Estimating the populations of three species of Volucella in an English woodland Roger Morris Stuart Ball

Volucella species studied V. inflata V. bombylans V. pellucens

Study site – Old Sulehay Forest, BCNP Wildlife Trust Reserve 35 hectares of ancient semi-natural woodland Managed as hazel coppice with oak/ash standards before 1940s Main ride is well managed and open

Sampling sites in the wood 20 visits from 7 June to 27 July 2003

Marking

Numbers marked and recaptured CaptureV. bombylansV. inflataV. pellucensTotal Total out of 985 marked flies were recaptured at least once = 16.25%

Some practical lessons The consistency of paint is important - too thin and the insect gets covered (and may be fatally damaged) Species with hairy thoraxes are much harder to mark clearly Constant effort is needed to ensure that new recruits to the population are marked before they displace existing members or disperse themselves

V. bombylans population estimates φ = (0.244) φ = estimate of daily survival (standard error)

V. inflata population estimates φ = (0.027)

V. pellucens population estimates = (0.013)

Summary of population estimates Estimated population size with 95% confidence interval V. bombylans200 (142, 339) V. inflata656 (468, 1097) V. pellucens1963 (1669, 2384) Estimate of the total population of each species using Schnabels method, Krebs (1989)

Some emerging questions? How big is the population of V. bombylans ? The wood is only 35 hectares! It is difficult to believe: There are sufficient sap runs large enough to support the larvae of 650 V. inflata There are sufficient social wasps nests to support 2,000 V. pellucens

Longevity

Distance moved by recaptured individuals of V. bombylans FemaleMale Recaptured at the same station 550%832% Moved within a ride 440%1352% Moved between rides 110%416% Total recaptures1025 Average distance moved (m) 84122

Behaviour of V. bombylans Mating strategy well known: males perch on prominent foliage and dart out at passing insects Our results suggest males are quite mobile. Therefore likely male does not return to the same perch each day Males moved more than females

Distance moved by recaptured individuals of V. inflata FemaleMale Recaptured at the same station 436%1765% Moved within a ride 655%623% Moved between rides 19%312% Total recaptures1124 Average distance moved (m) 13664

Behaviour of V. inflata Both sexes mainly captured around flowers Males make rapid flights around nectar sources (bramble & shrubs) Only one observation of copulation: male flew high round dogwood (Cornus sanguinea) and briefly coupled with female in flight Males moved much less than females Some evidence that males held a territory

Distance moved by recaptured individuals of V. pellucens FemaleMale Recaptured at the same station 436%24978% Moved within a ride 545%4515% Moved between rides 218%187% Total recaptures11318 Average distance moved (m) 16455

Details of movements of male V. pellucens At the same station Moved within ride Moved between rides 7-14 June 177%1430%1255% June 2811%2349%523% 7-13 July 6526%715%523% July 13956%36%00% Consecutive captures of the same individual

Behaviour of male V. pellucens Visiting flowers Resting on foliage Hovering 7-14 June 7763%43%4134% June 95%11%16194% 7-13 July 4418%21%20582% July 208%21%21991%

Behaviour of V. pellucens Mating strategy well known: males hover and defend an air space, dart after passing insects Male hovering extremely sensitive to sunshine: When the sun goes in they rapidly perch in trees When it comes out again, equally rapidly resume hovering Copulation observed just once. Coupling appears to be very brief and in flight, like V. inflata

Behaviour of V. pellucens (2) Both sexes visit flowers early during emergence and are fairly mobile Later on males almost exclusively caught hovering and become very immobile Some evidence that males hold a territory, sometimes over several days As season progressed, it was much more likely an individual male would be found at the same hovering post Suggests fierce competition for hovering posts early on leads to rapid turnover

Potential for further study Our knowledge of V. bombylans population size is incomplete Detailed survey for potential breeding sites is needed to better understand the population dynamics of V. inflata Questions remain over the degree to which V. pellucens moves from breeding sites to suitable territories for mate- acquisition

ANY QUESTIONS?