Journal of the British Dragonfly Society Volume 14 April Number 1 1998 Editor: B. H. Harley Assistant Editor: R. R. Askew The lournal 01 the British Dragonfly Society, published twice a year, contains articles on Odonata that have been recorded from the United Kingdom. The aims of the British Dragonfly Society (B.o.S.) are to promote and encourage the study and conservation of Odonata and their natural habitats, especially in the United Kingdom. TRUSTEES OF THE BRITISH DRAGONFLY SOCIETY Chairman: A. McGeenn Vice-Chairman: P.J. MiD Secretaty: W. H.Wain Treasurer: S.Jackman Editor: B. H. Harley Convenor of Dragonfly Conservation Group: N.W. Maore Ordinary Trustees: D. A. CI.rke J. D. Silsby D. J. Thompson T. G. Beynon ADDRESSES Editor: B. H. Harley, Martins, Great Horkesley, Colchester, Essex C06 4AH Secretary: W. H, Wain, The Haywain, Holiywater Road, Bordon, Hants GU35 OAD Librarian/Archivist: P. M. Alien, 'Little Thatch', North Gorley, Fordingbridge, Hants SP6 2PE Articles for publication (two copies please) should be sent to the Editor. Instructions for authors appear inside back cover. Back numbers of the Journal can be purchased from the librarian/Archivists al 1-4 copies £2.75 per copy, 5 copies or over £2.60 per copy (members) or £5.50 (non·members). Other enquiries (including membership applications) should be addressed to the Secretary. Annual subscription: £5.50; library subscription: £1 1. Overseas subscriptions: £7.50 and £13 respectively. All subscriptions are due on 1st April each year. Late payers will be charged £1 extra. life membership: £80. Front cover illustration of male Aeshna grandis by Roderick Dunn J. Br. Dragonfly Soc., Vol. 14, No. 1, April 1998 A population study of Coenagrion mercuria/e (Charpentier) in the New Forest. Part 7. Mark/recapture used to determine the extent of local movement D. K. lenkins 7 Lakewood Road, Ashurst, Hants 5040 7DH Introduction This work was carried out in 1992, on the Crockford stream in the New Forest, the year following an initial study (Jenkins, 1995) in which the area under observation had been treated as a single unit. As work progressed, it had become obvious that this length of stream contained two Coenagrion mercuria/e (Charpentier) populations, separated by a 200m stretch of the stream with mixed scrub (blackthorn, willow, bramble, etc.) some 2-4m high on the west bank only or on both banks. 5mall copses isolated the whole site upstream and downstream. No C. mercuriale exist further downstream and are very sparse for over O.5km above the upstream copse, and immigration from the latter seemed extremely unlikely. During the 1991 study and previous 'Pollard' type walks, no C. mercuriale had been recorded from the scrubby stretch between the two holding areas, although there is no barrier to flight along the stream. As previously noted, a tributary with good numbers of C. mercuriale along most of its length meets the main stream just below the upper study population but is cut off from it by about lam of scrub on both banks at the junction. However, above this, only a truncated triangle of open Forest lawn separates tributary from main stream with a minimum distance between the two of about' Om. The object of the current work was to use mark/recapture to see if (a) there was any exchange of C. mercuriale between the up and down stream areas of the study site and/or (b) exchange between the latter populations and the higher density population on the tributary. Methods Conditions and methods were all as reported previously (jenkins, 1995) except for an improved method of insect retention and release. The earlier technique was to net and mark insects uniquely and release them immediately. Working over periods of up to three hours and with very small numbers of insects involved, it was inevitable that some C. mercuriale were netted more than once. Although a few marked insects could be identified while perching and the remainder released immediately after checking in the net, any stress or damage from the latter could be avoided by the new technique. In addition, the previous method did not readily allow random release into the population as required for accurate calculation, although numbers were too small and insects taken from too limited a stre.tch of water for this to have much effect on the final figures. In the current work, the technique reported by Parr (1 965) was used. For a given population, as many insects as possible were captured, marked and retained in pill 2 J. Br. Dragonfly Soc., Vol. 14, No. 1, April 1998 boxes. After a set period of two hours at each site, the insects were released at intervals along the stream. Black