The Tanzanian Race of Swynnerton's Robin Swynnertonia Swynnertoni rodgersi

7 Pages·1997·5.7 MB·

by  Guy Q A Anderson

The Tanzanian race of Swynnerton’s Robin
Swynnertonia swynnertoni rodgersi
Guy Q.A. Anderson'1 Tom D. Evansb andLaura G. Watsonc
,
Summary: ThegloballythreatenedSwynnerton’s RobinSwynnertoniaswynnertoniis restrictedto a
fewwidelyseparated,forestedmountainblocksinTanzania,ZimbabweandMozambique3 Threeraces
.
have been described. This article clarifies and expands published information on the Tanzanian
subspecies.S.s. rodgersi,andassignstherecentlydiscoveredlowlandEastUsambarapopulationtothis
race.
The globally threatened Swynnerton’s Robin
Suynnertoniaswynnertoniis restrictedto a few
widelyseparated,forestedmountainblocksinTanza-
nia, Zimbabwe andMozambique3 (see Fig 1). Three
raceshavebeendescribed: thenominatediscovered
in 1905 in Chirinda forest, Zimbabwe18 and since
found in other small forest patches in the Eastern
HighlandsofZimbabwe;S.s.'umbratica’(considered
conspecific with the nominate race by Keith etaP)
endemictoMountGorongosa, Mozambique2 andS.
;
s. rodgersi, describedonthebasisoftwomalespeci-
menstaken in 1981 at Mwanihana in the Udzungwa
Mountains,Tanzania(arangeextensionof1,300km)20
.
Therehavebeensubsequentrecordsfromtwoother
sites in the Udzungwas3 Chita, in the Udzungwa
:
ScarpForestReserve12 andtheNdunduluMountains,
,
intheWestKilomberoScarpForestReserve".
The first records in the East Usambaras were in
1990, afurtherrangeextension ofc400km910 There
.
havesubsequentlybeenmanyrecordsinthefoothills
of these mountains1-8. This population was initially
believed to represent anothernew race, since it dif-
fered from the type description of rodgersi1,9,1(U1
.
However, thetypedescriptionandtype-specimenof
rodgersi were not wholly representative of the Fig 1. EastAfrica showinglocations mentioned inthetext.
UUddzzuunnggwwaa faonrdm,Uasnadmbiatrias appoppaurleanttionthsatbeblootnhgthteo 13==SCMhhtaidrGieondrdaoa,nrge2aosz=aaV,rue4mf=boraUesdHtzieugdhnmlgaownuadnstMat(siS.ne,lb5dloo=mcskCesh.einta),,
rodgersi, whose characteristics, as now understood, 6 =Mwanihana, 7 = NdunduluMts, 8= RubehoMts,
are describedbelow. 9 = Ngurus, 10=EastUsambaraMts.
Material examined
Specimensandphotographsoflivebirdsinthehand Table 1.Origin,ageandsexclassofallmuseumspecimensand
werecomparedbytheauthorsattheNaturalHistory photographsofSwynnerton’s Robinexaminedfromthe
Museum, Tring, UK. More than 30 specimens ofthe Udzungwasand EastUsambaras,Tanzania(photographed birds
nominate formwere examined, including males, fe- in brackets).
males and juveniles, fromvarious localities. Table 1 Origin AdultMales AdultFemales Juveniles
shows the origin, age and sexclass ofallTanzanian EastUsambaras: 0(3) 1(2) 0(1)
birds examined. J Fjeldsa kindly took notes on two Udzungwas: Mwanihana 2* 1 0
males in the Copenhagen collection, one each from Udzungwas:Chita 4 1 2
MwanihanaandChita,andthesebirdsareincludedin ‘Includingtheholotypeofrodgersi.
