'Ecology, voice and territorial competition of Fraser''s and Akun Eagle Owls, Fraser''s Eagle Owl Bubo poensis and Akun Eagle Owl B. leucostictus'

2006·5.6 MB·

by  Françoise Dowsett-Lemaire

Ecology, voice and territorial competition of two
forest eagle owls, Fraser’s Eagle Owl Bubo poensis
and Akun Eagle Owl B. leucostictus
FrangoiseDowsett-Lemaire
L’ecologie, les vocalisations et la competition territoriale de deux grands-ducs forestiers, le
Grand-due a aigrettes Bubopoensis et le Grand-due tachete B. leucostictus. Cet article presente
des observations de deux grands-ducs forestiers Bubo spp., provenant surtout du Congo et du
Cameroun (1989-2001) mais aussi du Ghana, du Nigeria, de la Guinee Equatoriale et du
Rwanda. Les aires de distribution du Grand-due a aigrettes Bubopoensis (forme nominale) et du
Grand-duetacheteB. leucostictusserecouvrentlargement, saufquelepremieratteintdesaltitudes
nettementplus elevees. B.poensisfrequentesurtoutleslisieresforestieres, les forets assezdegradees
et ne s’observe que rarement en foret primaire a voute fermee. II a un large spectre alimentaire
(insectes et petits vertebres), tandis que B. leucostictus est surtout ou meme exclusivement insec-
tivore. Ce dernier evite les milieux les plus degrades et est l’espece dominante des vieilles forets
secondaires ou forets primaires sempervirentes (dont la voute presente naturellement de petites
ouvertures): e’est dans ce type de foret que les deuxBubo peuvent entrer en contact.
Les emissions vocales les plus frequentes de B.poensissont des roulades courtes ou longues
(jusqu’aplusieurssecondes), emisespardesoiseauxseulsouenduo. Laforme vosselerideTanzanie
produit de longues roulades identiques (Lig. 1). On entend aussi en saison des appels siffles puis-
sants et aigus, apparemment produits par des jeunes; ces sifflements n’ont aucune valeur agres-
sive. Les emissions vocales les plus caracteristiques de B. leucostictussont des appels bas, etouffes,
courts et peu puissants (rob, rob . . . ), emis par des oiseaux seuls (apparemment le male adulte),
tandis que les couples peuvent chanter de concert des duos de roulades courtes, avec parfois un.
sifflement ascendant court. Ces roulades courtes sont en general un peu plus lentes que celles de
B. poensis (plutot un staccato), et au nord Congo et Cameroun adjacent il existe une variante
dialectale particuliere, ou le second oiseau termine sa roulade par une double exclamation
(kokokokok, ka-kab!). On entend aussi (rarement) des appels siffles longs, plus rauques et plus
‘sinistres’ que ceux de B.poensis se rapprochant un peu des longs cris du Grand-due de Shelley
,
B. sbelleyi. II est probable, mais non encore prouve, que ces longs sifflements soient le fait de
jeunes oiseaux.
Larepasse de lalongue roulade de B.poensisest le moyen le plus efficace de provoquer une
reponse agressive chez B. poensis comme chez B. leucostictus, mais ce dernier reagit avec ses
vocalisations propres. II semble que les deux especes defendent des territoires interspecifiques la
oil elles entrent en contact, comme les distances observees entre individus des deux especes dans
un meme type de foret sont de l’ordre de 1 km ou plus. La prudence s’impose quant a l’identifi-
cation d’un oiseau reagissant acetenregistrement, mais lalongue roulade n’ajamais ete entendue
chez B. leucostictus, et les notes rauques de ce dernier (rob, rob, . . . ) jamais chez B. poensis.
D’autres cas de ‘countersinging’ interspecifique chez des especes congeneriques ont ete observes
enAfrique.
Summary. Observations are presented from many encounters with two eagle owl species, main-
lyin Congo and Cameroon (1989-2001).The ranges ofnominate Fraser’s Eagle OwlBubopoen-
sis andAkun Eagle Owl B. leucostictus are fairly similar, except that the former extends to much
higher altitudes. These large owls are partlyseparated bytheirecological requirements (B.poensis
preferring secondary situations, B. leucostictus old secondary or primary forest with small open-
ings) and diet (B.poensis taking a range ofinsects and small vertebrates, B. leucostictusmainlyor
exclusively insects). However, they occasionally come into contact, especially in open-canopy
semi-evergreen forest. The most frequent vocalisations ofB.poensisare guttural trills (or purring
Fraser'sEagle OwlandAkunEagle Owl:Dowsett-Lemaire BullABCVol13No2(2006)-147
rattles), shortorlong (severalseconds), givensinglyorin duet; the form vosseleriofTanzaniapro-
duces identical trills (Fig. 1). High-pitched, far-carrying modulatedwhistles are heard persistent-
ly at some times ofyear and circumstantial evidence suggests they are produced by immatures;
theyhave no known aggressive or reactive purpose. The most characteristic call ofB. leucostictus,
always produced by single birds (apparently males), is a series oflow, soft grunts roh, roh, . . . ;
short, hoarse ascending whistles and short, slow trills are also given, singly or in duet. In north-
ern Congo andsouth-eastCameroon atleast, this duethas adistinctive dialectalvariant,with the
secondbirdproducingaslow (staccato) trillendingin two exclamatorynotes (kokokoko, ka-kahl).
