I bring exciting news from the Mara. I've copied in the TZ bird group here as this bird may well have passed through the Serengeti to arrive here.

Tyler Davis, Regional Manager of Angama Mara (and a fine birder), found and photographed this odd-looking swallow in the Mara Triangle yesterday (21st June 2018) which was seen associating with an unusually large congregation of Rufous-chested Swallows.

As luck would have it, I had recently been looking at African swallows in advance of a trip to the west of the continent and knew exactly which genus of swallows this one belongs to; the Petrochelidon or  'Cliff Swallows' (although only the North American 'Cliff Swallow' is officially known by this name now).

This is certainly a young bird, as it is mostly brown rather than blue, the wing coverts show pale edges and the secondary feathers appears quite short. Also note the pale rump, short-tailed and compact appearance and the dark smudge on the neck and sides to the breast.

With 11 representatives globally, only 4 are African;

1. Red Sea Swallow (Red Sea Cliff-swallow); only known from a single (dead) specimen found in Sudan. 

2. Red-throated Swallow (Red-throated Cliff-swallow); breeds mainly in southern DRC, Congo and Angola. 

3. Preuss's Swallow (Preuss's Cliff-swallow); West African but has wandered to NE DRC.

4. South African Swallow (South African Cliff-swallow); breeds in South Africa but an intra-African migrant into central DRC and countries westwards.

Although I have no field experience of any of these species, here are my thoughts on these contenders based on the existing literature and images online;

1. ~Red Sea Swallow can be ruled out as it is the darkest of the group with a dusky-grey rump.

2. ~Red-throated is also typically dark, red-throated and warm-rumped but few decent images exist to compare.

3. ~Press's Swallow is a good contender because it is known to show a cream-coloured rump in all plumages and is pale on the underwing. However, it lacks any essence of a necklace in the adult plumage.

4. ~South African Swallow is the best option. Even young birds show the early signs of a dark necklace*, it is whitish below and known to be the longest distance migrant of the group, with some individuals having been recorded in Mozambique, eastwards of the normal trajectory. Adults are quite dark and both the rump and under tail coverts are orange, but both are expected to be colder/ paler in juvenile plumage. Attis time of year, post-juvenile dispersal of South African Swallows is at its peak. (* I've attached an image of a juvenile South African Swallow from the Robert's Guide (thanks to Riaan Marais for this) for comparison.)