and red pens were used to mark the upper and lower populations on the main steam and green for the insects on the tributary. As noted previously, green marks were much less permanent than red or black but it was possible to recognize green or degraded green for about two weeks after application. Mark/recapture was done weekly and all insects were given the same number for a given week, rather than a unique number. Insects remained quiet in the pill boxes and on release, most flew a yard or two to a suitable perch to rest or dean themselves. Results In general (Fig. 1) the black and red marked populations on the main stream showed almost identical patterns of emergence. The figures for actual number captured (154, with 81 black, 73 red), calculated total (Fig. 2), and ratio of numbers captured to calculated total were similar to those of the previous year, despite the lower numbers per population resulting from the split into two groups. This shows that the mark/recapture experiments of 1991 had no serious effect on the overall population. As before, the fluctuation in numbers throughout the season reflected the summer weather pattern, although in complete contrast to 1991, the highest numbers occurred in the first half of the season, with excellent weather in June, followed by a rapid decline in July as poor weather dominated and few insects were on the wing. Figure 3 shows percentage of females captured. A maximum approaching 40 per cent of the overall population at maximum emergence is similar to previous figures, but while the number of females in the 'black' population remained more or less constant through the season, the number in the 'red', although initially higher on average, declined to zero by late July. Numbe� ca!cu!aled 80 " 20 0 ���h�+n���_���U4n����n._�Pn�nn� 2) May JIMay Bjun DJun 211un 27Jun "'u! !!Ju! !Blu! 25Ju! 1 !lug Dale of counl f2jBlack population D Red populatIon Figure 1. Calculated populations for black and red marked C. me rcuriale on main stream J. Br. Dragonfly Soc., Vo l. 14, No. 1, April 1998 3 Numbers 8() 60 40 20 23M�y 31M�y 61un 13jun 211un 271un 4 Jul 11 lui ISJul 2SJul 1 A.uS Dale of count • New capture E'3 RecJplures 0 Calculated populatIOn Figure 2. Calculated total population on main stream, 1992 f'eotceflta� 50 40 )0 20 10 o Jl M� 8Jun 1J Jun 21 Jun 27 June 4 Jul 1 A.ulI Dale of coonl .)Fe�1es in lotal capture e::J III blad population o in red populalJOn Figure 3. Actual percentage of females for C. mercuria/e captured on main stream Only limited marking was done on the 'green' population of the tributary as C. mercuria/e numbers were relatively high and there was no upstream boundary to limit exchange. However, no marked C. mercuriale from the tributary were found amongst the red or black (nearest) populations and of the total of 154 black or red marked insects, only two 'black' were found on the tributary and it is suspected that even these were two insects which had soared uncharacteristically on release in a strong wind blowing towards the tributary. There was no evidence for exchange of C. mercuriale between the two groups on the main stream. 4 J. Br. Dragonfly Soc., Vo l. 14, No. 1, April 1998 Conclusions These results seem 10 confirm that C. mercuriale is extraordinarily reluctant to move from its home location, even across a short, open area. However, it has been observed on several occasions that numbers of male C. mercuria/e can be found at O.Skm or more from the nearest site after emergence and initial dispersal. Poor colonization of nearby areas would therefore result only if females do not disperse far after emergence. The fact that none have been found well away from emergence sites may support this, or simply reflect the difficulty of seeing them when not attached to males. References lenklns, D. K. 1995. A population study of Coenagrion mercuriale (Charp.) in the New Forest. Part 6. Mark/recapture programme. Ioumal of the British Dragonfly Society 11 (1 ): 10-14. Parr, M. J. 1965. A population study of a colony of imaginal Ischnura elegans (Van der Linden) at Dale, Pembrokeshire. Field Studies 2: 237. Further Sites for Coenagrion pulchellum (Vander Linden) E. Waring 7 Amberlands Close, Backwell, Bristol BS48 3LW The list below is supplementary to that given in Waring (1995), but the scope is extended to include pariS of Wales and Scotland. Coenagrion pufchellum was recorded at the following sites, at some time during the period 1991 - 1997. An asterisk denotes good numbers. list of Sites WALES AND SHROPSHIRE SH47 Anglesey Valley Lakes RSPBR, lake and fen. SH47 Anglesey Maltreath Marsh, valley fen. SH58 Anglesey Cars Goch NNR, vallen fen.