Notul. odonatol., Vol. 3, No. 8, pp. 113-136, December I, 1991 123 The dragonflies of Hunter’s Lodge, Kenya, 1981-1991 P.L. Miller and A.K. Miller Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, United Kingdom Abstract — A in report is given of the occurrence level a region of Guinea savanna, 160 km Odonata of close the of at a site in Kenya comprising a south-east Nairobi, to main road to streamwhich has been dammed to form asmall Mombasa and near Makindu (37°32'E, 2°15'S) reservoir. Observations have been made at the (MILLER, 1982a, 1982b). During April daily the last site on six occasions during ten years. temperatures have a mean maximum of about 10 and The and Altogether zygopteran 35 anisopteran 29°C. main rains occur during April haVe been observed the and with lesser in November spp. at site, May, amounts falling December. evidence of breeding by 8 zygopteran and 26 and anisopteran spp. has been obtained. 17 spp. Two streams arise from springs which are fed the were reproductively active only at the stream by water falling on Chyulu Hills situated and 9 the reservoir. A further 7 about 20 km south-west of the site. The spp. only at spp. springs active in both habitats. Patterns of run the with little seasonal fluc- were daily throughout year the have tuation. smaller activity of some of commoner spp. The stream is used for irrigating been analysed and evidence for temporal parti- adjacent farmland and the larger runs approxi- is described. north-east for about 40 km before it tioning among some Zygoptera mately joins the Athi river. It has been dammed at Introduction several places along its length to form a series of While exist the odonate faunal small reservoirs. The the many reports on water near springs composition of various African habitats (e.g. smells strongly sulphurous and the stream is BAL1NSKY, 1961; CORBET, 1962; PINHEY, said by local residents to be undrinkable but 1961, 1964, 1970, 1984; PINHEY & PINHEY, adequate for making tea or washing in. Obser- 1984; SAMWAYS, 1989; S1LSBY, 1989), few vations have been made along the first 0.6 km the have dealt with changes over time at one habi- of the larger stream in vicinity of a small last Hunter’s tat. During the decade we have had the hotel, Lodge. opportunityto make six visits, each offrom 4 to Five zones were distinguished in this region 35 days in duration, to an aquatic habitat in as follows (Fig, I); Kenya where we have obseived altogether 45 (1) The springs which emerge amongst volca- species. This has allowed observations to be nic rubble in a densely shaded area under made onthe stability ofthe populations ofmost large trees, together with the first 10 m of but also species on changes in a few. We sum- the stream; the A above about marise observations here and also report on (2) reservoir the dam, which is the occurrence of be- 300 m and 80 m broad and temporal partitioning long up to tween some zygopteran species, a feature through which the water flow is impercep- known in damselflies and dragonflies elsewhere tible. The bank in this region is partly (e.g. MIZUTA, 1974). exposed to sunlight and partly shaded by many trees and bushes, with dense clumps Habitat of Typha domingensis growing along its above There The study site lies at just over 900 m sea margins. is little or no submerged 124 Notul. Vol. No. December odonatol., 3, 8, pp. 113-136, I, 1991 — Fig. A sketch of the and reservoir where made. — d: I. map stream surveys were [b; bridge; dam; — —h: hotel; main — A B: where — r: road; s: springs; — & regions counts were made; N: North; —1-4: zones(see text)] the vegetation except in a small upper region disappearance of only area ofsubmerg- of the reservoir. The reservoir which was ed vegetation (1986-1991); formed 50-60 After 1982 the smaller probably years ago supports (b) irrigation stream large populationsof cichlid and other fish; was dug out, straightened and lined with (3) Small waterfalls below the dam. where the stones, destroying its vegetation; drop is about 2 m, together with the first 10 (c) Considerable bush and tree clearance in the m of the stream where it has a fast flow lower stream region has taken place since been marked rate. This region is well shaded by large 1986 and there has a increase trees; in cultivation along the north side of the (4) The lower stream, partly shaded by trees site together with an increased density of (Acacia xanthophloea, Ficus spp.) but also human settlements in the vicinity; with exposed clearings where the bank (d) Some of the water from the largest spring has been and supports thick growths of Mukia madera- piped led away to supply tenuiro- since 1984. The reservoir has spatana (Cucurbitaceae), Ipomoea dwellings stris (Convolvulaceae), Commelina beng- become mildly eutrophic with periodic halensis (Commelinaceae), Impatiens algal blooms, most noticeable in 1991, and stuhlmanii (Balsaminaceae) and Dyscho- probably resulting from a reduction in riste radicans (Acanthaceae) (identifica- flow-rate together with increased agricultu- tions provisional); ral activity and human settlement. disused which The dates when made shown (5) A swimming pool usually surveys were are contained water to a depth of ca 0.5 m. in Table I: additional brief visits were made in Several changes in the habitat have taken I960, 1961 and 1973. On most days, observa- tions continued place in the last few years; for several hours. In addition The of the reservoir has become counts of all individuals made (a) upper 20% present were at entirely grown over by Typha domingensis approximately 30-minute, or shorter, intervals the in 1991 in leaving no open water and causing on three successive days two selected Notul. Vol. No. 199! odonatol., 3, 8, pp. 113-136, December I, 125 The first a 63 areas (Fig. 1). area (in zone2) was m stretch of the reservoir bank which was well and short exposed to the sun bordered by grass Juncus and small emergent plants (Canna, spp.). The second (in zone4) consisted of two stretches of the stream, totalling 65 m, partly shaded by trees and large stands of Typha and obser- Cyperus. The counts were made by two times indicated in vers independently at the Figures 2 & 3 and Table II, each count taking 10-15 min. Identifications have been carried out using kind P1NHEY (1961, 1964, 1970), and with the assistance ofS.J. Brooks ofthe Natural Flistory Museum, London. Results and Discussion Fig. 2. Counts of 4 species of Anisoptera along Table I shows the results of carried out surveys 63 m ofthe reservoir bank at thetimes indicated, six occasions between 1981 and 1991. It also on made on 14th April, 1991. indicates species for which proof of breeding was obtained (**) (i.e. presence of larvae, exu- the three species with marked crepuscular viae teneral for which there or adults), or was periods of reproductive activity had declined or indirect evidence of breeding (*) (copulation disappeared. The overall abundance of several and/or oviposition observed), togetherwith the species was estimated to be lower in 1991 than result zones where reproductive activity was seen to in previous years, possibly as a of habitat those occur. Estimates of numbers include seen changes. within 20 of the Phaon in six ca m water (e.g. many Records were made altogether months iridipennis were regularly observed feeding in ofthe year. Up to 25 species were represented in the 15 vicinity ofa leaking sewage plant, m from December but higher numbers of species and the 45 have stream). Altogether species been individuals were found duringthe main wet sea- observed: 16 were found to be present during all son, April and May. Several species, including visits, 26 in all but one, and 32 in all but two. N. farinosa, T. arteriosa, T. annulata, I. ferox, Six which each species were seen only once may O. chrysostigma and several zygopterans are have been However three of these be found the vagrants. probably to throughout year as were coenagrionids which were noted only cur- adults, although in variable numbers. The con- in earlier visits. sorily the siderable extension of Typha in shallower parts of The populations most of the commoner of the reservoir after 1984 with the consequent remained stable the obliteration of the species fairly throughout open water at upper end, but is in with the of decade, Tholymis tillarga an exception together region submerged vegeta- that it first appeared in 1984 and had almost tion, probably accounts for the reduction in 1991. numbers totally disappeared by This may be or disappearanceof Diplacodes lefeb- explained by a chance invasion of the habitat vrei, Urothemis assignata, V. edwardsi and followed by a gradual reduction of numbers Rhyothemis semihyalina, most of whose repro- better resulting from competition with species ductive activity took place close to the submer- absence adapted to local conditions. The of ged vegetation. Tetrathemis polleni was obser- Brachythemis lacustris in 1991 is puzzling since ved only in shaded areas close to the springs it had been reliably present on every previous (zone I), although elsewhere in Kenya we have visit its declined in be although numbers had 1986. seen it to active in exposed regions of ponds In contrast a small populationof B. leucosticta and streams. Three species, Pantala flavescens, was present in all visits. Thus by 1991, two of Crocothemis erythraea and Trithemis kirbyi Notul. Vol. No. December I, 1991 126 odonatol., 3, 8, pp.