In Ghana however, duets heard were hard to distinguish from those of B. poensis (with short
trills). Long whistles are also occasionally produced by B. leucostictus, but are somewhat lower
pitched, hoarser and more ‘sinister’ than those ofB.poensis; they tend to recall those ofShelley’s
Eagle Owl B. shelleyi. Tape playbackofthe long guttural trill ofB.poensis (never produced byB.
leucostictus) elicits strong reactions in B. leucostictus too, but species-specific vocal characters are
preserved in interspecific reactions. It appears that both eagle owls may defend interspecific ter-
ritories where theycome into contact; distances measured between eagle owls ofdifferent species
being 1 km or more. Interspecific countersinging is known in several other pairs ofcongeneric
species in theAfrican tropics.
W
hilst undertaking systematic searches for out the Guineo-Congolian region (including
forest nightjars Caprimulgus spp. in north- Bioko), from Sierra Leone and Guinea to Ghana,
ern Congo in 1997 (Dowsett-Lemaire & Dowsett and Nigeria to western Uganda and northern
1998a) we also played a few tapes ofowls, includ- Angola (Kemp in Fry et al. 1988, Dowsett &
ing the long guttural trill or purring rattle of Forbes-Watson 1993, Demey & Rainey 2004). It
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Fraser’s Eagle Owl Bubo poensis (last motif in covers a wide altitudinal range, up to 2,200 in
Chappuis 1978). This was done along a narrow, Cameroon (Mt Oku: Dowsett-Lemaire &
m
25 km-long track crossing broken-canopy semi- Dowsett 1998b) and up to at least 2,000 in
evergreen forest in Nouabale-Ndoki National Nyungwe Forest in Rwanda (Dowsett-Lemaire
Park. We located eight territories ofBubo species 1990) and 2,100 m in south-west Uganda
&
along this track (three ofB. poensis, five ofAkun (Friedmann Williams 1968). Another form, B.
Eagle Owl B. leucostictus), and itwas soon obvious p. vosseleri, iswidespreadintheforestsofTanzania,
that both species were equally interested in tape from theUsambaras (Evans etal. 1994) andSouth
playback ofB. poensis. Pare (Burgess etal. 1998), south to the Ulugurus
This note assembles various observations on (Hunter et al. 1998) and Udzungwa Mountains
&
the ecology and vocal behaviour of both Bubo (Butynski Ehardt 2003); the overall altitudinal
species, collected mainlyin Congo-Brazzavilleand range is at least 200-1,700 m. The Tanzanian
Cameroon overaperiod of12years (1989-2001). form is often considered a separate species,
Otherobservations come from Ghana (2004-05), Usambara or Nduk Eagle Owl B. vosseleri, but
south-east Nigeria (1988), Equatorial Guinea recent vocal evidence supports conspecific treat-
(1998) and Rwanda (1989-90). Unlike other for- ment (see below). Nominate B. poensis is a
est owls ofthe genera Glaucidium, Scotopelia and Guineo-Congolian near-endemic, extending to
Jubula, these two Bubo are rather bold: either high altitudes in Cameroon and the Albertine
spontaneously or when responding to playback, Rift, whereas B. poensis sensu lato belongs to two
they do not hesitate to expose themselves in full biomes, Guineo-Congolian and Eastern
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viewon large branches, facilitatingpositive identi- (Dowsett-Lemaire Dowsett 2001), with
fication. It has thus been possible to learn some- Afromontane intrusions.
thing oftheir vocal behaviour and interactions.
B. leucostictus. This is a Guineo-Congolian
Distribution endemic with much the same horizontal distribu-
B. poensis. Nominate B. poensis is somewhat more tion as nominate B.poensis, except that itdoes not
widespread than its congener, occurring through- appear to reach East Africa. It is much more
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restrictedinaltitude, as itisknownonlyfromlow- untraced); in a Kupe garden a B. poensis also cap-
landforest.Altitudes aregenerallynotgiven in the tured several tortoises in an open terrarium (C.
literature (e.g. Fry et al. 1988). My own records Wild pers. comm.). Playback ofthe purring calls
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are from near sea level to only 600 (Congo, of this owl often elicits vocal responses in other
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Odzala) and 500 (south-east Cameroon), species, apparently through alarm: Demidoff’s
whereas I heard it to 700 m in Ghana (Atewa Galago Galagoides demidoff(frequently), Guereza
range). In particular, it appears to be completely Colobus Colobusguereza, andalso apparentlyonce
absent from montane western Cameroon, with among a group of roosting Plumed Guineafowl
firm records in the west only from very low alti- Gutteraplumifera and in a small owl, SandyScops
tudes, in Korup National Park, Yabassi and the Owl Otus icterorhynchus (pers. obs. in Cameroon
Campo area (Important Bird Areas CM019, and Congo). Similarly Butynski & Ehardt (2003)
CM026 and CM031 in Fishpool & Evans 2001). noticed that dwarfgalagos Galagoides spp. reacted
AtYabassi (nearYingui), mysingle recordwasjust strongly to the calls of B. p. vosseleri in the
below 500 m. Udzungwas ofTanzania, ‘by giving long series of
alarm and other calls,’ and relate this behaviour to
Ecology that ofpotential prey.
