i. Tarifa: a raptor bottleneck.

The western flyway is particularly important for storks and raptors. These birds generally use soaring flight, as flapping flight is too costly in terms of energy to be sustained by large birds (see table 1). Soaring relies on thermals generated by the upward movement of air warmed by the earth, and hence cannot be upheld above the sea for long distances. At Tarifa raptors and storks use the thermals to gain height before ‘attempting to soar over one side of the strait and glide to the other’⁷. The migration at the western flyway is dominated by three species, all of which use soaring flight:

White Stork: (up to 50,281 individuals observed in one seasonal crossing)
Honey Buzzard: (up to 115, 696 individuals observed in one seasonal crossing)
Black Kite: (up to 63,032 individuals observed in one seasonal crossing)

Important numbers of the following species also use this flyway: Egyptian vultures, Short-toed eagles, Montague’s harrier, Booted eagle, Griffin vulture, Marsh harrier, Sparrowhawk and Buzzard⁷.

Table 1: A summary of the various flight strategies.

Strategy	Advantage
Slow and Steady Wins the Race	The most basic technique is to keep flapping until you land. This technique is used by the Canada goose and many other migrants.
Soaring	Some birds ride thermals (updrafts of air caused by solar heating) to take a free ride. These birds, including Swainson's hawk, can only travel during the day, and preferably over flat land, with restricted movement over water.
Flapping and gliding	These birds flap their wings for a few beats, then glide. After they lose some altitude and/or speed, they flap again.
Bounding	This is a combination of flapping and closed-wing glide. Although their aerodynamic bodies do create some lift, the birds tend to lose altitude and the flight pattern is up-and-down, like the flap-and-glide pattern.

ii. Marine productivity

At the Strait, cold Atlantic waters meet warm waters from the Mediterranean. This simple difference in temperature has a profound effect on the surrounding area: it causes marine currents to form, which bring waters rich in nutrients deep from the Mediterranean up to the surface waters where more light reaches. This acts like a natural fertilizer, causing plankton (microscopic marine plants) to grow in great watery clouds that can stretch so far that they are sometimes visible from space. This concentration of life attracts other ocean dwellers looking to feed on these tiny creatures and makes the area a rich feeding ground for seabirds. Many reside here year-round whilst others, such as Audouin’s gull, lesser crested tern and gannet, cross the Strait towards Senegal after breeding, and move back towards the Mediterranean in Autumn.

iii. Wetland stepping-stones all the way to Africa

Wetlands are areas of land where the top layer of soil is saturated or covered with water. They are areas often forgotten by humans: being muddy and boggy by definition, sometimes inaccessible, and as such, of little value for development or agriculture. However, wetlands are vital habitats for a huge array of wildlife. Bogs, reedbeds, salt marshes, fens and mudflats all support diverse communities of insects and other invertebrates: rich pickings for birds. Many birds depend on wetlands, from grey wagtail and other small river birds, to flocks of waders and fish-eating raptors like the osprey.

The area surrounding Tarifa is important for its wetlands. These marshes, from Odiel in the north of Iberia, to Merja Zerga on the African coast, form part of a chain of wetlands from Britain right down to West Africa. Vast populations of waterbirds winter around the Strait and West Africa, around 675,000 to 900,000 waders may be found in transit on the Moroccan coast in Spring⁷.