Dragonfly and Damselfly monitoring on the Writtle College estate - the first five years
TIM GARDINER, MARTIN HEYWOOD, ROBIN FIELD & MICHELLE PYE
Centre for Environment and Rural Affairs (CERA), Writtle College, Lordship Road, Writtle,
Chelmsford, CM] 3RR
Abstract
Transect based monitoring of Odonata has occurred on the Writtle College estate since 1997,
providing five years of data which illustrates short term trends in species abundance. Fourteen
species of Odonata were recorded during the five year period, which compares favourably with
other sites in Essex. Several localised Essex species were observed and these include Large Red
Damselfly Pyrrhosoma nymphula and White-legged Damselfly Platycnemis pennipes. The latter
species is sensitive to pollution and may therefore indicate that the water quality of the aquatic
habitats on the estate is good. The abundance of all species of Odonata increased during the first
four years of monitoring, but severe reductions in abundance were noted in 2001. Banded Demoiselle
Calopteryx splendens was the most abundant species on the estate and became increasingly
common as the survey progressed, particularly in its favoured habitats which were the Rivers Can
and Wid. These two slow-flowing rivers possess an abundance of bank-side, floating and emergent
vegetation and have consequently proven to be rich in Odonata during the monitoring period.
Introduction
Habitats which are favourable for Odonata need to be monitored on a regular basis to ascertain
whether habitat quality is being maintained (Moore & Corbet 1990). Transect methods for recording
insects have become widely utilised, mainly due to the use of this method in the National Butterfly
Monitoring Scheme (Pollard & Yates 1993). Regular counts of adult Odonata, on a weekly or
fortnightly basis, produce a simple annual index of abundance which is comparable with subsequent
years. Brooks (1993) states that long term monitoring at a site can detect trends in species abundance
and that the impacts of management regimes can also be ascertained. A transect monitoring scheme
has been in operation on the Writtle College estate since 1997 and this paper aims to present the
results from the first five years.
Method
Writtle College (TL 670070) is situated in the south-east of England, two kilometres west of
Chelmsford in Essex. The College estate extends over 210 hectares and consists of agricultural,
horticultural and conservation areas, with amenity sites in the College grounds (Neale 1979). Since
the mid 1970s many conservation areas have been established and these include mixed broadleaf
plantations, wildflower meadows in field corners and re-instated hedgerows along old field
boundaries (Sellers & Field 1997).
The method used for monitoring Odonata was adapted from that used by Brooks (1993). This
involved recording all adult Odonata, either perching or flying, which were identifiable by an
observer walking at a slow strolling pace along a set transect route. Individuals were only recorded
if seen in front or to the sides of the observer. For certain species such as Red-eyed Damselfly
Erythromma najas which rest on floating vegetation, the observer stopped periodically to scan
180° with binoculars.
One transect route was established on the College estate (Fig. 1), covering most of the areas close
to watercourses. The transect was divided into eight sections with distinct habitat types, as with
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Essex Naturalist (New Series) 19 (2002)