Newsletter 26
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Norfolk Moth Survey c/o Natural History Dept., Castle Museum, Norwich, NRi 3 JU. Newsletter No. 26. April 1990 Since our survey was launched in 1985 we have produced a number of newsletters, information sheets and so on. For ease of reference we have decided to start numbering these, including back issues of the previously published ones. The complete list to date is as follows:- Number 1 December 1985 Introductury letter / instructions for record cards. 2 June 1986 Letter to recorders and list of species requiring information. 3 July 1986 Information letter to local natural history scieties etc. 4 September 1986 Guidance notes for genitalia preparations 5 September 1986 Notes on identification of some autumnal species 6 October 1986 Autumn newsletter 7 November 1986 Letter to National Biological Records Centre recorders 8 February 1987 Reminder letter for workshops 9 May 1987 Notes on identification of some critical species 10 May 1987 Letter including list of events 11 August 1987 Letter 12 August 1987 Newsletter including review of survey so far. 13 October 1987 Letter following collectors workshop 14 January 1988 Reminder letter for workshops 15 April 1988 Spring newsletter including species list etc.. 16 May 1988 Notes on identification of Pugs 17 May 1988 Updated introductory letter 18 September 1988 Reminder letter for review meeting 19 October 1988 Autumn newsletter including field meeting reports 20 March 1989 Reminder letter for workshops 21 April 1989 Spring newsletter including flight times, migrants etc.. 22 May 1989 Notes on identification of Wainscots 23 September 1989 Reminder letter for review meeting 24 November 1989 Autumn newsletter including field meeting reports 25 March 1989 Reminder letter for workshops Spare copies of some of these are still available on request. As we are all aware, the weather conditions have a considerable effect on moths and consequently on our recording of them. Dr. Clive Sheppard has written a very interesting article for us based on his experiences of attempting to predict "good" moth nights by examining the weather data. Each year we are very grateful to receive records sent in to us by lepidopterists who live elsewhere but visit Norfolk on occasions, This serves to remind us all that when we visit other parts of the country there will be local groups, County Trusts, etc., who will be equally pleased with any records that we can pass on. By way of an example, Roland Rogers tells us of how he discovered a rare oecophorid while on holiday in Cornwall last year. In fact microlepidoptera are somewhat to the fore in this issue with an introduction to pyralids in Norfolk and a note of last years Yponomeutid invasion. If however you are getting fed-up with moths, then Gerry Haggett offers advice on collecting and rearing larvae. Of course you can as always gain first-hand experience by joining us at any of our field meetings or the workshop sessions at the Castle Museum. All are free of charge and our complete programme of events for the summer is as follows:- Tuesday 8th. May Castle Museum 7.30p.m. We continue our series of identification workshops with a look at Footmen and Nolids. Thursday 31st. May Upton Fen. Meet 8.00p.m. at reserve entrance TG 379137 Saturday 23rd. June Surlingham. Meet 8.00p.m. at Coldham Hall TG 324071. This event is organised in conjunction with the R.S.P.B. and also forms part of the Broads Authority's "Fun in the Broads" programme. Tuesday 26th. June. Weeting Heath. Meet 8.30p.m. at the N.N.T. car park at TL 756881. Saturday 21st. July Roydon Common. Meet at 3.00p.m. to search for caterpillars and dayfliers, or 8.30p.m. for light trapping. Please note that we are visiting a different part of the Common this year. Park alongside the track at TF 687218. Saturday 28th. July Beeston Common. Meet 8.00p.m. in the lay-by at TG 165426. Saturday 18th. August Holt Country Park. Meet 8.00p.m. in the carpark TG 082376. Wednesday 12th. September. Buxton Heath. Meet 7.00p.m. on the track just off the road at TG 171213. Wednesday 19th. September. Wheatfen. Meet 7.00p.m. at TG 324056. Organised in conjunction with the Friends of the Ted Ellis Trust. Tuesday 20th. November. Castle Museum, 7.30p.m. A meeting to review the work of the survey during this year. Thetford Naturalists Society will again be pleased to see anyone at their informal moth evenings. These will be held on Thursdays 31st. May and 30th. August at 4 Mackenzie Road, Thetford (IL 853831) and 28th. June and 26th. July at 5 Melville Road, Croxton (IL 874867). Further details from Nick Gibbons, Tele. Thetford (0842) 7523+55. We have been informed that the British Museum (Natural History) is currently selling copies of the two-volume monograph on the British Tortricidae (published by the Ray