B. poensis. All general works seem to agree that B. leucostictus. Data on the habits ofthis owl are
this species is rather unspecialised, beingfrequent- more scanty. In Gabon Brosset & Erard (1986)
ly found in secondary situations (e.g. at forest considerthatit is probablymore abird ofveryold
edges or in farmbush, early stages offorest regen- secondaryforest, found overall in more developed
eration, old secondary forest) and much mor&e stagesofforestregeneration thanB.poensis. My21
rarelyintheheartofprimaryforest (e.g. Brosset personal observations were in the following
My
Erard 1986). 27 personal encounters with the
habitats:
species were in the followinghabitats:
• edge ofold secondary forest along roads: two
• gardens and farmbush some way from forest (Congo);
edge: two (Cameroon, Congo);
• in open canopy of selectively logged forest:
• ecotone between forest and cultivation/farm- four (Ghana, Congo);
bush: nine (Ghana, Cameroon, Equatorial
• in asmall natural clearing (salt-pan) with scat-
Guinea, Congo, Rwanda);
tered trees, in the middle of primary forest:
• edge ofold secondary forest along roads: five one (Nki in Cameroon);
(Ghana, Cameroon, Congo);
• in (almost) untouched semi-evergreen forest,
• edge ofprimary forest giving onto large natu- with naturally open canopy: 14 (Congo,
ral clearing (salt-pan): one (Lobeke in Cameroon). This includes six observations
Cameroon);
near a small track in Nouabale-Ndoki
• mosaic of forest patches and savanna: two National Park (Congo), where the track was
(Bakossi Mts in Cameroon, Kyabobo in rather overgrown and no wider than 2-3 m.
Ghana); The other eight observations were in
• inside selectively (moderately) logged forest: untouched (unlogged) forest, mainly in
two (Congo); Odzala National Park and Nouabale-Ndoki
• inside primary or near-primary forest with a National Park in Congo, also at two sites in
naturallybroken canopy, eithersemi-evergreen south-east and western Cameroon.
(Nouabale-Ndoki in Congo) or Afromontane Food-wise, although slightly larger than B.
(Nyungwe in Rwanda): five; poensis, this owl seems to be essentially insectivo-
• inside closed-canopy evergreen forest: one rous, which Bates (1930) and Chapin (1939) ten-
(Oban Hills, Nigeria). tativelyattributed to itsweak-footedstructure and
Prey choice seems to be very wide in this small bill. All stomach contents ofspecimens con-
species, ranging from insects to frogs, birds, small tain exclusively insects, although a captive bird
mammals (Bates 1930, Chapin 1939) and ‘also acceptedoil-palm fruits andoncenibbledleavesof
occasionallyfruit’ (Kemp inFryetal. 1988, source aFlamboyanttreeDelonixregia (Jellicoe 1954). In
Fraser'sEagle OwlandAkunEagle Owl:Dowsett-Lemaire BullABCVol13No2(2006)-149
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Gabon, Brosset Erard (1986) noted that a cap- south-east Cameroon and at Yabassi in the west,
tive immature accepted only large insects and we spent many nights inside primary forest on
refused small vertebrates. Jellicoe (1954) observed walking expeditions: by far the main Bubo species
similarbehaviourinhercaptive, butitdidswallow encounteredwas leucostictus, the onlycontactwith
pieces ofrodentifpreviouslychopped up. Beyond B.poensisbeingon theedgeofaverylargesaltpan
the age ofsix months, it managed to break up a (Lobeke). The two species were nevertheless
whole dead rat by dragging and ‘walking’ on it, observed in relatively close proximity in the
but this andtheprocess ofeatingitmight take the Mayombe ofCongo (old secondary forest at road
whole night. If ‘accidentally given a rat that was edges) and in semi-evergreen forest in Nouabale-
not quite dead, the bird appeared terrified ofthe Ndoki National Park.
slight movement’ (Jellicoe 1954: 160). Bates
(1930) sawone catchingcockroaches in the air; in Voice
southern and northern Congo I observed birds in The voice of both species is rather varied, with
moonlight flycatch on the edge ofa small track. calls falling into two main categories: whistles and
Chappuis (1978) saw one flycatching in Cote low-pitchedguttural trills. In addition B. leucostic-
d’Ivoire. I have never noticed reactions of fear tusfrequentlyproduces ashortgruntwhichhasno
among small mammals or other bird species near equivalent in its congener.
a calling B. leucostictus.
