Conservation and habitat requirements of the large heath butterfly (Coenonympha tullia)
In recent years, the large heath butterfly has undergone a considerable decline
throughout much of its European range. In consequence the species is now classified
as vulnerable in a European context, although the butterfly is still locally common in
northern parts of the United Kingdom. The majority of English colonies are located
on expanses of blanket bog in the county of Northumberland, although recent
extensive surveys have shown that substantial numbers of colonies have been lost
from this area within the last twenty years. C. tullia is one of only four butterfly
species with a southern limit to its British distribution, suggesting that climatic change
may constitute an additional threat to that faced by many other butterfly species,
namely habitat destruction.
This thesis consists of an autecological study of C. tullia. Research showed that adult
butterflies were most abundant in areas where vegetation was relatively short and
sparse. Females oviposited more frequently in short, sparse vegetation than they did
elsewhere, suggesting that observed female microdistributions may be consequential
of their ovipositional requirements. It is suggested that eggs laid within such areas
will experience warmer micro climatic conditions than those laid in taller vegetation,
as will resultant larvae. Most sources in literature suggest that large tussocks of the
foodplant hare's-tail cotton grass (Eriophorum vaginatum) (L.) are an important
requirement of the species. The current study shows that large tussocks are of much
lesser importance than previously assumed on sites that are not prone to flooding.
The efficacy of heather cutting as a habitat management strategy was investigated.
Higher numbers of male butterflies were recorded in cut areas, while the oviposition
rates of females within cut areas were higher than in uncut controls. It is therefore
suggested that heather cutting renders overgrown habitat more suitable for adult
butterflies, and would therefore constitute an effective conservation management
strategy on certain sites.The mobility of adult butterflies was investigated. Males were found to move for
greater distances than females, and were found to be capable of dispersion between
sites separated by 500m of unsuitable habitat. Females were found to be extremely
sedentary, and no between-site movements were detected. It is therefore suggested
that gene flow between populations at Border Mire sites is probable, although
colonisation of remote sites is not.
A series of absolute population estimates were made at three study sites. These data
were significantly related to same-day relative estimates made using transect counts,
although the relationship was not sufficiently close to confidently predict absolute
values from transect counts alone. However, were more time devoted to a similar
study, it is probable that this outcome could be achieved. The annual abundance at
each site was calculated for each of the flight periods 1999-2001 inclusive.
A life table study, investigating mortality in the pre-adult phases, was undertaken.
Essentially, this study revealed that egg mortality and pupal mortality rates were both
low, while larval mortality, particularly of the first instar was relatively high. Causes
of mortality were not confirmed. Dissection of freshly emerged females suggested
that females are probably capable of producing 65-90 eggs during their lifetimes.
Adult feeding behaviour was studied. The preferred nectar source of both sexes was
cross-leaved heath (Erica tetralix) (L.), although other nectar sources were also used.
A study of post-copulatory behaviour revealed that females commenced oviposition
prior to feeding. The importance of nectar to the butterfly was investigated by means
of a trial using captive female butterflies. A group of females provided with food in
the form of sucrose solution produced a similar number of eggs to a group of identical
size provided only with water, suggesting that nectar availability is of less importance
than has been shown for some other butterfly species.