Just writing to let you know that there has been the first really
significant movement this year of Barn Swallows across northern Tanzania.
I first saw birds in good condition, that is in shining blue breeding
plumage; including several males with fine, tail wires; on 24 February.
This was on the plains north of Mount Meru where on Tuesday of last week
(21st) the very first and very light rains have fallen in more than three
months of dryness. The swallows were moving east or north east across the Angyata
Osugat: the very dry treeless expanse lying in the rain shadow of the two
great mountains of Meru and Kilimanjaro.
In the same place we saw a much bigger movement of many hundreds on February
27. There were relatively few birds on February 24 yet interestingly by
midday they were much concentrated around tight flocks of piebald sheep,
tended by Masai boy goatherds. The sheep were grazing in very
lightly-grassed glades amongst groves of sweet-scented white-flowering
Acacia mellifera. The swallows were feeding almost entirely on insects being
disturbed by the feet of the quickly moving sheep flocks and there was none
of the several local swallow species with them. An insight perhaps into the
evolution of Hirundo rustica ?
The swallows on February 27 were moving on a broad front, passing all
morning in straggling lines, with maybe as many as two hundred per half
kilometre in an hour. This is by far the largest number of Barn Swallows
observed in the area during this boreal winter period. They were all headed
purposefully east or north east, from at the latest 0750 until past midday,
at heights of between a couple of centimetres and 10m. Perhaps they were
coming from the Lake Victoria basin via the northern Rift Valley heading in
the direction of Mount Kilimanjaro and then perhaps to the coastal strip. We
intercepted them whilst they were crossing the arid lowlands that extend for
at least 50 km between Longido mountain in the north and Mount Meru to the
south. Incidentally there was a similar, noticeably purposeful, movement of
a few hundred very dark swifts in the same direction on February 20 that
might have been made up entirely of Apus apus.
The Barn Swallows yesterday were accompanied by a repeating wave of African
Emigrant (or African Migrant) butterflies Catopsilia florella travelling in
exactly the same direction that lasted all day and which has resumed today,
at least in the vicinity of Arusha itself – between the heavy showers.
Yesterday on those bare, dry plains to the north we met two young Masai men
with their cattle, as well as many small children tending a by-now vastly
increased number of sheep and goats. When asked as to their intended
direction one said that they were searching for pasture, watching the clouds
and identifying where those desperately needed rains should have fallen.
For many in semi-arid Africa it has long been necessary to chase the rain!"
In this part of East Africa we have received a tremendous volume of rainfall this past month and the thorn bush of the Somali-Maasai ecological zone, which constitutes the majority of the aforementioned area, is lush beyond belief – teeming with invertebrate life especially beetles, flies and 'leps'.
Travelling along the main highway toward the Indian Ocean on April 6 we passed through massive 'pewter-pot' thunder storms piling-up against Kilimanjaro and the Pare Mountain highlands, which are aligned NW-SE, forming a barrier to lower level bird migrants heading for Eurasia. We saw flock after flock of Swallows feeding low over the road or, beside it, in areas where rainwater was forming ephemeral wetlands. In many places there were a few dead Swallows carelessly extinguished, squashed flat on the road. The traffic of 'human progress'; local minibus taxis, the 4WD vehicles of the VIPs, long distance trucks and especially the many Dar-Arusha-Nairobi Express coaches, many averaging over 100k per hour, slows for no living thing!
In the rainiest places we saw hundreds of swallows assembled on the telegraph wires (power lines) in numbers that I have not seen since Europe in the early 1960s. Here they would occasionally be scattered every which way by marauding European Hobbies that scythed through the wheeling flocks like giant black swifts. At one point an even larger Sooty Falcon, the nemesis of so many a passerine migrant, was seen pursuing another unfortunate swallow!
In clearing conditions on the evening of April 9, where a low shoulder divides these mountains into the North and South Pares, just inside Mkomazi Reserve, there were little groups of swallows passing northward across the broad acacia-studded plain well into a glowering tropical orange dusk. When would they sleep again we wondered?