B. poensis. The most frequently heard calls are
To summarise, despite the fact that R. J. gutturaltrills (alsocalledpurringorgruntingtrills,
Dowsett and I camped more often at forest edges as in Borrow & Demey 2001); they can be given
than inside forest, there is no doubt that B. poen- in isolation or by pairs in duet. They are the
sis is more often encountered in secondary situa- ‘roulades’ in Chappuis (1978, 2000). Unprovoked
tions (even gardens) than its congener; the main pairs often call to each other softly korororororo,
habitat ofB. leucostictusis probablyold secondary kororororo, each call lasting 1-2 seconds (Fig. IE).
and primary forest, provided the canopy is some- Birds can give longer trills under certain circum-
whatopen (naturallyorthroughselectivelogging). stances, and usuallydo sowhen provokedbyplay-
On the other hand, it seems that B.poensisis only back.Theselongtrills canagainbegivenbyisolat-
exceptionally encountered in closed-canopy pri- edbirds aswellas in duet; theylastseveral seconds
mary forest: my single record in such habitat (often 3-5) and are somewhat modulated in pitch
(Oban Hills, Nigeria) is based on a birdgivingthe or volume. Examples are illustrated in Fig. 1, B
high whistle all night long, probably an immature and C belonging to two members ofa pair react-
(see below). We were miles away from the edge of ing to playback, one starting to call before the
the forest, having become lost for two days. In other finished; they show some individual varia-
Captions to figures on opposite page
Figure 1. A-E: sonogramsofguttural trills ofFraser’sEagle Owl Bubopoensis, includingUsambaraEagleOwl B.p. vos-
seleri(Tanzania): A: UluguruMountain,Tanzania (tape-recorded in November 1995 byC. Carter); B andC: Nyungwe
Forest, Rwanda (produced byboth membersofapair, tape-recordedbyFD-LinNovember 1989 on SonyTCM-150
cassette recorder, modified byMineroff,with Beyer Dynamicmicrophoneandparabolicreflector); D: captivebirdheld
in Antwerp Zoo, Belgium (from Chappuis 1978); E: pairduettingin Coted’Ivoire (fromChappuis 1978). F: short,
slow trill (staccato) produced byAkun EagleOwl B. leucostictus, Coted’Ivoire (from Chappuis 1978); G: highwhistle
of(presumed) immature B.poensis(Nyungwe Forest, Rwanda,January 1990, tape-recordedbyFD-L). Sonogramspro-
duced on a KayElectricSonagraph 7029A, usingwideband filter.
A-E: sonogrammesde rouladesdu Grand-dueaaigrettes Bubopoensis, ycompris laformeB.p. vosselerideTanzanie:
A: Uluguru Mountain,Tanzanie (enregistreen novembre 1995 parC. Carter); B etC: ForetdeNyungwe, Rwanda
(roulades produites par lesdeux membres d’un coupleetenregistrees par FD-Len novembre 1989, avecun
enregistreur-cassetteSonyTCM-150 modifie par Mineroff, et un microphone Beyer Dynamiccentresurparabole);
D: oiseau captifduzood’Anvers (enregistrement publie parChappuis 1978); E: duo d’un coupleen Coted’Ivoire (tire
deChappuis 1978). F: trille (staccato) du Grand-due tacheteBuboleucostictus(Coted’lyoire, tiredeChappuis 1978);
G: sifflement purd’un B.poensis(probablement un immature, Rwanda, janvier 1990, enregistreparFD-L.).
Sonogrammes produitsavecun spectrographe KayElectric7029A, en bande large.
150-BullABCVol13No2(2006) Fraser'sEagleOwlandAkunEagle Owl:Dowsett-Lemaire
kHz
1~ A
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1-J B
(M if# »*<ilwwiyiiiiii.tiiaiiNw *
i_ C
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o- f ?!
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— MMMl—iu
0- „^TTt —1—1 ““”T ,‘ -j- j
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Fraser'sEagle OwlandAkunEagle Owl:Dowsett-Lemaire BullABCVol13No2(2006)-151
tion. Playback attracted these birds to within 3-4 moved slightly or because they had entered into a
m
ofthe car, onwhich the recorderwas resting; at rest phase.
one point one birdwas on one side ofthe car, and The form vosselerifromTanzania is not as well
its mate on the other. known but it produces guttural trills identical to
Two young birds fledged in the same territory those of nominatepoensis (compare Fig. 1A with
in Nyungwe Forest, Rwanda, in December 1989, IB recorded in Rwanda). Until C. Carterobtained
amonthafterI recordedtheadults: theyproduced a good tape-recording in the Ulugurus (Hunter et
high-pitched, thin weeeu whistles, whilst the al. 1998) ithad been difficultto interpretthewrit-
adultswere rattlingin duet nearby. Amonth later, ten descriptions of this owl’s calls (as in Olney
when campingatexactlythesame spot, all I heard 1984, Evans et al. 1994). A copy of Evans’s tape
was a pure, drawn-out, powerful, eerie whistle from the Usambaras is virtually inaudible. Olney,
(Fig. 1G, as in cut one in Chappuis 1978, 2000), who observed them in captivity mentioned a
givenalmostallnightlongwithoutinterruptionat repeated (three or four times) regular double sylla-
a mean rate oftwo whistles per minute. This bird ble’ and Evans et al ‘bursts ofwubbering notes.’
