IIABITAT CHANGE BY CAI'E SUGARBIRDS AND ORANGEBREASTED SLINBIRDS IN AN APPARENT RESPONSE TO FIRE IN OLD MOT]NTAIN FYNBOS

Mike Fraser and Liz McNlahon

Sondbanks, Kenmuir Srcps, Hopkirk Way, GLENCAIRN, 7995

The Cape Sugarbrrd Promerops cafer respeclively over two years. Malachite and Orangebreasted N..rar.rard N. famosa were more violacea are two nectarivores endemlc numerousl occuring at a density of to rhe Fynbo\ Biome Within this 0,60 ha '. Lesser Doublecollared biome, which comprises over 20 Sunbird M cial_}bed was the most discrete vegetation types (Moll er a/. numerous of all in the Strandveld 1984) they are. in turn, rarely plot, with an average density of 1,86 encountered outside Fynbos itself. ha-' fttl, unpubl. data). But when They feed mainly frorn Proteaceae and congregating at the nearby flowering Ericd flowers and occur in high Leorori.r numbers of these two sunbirds numbers at these plants when they are greally exceeded the local population, in bloom. as our ringing and statistical projections have demonstrated (Underhill & Fraser Mistnetting a o,rtmifolia 1990). (Wild Dagga)^t patch on the Cape Peninsula has denronstrated how Despite its undoubted attraction to reluctant these are to move even a Malachite and Lesser Doublecollared shon distance beyond their preferred Sunbirds, we have consistently failed to habirat. de\prle the pro{rmrr) oi rhis catch more than a sprinkling of Cape rich nectar source (Fraser et al. 1,989). Sugarbirds and Orangebreasted The Leonotis occurs in small stands Sunbirds at the Leonotis. The 929 amounting lo about I ha located withrn nectadvores we ringed at Olifantsbos sparse Strandveld (evergreen coaslal prior to autumn i99l included only 3 thicket) vegetation at Olifantsbos on the Sugarbirds and 3,1 Orangebreasteds. west coast of the Cape of Cood Hope The average contributions made by each Nalure Resene (CoGH7. The site is species to the total number of Iocaled on a narrox coastal plain and is nectarivores caughr during the Leonotis bounded by the sea to the west and flowering periods from 1984 to autumn Strandveld scrub on a rocky slope l99l are detailed in Table 1 leading up to Mountain Fynbos about 100 m to the east- One or two plants In March and December 1991, four may be found in bloom at almost any mistnetting sessions at the Leonotis time of year, but its peak flowering patch produced relatively high numbers periods are November - December and of Orangebreasted Sunbirds. In March March - April. 1992, two days of ringing resulted in a catch of Cape Sugarbirds and In a Strandveld study plot (which did Orangebreasted Sunbirds which was our not contain Leonotis) at Olifantsbos, highest ever there (Table l), although Cape Sugarbirds and Orangebreasted still very modest by Malachire Sunbirds occurred at very low densities, standards. Incidentally, the number of averaging 0.04 ha-r and 0.10 ha nectarivores we have ringed at

Safring News 21 5l 1992 Olifantsbos frorn Augusl 1984 to June imrnediately afier the fire. The plants 1992 li.e. at all seasons, nor only recovered completely over the winter during the Leonotis flowering period) and blossomed again the following now stands at I 501. This cornprises; surnmer. resulting in a good catch of Cape Sugarbrrd 7 r0.4%). Mala.hrte Malachrles {Table I). Ne\enheless. ir Sunbird 983 (65.5%); Orangebreasted was not until the next flowering period Sunbird 16 (5,17a): Lesser (March April 1992) that the arrival Doublecollared Sunbird 435 (29.0 % ). of suga.birds and Orangebreasteds was Only 73 nectarivores have been caught recorded. The absence of a more when the Leonoris is not in flou,er- immediate reaction. by sugarbirds in particular (i.?. there were no relatively Although necla vorcs are highly lrrqh numbers at lhe Leonois in itinerant and their nurnbers fluctuate November - December), may have dramatically in response to the been the result of flowering of lheir food plants. rve conocarpodetulron nectar being suspect that in 1992 these birds were available elsewhere in an unburnt part forced to s$irch hahrtit from Nlounrain of the CoGH. This pincushion was Fynbos to the Strandveld LeonorJ flowerrng profuscly in Mountain becarrse of fire. In Fcbruarl l09l a fire Fynbos near Rooikans in the southern swept through about one third of the part of the reserve at this time and reserve. destroying some of the oldesl would have tided the birds over until Mountain Fynbos veBetalion. Part of mldsummer, the Olifantsbos Strandvcld and nranv of the Lconotis clt rps were also burnt. In which case. the response, if such it The lalter resprouted vigororrslv. but was, to rhe loss of one area of Mountain skipped one flowering period: hence the Fynbos was manifested at the flowering low catch of sunbirds in l\,larch Leonotis only twelve months later.

