42 Shortcommunications SHORT COMMUNICATIONS Wahlberg's EagleAquila wahlbergimigration in Uganda Wahlberg's EagleAquila wahlbergi is the most migratory African eagle and is said to visitEastAfricafromAugusttoApril(Britton 1980).Evidenceforlarge-scalemigration rests on observationsfromMarahari Mt(6° 12S, 29° 50E) on theeastern shoreofLake Tanganyika, in west Tanzania, where large numbers moved southward between mid- JulyandearlySeptember(Ulfstrand&Lamprey 1960),andnorthwesternUgandawhere more than 1000wereseendaily byThiollay (1975) on 25 and26July. Furtherinformationonthescale, seasonanddirectionofthismigrationwill begained by the gradual accumulation of scattered observations of the above and the following kinds. Further observation in southwestern Uganda and Rwanda by Thiollay (loc. cit.) helped to provide a link between the observations in northwestern Uganda and Mt Marahari. My own observations in western Uganda between 28 July and 18 August 1983 confirmThiollay's findings,butat c. 10days laterthan his there were fewerbirds (376 tr1 compared with 504h-1)- Observations inUganda I noted Wahlberg's Eagles fairly often, including breeding birds, active migrants, and others.Anadultbroughtfoodforadependantjuvenileontheunexpecteddateof28July at Kiganda(0°26N, 31°41E) and others, but never more than two at a time, were seen alongtheroutetoFortPortal(0°50N,30°20E)andMasindi(1°40N, 3T43E),including oneinpalmsontheshoreofLakeAlbertatButiaba(1°50N,31°20E)on3August.There wasnoindicationthatanyofthesewas actuallymigrating. Soonafter 11:00on5Augustwhiletravellingwestthroughhillygrasslandsjustsouth of Pakuba at c. 2°16N, 31°26E occasional Wahlberg's Eagles became increasingly frequent overhead, often associated with Bateleurs Terathopius ecaudatus. Then at 11:45 a shortdistance southwestofPakuba, several groups ofWahlberg's Eagles were sighted,allmovinginthesamedirection. Inthenext 15 min atotal of161 wascounted, followed by26, 29 and 160in thesubsequentthree 15-minperiods: atotal of376 in an hourattheone site. I movedoffwestwards, in anattempttodeterminethe width ofthe flight, butitsoon becameobviousthateitherthemovementwasover, orthatthestream ofbirds hadbeenleftbehind. Theirmannerofflightwastypicalformigratingraptors. Mostofthemwereveryhigh and could be discerned through binoculars approaching from the north over the broad Nilevalley.Theirprogresswasinlongglides,withonlyoccasionalwingbeats,between risingthermalswherearrivingbirdswouldquicklyaccumulatetobuildupinawheeling cloudamountingtoasmanyas80; ononeoccasiontherewere 131 birdstogetherinone thermal and 29othersinthearea.Attheheightoftheirascentthebirdswerepractically invisible to thenaked eye, even againstwhiteclouds, beforethey moved on to the next thermal. Throughout the flight Bateleurs constantly cruised about and there were several vultures and afew Fish Eagles Haliaeetusvociferin the air, but the only otherspecies possibly migrating were two BlackKitesMilvusmigransaccompanying theeagles.As far as could be ascertained from topography and the map, flightdirection was north to Shortcommunications 43 southduringthelongglidesabovetheriver,butoverlanditwaslessclearbecauseofthe birds' tendencytoaltercoursetojoin thermals. The height ofthe observation site was c. 650 m, the weather hot and mostly sunny, with a light northerly breeze under 4/10 cover of cumulus. There was also marked instabilitywithactiveformation ofthermals, althoughtheareaoverthebroadriverwas cloudless and therewaspresumablylittle,ifany,thermalformationthere. There was no sign ofmigration on the nextday along the Nile valley between Paraa (2°18N,31°35E) andKabalegaFalls(2°15N, 3P41E), butfurthernorthon7Augustat 10kmnorthofNebbi(2°31N,31°07E)inWestNileProvince 17A.wahlbergiflewc. SE inthe samemannerastheearlierbirds. On8Augustat 11:20twoflew c. SSEat3°13N, 31°07E. During the next 11 days only sixA. wahlbergi, not obviously migrating, were seen on thejourneythroughArua, Moyo, Gulu, Chobi, Masindi and FortPortal back to Kampala. In particular, notone was seen between FortPortal and Ntoroko at the south end ofLake Albert. However, ifthey were travelling on a narrow front they could be missedeasilyiftheirroute werecrossed atthe 'wrong'time oftheday. Discussion Wahlberg'sEagleiswidespreadinAfricabetweenc. 30°Sand 18°N,westtotheAtlantic in Senegal and east to northern Somalia; it breeds mainly south of the equator in September-January, more rarely to 14°N; non-breeding areas are to the north in the northern tropical savannas ofthe Sudan, Chad, westtoGambia,from March toAugust; it migrates south in July-August and, by inference, north in January-February (Brown etal. 1982). There is a small breeding population in the north which may not migrate, and it is absent from southern Africa in March-August (Brown et al, loc. cit.). Con- centrations ofbirds between late January and early April in Tsavo East National Park (3°30S, 39°00E) in Kenya are probably migrants moving north to presumed non- breeding season areas during May-July (Britton 1980). It is possible that birds follow well-definedrouteson rathernarrow fronts. References Britton, P.L. (ed.) 1980. Birds ofEastAfrica, theirhabitat, status anddistribution. Nairobi: EANHS. Brown,L.H.,Urban,E.K.&Newman,K. 1982.ThebirdsofAfrica.Vol. 1.London:Academic Press. Thiollay,J.M. 1975. MigrationsderapacesafricainesenOugandaetauRwanda.L'Oiseauxet R.F.O.45: 192-194. Ulfstrand, S. & Lamprey, H. 1960. On the birds of the Kungwe-Mahari area of western Tanganyika.JournaloftheEastAfricaNaturalHistorySociety23:223-232. DrJ. S.Ash, GodshillWood,Fordingbridge,HantsSP62LR,England Scopus 15: 42-43,August 1991 Received 11 June 1990