wasjoinedbyanother, producingthesame typeof Carter’s tapeputanendto themystery, andindeed
whistle, in the middle of the night. Although I by playing my tape ofthe duetting pair ofnomi-
assumed at the time (Dowsett-Lemaire 1990) that nate B.poensis from Rwanda, he was able to bring
thesewere produced by the adult pair, it seems far the Uluguru bird closer whilst a second was also
&
morelikelytheywereproducedbythe immatures; stimulatedtocall. Butynski Ehardt (2003) heard
they were no more than a louder, slightly longer many similar guttural trills (‘loud purring’) in the
version ofthe whistle produced by the fledglings. Udzungwas; they also remarked that high whistles
Playback ofthis vocalisation did not produce any have notyet been heard in this form, but the lim-
reaction. I have heard this eerie, powerful whistle itedfieldobservations are insufficientto prove that
in several places (Nigeria, Congo, Ghana), some- they do not exist, and surely immatures are likely
times close to a pair ofadults producing a duet of to produce a call differing from the adult trills.
trills, i.e. the whistling bird is clearly tolerated by The trills of members of a pair of B. poensis
the territorial pair, which again suggests the whis- show some individual variation, probably sexual.
tles come from a young bird. On other occasions, The structure of the notes in one bird is a little
the whistle was produced in isolation, often all more square, less narrow and high than in its
night, but this bird orothers present neverreacted mate; these structural differences appear clearly in
to playback, not even to the aggressive trill call. In the duet recorded in Rwanda (Fig. IB, C) and
Ghana in particular, two trials ofplayback in late appear again in another duet recorded in Cote
December and January near whistling birds d’Ivoire (Fig. IE). If indeed they are sexually
together with trilling birds (presumably a family) based, the main bird recorded by C. Carter in the
did not provoke an aggressive reaction, whichsug- Ulugurus (Fig. 1A) was presumably of the same
gests that the breeding cycle was far enough sexas B, and the captive bird recorded inAntwerp
advanced that the adults had entered a period of (nominatepoensis Fig. ID) ofthe sex ofC.
,
territorial rest.
As in other owls, B. poensis is most vocal c.1 B. leucostictus. This species overall appears less
hour after dark (presumably after the first bout of demonstrativeand noisythan B.poensis, butvocal-
feeding), though some short trills can be given isations are quite varied. By far the most frequent
long before that, in late afternoon and around and characteristic call is a low-pitched short grunt
dusk. Birds also call at other times in the night, roh, roh, roh . . . repeated at intervals ofa few sec-
and until just before dawn. The persistent long onds (presented in cut one in Chappuis 2000). I
whistlesofpresumed immaturesareoften heardall heard it on 14 of my 21 encounters with the
night, shortlyafterdusk until dawn. Adults do not species, usually unprovoked by playback (but see
call everynight: atanycamp nearan occupied ter- below).This has never been heard in B.poensisand
ritory it is indeed usual to hear vocal activity on appears to be the mostreliablecallforspecies iden-
only one ofthree or four nights, or even a single tification. It is produced by a single bird, even ifa
night in aweek.Tapes have been played at known mate is present. There is specimen evidence that
spotswithout reaction, either because the pairhad the bird responsible is the male, as A. Forbes-
752-BullABCVol13No2(2006) Fraser'sEagleOwlandAkunEagle Owl:Dowsett-Lemaire
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Watson in Liberia (in Colston Curry-Lindahl eehoooooooh, lasting2-3 secondswithaslightdrop
1986) collected a male after following it for some inpitchattheend.Theyareintermediatebetween
time, andthebirdwasgiving adeep, measuredsoft the high, powerful whistles of (presumably)
grunting hu (2 sec interval).’ As Forbes-Watson immature B. poensis and the dismal screams tape-
remarked, it does not carry very far. I measured a recordedinacaptiveShelley’sEagleOwlB. shelleyi
distanceofaudibilityofbarely500 m, inanareaof from Liberia (in Chappuis 1978, 2000). One bird
fairlyopen-canopyforest (Congo). The call can be tape-recorded in the Mayombe was answered by
produced over long periods ofup to an hour, just another with a short, hoarse whistle. The night
after dusk and at any time during the night until before, all I had heard in the—areawas the distinc-
almost dawn. This most distinctive call was not tive roh—. Possibly this call is by analogy with B.
described byKemp (in Fry etal. 1988). poensis produced by immatures, but why it
B. leucostictus also produces short trills, some- seems to be given so rarely is unknown.
times very similar to B. poensis but usually slower
To conclude, vocalisations ofB. poensis carry
(thenmorestaccato than atrill, Fig. IF); theyusu-
furtherafieldthan thoseofB. leucostictus, especial-
lailkley ltahsattc.o1fsB.ecpoonedn.sisI.haOvneenebviredr Ihewaartdchaeldonigntfruillll ly the high-pitched whistles of presumed imma-
view on a dead tree in Congo started with a low, tures. Thesewhistles do not seem to have any ter-
ritorial value. The most characteristic call of B.
hoarse ascendingwhistle whoooeefollowed bysev-
poensis is the long guttural trill (several seconds
eral short, soft staccato trills kokokokokok; it then
duration), while that ofB. leucostictus is the low
continued with a series ofgrunts roh roh ... for
, grunt roh. Both species give short trills or staccato
at least 40 minutes. These staccato notes and
hoarse whistles are all presented by Chappuis trills, singlyor in duet, and it is not always easyto
attribute them to species.
