Tuesday 25 July 2017

Dragon Hunt

Within Orkney, there are only eight breeding species of dragonfly and damselfly, four of each. All eight species occur in Hoy, the island to the south west of mainland Orkney, but no other island of the archipelago has the full assemblage. None of the species are rare in a UK context, but one, the Four-spotted Chaser, has a very local distribution on Hoy and appears to be confined to a few pools in the Rackwick valley.

In 2014, no records were received for Four-spotted Chaser. In 2015, only one exuvia, the shed larval skin, was found. This, at least, proved that one had emerged to be an adult insect. Last year, 2016, there were no recorded sightings of the species on Hoy, raising the question "Are they still there?"

It appears that there is only a small population, so it might be that, as the dragonfly has a two year life cycle (perhaps longer in a harsh environment), flying adults will only be seen every two years. In this scenario, the 'missing' years being explained by the fact that the larvae are only half-grown. Equally, as the pools are not readily accessible, it may just be that lack of recorder effort is the reason for the dearth of sightings. Having not seen a Four-spotted Chaser in an Orkney context, I was keen to see if they were present in 2017. An added complication to surveying for dragonflies, especially in Orkney, is the presence of breeding Red-throated Divers on many of the same pools that the odes use. The level of protection (Schedule 1) afforded to these divers means that a licence has to be obtained to approach them during the breeding season.

It is also possible, though perhaps unlikely, that the Red-throated Divers on Hoy are predating the Four-spotted Chasers, either as larvae or as emerging adults, on the pools which they share. Having liaised with a Field Club colleague who possessed a Schedule 1 licence, it still remained necessary to find a convenient date where we were both available and also when the weather was suitable for dragonflies and surveying.

The chaser's flight season within Orkney begins in mid-May and lasts until mid-August, with the peak time being mid-June until the end of July. As this time ticked by, it began to look as though we might miss the opportunity for another year. But this does rather suggest that recorder effort is the problem! Fortunately, several days before National Dragonfly Week commenced, all the planets aligned and the Hoy trip went ahead. Hours before setting off, we learned that the divers on site had failed in their breeding attempt for this year, which took away a bit of the pressure we were feeling.

Once on Hoy, a local minibus dropped us off on the nearest bit of tarmac road to the pools in question, then it was a yomp across country, very off piste, over heather, bogs, burns and hills. En route, we saw several Large Heath butterflies, which I mistakenly presumed were day-flying moths until I was educated otherwise. At the pools, there were many damselflies on the wing, the day being very sunny and with a gentle breeze. An immature Black Darter dragonfly was seen, then we discovered an emerging Common Hawker, hanging beneath some heather at a pool edge.

The Admiral busy logging all Odonata activity

Common Blue Damselflies in tandem

Blue-tailed Damselfly female, form rufescens-obsoleta

Recently-emerged Common Hawker

Our guide pointed out another dragonfly, whizzing low over the water, which soon resolved itself into a Four-spotted Chaser. So they were still present! Yay! Then we spotted another and another.

Four-spotted Chaser, with minimal wing damage

Four-spotted Chaser, with quite a bit of wing damage
We did not witness any breeding activity, and our photographs from the day can only confirm that two of the chasers were male, so there's a bit of a question mark over the future. Hopefully, our brief snapshot of their flight season is not typical, and sufficient numbers of males and females made it onto the wing and were able to mate. Pond dipping for larvae would be an option, but I think it would fall foul of the Red-throated Diver issue.

Returning to the ferry on foot, we popped into another site and found evidence of Emerald Damselfly emergence, meaning that on the visit to Hoy we had seen seven of the eight Orkney species. A good day's work.

All photos courtesy of Alan Nelson, less for the first one.

Next time: National Dragonfly Week begins...


Spadger said...

Nice work boys! Never mind about the divers they're only birds - lol :o) !!!

Imperfect and Tense said...

Whilst the restrictions on access are a little frustrating, the Red-throated Divers are rightly the priority species in this context. None of the Orkney dragons and damsels are endangered species in the UK. Which doesn't mean that this topic won't be a recurring theme in the coming blogposts about National Dragonfly Week!

Anonymous said...

Nicely done. I've got a pic of a golden- ringed dragon on my blog today. A new species for our garden. Will look forward to reading more of your dragon posts.

Imperfect and Tense said...

Thanks, CT, and yes, Golden-ringed Dragonfly was the species we didn't see on that trip. I am very envious of your garden visitor :o)

Anonymous said...

Wow that was truly exciting in an odanatic kind of way, great build up. Welcome back to the blogosphere by the way. Toodles, Mark.

Imperfect and Tense said...

Mark, thank you.