Regarding Itai's last e-mail:
 
A few thoughts re Olive Tree Warblers as I studied them in Botswana and discussed them at length with David Pearson.
 
1.  Where they winter in Botswana and similarly in other suitable areas in Southern Africa, they take up winter territories and regularly sing in holding those territories between December and February.
 
2.  These territories were usually tied to Acacia melliphora thickets.
 
3.  David Pearson felt they were mainly a passage bird in Kenya and I think this is also true of Malawi (where I lived for 8 years).
 
I am not suggesting they do not winter in the Southern Rift valley, but the above points may help in investigating further.
 
Regards
 
Nigel