thefiguresinTable1.NospecimensfromtheNdundulu
TanzanianraceofSwynnerton’sRobin:Andersonetal BullABC Vol4No2-83
Plate 1. Adult male (left) and adult female (right) Swynnerton’s RobinSwynnertoniasuynnertonirodgersi, EastUsambara
lowlands, 1992 (Laura Watson)
Plate 2. Adult male Swynnerton’s RobinSwynnertonia Plate 3. Adult female Swynnerton’s Robin Swynnertonia
swynnertoni rodgersi showing grey upper-tail coverts swynnertonirodgersi, showing pale chin and throat, East
,
and lowerrump, EastUsambara lowlands, 1992 Usambara lowlands, 1992 (Laura Watson)
(Laura Watson)
84-BullABC Vol4No2 TanzanianraceofSwynnerton’sRobin:Andersonetal
Mountains or ofS. s. ‘umbratica’ were available for male in breeding condition6). It is possible that the
comparison. type-specimenwas a first-yearbird, sexuallymature
Adultsweretakenasthosewhichlackedanytrace but retaining subadult plumage. If it was not fully
ofjuvenilespottingorscaling.Specimensweresexed adult, itmaybeinvalidtocompareitsotherplumage
accordingtothecollectors'notesthroughout.Forlive featureswithadultsfromotherpopulations.Thesec-
birdscaughtandphotographed, allbrighter, darker- ondmalespecimenfromMwanihana doesnotshow
headedindividualswereassumedtobemaleandall these fringes to the breast feathers (J Fjeldsa in litt)
duller, pale-headed birds female (for the latter as- and isthusamoretypicaladult.
sumption, see the caveat within the description of The race of birds in the Ndundulu Mountains
juvenilebirdsbelow).Thisconsistentdivisionfitsthe couldnotbereassessed,butwaslistedasrodgersiby
sexualdimorphismdescribedforthenominaterace13 the finders". This seems likelyas the Ndundulus are
.
only 15 kmfromMwanihana.
Racial status ofthe Tanzanian
populations Distinctive plumage features of
No consistent plumage differences were found be- S. s. rodgersi
tweentheEastUsambaraandChitabirdsofeithersex, The following discussion contrasts rodgersi in the
,
which are therefore considered to be the same sub- broad sense justified above, with the nominate race
species, S. s. rodgersi. The one Mwanihana adult (described and illustrated by Keith et al15) and
female specimen is also inseparable from the single umbratica (see Clancey2).
adultfemalesfromChita andthe Usambaras. Males ofthe nominate race and rodgersimaybe
However,thetwomalespecimens(includingthe inseparable except by direct comparison. The best
holotype) and type description of rodgersi from featurefordiagnosingmalerodgersiappearstobethe
MwanihanadifferslightlyfrommalesfromChitaand yellow, ratherthanorange-yellow, breast. The other
the Usambaras. Although it is conceivable that the diagnosticfeaturesgiveninthetypedescription,20 a
Mwanihana birds are racially distinct from those of more olive crown and a greyer, less olive backthan
Chita and the Usambaras, this would be very unex- thenominateracearebothvariableanddonotapply
pectedforfourreasons: (i)Mwanihana liesbetween tomostspecimens. Theundertail covertsofrodgersi
ChitaandtheUsambaras,(ii)ChitaandMwanihanalie areindeed‘almostwhite’asstatedinthetypedescrip-
much closer to each other than either does to the tion,butsoarethoseofseveralspecimensexamined
Usambaras, (iii)ChitaandMwanihanaarepartofthe ofthenominaterace.Agreyrump,ifpresent,maybe
samemountainrange, and(iv)nootherbirdsubspe- diagnosticinadultmalerodgersi(seePlate2)butnot
cies are known to differ between Mwanihana and all individualsshowthisfeature.
Chita.ThelastpointisincontrastwiththeUsambaras, Thetypedescriptionofrodgersidoesnotinclude
where manysubspecies andallospecies ofmontane females, but, as described below, these are more
forest bird differ from those present in the distinctivethanmales,onaccountoftheirpalethroats.
