Land mass movements.

Any discussion of habitats, whether they be aquatic or terrestrial needs to start with an understanding of land mass movements during the long period of time during which birds have been evolving. Habitats have clearly been changing during this period so we need to know something about the surface cover of the earth.

It is generally accepted that our modern birds evolved at various times during the last 100 million years. If we want to talk about the geographical location and nature of the habitats in which the birds evolved we need to touch briefly on the land mass movements which are responsible for the location of the continents as we know them today.

The World 250 million years ago.

About 250 million years ago all the continents were joined together in a single large mass known as Pangea. This land mass split to form Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere. These two land masses then began to fragment further. Laurasia eventually formed North America and Eurasia.

Gondwanaland broke up to form Africa and Arabia. A small land mass broke away from the mass which was Africa to form Madagascar. On the other side of Madagascar, India broke away from the rest of Gondwanaland. Some time later Australia and New Guinea broke away and were followed by the land mass we now call South America, leaving the mass we know as Antarctica to move south over the pole.

The World today.

By about 90 to 100 mya the continents were roughly in the positions we know them today. Very broadly we can divide the earths surface into:-

  • Northern hemisphere.
  • Southern hemisphere.
  • Eastern Hemisphere or Old World.
  • Western Hemisphere or New World.

Eastern Hemisphere versus Western Hemisphere.

A noticable difference, when we look land cover (excluding the polar regions) is seen in terms of barren, sparsely vegetated land (12.3%) which is almost entirely in the Eastern Hemisphere apart from a very small area in North Chile. The main areas with this habitat in the Eastern Hemisphere are a roughly rectangular area covering Morocco, Algeria, Libya, Egypt, Northern Mauritania, Mali, Niger, Chad and Sudan plus Saudi Arabia, Iran, parts of Pakistan, Kazakhstan, Mongolia and Northern China.

Open scrubland (17.2%) habitats are seen in Central Australia, Kenya, Somalia and South Africa in the Eastern Hemisphere and in North America, Arizona, South America, Bolivia and Western Argentina.

Climatic regions.

  • Polar and High Altitude regions (Arctic – latitude >66 degrees north, Antarctic - latitude >66 degrees south and Mountains with snow cover, usually 3000 m or more).
  • Temperate – between 35 and 66 degrees north and 35 and 66 degrees south.
  • Tropical / Sub-tropical – either side of the equator, between 35 degrees north and 35 degrees south.

These regions account for 10.6% of the land cover.