Crane fly project

A  s part of our overall project investigating balnket bog management impacts on ecosystem services across three UK upland sites we are now also going to determine both crane fly (tipulid) emergence and abundance. This happens at all three sites and for both, the burnt and mown catchments. Comparison over time (years) and between replicated catchments of different blanket bog management (burn versus mow) will reveal main factors impacting on cranefly numbers and thus bird populations depending on this food source. Notably Red Grouse, but also important upland birds such as Golden Plover depend on this protein rich food source for chick survival and growth.

We shall work by a modified method as used by Matthew Carroll (PhD at York as part of a CASE studentship with the RSPB). Using crane fly emergence traps of 0.11 m2 (upside down basket with sticky traps inside) and also walk several 10 m transects across each catchment to count adult crane fly abundance.

The work will also involve modelling impacts on upland birds depending on tipulids by predicting crane fly abundance based on environmental data. This will be done in collaboration with the BTO (James Pierce-Higgins).

                           Setup of crane fly traps in the field                    The baskets used for trapping emerging crane flies          The final result ... from a distance - looks just like sheep

Finally, all traps set ... time to wait and then come back and count. The first counting in May 2014 (see right hand chart) showed a difference between sites (highest counts at Nidderdale, then Mossdale and Whitendale) but also an indication of treatment (T; mown) supporting larger numbers of emerging crane flies than on control (C; burnt) plots, further enhanced on brash removal (Br) plots.


Images for crane fly larvae and adult crane fly.     

Relationship between emergence of crane flies and soil moisture 2014 for all sites (trap data only).
Note that the Mossdale site seems to have supported a similar population to Nidderdale but at lower soil moisture and overall Whitendale showed lowest Tipulid counts.

Overall analyses (generalised linear model with negative binomial distribution) for 2014 data showed:
  • Significant positive relationship between Tipulid count and soil moisture. 
  • Significant difference in Tipulid abundance between treatment and control catchments (greater in treatment than control).