Udzungwas21. For these reasons it seems far more Althoughnodirectcomparisonsweremadewith
likelythatonlyasingleraceiscurrentlyknownfrom specimens ofS. s. ‘umbratica’, its type description2
Tanzania.ThetwomalespecimensfromMwanihana suggests that both sexes have darker and browner
may be slightly anomalous, or the main plumage upperparts,andevenricherorangeonthebreastthan
difference (rump and uppertail covert colour) may the nominaterace(andthus also rodgersi).
be a variable feature in all known populations ofS. Thedifferentage andsexclassesofS.s. rodgersi
s. rodgersi. A detailed examination of further indi- showthe followingfeatures:
viduals from the Usambaras and the Udzungwas is
required, especially from Mwanihana. Adult males (illustrated in plates 1 and 2):
TheageingoftheholotypefromMwanihanaisin • The head of rodgersi is slate-grey, with the face
doubt. Ithasfine olivefringestothebreastfeathers, andearcovertsslightlypalerthanthecrownand
especially at the breast sides, a feature apparently centre of the throat. Some specimens from the
characteristic of a young bird, as it appears on all Udzungwas have an olive tint to the crown and
immature/juvenile specimens of the nominate race nape, giving a slight ‘capped’ appearance. The
(aged by the collectors). Thus the type specimen of head ofthe nominate race is pure grey, slightly
rodgersi may not be a full adult, although it was darkerintone.
describedassuch(thespecimenlabelindicatingthat • Themantle,upperrumpandscapularsofrodgersi
the testeswere enlargedwhencollected, implyinga arebrightolive,contrastingwithgreyhead,nape,
TanzanianraceofSwynnerton'sRobin:Andersonetat BullABC Vol4No2-85
tail, uppertail coverts andlowerrump (see Plate • Post-juvenile immature birds from Zimbabwe
2).Thenominateraceshowsslightlylesscontrast and Mozambique are described as having adult
betweenthedullermantleandheadthanrodgersi, female-like plumage but with paler breast and
andtheuppertailcovertsandrumparethesame belly13, and a paler grey throat2. There is no
olive colouras the mantle. This greyratherthan published record or specimen of this plumage
olive rump and uppertail coverts would form a from Tanzania. If an equivalent plumage does
valuable diagnostic feature of rodgersi except exist for rodgersi it is possible that one ormore
,
that, curiously, the two Mwanihana specimens ofthebirdsfromtheEastUsambarastreatedasan
have these feathers olive (with grey bases), like adult female may be an immature individual of
the nominate race. eithersex. However, theconsistencyofplumage
• Thewingsofrodgersiarealmostpureslate-grey, ofall adult female-type birds caught in the East
withpalerfringingtotheremiges,andslightolive- Usambaras, and their common occurrence in a
tinting on the coverts on some specimens. The pair with an adult male-type individual (see
nominateraceshowsveryslightolive-tintingtoall section on the species’ ecology, below) would
wingfeathers. suggest that these individuals are indeed adult
• Below, rodgersi shows a rich yellow breast and females and that the plumage characteristics
yellowbellyfading to pure white undertail cov- described above are valid.
erts. A thinwhite gorget, bordered black on the
loweredge, separatestheyellowbreastfromthe Biometrics
grey throat. The nominate race has a richer or- OnlylimitedbiometricdataareavailablefromTanza-
ange-yellowbreast, paling overthebellytobuff nia (see appendix). Also, caution should be used in
orwhiteundertailcoverts,andtheblackedgingto comparingmeasurementsfromspecimenswiththose
thethroatgorgetiswiderthanonmost rodgersi. from live birds, as some shrinkage in bone material
canoccurindryspecimens. Thedatadonotsuggest
Adultfemales (illustrated in Plates 1 and 3): any clear differences in wing length, tail length or
• Thecrown,napeandsidesofheadofrodgersiare weightbetweenthepopulations. Ifslightdifferences
slightly paler and more olive-grey than in the in means exist, they are undetectable in such small
nominaterace,andthemantleisaslightlybrighter samplesizes,andtheoverlapofvaluesisclearlylarge.
