Worcestershire Record No. 6 April 1999 p. 6


Digby Wood, Reply by Harry Green

I always enjoy the meetings of the Worcestershire BRC and the March meeting was no exception, giving a glimpse into the unfamiliar worlds of longhorn beetles, spiders etc. All fascinating stuff, but the presentation which gave me most food for thought occurred towards the end of the meeting when Harry Green put up a series of maps showing the distribution of mammals within the county on a tetrad (2km squares) basis. The maps were prepared in 1982 and show a fairly sparse distribution across the county, even of common species like mice. One suspects that the usual comment about being more representative of the distribution of the recorders than the subject being recorded might well apply. The reason for showing these maps was to enquire if anyone could suggest a use for them, but no suggestions were forthcoming from the meeting, and I wonder if there have been any since then?

The thing that struck me so forcibly as I made my way home was the amount of effort that had gone into collecting this data that apparently had no use, and that we were still continuing to collect such data. Surely it wasn't all a waste of time and effort! What could we do to increase the usefulness of such records? I don't pretend to know the answer but perhaps we can find a few clues. Historically this recording business was the basis for the classification of all living things and that work is to all intents and purposes completed. We have moved on. What engages us all now is the task of conserving that which remains or, hopefully in the longer term, reinstating that which has been lost. A vast task which is only just beginning to be planned and implemented, and to establish priorities in that task we need numbers. Remember, we only realised the plight of the otter because the hunters recorded numbers of kills and sightings.

Now, it is very easy to devise ways of putting numbers to some groups, butterflies being the obvious example. They present themselves in the most visible way possible to permit counting. Most other groups are not so obliging. However, butterfly counting methods may offer a lead. There are two systems in widespread use; firstly mapping, when as many observations as possible scour as many tetrads as possible, producing a map - a snapshot showing distribution during a fairly short period of time (say five years). These maps can be useful for such things as opposing planning and development applications if they are comprehensive enough, and may show changes in distribution if repeated some years later, although they always suffer from the problem of the distribution of recorders. The second counting system used is the transect count, where a recorder walks a set route weekly and records the numbers of each species seen in each of a number of predetermined sections usually based on habitat type. This is a very powerful tool when used alongside weather data, changes in habitat etc. The essential point is that the changes in numbers with time on a particular site is recorded and can be compared with other sites, perhaps leading to ideas on site management.

Can this sort of idea be adapted to cover a whole range of other groups? I can only see masses of problems! But give it some thought. How can it be used for the conservation of your particular speciality?

A Short-ish comment in Response to Digby

By Harry Green

The maxim - all records are valuable - should guide us, but there must be modifications to this because we know so much more about some species or groups than others. Ensuring that we do record what is common now is a difficult discipline to follow, but it is important because what is common now may decline later. But for most species any records are valuable. Birds, butterflies, and flowering plants comprise a small proportion of the species in Worcestershire. The Natural world is dominated by invertebrates and species which are too small to see without a microscope.

Butterflies are in some ways following where birds, and possibly flowering plants, have gone before. Birds, in particular, are fairly well understood, mapped and counted, summer and winter, hence our ability to produce "alert" warnings when numbers decline. But we don't need to record blue tits every time we see them because various monitoring techniques now keep tabs on their national population changes, but we should record red kites! Our knowledge about birds comes from the British Trust for Ornithology's two breeding bird atlases, a winter atlas, and a continuing programme of counting through Common Bird Census (map every bird within a small area through the breeding season year in year out) and the Breeding Bird Survey which uses standardised transect methods within randomly selected 1km squares (and there is more). The national bird atlases have been produced for many countries round the world and the mammoth European Atlas based on 100km squares is a truly stunning effort. A few countries have attempted a round-the-year atlas - distribution every calendar month (Holland) At a more local level many counties have produced tetrad atlases of breeding birds. I could list even more examples of bird work which makes them by far he best recorded group - yet more information is still needed and the juggernaught must be kept on the road to keep up the monitoring because birds are good indicators of the health of our countryside and their responses to change can be seen fairly easily. In this they are akin to butterflies.

Flowering plants are probably the next best recorded group. The BSBI National Atlas led the field alongside the first BTO Breeding Birds Atlas. And an update, Atlas 2000, is in production. There are now many detailed county floras usually based on tetrad mapping supported by brief written comment on numbers. The Worcestershire Flora Project is in full swing and will produced the first detailed account of local plants for one hundred years together with tetrad mapping. The bird atlases attempted to estimate actual numbers of individuals, at first roughly, but in a much more sophisticated way with the last Breeding Birds Atlas. This estimated abundance by timed counts per tetrad for a minimal number of tetrads within each 10 km square. A system of estimating "plant rarity" has been proposed (Pearman 1997 Watsonia 21:225-245) involving a frequency ratio of tetrads occupied per 10 km square.

Butterflies soon followed birds and plants with a variety of published maps, county butterfly faunas and the forthcoming Millennium Atlas which I expect will be on a par with the last Breeding Bird Atlas. There is also an increasing amount of information on Dragonflies including Mike Averill's Dragonflies of Worcestershire. There are also national Bryophyte atlases and a number of provisional atlases of some invertebrates.

There is even an Atlas of Mammals in Britain (Arnold 1993, published by HMSO) based on 10km squares, and this brings me back to Digby's concern. The problem with the Worcestershire Mammal maps comes down to visibility of species, intensity of recording, scale of recording, and lack on knowledge, especially documented knowledge. But providing these limitations are clearly understood the maps are the first steps along the road already followed by birds, plants, and soon by butterflies. On a coarse grain (hectads) the maps tell something previously undocumented about Worcestershire's mammals but on a fine grain the tetrad maps are not much use for some species such as wood mice but interesting for moles, dormice and muntjac deer, because moles have probably declined since the field work, muntjac have certainly increased, and the maps for dormice are probably surprisingly accurate. To state the obvious, we know wood mice are common in every wood and many other places, but to prove this on a tetrad basis would require a gigantic effort because the animals are nocturnal and difficult to find. It is much easier to record less common species like rabbits!

There are probably many species (especially invertebrates) when local recording on a tetrad basis is not immediately useful. However these base records with full grid references may well be useful in indicating important sites, and they are the first steps on a very long road. Conclusions? Record everything! But we need discipline. Under-recorded, difficult-to-see species should always be recorded. For a few groups we need time frames - record all the bird species every ten years, and re-map the plants every 50 years, perhaps! But for most other groups we simply need base grid referenced records leading to knowledge of sites, provisional hectad then tetrad maps, followed by estimates of abundance. The amount of effort needed to follow this route is immense but necessary if we are to understand and conserve our fauna and flora. This is what I think recording is for and why the Worcestershire BRC should exist and thrive.



I have not included a reference list because most of the texts mentioned are well-known. If anyone wants further information I shall be happy to supply it.

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