(1978, 2000). Duets exist but consist only ofthe
short staccato trills. I have heard duets ofstaccato
trills in six pairs (Congo, Cameroon and Ghana). Tape playback and interspecific reactions
In northern Congo and south-east Cameroon, B. poensis. This species reacts well to playback of
several pairs observed in moonlightwith powerful shortorlongtrills, butwas neverobserved (so far)
torches produced duets of staccato kokokoko, to react to playback ofhigh whistles. Playing the
kokoko ka-kah, the first being close to a slow ver- long trill from Chappuis 1978 (Fig. ID, obtained
sion of a B. poensis trill, the second (by the in a captive bird) can elicit pairs to answer with a
female?) endingin amostdistinctivedoubleexcla- duet ofshort or long trills, and isolated birds also
mation (heard throughout Nouabale-Ndoki in answer with long trills. Similarly, a positive reac-
Congo, Boumba-Bek and Nki in south-east tion was obtained with B. p. vosseleri from
Cameroon). In Cameroon, one member ofa pair Tanzania by playing a duet of trills ofB. poensis
precededtheslowtrillsbyseriesofwoff,wojf,woff. from Rwanda (Hunter etal. 1998).
A
... sort ofbark can also be heard in an excited
B. leucostictus. None of the usual vocalisations
(or alarmed) bird. In Ghana, the duets heard in
two places consisted offaster trills nearlyidentical carries very far, and practice taught me that the
topoensis, but eventuallyone bird switched to the bestwayoflocatingthis owl on asilentnightis by
typicaldeepgruntroh, roh, roh. . . . Someduetsare pClhaaypipnugisth1e97l8o)n.gTthriellfoolfloBw.inpgoeenxspiseri(lmaesnttscuwterien
producedspontaneously, others provoked byplay-
carried out.
back, thus there is no doubtthattheyhave territo-
rial value. Neither the roh calls nor the slow trills 1. Mbeli Camp in Nouabale-Ndoki National
are given everynight; as in B.poensis, theymaybe Park, Congo, April 1996. Small clearing in pri-
heard on one ofseveral evenings or nights, orjust mary semi-evergreen forest. No owl calling.
once in aweek. Playback oflong B. poensis trill provoked a vocal
High-pitched whistles have been heard twice reaction in the local pair ofB. leucostictus within
in Congo (Mayombe at Goumina, Odzala seconds: pair started duetting with briefstaccato
National Park),with onebirdeventuallyseenwell. trills, second bird ending with a double exclama-
These differ from B. poensis by being noticeably tion, thus kokoko, ka-kah! (birds well seen in
hoarserin tone, lowerpitchedand rather ‘sinister’: strong torchlight).
Fraser'sEagle OwlandAkunEagle Owl:Dowsett-Lemaire BullABCVol13No2(2006)-153
2. Nouabale-Ndoki National Park, 25 km of Discussion
track from near Bomassa to Ndoki, April-May There is no doubt that the long aggressive trill of
1997. Systematic searches for nightjars were car- B. poensis is well understood by B. leucostictus;
ried out in the second halfofthe night (Dowsett- many pairs or individuals ofthe latter react to it
Lemaire & Dowsett 1998a). The B. poensis tape with their own typicalvocalisations, lowgrunts or
was played on seven of eight nights, but not at short staccato trills (usually in duet ifboth mem-
every stop (through lack oftime); distances were bers of the pair are present). B. leucostictus has
measured with the car odometer. Three initially never been heard producing the long trill even
silent individuals replied to playback ofB. poensis when clearly reacting to the B. poensis tape (as
trills with a series oflow grunts roh, roh. ... A above). Species-specific characters are preserved in
fourth bird was uttering this call spontaneously interspecific reactions. Despite these two eagle
and playback of the B. poensis rattle provoked it owls being partly separated by their ecological
into a short staccato kokokokoko. The fifth bird requirements, by diet and certainly by altitude in
was also calling spontaneously; the roh roh call montane regions, they come into competition in
,
was tape-recorded and played back, but this did several places, particularlyin semi-evergreen forest
not produce much reaction (more grunts at the withanopencanopy, orinlightlyloggedforest. In
same distance). Three B. poensiswere also located two places in the Mayombe, I had both species
alongthis track; locations ofeitherspecies ofBubo within 1 km or slightly less of each other. In
were from one to several kilometres distant. The Nouabale-Ndoki, the interspecific distance was of
highest concentration was one B. leucostictus fol- the order of 1 km or more. Playback experiments
lowed bya B. poensisjust under 1 km further, fol- and direct observations of localised individuals
lowed by a B. leucostictus 1 km further. The other suggest that they maintain separate territories.
two B. poensis were many kilometres away from However, these birds do not call every night, lim-
the nearest B. leucostictus. its ofterritories are difficult to define in nocturnal
3. Boumba-Bek, south-east Cameroon, species, and further observations are required to
December 1997. Playback ofB. poensis trill pro- establishwhether territories are totallyexclusive of
those ofcongeners.