olive.Unliketheadultmale,theuppertailcoverts Birds of the nominate race appear, on average, to
andloweraimpoffemalerodgersiareconcolorous have smallerbills and largertarsi then S. s. rodgersi
with the upper rump and mantle. In the latter butsinceManson14didnotspecifythemethodsused,
respect they resemble females of the nominate
tomeasurethese,itispossiblethatthemeasurements
race.
are not equivalent.
• Onrodgersithechinandthroatabovethegorget
are creamy-white or buff, compared with slate Vocalisations
grey(concolorouswiththecrown)onspecimens
ofthe nominaterace. Thisgives rodgersiamuch ThecallgivenbybirdsintheEastUsambarasisasoft,
ticking rattle, often in alarm. This matches the call
lesswell definedupperbordertothethroatgor-
describedfromotherpopulations, reportedasa ‘de-
get.Thedarklowermarginofthewhitegorgetis
thinneronrodgersithanonthenominateraceand scending squeaky trill or purr’13, a ‘thin trill' and a
‘high-pitched,monotonous,purringnoiseofnogreat
darkgreyratherthanblack.
volume’14 The song, most frequently heard around
.
Juveniles: dawn and dusk in the East Usambaras, varies geo-
• The single juvenile individual caught in the graphically13. In the East Usambaras it was a sweet,
Usambaras resembled juveniles ofthe nominate high,leisurelywhistleoffournoteswiththefirstnote
race, which are variable according to exact age or pair of notes higher in pitch and the last note
and sex. The only noteworthy difference is a sometimesomitted,orafifthadded1.Allpermutations
contrast between the dull olive crown, scaled couldbeheardfromasingleindividualinsomecases.
with black, and the slightly rufous, mid-brown A recording has been deposited at the Wildlife Sec-
forehead,lores,superciliumandearcovertsofthe tion, National Sound Archive, 29 Exhibition Road,
East Usambara bird. Juveniles of the nominate London, UK. In Chirinda, Zimbabwe, the song has
race have only the forehead slightly paler and threeorfournotes13 inSeldomseen,Zimbabwe,three
;
more aifous thenthe crown, the rest ofthe face notes, sometimes two1,4 and in the Ndundulus three
;
being pale olive-brown. notes, occasionallyfour7
.
86-BullABC Vol4No2 TanzanianraceofSwynnertonsRobin:Andersonetal
Ecology to the Usambara population ofSwynnerton’s Robin
Swynnerton's Robin in the East Usambaras appar- is probably habitat degradation from illegal pitsaw
ently only inhabits lowland evergreen forest from logging, which continues apace in some areas1,84°.
130-550m.Breedingatthesealtitudesissuspected12. Two major international conservation projects
The species is almost certainly absent from operateinthearea.TheEastUsambarasConservation
submontane forests in the East Usambaras at 800- andDevelopmentProject(EUACDP)isagovernmen-
1,500m.whichhavebeenintensivelystudied5’940’15’16’17. tal project focusing on agriculturists and village-run
Thisisinstarkcontrasttoallotherknownpopulations, forests,whichreceivestechnicalsupportfromIUCN-
including the three Udzungwa populations, which TheWorldConservationUnion.TheEastUsambaras
are found at 850-1,750 m in montane forest3. This Catchment Forest Project (EUCFP) concentrates on
remarkable difference in habitat is currently unex- Forest Reserves, and is funded and technically ad-
plained. vised by the Finnish aid agency, FINNIDA, and
BirdsintheEastUsambaraswereseensinglyorin undertakenbythegovernmentalDivisionofForestry
pairs, keeping largely to the forest floor. On several andBee-keeping.Athirdventure, theKambaiForest
occasions, pairswere mist-nettedtogether. The spe- Conservation Project, is a smaller scheme, based in
cieswasfoundonbothgently-slopingandverysteep villages near the main lowland forest areas, and is
terrain, and in a variety offorest habitats from rela- supportedbytheTanzaniaForestConservationGroup.