TABI-E T

Relaiive rnd Absolute Numbers (in brackets) of Nectarivores cnught at Ofif!ntsbos during l'lowering Seasons of aeororrs oxlmifolis

PRE-FIRE POST.FIRE Mean % Percentape (actual ranse) (total)- 1984'Feb 9l Mar-Apr 9l Nov-Dec 9l Mar- Apr 92

Cape Sugarbird 0.3 % (0,r) |,7% (4)

Malachite Sunbird 50,0% {4-?02) 42,5Va(t7) 85,0%(187) 68,57o(r57)

Orange B. Sunbird 2.'1v. 10,6) 20.0% (8) 3,270 (7) t7,9%l4t)

L. D. C. Sunbird 41.0%(ta-66) J7.5 d, 1151 ll,8%(26\ ll,8d"(27)

Total r00,0% (939) 100,0% (40) tw,0vo(220\ t00,0va(229)

52 The mean annual density of these birds particularly Watsonia spp. in CoGH study plots in Taylor's (1984) "Mixed Upland Fynbos" (that In early 1992 a large part of the component of Mounlain Fynbos in Silvermine Nature Reserve, which is on which the birds' food plants the Cape Peninsula 20 km nonh of predominantly occur) is 1,2 ha-t for CoGH, was burnt. This may also have Cape Sugarbird and I,l ha-L for contributed to the high numbers of Cape Orangebreasted Sunbird (Fraser 1990). Sugarbirds and Orangebreasted Monthly densities fluctuate Sunbirds at Olifantsbos in March of that tremendously, however, and mid- to year. Our ringing has demonstrated late summer is the time of year when that suSarbirds can easily cover this sort Cape Sugarbirds and Orangebreasted of distance. Although we have no Sunbirds are at their lowest. They direct evidence, it would be reasonable were, in fact, often absent from study to expect that Orangebreasteds can also plots, presumably in response to the readily travel 20 km in the course of scarcity of flowering food plants. seasonal wanderings as rhe) rrack their Perhaps only species which provide a food plants. A more local origin was "pivotal" food source (sensir Knight suggested by only one bird, a retrap 1986). such a5 widely \cattered. long- from I January 1990. The two fires flowering Erica gilva and E. together destroyed a large area of ceinthoides, represent a dependabte Mountain Fynbos and must have food supply before the repens deprived many nectarivorcs of feeding and P. lepidocarpoderdroa (both much hablat. The increase of sugarbirds and utilised by neclarivores) come into Orangebreasteds at Lhe Leonotis oj.ay, flower in auturnn. therefore, have been part of a more wide-ranging response to displacement In which case, why do sugarbirds and from their preferred into marginal Orangebreasted Sunbirds not use lhe feedrng arear. we have no recoveries Leonotis as a reguiar. if relatively short to indicate where the birds moved when lived, stop-gap during these lean lhe Leonotis finished flowering by the months? Do the relatively high end of April. numbers of these birds seen at the flowering Leucospermum As far as the other species are conocarpodendron and concerned, Malachite Sunbird was very fnbiifolius in spring and sunlmer leave scarce in Mountain Fynbos study plots the area altogether? Or do rnany of and ksser Doublecollared did not them remain in the general vicinity and occur at all (although it has been Just become more thinly dispersed and recorded al llowering Enca gilva in less conspicuous than the chaltering Mountain Fynbos elsewhere in the groups which atlend flowering reserve). The impact of the fire would pincushions, for example? lf the last inevitably be less severe or even non- menlioned is the case, then after fire in existent on these species. The numbers Mountain Fynbos the birds would be of Malachites caught in December 1991 expected to concentrate at any available and March 1992 (Table 1) were food source, even a less paeferred one impressive but not unprecedented. srch as Leonotis. Suitable food plants Such catches (including over 200 in early post-fire Mountain Fynbos at Malachites in a weekend) have also CoGH are generally scarce and limited been made in years without a recent to a few resprouting species such as fire. The high proportions of Erica cerinthoides and bulbs. youngsters would reflect a good

