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The Great Yellow Bumblebee (Bombus distinguendus) in Caithness in 2010 (by Bob Dawson)

1st June 2013

This article was first published in the Caithness Field club Bulletin 2011

(Bob Dawson is the Scottish Conservation Officer for the Bumblebee Conservation Trust – Ed)
This was a very successful year, although the season was about two weeks later than last year. Many more people reported seeing, and are now more familiar with, the Great Yellow Bumblebee. Verified records came from many new locations, including two new 10km squares. There were more records in July than previously, helping our understanding of what flowers are important at this time in Caithness. A three-year pollen & nectar project was initiated by Caithness Biodiversity Group in partnership with the Bumblebee Conservation Trust. Monitoring was carried out by a dedicated team of volunteers, co-ordinated by Phyllida Sayles of CBG. As well visiting the plots themselves, Great Yellow Bumblebees were recorded on agricultural red clover among “unharvested crops” sown under the SRDP, and occasionally in very high numbers. There was also a well-publicised series of records from Dounreay.

The first of the year was, as we have come to expect (!), a queen in Mary Legg’s garden on 3st May. On 16th June, there were several queens seen at Dunnet Bay, with at least 4 queens on kidney vetch at the main Small Blue colony and another 3 queens at the south end of Dunnet Bay (Fig 1) on red clover, a flower-rich area identified as promising by Murdo Macdonald several years ago. The red clover here was already flowering, possibly a result of the stony ground and warm aspect. July saw a surge in records, large associated with the farm visits carried out by volunteers in relation to the pollen & nectar mix project. The first records were of queens collecting pollen from agricultural red clover on 13th July, with the first worker (and two sightings of queens) seen on 20th by Paul Castle at meadow vetchling. I saw another worker on red clover at a roadside verge by Barrock on 24th July, with 5 workers seen at Achscrabster on 26th, visiting tufted vetch and meadowsweet. At Milton, near Gillock on 27th a worker was seen at common hemp-nettle on 27th (with two on phacelia at the pollen & nectar mix there). Another worker was seen at Sarclet near Thrumster on 28th and had pale green pollen suggestive of meadowsweet, and the same day one was at tufted vetch near Lochend. To put into context, there was just previous record of a worker Great Yellow Bumblebee in July, seen by Murdo Macdonald at meadowsweet at Nybster. A dead Great Yellow Bumblebee found in the Castletown area was thoughtfully left for Dave Jones of the RSPB at his office, and he sent it down to Stirling where it has been included in genetic work.

In August, numbers had increased, and the first males were reported around the middle of the month (Fig 2). Angus McBay, at a large area of unharvested crop, had the first ever double-figure count of Great Yellow Bumblebees in Caithness, with 9 queens and six worker Great Yellow Bumblebee on 5th August – and there were thought to be quite a few more present. Common knapweed, marsh/hybrid woundwort and spear thistle were the most favoured foodplants away from the pollen & nectar mixes and unharvested crops. At a new site in Freswick, three males were seen one evening and seven workers the following day. As well as the wider countryside, there were two welcome records from the east end of Thurso, seen by Angus McBay on 19th July around common knapweed and one at bush vetch and common knapweed there by Karen Bell and Ken Butler on 15th August. In late August, numbers seemed to peak, but there were also some very weary and worn workers around, resting on common knapweed and spear thistle. Sightings of new queens were very scarce, though one was seen at one of the pollen &nectar mix plots. Another queen to round off the year, was (appropriately enough) in Mary Legg’s garden for a couple of days at the end of the month, visiting sweet pea, but was later sadly found dead and is also destined for Stirling.

Finally, there was an unprecedented sequence of records from Dounreay SRL, with ‘flower power’ capturing the imagination of the media. The first Great Yellow Bumblebees were seen on 26th June, at Rosa rugosa, with a first worker on 23rd July, and a scatter of records through to 26th August, mainly on common knapweed.

Volunteer training and recording
There was a training event at Seadrift on the evening of 16th June and a visit to the southern part of Dunnet Bay dunes. A report for the first year of the pollen & nectar project was circulated and prospects look excellent for the next two years. The data from Species Action Framework sites in Caithness will be analysed separately. There has also been some very helpful feedback already received regarding identification, recording methods, and suggestions for improving the forms. More feedback is always welcome!
The project has been a tremendous success to date and I would like to thank everyone involved for their time and enthusiasm. Thanks especially to Phyllida Sayles for holding the monitoring not just for the pollen & nectar mix project, but also the wider Species Action Framework effort. There was an end of season event for the pollen & nectar mix project, held at Westfield Farm in August, which saw a great turnout by farmers and volunteers. We did see a Great Yellow Bumblebee too!

Pollen & Nectar mix project
The seed mix intended for Caithness in spring for some reason ended up on the Isle of Coll. So, in mid-May, and coinciding with Scottish Biodiversity Week, I travelled north with 12 packs of replacement seed mix. Some farmers were able to sow this straight away, but some were only able to sow in June. However, for nearly all plots, germination was excellent (Fig 3A), and only in one case – where chickweed had swamped the clover seedlings – was resowing required.

The mix contains agricultural varieties of six legumes and phacelia. Phacelia well known nectar source for bees and from work on Orkney it is known that Great Yellow Bumblebees collect its pollen too. In the first year, three annual species were expected to flower and duly did: phacelia, crimson clover and “winter vetch”. The lattermost seems to be a bionic version of common vetch, with a large pea-like flower. The main perennial is red clover, as this is known to be a favourite of long-tongued bumblebees. Also included are alsike clover, sainfoin and bird’s-foot trefoil. It will be interesting to monitor the sequence of flowering of the perennials next year, in terms of forage availability for bumblebees. This year, it was interesting to see that as the phacelia reached its peak, the crimson clover came into flower (Fig 3B), thereby extending the period over which the plots were useful for Great Yellow Bumblebee. At Biggins Farm in late August, there was a remarkable count of 22 workers and just one male in the pollen & nectar plot. Previously, there were no records for this 10km square!

By mid-July, the earliest sown plots were showing plenty of phacelia flowering, as well as a good diversity of arable wildflowers. A month later, and in these earliest plots all seven of the components had started flowering – even the perennials that we did not expect to flower before next year. David King, at one of the plots, took what I believe is a unique photograph of a Great Yellow Bumblebee at crimson clover (Fig 4).

Bob Dawson would like to thank Scottish Natural Heritage and the Esmee Fairburn Foundation for supporting the work of the BBCT Conservation Officer in Scotland, and for assistance and enthusiasm of all partners in the Species Action Framework. The pollen and nectar mix project is funded by Highland Council’s Landfill Communities Fund, with thanks to both Janet Bromham and Jonathan Willett for their assistance and support. Nick Owens, James Morrison and Carolyn Goldie also assisted with my work in Caithness this year.

Bob Dawson
Bumblebee Conservation Trust
UK Charity 1115634


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