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The larval ecology of most species is poorly known,
but it is apparent that only a small part of a wetland
complex may provide suitable larval habitats, even if
the adults range widely over the whole site, as is
often the case with the larger Anisoptera. Proof of
breeding is often crucial in site evaluation and
protection, and larvae and exuviae provide the best
possible evidence.
Finally, the larvae of Odonata are, in a very different
way, as striking as the adults, often subtly coloured
and camouflaged, and structurally diverse. In an
Order containing rather few British and Irish
species, the larvae can provide an extra challenge,
requiring a new set of field skills for the observer
who has already mastered the adults.
Transect methods
As early as the 1950s, the counting of adult male
Odonata along a waterside transect was being used
to monitor dragonfly populations (Moore 1953,
1964, 1991c). The method has since become more
widely known through its development for butterfly
monitoring (Moore 1975; Pollard 1979, 1992).
Butterflies are perhaps even better suited to transect
counts than Odonata: most butterflies are not
strongly territorial, and unlike many Odonata do not
move far from their breeding sites. However, if
counts of adult male Odonata are repeated regularly
(ideally, once a week) in suitable weather conditions
(sunny and with little wind) and close to mid-day,
they can provide results which are comparable and
thus a simple annual index of abundance. This
method is very useful in quantifying flight period
(see below), and can detect long-term trends in a
species, perhaps reflecting site management
(Brooks 1993); Moore (1991c) follows the pattern of
colonisation and faunal change at ponds at
Woodwalton Fen over 27 years using transect
methods.
Comprehensive monitoring
Useful though transect counts can be, they are
probably best used as part of a wider-ranging
programme of monitoring. A review of the
techniques for comprehensive monitoring has been
provided by Moore and Corbet (1990). They
discuss the need for monitoring, and aspects of the
behaviour of Odonata which influence the ways in
which methods may be applied. They conclude that
the choice of survey methods will depend on the
habitats involved, especially the accessibility of the
water's edge, and the time available for monitoring.
They make several recommendations.
The preferred technique for monitoring
Anisoptera is by counting exuviae, which should
be collected as frequently as possible,
throughout the emergence period.
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Because of the difficulty of finding and
identifying their exuviae, Zygoptera are best
monitored by counting teneral adults, as
frequently as possible, throughout the
emergence period.
Adult counts are comparable only when
restricted to adult males by water, and when
made within 1-2 hours of mid-day on sunny days
with little or no wind.
Whatever methods of assessment are used, it is
preferable if they can be applied at regular
intervals, and at the same time each day.
As a minimum, Moore and Corbet recommend that
counts of anisopteran exuviae, zygopteran teneral
adults, and mature males by water should be made
once a week throughout the season. With this
required level of commitment, it is important to
establish the purpose of monitoring, and to decide
what level of detail is required. Can monitoring be
focused on one or two species of particular
importance? If management is being monitored, can
representative sections of habitat be chosen rather
than attempting to monitor a whole site? Does the
monitoring need to be repeated annually? (A
thorough survey every third year may be more -
useful than incomplete or inconsistent surveys every
year.)
DESCRIPTION OF DATA SET
The maps presented in this Atlas are based on all
records received by the Odonata Recording
Scheme up to the end of 1990. Some later records,
of particular importance, are mentioned in the
species accounts and elsewhere, but do not appear
on the maps.
Recording is a continuing process, because species
distributions are not static and there remain large
gaps in our knowledge of the biology of even the
commonest species. The methods of data collection
and validation described in this section refer both to
the data included in this Atlas and to ongoing
recording.
Management of data collection
The history of the Scheme and data collection has
already been described. For most of the duration of
the Recording Scheme, a national scheme organiser
has been responsible for collating incoming records
and providing feedback to recorders. This feedback
has included comments on the significance of the
records supplied, and requests for further
information in support of particularly outstanding
records. Additionally, through the newsletters,
recorders have been urged to visit under-worked