Fragmentary knowledge of bird evolution, derived from fossils time-stamped against the geology of the rocks within which they lay, paints a picture of a seabird family tree extending new members. Species resembling Gannets and Cormorants occurred over forty million years ago. Then, in an epoch known as the Oligocene, the first ‘modern’ seabirds diversified. Among the newcomers were albatrosses, fulmars and shearwaters. One million years ago (the Pleistocene) the oceans approximated to what we see today. Central America straddled two oceans, the North Atlantic joined the Arctic Ocean and the Mediterranean became connected to a greater maritime universe. Many types of seabirds date from around this time. Manx Shearwater is one.

Of all the North Atlantic’s seabirds, shearwaters appear to be the most perfectly adapted to the ocean’s frequent windy weather. The more savage the gale, the more effortless their flight. They are built like gliders. Their humerals (wing bones) are long and the flight feathers are rigid. In fact, the wings are somewhat inflexible. Hovering or dip-feeding like a petrel or tern are out of the question. Instead the flight track has the long easy reach of a skier. The bird proceeds by tilting from side to side. It is cruising. By tacking into the wind it gains lift. For each rise there is a fall. Although momentum is lost on the ascent, every descent restores power through gravity. Downward lunges carry the bird onward, skimming low and then riding high. Wing beats are quick and dextrous and, like a child kicking legs on a swing, only needed to boost momentum on the way up. With high wind at its back, a shearwater can easily clock up in excess of 90 kilometres per hour.

Design plays a huge part too. Looked at head on, the wings are slim in cross section. They slice into the breeze. Despite a flat outward appearance, each wing is scooped. Concave undersides catch the wind to maximise buoyancy and tap energy. In light airs or calm, flight is close to the sea so that, once again, the cushion of air trapped by the wings’ undersides contributes lift. In full-on travel a Manx Shearwater often presents alternating views of a black back, then white undersides. First an observer sees the dark back facing. Next it rises; perhaps interjecting progress with a pulse of wing beats before swinging over to present a white belly as it glides and gathers momentum for the next arc.

What if a seabird travels with a turbulent wind that brings it close to shore? In autumn, great wheels of migrants — shearwaters, petrels and skuas — track around the North Atlantic en route for winter quarters in the Southern Hemisphere. To begin with the winds are favourable yet, all the while, the troops are being displaced towards the windward coast of Ireland, like the Spanish Armada. To return back out to sea they must turn and fly into wind. Smaller seabirds, such as petrels, Sabine’s Gulls and Grey Phalaropes, are able to help themselves by avoiding those parts of the surface where the wind is strongest. They fly along troughs and avoid gusts blowing at crests. Being buffeted is not necessarily bad news: the upwards-and-backwards deflection can be turned to advantage by using gravity to swoop down and forward along a lee surface of a swell. It may take some time for a benighted flier to get back on track. Either the wind drops or the bird reaches clement conditions under its own steam. Smaller seabirds only become exhausted when stormy winds shift capriciously and blow parallel to the swell, depriving tired, wing-beating waifs of sheltering troughs along which to make progress.

Among seabirds, fatalities due to weather are uncommon. Casualties are usually the young and inexperienced. Once a youngster completes its first year at sea — reaching winter quarters and gaining familiarity of ocean routes connecting them with its breeding area — it is most unlikely to be bothered by storms. The truth of this statement is borne out by the fact that most of the world’s seabirds live in the southern oceans, in the Roaring Forties, where rough weather rages almost continuously for six months of the year. Not only do countless numbers of seabirds feed in these conditions but they also roost or sleep on the sea. What controls seabird numbers and, in particular, the Manx Shearwater population?

Far from terra firma, direct predators are few. Man’s fishing activities are a worry. How many die by swallowing baited hooks cast out over hundreds of kilometres to catch tuna and other commercial quarry? Being safe at sea permits longevity. Consequently there is a lengthy age gap between younger generations and breeding birds. Just one young is reared from a single large egg. Recruitment of the new generation is a slow process. Many Manx Shearwaters do not find a mate or a vacancy at a nest burrow until they are seven years old. Finding a nest site is not, therefore, a serious problem because an adult — or young pretender — has only to occupy and defend an existing breeding site. Not surprisingly, many pairs mate for life although they do not remain together once they leave the breeding area.

Returning to land is, nonetheless, dangerous. Despite coming ashore at night, some are caught in flight by Peregrines and gulls swoop on others as they scramble over the ground to reach burrows. Manx Shearwaters cannot walk or perch and shuffle on their tarsi. Although supreme in the air they are easy targets on the ground. Black, moon-less night is their friend. A much more serious mammal predator is the rat. Accidentally introduced onto remote islands, Brown and Black Rats have decimated once enormous populations of Manx Shearwaters and Puffins. Even the eponymous home of the species — the Isle of Man — lost its namesake due to rats. Rodent-free islands are vital for nesting and herein lies Manx Shearwater’s Achilles heel. Around the Irish coast, several suitable nesting islands are unused due to the presence of rats, an encouragement to prevent rodents from reaching, among other important colonies, those on the Copeland Islands.

Little is known about the internal parasites of sea-birds. Among Manx Shearwaters, episodes of ‘puffinosis’ (a virus coined from the bird’s Latin name) periodically kills hundreds of young shearwaters among crowded populations on colonies off the Welsh coast. External mites, ticks and fleas also attach themselves to the birds once they set foot on land. If Manx Shearwaters can find rat-free islands they can tolerate attacks from bacteria, viruses and parasites. What about food? With warming seas, availability could become an issue, especially when provisioning chicks. Unlike Guillemots and Razorbills, Manx Shearwaters are not tied to home waters from which fish is carried in the bill and transported on whirring wings. The bird’s aerodynamic shape and free-wheeling style emancipates it from high-energy flight demands. Food — small schooling fish captured in shallow dives — is converted into an oily porridge and stored until luggage limits are reached. At which point the parent flies back to junior. But from where? This we do not know fully. However, benign tracking devices are set to reveal foraging patterns. Hopefully the days are gone when the feeding grounds of Pembrokeshire birds were discovered because Spanish fishermen’s nets drowned Manx Shearwaters (some of which were ringed) that were catching Sardines to raise chicks on Skolkholm Island, Wales.