tivelyundisturbedforestwith canopyupto40 m, to Potential alternatives to forest products are being
shorter,loggedforestwithanunderstoreydominated developedandthere are planstoplanthabitatcorri-
bythebamboo-likegrassOlyralatifolia. However, it dorstoreducethe effects offorestfragmentation.
appearstooccurprincipallyintheleast-loggedareas It seems possible that other populations of
wherethereisahigh, closedcanopyandarelatively Swynnerton’sRobinremainundiscovered,sincethere
openunderstoreywithoutextensivethicketsofOlyra are a numberoflowland and montane forestblocks
or other species8 Accounts from other populations which haveyettobe surveyed.
.
alsoindicatethattheyareprincipallyground-feeders
Acknowledgements
favouring areas ofleaflitterin evergreen forestwith
an open understorey74244 Themanyindividualsandorganisationswhoassisted
.
inthefieldworkreferredtointhispaperarethanked
Distribution and conservation status in the relevant expedition reports1’8,9. Neil and Liz
The species is listed as Vulnerable because of the Baker,thestaffoftheWildlifeConservationSocietyof
small,fragmentedanddecliningextentofitshabitat3. Tanzania, Dr Alan Tye, Dr Neil Burgess, Norbert
Highdensitiesoccurintheverysmallareasofhabitat Cordeiro,AlexHipkiss,JacobKiure,AndyPerkinand
occupiedbythe nominate race4 The status offorest the staffand volunteers ofFrontier-Tanzania all de-
.
birds onMount Gorongosa is unknown'. Rodgersiis serve special mention for their help with the
commonatChita12andinpartsoftheNdundulus7 but ornithological studies. Peter Colston, Robert Prys-
,
scarceratMwanihana12 However,neithertheareaof Jones and Michael Walters at the Natural History
.
habitatatsuitablealtitudes, northedegreeofhuman Museum(Sub-departmentofOrnithology),Tring,gave
pressure onthe habitatintheseareasare clear. adviceandaccesstospecimensandJonFjeldsaofthe
Therearecl40km2offorestintheEastUsambaras ZoologicalMuseum, Copenhagenkindlyloanedsev-
within the altitudinal range in the area from which eral specimens inhis care andtook notes on others.
Swynnerton’s Robin is known (TDE, unpublished Louis A Hansen provided biometrics on birds mist-
data). Almost all of this is within existing Forest nettedintheUdzungwas.NorbertCordeiro,Matthew
Reserves,butvirtuallyallhasbeendegradedtosome DennyandFionaHunterprovidedhelpfulcomments
extent and large areas, including Manga Forest Re- onthemanuscript. ('t
serve and the north part ofLonguza Forest Reserve,
may no longer support more than isolated pairs of References
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Forest Reserves probably have much larger logicalandHumanImpactSurveyoftheLowland
populations, and Marimba, Kambai, Semdoe and Forests,EastUsambaraMountains, Tanzania.Cam-
MtaiForest Reserves are also important. Some clear- 2. bCrliadngcee,y,UKP:.AB.ir1d9L7i4f.eSIunbtserpneactiiaotniaolnSsttuuddyieRsepionrsto5m9e-
ance for agriculture occurs in the limited areas of Rhodesian birds. Arnoldia 6: 1-43.
forestoutsideForestReserves,butthegreatestthreat 3. Collar,NJ.,Crosby,M.J. andStattersfield,A.J. 1994.