voked a pair ofB. leucostictus to answer, first by a
Interspecific countersinging between con-
short loud bark (in alarm?), then a duet ofstacca-
to kokokoko, kokoko ka-kah! generic species is an uncommon phenomenon in
the African tropics, but is used persistently
4. Nki Forest, south-east Cameroon, January betweencertainspeciespairs. Onecommonexam-
1998. Small natural clearing (salt-pan) with scat- ple is that ofYellow-billed Tauraco macrorhynchus
tered trees, in the heart of primary forest. We and Green Turacos T.persa, where they meet in
camped for five nights at this spot. No Bubo spp. Gabon and Congo. They defend interspecific ter-
called on the first night; the second evening I ritories through countersinging, i.e. the song of
played the long trill ofB. poensis: a pair ofB. leu- one provoking a vocal response in the other
costictus immediately perched on a bare branch of (Brosset & Erard 1986, Dowsett-Lemaire 1997).
a large tree and, after one or two woff-woff, In the forests ofnorthern Malawi, three species of
answered with the usual duet of staccato trills, apalis warblers defend interspecific territories
ending in ka-kah!On the third evening, one bird through countersinging, keeping separate territo-
was grunting {roh, roh . . . ), without prompting, ries either horizontally (GreyApalisApalis cinerea
just after dusk. On the fourth evening, the pair and Chestnut-headed Apalis A. chapini), or verti-
was flying around the clearing, from tree to tree, cally (Bar-throated Apalis A. thoracica, with A.
uttering series of wof-wof-wof-wof-wof. . . and chapini above it): Dowsett-Lemaire (1989). In
occasional briefstaccato notes; theywerequitevis- parts of northern Ghana, Red-winged Warbler
ible, as the night was clear, with halfmoon. They Heliolais erythropterus and Tawny-flanked Prinia
were quiet on the fifth night. This demonstrative Priniasubflavaoccur in high densities side byside
behaviour gave the impression that it had taken in open woodland, and have been heard counter-
them three nights to make quite sure that the singing on numerous occasions (pers. obs.,
intruding’ B. poensis had been scared far away. 2004-05); they seem to maintain (at least partial-
154-BullABCVol13No2(2006) Fraser'sEagle OwlandAkunEagle Owl:Dowsett-Lemaire
&
ly) exclusive territories, at least at the peak ofthe Burgess, N. D., Fjeldsa, J. Botterweg, R. 1998.
rainy season ifnot in the dry season (when seen FaunalimportanceoftheEasternArcMountainsof
closer to each other). These two warblers have KenyaandTanzania.J.E.Afr. Nat. Hist. 87:37-58.
sometimes been placed in the same genus; they Butynski, T. M. & Ehardt, C. L. 2003. Notes on ten
appear to compete where Heliolais is particularly restricted-rangebirds in theUdzungwaMountains,
common. InMalawiwherethelatteris morelocal, Tanzania. Scopus23: 13-28.
I had not noted this type of interaction. In all Chapin, J. P. 1939. The birds of the Belgian Congo.
these cases, as in the Bubo species, each bird uses PartII. Bull. Amer. Mus. Nat. Hist. 75: 1-632.
its own species-specificvocalisations andevidently Chappuis, C. 1978. Illustration sonore de problemes
bioacoustiques poses par les oiseaux de la zone
learns to recognisetheotherspecies’ssongthrough
ethiopienne. Alauda 46: 327-355. (With disc no.
competition.
One more case ofinterspecific countersinging 9.)
Chappuis, C. 2000. Oiseaux dAfrique (African Bird
involves two small forest batises, Verreaux’s Batis Sounds), 2. WestandCentralAfrica. 11 CDs. Paris:
Batisminimaand Bioko BatisB.poensis. In north- Societe d’Etudes Ornithologiques de France &
ern Congo (where I never found B. minima), the London, UK: British Library National Sound
tape ofB. minima often provoked B. poensis into Archive.
song, and in Equatorial&Guinea (where both Colston, P. R. & Curry-Lindahl, K. 1986. TheBirdsof
occur: Dowsett-Lemaire Dowsett 1999), B. Mount Nimba, Liberia. London, UK: Brit. Mus.
minimareadilyreactedto B.poensis. However, this (Nat. Hist.).
problemis complicatedbythefactthattheirsongs Demey, R. & Rainey, H. J. 2004. The birds ofPic de
are rather similar, even sometimes identical, and Fon Forest Reserve, Guinea: a preliminary survey.
Erard (in Urban etal 1997: 599) observed coun- Bull.ABC11: 126-138.
&
tersingingin Gabonwhere ‘theyseem to copyone Dowsett, R. J. Forbes-Watson, A. 1993. Checklistof
anotherwhen theymeet’! BirdsoftheAfrotropicalandMalagasyRegions. Vol. 1:
Finally, aword ofcaution: since playback ofa Species Limits and Distribution. Liege: Tauraco
tape-recording ofBubopoensis is equally likely to Press.
call up a B. leucostictus, observers should ascertain Dowsett-Lemaire, F. 1989. Ecological and biogeo-
whichspeciesis responding, andwithwhattypeof graphical aspects of forest bird communities in
call itresponds. Ashorttrill is perhaps insufficient Malawi. Scopus 13: 1-80.
to identify the species with certainty, but short Dowsett-Lemaire, F. 1990. Eco-ethology, distribution
and status of Nyungwe Forest birds (Rwanda).
grunts roh, roh are the signature tune ofB. leucos-
TauracoRes. Rep. 3: 31-85.
tictus, whereas a long guttural trill is that of B. Dowsett-Lemaire, F. 1997. The avifauna of Odzala
poensis. National Park, northern Congo. Tauraco Res. Rep.
