The history, ecology, and reintroduction of the chequered skipper butterfly Carterocephalus palaemon in England

Abstract

Over 41% of global insect species have declined over the past decade, compared with 22% of vertebrate species. For Lepidoptera, 53% of species are declining and 34% are threatened globally. Since 1976, 80% of butterflies species have declined in either abundance or occurrence or both in the United Kingdom (UK). A total of 24 of 62 (41%) UK butterfly species assessed as part of a 2022 Red List of British Butterflies published by UK conservation charity Butterfly Conservation are classed as Threatened, with a further five (9%) as Near Threatened. The number of Threatened UK butterflies continues to rise and shows no sign of abating. A total of six butterfly species have been declared extirpated in the UK in recorded history, including the chequered skipper butterfly Carterocephalus palaemon, which was lost from England in 1976 after a precipitous decline that was believed to have started in the 1960s. However, due to a paucity of available data, the species’ historic distribution and abundance in England was poorly understood.

As part of the Butterfly Conservation-led reintroduction of C. palaemon to Rockingham Forest in Northamptonshire known as Back from the Brink – Roots of Rockingham (2018-21), a research project was developed to enhance the 266 historic records of C. palaemon that exist on the Butterflies for the New Millennium (BNM) database through museum and other uncollated data, and use the enhanced dataset used to analyse the pattern of C. palaemon decline and extirpation in England. In 2018, 42 adult C. palaemon were released at Fineshade Wood using stock translocated from donor populations in Belgium. The Fineshade Wood population was sampled in 2019, 2020, and 2021 to estimate its size, determine the mobility and dispersal of individual butterflies, and describe the ecology of the reintroduced species. A complementary review was undertaken to determine the global status of butterfly reintroductions, and the impact of woodland management on other taxa at Fineshade Wood was assessed.

A novel, non-invasive photographic-mark-recapture (PMR) population sampling technique was developed using the unique wing markings of C. palaemon to detect the movements and lifespan of individual butterflies photographed during timed counts at Fineshade Wood. Population size was estimated annually by a POPAN model using PMR data and tested against encounter rates generated from C. palaemon timed count data to determine the reliability of this sampling method. In addition, over 3500 new historic C. palaemon records were collected from museums and other sources of uncollated data and added to the existing BNM dataset. Extinction trajectories were generated to identify a pattern of decline in England that started approximately a decade earlier than the 1960s, in the late 1940s-early 1950s. Spatiotemporal variables tested for association indicated that colonies at larger sites, and larger sites in metapopulation networks (<2km apart) were buffered against extirpation to a greater extent than more isolated colonies at smaller sites.

A global review of butterfly reintroductions found that reintroduction had been attempted in 394 cases in the UK and Ireland, 69 in Europe, 48 in North America, and 15 in the rest of the world (526 total). When considering cases only with definitive outcomes (348 cases), 36.8% reported reintroduction success. The UK and Ireland had the largest number of successful cases (87) and Europe the highest percentage of successful cases (40.7%). Abundance and density of primary C. palaemon nectar source bugle Ajuga reptans on woodland rides was found be positively correlated with adult female C. palaemon encounter rates. Butterfly species richness and abundance was higher on managed versus unmanaged woodland transects. An increase in survey effort through moth trapping associated with Back from the Brink – Roots of Rockingham was considered responsible for increases in moth species richness and abundance.

PMR enabled us to detect that individual adult C. palaemon moved up to 1.76km from initial capture point using a ride-level measurement technique, and five of 30 C. palaemon photo-recaptured between 2019-21 (16.7%) moved a total distance >1km between captures, belying the sedentary reputation of the species. Gross population size was estimated at 314 in 2019, 332 in 2020, and 721 in 2021. Statistically significant correlation coefficients between daily C. palaemon timed count encounter rates and daily population size estimates generated from PMR data were only found when 2019-21 data was combined. Broad agreement between model estimates and C. palaemon encounter rates increased confidence in the accuracy of population size estimates that can be generated using less-intensive sampling methods such as timed counts.

The results of this thesis show the importance of provision of suitable habitat within woodland through wide rides, good landscape permeability and site connectivity within landscapes to support reintroduced populations of C. palaemon in England. The value of museum and other sources of uncollated data for describing the historic distribution, abundance, and timings of decline of endangered or extinct UK butterfly species is also demonstrated. In conclusion, given habitat is being restored across Rockingham Forest networks to improve suitability for C. palaemon and the mobility of photo-recaptured individual butterflies at Fineshade Wood is encouragingly high, there is reason to be optimistic about the future of C. palaemon in England.

Date of Award	May 2023
Original language	English
Supervisor	Jeff Ollerton (Supervisor), Duncan McCollin (Supervisor) & Nigel Bourn (Supervisor)