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Birdsto Watch2: theworldlistofthreatenedbirds. 14. Manson, A.J. 1990. The biology of Swynnerton’s
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4. Collar, N.J. and Stuart, S.N. 1985. Threatenedbirds 15. Moreau, R.E. 1935. A synecological study of
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Bird Preservation. 16. Sclater,W.L. andMoreau,R.E. 1932-33.Taxonomic
5. Cordeiro,N.J.submitted.Apreliminarysurveyofthe and field notes on some birds of north-eastern
montane forest avifauna of the East Usambaras, Tanganyika Territory (in five parts). Ibis 13: 487-
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88-BullABC Vol4No2 TanzanianraceofSwynnerton’sRobin:Andersonetal
0
Appendix: Biometricsofmist-nettedSwynnerton’s RobinsfromtheEastUsambarasin 1990and 1992,theUdzungwasin 1991 (LouisA
Hanseninlift),Zimbabwefrom 1977to 198514andmuseumspecimensfromtheUdzungwas. (Meanvaluesonlygivenforsamplesizes
greaterthantwo.)
Age/Sex Area Live/Specimeni Wing (mm)a Tail (mm)b Tarsus (mm)1
Range Mean n Range Mean n Range Mean n
Male Udzungwa Live 69.5-72.0 - 2 44.0-47.0 - 2 24.0 1
Udzungwa Specimen 73.0-75.0 74.0 4 - - - 24.7-25.1 25.0 4
Zimbabwe Live 66.0-73.0 70.4 106 43.5-52.0 49.8 98 23.0-28.0' 26.1' 164'
Adult Usambara Live 67.0-69.0 67.7 6 43.0-45.0 43.8 5 22.5-23.0 22.7 3
Female Udzungwa Live 67.0 - 1 45.5 - 1 24.0-25.1 2
Udzungwa Specimen 64.0-69.0 - 2 - - - 22.7-23.3 2
Zimbabwe Live 65.0-70.0 67.3 41 41.0-47.0 44.2 37 - -
Juvenile Usambara Live 67.0 . 1 43.0 - 1 - .
Udzungwa Live 67.0-69.5 - 2 42.0-46.5 - 2 24.0-27.7 2
Udzungwa Specimen 71.0-72.0 - 2 - - - 24.1-26.0 2
Zimbabwe Live 63.0—69.0e65.5e 19e 40.0—46.0e42.6e 18e - -
Age/Sex Area Live/Specimen' Bill (mm)dWeight(g)
Range Mean n Range Mean n
Adult Usambara Live 16.5-17.0 16.7 3 15.2-17.1 16.3 6
Male Udzungwa Live 16.3-17.3 - 2 14.4-15.9 15.4 3
Udzungwa Specimen 15.7-17.4 16.7 4 - - -
Zimbabwe Live 12.0-16.0' 14. f 164' 13.8-20.4 15.8 105
Adult Usambara Live 16.0-17.0 16.4 4 14.9-18.0 15.9 5
Female Udzungwa Live 17.7 - 1 14.8 - 1
Udzungwa Specimen 16.0-17.3 - 2 - - -
Zimbabwe Live - - - 14.4-19.5 16.3 44
Juvenile Usambara Live - - - 16.8 - 1
Udzungwa Live 16.0-17.0 - 2 15.0-16.5 - 2
Udzungwa Specimen 16.8-18.4 - 2 - - -
Zimbabwe Live - - - 13.0-20.0 15.5 20
3 ‘Maximum chord’ method used forUsambara and Udzungwa birds
b Measured as baseoftailfeatherstotipoflongesttailfeatherfor Usambara and Udzungwa birds
c Measured as distancefrom notch on tarsaljointto lowestfixed scale ontarsusforUsambara and Udzungwa birds
d Measured astipofbilltoskull forUsambara and Udzungwa birds
eSeparatevaluesformalesand femalesfrom Manson14 pooled here
f Manson14 pools all age/sexclassesforthese measurements
TanzanianraceofSwynnerton’sRobin:Andersonetal BullABC Vol4No2-89