Society) at approximately half their original price. The cost is £30 for the two volumes or £10 for Volume 1 and £20 for Volume 2. These are excellent and comprehensive books, beautifully illustrated and well worth the money. For further details contact Tony Irwin at the Castle Museum, or the British Museum bookshop direct. Finally, a reminder as usual to send your records in, with many thanks to all of you who already have. We hope that this season will provide us with yet more information on the moths of Norfolk. Good hunting! Ken Saul METEOROLOGY AND MOTHS One of the most endearing features of moths is their sheer cussedness. Try to demonstrate the wonders of the night to an expectant crowd and you can be almost certain to have a dreadful flop on your hands! Murphys' law applies - whenever you think it's a great night for trapping in that distant fen,' the moths think otherwise. It was about fifteen years ago, when casting around for an A-level biology project, that I first looked into the effects that various different weather conditions could have upon the numbers of moths caught at light traps. More recently I have been trying to find the meteorological measurements most useful for predicting the size of moth trap catches. Although interesting species may obviously turn up at any time, it would. be helpful to have some guide for picking a 'good' night to go on that long trip! Large samples also provide a statistically more valid picture of the species present at a site. The main consideration for the factors was that they should be easily measurable with minimal requirements for equipment. Few people are going to have access to recording anemometers for example, but most could stretch to a thermometer and a simple aneroid barometer. In extremis even the regional weather forecasts will give approximate values of many weather conditions (especially the early evening local broadcasts). The catch of positively phototropic moths at a light trap is proportional both to the available population and to their activity. The population to be sampled for any individual night can be considered to remain roughly constant. It is therefore activity which is going to largely dictate the catch and it is this which the meteorological factors are likely to affect. These factors are also interrelated. To try to assess their relative contribution I have had to apply some statistical analysis to them. Multiple regression analysis (MRA) is a method which allows the comparison of a series of samples whose variation is considered to be due to several factors. It then allows one to calculate the regression of a predicted variable upon a weighted combination of predictor variables. MRA will always maximize the correlation for the particular set of data from which it was derived. METHOD ****** A 125w Robinson pattern MV trap was run for 33 consecutive nights in July and August from 2200 BST to 0400 BST and records of the following weather conditions were kept: * Maximum shade temperature (centigrade) of the preceding day (Mx). * Minimum temperature (centigrade) of the trapping night (Mn) * Atmospheric pressure in mmHg (Pr). * Cloud cover - estimated at start of trapping in tenths (C). * Rainfall (inches) - standard rain gauge (Rn). * Relative humidity % - Wet & dry bulb hygrometer (RH). * Windspeed - estimated on Beaufort scale at start of trapping (W). N.B. To approximately convert millibars to inches of mercury and In.Hg to mmHg: In.Hg = (0.02956 x millibars)- 0.0327 mmHg = In.Hg x 25.4 ANALYSIS ******** The simple correlation coefficients (r) which related the catch numbers to the different factors were as follows (p = measure of significance): r p Pressure 0.4735 0.01 RH 0.1697 NS Wind -0.1525 NS Cloud -0.0840 NS Min Temp 0.3886 0.05 Max Temp 0.5431 0.001 Rainfall -0.3107 NS (NS = Not significant) Such correlation coefficients relate each factor individually to the numbers of moths caught, ignoring any effects that the other weather conditions were having. Perfect correlation would be shown by an 'r' value of 1 (or -1), no correlation by a value of zero. The minimum temperature is not useful for prediction as it can only be read after trapping has finished. It looked as if I should concentrate upon the other two factors. I was interested to see if I could find any combinations of factors which might be of greater predictive value than maximum temperature alone. A multiple regression analysis including all the factors showed that there was a very significant relationship (p=0.0036) between weather conditions and catch size. Significance test for prediction of Nos: Mult-R R-Squared SEest F(7,25) prob (F) 0.7343 0.5392 97.6746 4.1794 0.0036 Next the contribution of each factor to the correlation was examined to decide upon the most promising combinations of conditions to examine subsequently.