5l breeding season rather than a response In summary, we attribute ,14{ the increase in to fire {61% anrl in Dec Jnd Mar. relative and actual numbers of Cape respeclively). In conrrast. onll 29% of Sugarbirds (albeit small) and the Orangebreasleds were s ubad u ll!. Oraneebreasted Sr..rnbrrds in lhe Leo4ottt patch at Olifantsbos ro a delaved results but not The enrphasise (but do not alrogelher surprising response lo fire in explainr the :harply.dt'fi ned pd rrronine adjacent Mountain Fynbos. We accept habitar of and resources between thi that lhis is indicative rather than two pairs of neclilrivorous specjes. definitive, and raises more questions This exclusivity may be disrupied by than it answers. Fynbos is nothing iI catastrophlc changes to the nor hidcously complexl Nevenheless, environment. forcine the birds ro we hope that it will encourage ringers to congregate at food sources where try and interlrret such incidental results prevrously thev d;d nor co-occu.. And whi.h arise through ringing. to add ro because temporal \ ariation in the lhose alriady derived from recoveries, densil) of necrrrir.r-es tn Vounrain measuremenls and moult. Fynbos is so -greal. fire-related fesponses (e.g. a reduction in the ACKNOWLEGMENTS densities of birds) rnav be masked by We thank Howard Langley, Adam normal seasonal movements. Mecinski and Western Cape Regional Paradoxically. theretbre. i1 lnay be Services Council for permission tJwork more practtcal 1() assess the effects of at Olifantsbos. and our ringing fire on nectarivorcs in l\tountain Fynbos colleagues. particularly George by counting the birds rlr stands ol foocl U derhill. fbr help wirh mistnetting. plants (in their flouering and non- flowering seasons) in nearb-y unbLrrnt or REFER E NC ES non-Fynbos vegetation (such as FRASER. Nl W 1989 Shon term resDon\€s hirds (!d Strandveld or Kloof Woodland) and nor oi lo ilre in Mounrain Fvnbos. the area Orttk:h 60: 112-lR2 lo be burnt. This would onll I:RASER. lU.W 1990. The etTecrs of narurar be possihle. of corrrsc. in rnanaeemenr v.ageralion. lire and alien Dlani invasion on burns where lhe areas to be retained l.rrJ-:f((re. a.s(mhlrrej rn Vounrain wotrld. theoreticallv Fynhr;s of rhe sourhwesiern CaDe P.ovin!e. at least, rematn S,,urh Alrjia. t apuhl. .US, &esis. unburnt. This would allow prc- and Uni\ et\iry ,,t.Cdne To" n 160 Dn posl-hre censuses_ To be al all FRASER. Yw. IITMAHON. t. UNDER- reprosentalive. a minimurn of one HILL. L.C. UNDERHILL. G.D, & srudl errher (iLlr REBEL O. .\ C. la80 Necraflvnre ngrng lear'r ot rhe fire in rhc !'urn$e,r Cdnc S,rttrg N, rr t8-: li would be required to cover the lti flowering of all food planrs (Fraser KNICHT. R S 1986 Fruit disptavs of 1989). Other complicarine Indrgenous and alien planrs in rhc aouth- facrors wesrcrn Cape. S. Aft. J. Bot.52:219-255. include the size and season oithe bLrrrr. MOLL. E.J . CAMPBELL. B M.. COW- the age of the veeetation when burnl. Llx"C. R.Nl.. BOSSI. L.. JARMAN. M L. & BOUCHER. lhe density of fo,\d f'lrlnl\ before rhe fire C. 1984. A descriprion of \cg(tdfion Jatcg"ri(s in and ddrdcent to the and their^ Ilo*erin-e phenology. rhe Flnhus bi,rmc S Alr. Nat. Scidr. pro|. drslance lrom thc brrrnl area lo the R?p.83: I11. neargst food plants, the interval between TAYLOR. H C 1q84. A \cgerdth)n \urvev ul the CJp< ot G.)od Hope N;rure Reserve.' the fire and the flowerine of the nearest II Dc\!nnrivc !!uounr Bothalid 15. 259-291 food plants, and the fire-survivar UNDIRHILL. LC & FRASER. MW strategy (reseeders or resprouters the 198q. Bayesran esrimare of Matachire - Sunhlrds laller will mature more quicklv) of the Npard.r'rid Jamosa feeAfig at a plants trans,en( dnJ r.olaleai tboJ resourci. J food concerned. FielLl Orn.60 3a2-381

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