What was the average travel time for African slaves being moved from the interior of Africa to the coast for export?
Also, how long did they tend to wait on the coast until they were exported?
I couldn't find any references on this.
There are few "references" on the interior traffic on this subject and the few that exist, like that of Fowell Buxton, I consider highly unreliable for various reasons where he writes of matters of which he knew nothing but secondhand stories.
First of all, slaves were not moved from the deep interior of Africa. Africa is mostly populated on the coasts, not the interior. The occupants of the interior tend to be few in number and consist largely of pygmies and other populations which were unsuitable for transport into slavery. Nearly all slaves were from within 600 miles or so of the coasts.
How long a slave might spend in transport depended entirely on how they were enslaved. In many cases local slave traders would go by boat up rivers such as the Niger or Volta offering money for slaves which would be provided locally. Such an expedition might last several weeks.
Concerning caravans you can read the travels of Mungo Park, one of the few accounts with any kind of authenticity. His caravan left "Kamalia" on the 19th of April and reached Medina on the 4th of June 1797, a journey of 500 miles over about 45 days. The longest caravans were probably the Nubian caravans to Cairo, which I would guess might take as long as 3 months. Note that caravans move at very different speeds.
Generally, there are a large number of useful references to the Eastern and Central African slave trade in the contemporary traveler and missionary texts and the Geographical Journal. Many may be accessed via the Internet Archive or the RGS Library in London. Caravan speed can be computed from some of the better accounts [eg. Tipu Tip’s biography by H.Erode, 1907 online – usually 4 hours p.d., not more than 10 miles, usually much less, depending on hundreds of factors].
Much of the picture depends on the ‘where and when’. Just dealing with my own area, the main trade in East, Central and West Africa, of the numerous contemporary accounts, Sir Harry Johnston’s slavery route map and discussion in ‘British Central Africa’ [esp Ch V] is useful. There are large numbers of modern analyses, some good [see eg. Abdul Sherriff’s ‘Slaves, Spices and Ivory in Zanzibar’ 1987]
Down here in Central Africa,
a] the trade went progressively completely across the continent in the 19th Century.
b] the idea that Central Africa was thinly peopled before the Second Arab slaving decimation is untrue [see eg Livingstone, Wissmann etc.]
c] As to the BaMbuti, BaTwa etc most writers suggest a few tens of thousands while all agree that the interior Bantu and Sudanics were very populous. In the latter part of the 19th C, the Arabs dominated the centre of the continent West of Lake Tanganyika as well as the coast, until the arrival in Tanganyika of Peters and pals, and, in the Congo Free State, of Leopold's pals. [See generally eg. Tippu Tip’s so-called ‘New Bengal’ and the predations of his friends and relatives.]