tits, Goldcrests, Wrens and even Treecreepers, back in high summer, juvenile and adult Blue Tits will be keen to maximise the advantage that groups can offer, foraging right the way through the darkest and coldest days ahead. Containing a core number of resident Blue Tits familiar with the area, these roving, mixed species flocks will also include nomadic individuals from further afield, which may come and go as they see fit. Despite their mobile nature, these flocks will nevertheless remain within a comparatively small home range, with almost 90% of ringed Blue Tits recovered being found within 20km of where they were originally caught.

Unlike the roaming Blue Tits, adult Kingfishers will remain rigidly attached to their territory throughout the winter, only possibly accepting any other kingfishers' presence on their patch during the rare occasions when the weather becomes so severe that it will concentrate feeding to a very few locations. After parting ways with their curmudgeonly parents, the importance to juveniles of acquiring a territory cannot be overstated. Most juveniles are not thought to travel far, with few recorded moving more than 12km from their original nest site. During this dispersal period, young birds can occasionally be seen crossing over land as they get ushered out of territories already jealously guarded, or in
the process of branching out suddenly turn up at surprising locations, such as garden ponds.

By late September, Robin territories will be becoming quickly delineated as the birds battle it out, initially with birdsong and then with aggression if newly acquired boundaries are not being respected. One of the many astonishing facts about Robins is that at least half of all the females are thought to regularly sing. This is a feature that is decidedly uncommon in the bird world; the only other British species where females are known to commonly join in the dawn chorus are Starling and Dipper. The fact that female Robins sing was already known before being definitively stated by Charles Darwin in 1871, but this unusual behaviour still didn't change the great man's opinion that bird song was primarily ‘for charming the female'. It was not until the 1920s that the naturalist William Henry Hudson argued that the reason why females sing as well as males is that both must hold separate territories in autumn and winter. Even though the singing females tend not to be either as vocal or possess quite the repertoire of their male counterparts, we now realise that Mr Hudson's assertion was indeed the correct one.

By now, those juvenile Peregrines that began moving away from their parents' territory in high summer should certainly have become much more proficient at hunting. Such is the immense pressure for young Peregrines to perfect the art of catching prey quickly that raptor expert Ed Drewitt believes that first-year mortality of juveniles could well be similar to that of relatively short-lived birds like Robins and Blackbirds. However, for those young that do manage to
make it through the perilous bottleneck of their first year, a longer life expectancy can then be expected, with the current longevity record being that of a male Peregrine ringed as a nestling in Cumbria, which reached at least 17 years and two months.

The most commonly recorded technique for a Peregrine catching and killing prey is with their mightily impressive stoop dive. This method involves the falcon closing its wings to form an aerodynamic teardrop in order to descend at huge speeds as it aims to catch its prey by surprise. Recent research work suggests that Peregrines have learnt to attack in a spiral, which enables them to keep a constant eye on their prey, without frequently turning their head, which could increase drag to such an extent that the inevitable slowing up might result in their quarry potentially escaping. Even though this curved flight path is slightly longer than the straight line, the extra speed generated by significantly reducing the air resistance will more than compensate for the extra distance as they attempt to strike lucky. The Peregrines additionally possess a nictitating membrane, which helps keep their huge, sensitive eyes both dirt-free and moist during the descent. Unlike an eyelid, the translucent nature of the membrane will still enable the bird to detect light while the eye is covered, meaning their eyes can be cleaned without a temporary loss of sight at the crucial moment. The Peregrine's aim is to strike the target so hard with its talons that the prey will instantly be killed, but should this not be the case, the hapless victim will usually be quickly dispatched with a bite to the neck, severing the spinal cord. This lethal bite is executed with a sharp triangular-shaped ridge on the outer edge of the upper mandible called the tomial tooth.

How fast the Peregrines travel during these spectacular dives is difficult to measure, but with speeds estimated to top 200mph, this should enable them to easily catch up with any unsuspecting prey, while also comfortably holding the record
for the world's fastest bird. Moving at such phenomenal speeds means the birds will also have to cope with incredibly high G-forces when pulling out of any dives or altering their flight path. In fact, researchers have calculated that the birds may experience forces as high as 28G during these manoeuvres, making light of the maximum G-force recorded on a roller coaster of 6.3G, or even the 9 to 12G fighter pilots will experience when executing turns at high speeds. The ways in which Peregrines are able to cope with this immense force without losing consciousness include the maintenance of a very high heart rate during the stoop and also the use of valves in the veins, which prevent the blood draining away from key areas like the brain at the crucial moment.

For young Tawny Owls, mastering the art of hunting doesn't quite require them to subject their bodies to the extreme forces experienced by Peregrines, but their technique certainly requires no less skill. Unlike Barn and Short-eared Owls, which mostly hunt on the wing, Tawny Owls are the classic ‘perch and wait' predators. Using a suitable branch as a base, the owls employ a combination of eyes and ears to constantly scan the ground below. Once movement has been picked up, they will then simply drop down on to the prey with the talons doing the damage. Thrust out in front, the talons are fully opened just prior to impact in order to maximise the ‘killing zone', and on the few occasions when the momentum of the strike doesn't kill the mouse or vole outright, the powerful follow-up clench of the talons will. The rough underside of their toes also combines with the incredibly strong grip to ensure that any ensnared prey not immediately killed by the strike will have no chance of escaping. Obviously for rural Tawnies which concentrate principally on mammal prey, in those years when mice and vole populations are at a cyclical high then a far larger
proportion of young owls will survive. However, irrespective of the abundance of prey each year, a Finnish study of Tawny Owl mortality still showed the odds being stacked against young birds, with just 33% surviving to their first birthday. Those birds which do manage to survive their first year will then see their survival rates leap to 64% for every subsequent year. These enhanced survival statistics can easily be attributed to the greater experience of older birds and the advantage of an exclusively maintained territory.