The team has already collected feathers from a range of surrogate species around Lake Chad in Nigeria, and is looking for further sites where warblers may be wintering.

BBC: Feathers clue to warbler's travels

Several thousand troops from Mali's neighbours, including Chad, Niger, Nigeria, Togo and Senegal have already been sent to Mali to retain control of the retaken northern towns and also to take care of security in the south.

BBC: Mali 'hesitant' over UN peacekeeping force

Several thousand troops from nearby African nations, including Chad, Niger, Nigeria, Togo and Senegal, have already been sent to Mali to retain control of the retaken northern towns and also to take care of security in the south.

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The French foreign ministry said on its website citizens were "officially advised not to go to the far north of Cameroon (the shores of Lake Chad in the South Maroua), and the border with Nigeria, until further notice".

BBC: French Cameroon hostages 'not released'

Algeria, Chad, Mauritania, Niger, Senegal, Nigeria, Morocco and Tunisia are also involved, with Libya perhaps to be added if its relations with the United States improve.

ECONOMIST: Deserving cases, getting too little help | The

Of course there are exceptions, such as Botswana and Namibia (both in the African top five as far as governance is concerned), but most resource-rich countries are well down the table: the DRC, Sudan, Chad, Equatorial Guinea, Congo (Brazzaville), Nigeria and Angola are all ranked between 34th and 46th in the World Bank's regional rankings.

ECONOMIST: Is Africa recovering?

The GGW was conceived by the 11 countries located along the southern border of the Sahara with the goal of containing the desertification of the Sahel zone, which is the transition between the Sahara in the north and the African savannas in the south, and includes parts of the countries of Senegal, Mauritania, Mali, Burkina Faso, Algeria, Niger, Nigeria, Chad, Sudan, Somalia, Ethiopia and Eritrea.

FORBES: Great Green Wall Plans to Stop Sahara