6: 15-48.
AIcakmngorwatlefeudlgteomLe.nD.tCs. Fishpool forprovidingsome Dowsoetthte-rLepmecauilriear,itF.ie&s oDfowBsreotwt,nRN.igJ.ht1j9a9r8aC.apVroicmalulagnuds
referencesandC. Carterforsendingmeacopyofhis binotatus. Bull. ABC5: 35-38, backcover.
tRaapienefyroamndthPe. UStleuygnurcuomMmoeunnttaeidnso.nNa.dBraofrtroowf,thHi.s DowsoefttO-LkeumaiMrte, aF.nd&oDtohwesretItB,AsR.iJ.n 1N99W8b.PrSuorvvienycse
paper. (Cameroon), February-March 1998. Unpubl.
report. BirdLife International.
References Dowsett-Lemaire, F. & Dowsett, R. J. 1999. Birds of
Bates, G. L. 1930. HandbookoftheBirdsofWestAfrica. the Parque Nacional de Monte Alen, mainland
London, UK:John Bale, sons & Danielsson. Equatorial Guinea, with an updating ofthe coun-
&
Borrow, N. Demey, R. 2001. BirdsofWesternAfrica. try’s list.Alauda67: 179-188.
London,&UK: Christopher Helm. Dowsett-Lemaire, F. & Dowsett, R. J. 2001. African
Brosset, A. Erard, C. 1986. Les oiseaux des regions forestbirds: patternsofendemismandspeciesrich-
forestieres du nord-est du Gabon. Vol. 1. Ecologie et ness. In Weber, W., White, L. J. T., Vedder, A. &
comportementdesespeces. Paris: SocieteNationalede Naughton-Treves, L. African Rain Forest Ecology
Protection de laNature. and Conservation. An Interdisciplinary Perspective.
NewHaven & London, UK:Yale UniversityPress.
Fraser'sEagle Owla?idAkunEagleOwl:Dowsett-Lemaire BullABCVol13No2(2006)-155
Evans, T. D., Watson, L. G., Hipkiss, A. J., Kiure, J., blunter, N., Carter, C. & Mlungu, E. 1998. A new
Timmins, R.J. &Perkin,A.W. 1994. Newrecords locationfortheUsambaraEagleOwlBubovosseleri.
ofSokokeScops Owl Otusireneae, UsambaraEagle Scopus20: 52-53.
Owl Bubo vosseleri and East Coast Akalat Jellicoe, M. 1954. The Akun Eagle Owl. Sierra Leone
Sheppardia gunningi from Tanzania. Scopus 18: Stud. 1954: 154-167.
40-47. Olney, P.J. 1984.TherareNdukEagleOwlBubopoen-
Fishpool, L. D. C. & Evans, M. I. (eds.) 2001. sis vosseleri or B. vosseleri at the London Zoo.
ImportantBirdAreasinAfricaandAssociatedIslands: Avicult. Mag. 90: 129-134.
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Priority Sites for Conservation. Newbury: Pisces Urban, E. K., Fry, C. FI. Keith, S. (eds.) 1997. The
Publications & Cambridge, UK: BirdLife Birds ofAfrica. Vol. 5. London, UK: Academic
International. Press.
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Friedmann, H. Williams, G. 1968. Notable
J. Le Pouget, 30440 Sumene France. E-mail:
records ofrare or little-known birds from western ,
[email protected]
Uganda. Rev. Zool. Bot. Afr. 77: 11-36.
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Fry, C. FT, Keith, S. Urban, E. K. (eds.) 1988. The Received 2 January 2006; revision accepted 2 June
Birds ofAfrica. Vol. 3. London, UK: Academic 2006
Press.
Appendix.Gazetteerofsome localitiescited.
Annexe.Coordonneesdecertaines localitescitees.
AtewaRange,Ghana 06°14’N 00°34’W Nouabale-NdokiNP,Congo 02°20’N 16°30’E
BakossiMts,Cameroon 05°00’N 09°40’E NyungweForest, Rwanda 02°26’S 29°10’E
Boumba-Bek,Cameroon 02°40’N 15°00’E ObanHills, Nigeria 05°35’N 08°20’E
Goumina,MayombeofCongo 04°08’S 12°07’E OdzalaNP,Congo 00°30’N 14°45’E
Kyabobo,Ghana 08°25’N 00°36’E Oku Mt,Cameroon 06°10’N 10°30’E
Lobeke,Cameroon 02°15’N 15°45’E Yabassi(Yingui),Cameroon 04°30’N 10°20’E
Nki,Cameroon 02°20’N 14°30’E
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