Road casualty survey results 2008 - provisional analysis

2008 was the final year of the stag beetle road casualty survey, which was first carried out in Suffolk with 10 volunteers in 2000. Since then stag beetle road casualty data have been collected annually (except for 2002) from Suffolk and a number of other counties.

19 volunteers returned stag beetle road-casualty data,
16 returns were from Suffolk,
2 returns were from West Sussex and one from Surrey,
23 road belt-transect data sets were returned,
6 transects yielded a nil count over the season.

Table 1. Numbers of beetles counted in the 2008 roads survey

A total of 371 stag beetles (or their remains) was observed on the roads.
The number of times a route was surveyed varied from 6 to 83, the average being 30.
13 volunteers surveyed throughout the ‘stag beetle season’.
11 volunteers surveyed at least once every 4 days throughout out the stag beetle season.
4 surveyors surveyed daily throughout the stag beetle season.
The total number of road casualty and live stag beetles observed along an individual transect over the stag beetle season varied from 0 - 91.
Excluding beetles where the sex was not identified by the surveyor (Unident.), female beetles killed on the roads outnumbered males in a ratio of 2.8: 1. Previous stag beetle road casualty surveys (Hawes 2000, 2003, 2004, 2005, 2006 and 2007) show a female to male ratio of 3.5, 2.4, 3.4, 2.2, 1.6 and 3.1:1 respectively. The mean ratio of female to male stag beetle road casualties for the years 2000, 2003, 2004, 2005, 2006, 2007 and 2008 (excluding those where sex was not identified) is 2.7: 1.

Of the 61 stag beetles whose sex could not be identified by the surveyors (corpses too damaged; tibia of front legs not examined; genitalia not examined) the proportion of females to males is to date unknown.

Comments and discussion

Six transects gave zero sightings.
24 stag beetles of unidentified sex were collected and recorded along one surveyor’s transect.
Surveyors have submitted the stag beetles (and remains) collected to the author, so that foreleg tibia, and genitalia can be used to determine sex, where this is needed.

Annual index of abundance
Analysis of the data collected in the eight years of the survey is underway (the data submitted in 2001was incomplete and will not be included in the final analysis). The aim is to produce an annual index of abundance for each transect site, which will be included in a paper to be entitled ‘Development of non-invasive monitoring methods for larvae and adults of the stag beetle Lucanus cervus’ which will be submitted to the Journal of Insect Conservation in early March 2009.

Table 2. Stag beetle road casualty surveys:
cumulative totals for 2000, 2003, 2004, 2005, 2006, 2007 and 2008

Further analysis
Further analysis of the stag beetle road casualty survey data is being undertaken in 2009 to:
Compare transects where stag beetle road casualties occurred with control transects where no stag beetles were observed.
Compare landscape characteristics which might facilitate stag beetle road casualties, e.g. proximity of decaying tree stumps, dead wood in hedgerows, proximity of houses and their gardens, etc.
Predict where stag beetle road casualties are likely to occur, using landscape features, accumulated day temperature and soil type as pointers. Preliminary findings suggest that stag beetle road casualties occur more frequently in residential areas than in the open countryside.

Acknowledgements

I am indebted to all the volunteer surveyors who took part in the 2008 survey and especially to those* who have contributed to all seven surveys referred to above. Suffolk: Janet Baker, John Baker, Janet & Jim Buis, Malcolm Cook, Bob Deex, John Glazebrook, Doug Harper*, Rosemary Milner*, Nicola Moxey*, Naomi Newton, Gill & Chris Pink, Ann Ratford, Keith Rawlings, John Tombs*, Mark Usher; Sussex: Norman Allcorn, Miss C.P.S. Griffiths; Surrey: Mark Wagstaff. Any errors and omissions in the above are the responsibility of the author.