Question: At least how many tropical islands are found in middle leg of the journey from the continent Tekezé River is located to the Americas?

<P0-S0> (See the list.) <P0-S1> These islands generally form island arcs that delineate the eastern and northern edges of the Caribbean Sea. <P0-S2> Situated largely on the Caribbean Plate, the region comprises more than 700 islands, islets, reefs and cays. <P0-S3> The Caribbean islands, consisting of the Greater Antilles on the north and the Lesser Antilles on the south and east (including the Leeward Antilles), are part of the somewhat larger West Indies grouping, which also includes the Lucayan Archipelago (comprising the Bahamas and Turks and Caicos Islands). <P0-S4> The Lucayans and, less commonly, Bermuda, are also sometimes considered Caribbean despite the fact that none of these islands border the Caribbean Sea. <P0-S5> In a wider sense, the mainland countries, regions, and territories of Belize, the Caribbean region of Colombia, Cozumel, the Yucatán Peninsula, Margarita Island, the Guyanas (Guyana, Suriname, French Guiana, Guayana Region in Venezuela, and Amapá in Brazil), are often included due to their political and cultural ties with the region. <SEP> <P1-S0> The Tekezé River rises in the central Ethiopian Highlands near Mount Qachen within Lasta, from where it flows west, north, then west again, forming the westernmost border of Ethiopia and Eritrea from the confluence of the Tomsa with the Tekezé at to the tripoint between the two countries and Sudan at . <P1-S1> The Tekezé is perhaps the true upper course of the Atbarah, as the former follows the longer course prior to the confluence of the two rivers. <P1-S2> After entering northeastern Sudan at the tripoint it joins the Atbarah River, which is a tributary of the Nile. <SEP> <P2-S0> It flows about 805 km (500 mi) to the Nile in north-central Sudan, joining it at the city of Atbarah (). <P2-S1> The Atbarah River (; transliterated: Nahr 'Atbarah) in northeast Africa rises in northwest Ethiopia, approximately 50 km north of Lake Tana and 30 km west of Gondar. <P2-S2> The river's tributary, the Tekezé (Setit) River, is perhaps the true upper course of the Atbarah, as the Tekezé follows the longer course prior to the confluence of the two rivers (at 14° 10' N, 36° E) in northeastern Sudan. <P2-S3> The Atbarah is the last tributary of the Nile before it reaches the Mediterranean. <SEP> <P3-S0> north dakota is in the u.s. region known as the great plains. <P3-S1> the state shares the red river of the north with minnesota to the east. <P3-S2> south dakota is to the south, montana is to the west, and the canadian provinces of saskatchewan and manitoba are to the north. <P3-S3> north dakota is situated near the middle of north america with a stone marker in rugby, north dakota marking the ``geographic center of the north american continent ''. <P3-S4> with an area of 70,762 square miles (183,273 km), north dakota is the 19th largest state. <SEP> <P4-S0> many adult insects use six legs for walking and have adopted a tripedal gait. <P4-S1> the tripedal gait allows for rapid walking while always having a stable stance and has been studied extensively in cockroaches. <P4-S2> the legs are used in alternate triangles touching the ground. <P4-S3> for the first step, the middle right leg and the front and rear left legs are in contact with the ground and move the insect forward, while the front and rear right leg and the middle left leg are lifted and moved forward to a new position. <P4-S4> when they touch the ground to form a new stable triangle the other legs can be lifted and brought forward in turn and so on. <P4-S5> the purest form of the tripedal gait is seen in insects moving at high speeds. <P4-S6> however, this type of locomotion is not rigid and insects can adapt a variety of gaits. <P4-S7> for example, when moving slowly, turning, or avoiding obstacles, four or more feet may be touching the ground. <P4-S8> insects can also adapt their gait to cope with the loss of one or more limbs. <SEP> <P5-S0> Historically the particular routes were also shaped by the powerful influence of winds and currents during the age of sail. <P5-S1> Returning from North America, it is easiest to follow the Gulf Stream in a northeasterly direction using the westerlies. <P5-S2> A similar triangle to this, called the volta do mar was already being used by the Portuguese, before Christopher Columbus' voyage, to sail to the Canary Islands and the Azores. <P5-S3> Columbus simply expanded the triangle outwards, and his route became the main way for Europeans to reach, and return from, the Americas. <P5-S4> For example, from the main trading nations of Western Europe it was much easier to sail westwards after first going south of 30 N latitude and reaching the so - called ``trade winds ''; thus arriving in the Caribbean rather than going straight west to the North American mainland.