GUEST BLOG – Otters on Orkney by Anne Bignall
When Anne contacted me regarding her exciting quest to discover more about the rather elusive otter population on Orkney, I was keen to help. Anne was desperate to get her hands on as many trail cams as she could, as these were going to be her best chance of locating and filming them. I was able to lend Anne two Bushnell trail cameras to help her with her work.
I was delighted when Anne said she would write a guest blog post to explain how she used the Bushnells and how they helped her find out more about otters on Orkney.
Orkney is thought to have a relatively low number of otters compared to other Scottish Islands. Indeed, Shetland some 60 miles to the north east, has an estimated population of 900 and these animals are active during the daytime. Therefore, careful scanning of a rocky shore may well reward the hopeful otter watcher in Shetland.
Not so, in Orkney. After living on the islands for a decade I had only seen a handful of otters – nearly all fleeting, chance encounters.
However, in December 2014 my partner Mark and I spotted a lone otter at one of the few places in Orkney where otters are fairly regularly sighted – the ‘Brig of Waithe’, a sea inlet leading to a large saline lagoon. Over the coming weeks, we made repeated visits to the site and started experimenting with trail cameras. After only a few nights a family of three otters appeared on a camera that had been set on a sprainted trail along the coast. We made regular visits in all weathers and they began to pay off, seeing the family in the flesh. Our sightings became more and more frequent and we became increasingly proficient at anticipating where they’d be. It wasn’t long before we could almost guarantee seeing them, and over the months we watched the two cubs grow up and finally, separate from their mother.
It was an inspiring time – further fuelled by discussions with wildlife photographer Richard Shucksmith who had studied and photographed Shetland’s otters extensively. I wanted to find out what Orkney’s elusive otters were up to and with Richard’s help developed a project to estimate the population of otters on one of Orkney’s smaller islands by identifying holt sites and using trail cameras to monitor activity. The technique of estimating otter populations from holt numbers was developed on Shetland by ecologist Hans Krukk. He studied Shetland’s Otters and calculated overall numbers by determining the average number of holts used by females and also the ratio to males to females in the population. I would use the ratios he calculated for Shetland in my study on the island of Eday.
In Summer 2015 I was working on Eday surveying seabirds and cetaceans. When not working I spent as much time as possible looking for otters on the shore. Having ‘got my eye in’ earlier in the year, I had a number of brief sightings along the coast – until finally in September 2015, all my Christmases came at once and I spotted a young family on the shore.
However, my joy was short lived. Despite obsessively searching the coast, the family did not show themselves and I would have to wait 6 months before I saw them in the flesh again.
Luckily the trail cameras succeeded where I failed. I was able to follow the progress of these animals and started to get some idea of their range.
A license is required to use a trail camera on an active holt site, and after obtaining this I began surveying the whole of the Eday coast and recording all the potential otter holts. Most of these were in areas also well used by rabbits and although the spraint I found often contained rabbit hair, it seemed that these animals lived in close proximity to each other and it seemed very possible that otters were using burrows that were at least partially being excavated by rabbits.
It wasn’t long before the trail cameras started doing some excellent work, where my hours of shoreline observations were failing! Groups of holts were present around the coast and the cameras picked up families in some of these groups.
One particularly charismatic young family used a group of three or four holts on a section of low cliffs.
I never saw this family in the flesh and without the trail could have only surmised from the amount of spraint present that a family was probably in residence.
The camera also picked up males passing holt groups. Unfortunately, it was not possible to identify individual animals on the camera so it was uncertain as to the extent of the males’ ranges and how many holt groups they were visiting.
Picking up trail cameras and downloading the results became an addictive part of the study. What would I find? Sometimes a piece of grass that had miraculously appeared in front of the camera and triggered it every three seconds for several hours – groan. Sometimes a rat, vole, mouse, rabbit or bird. And then sometimes one otter video in amongst a sea of negative one – 485 videos of a rippling water for the one glimpse of a male exploring a peatland pool next to a suspected holt site…..
Then, after a winter and spring of sightings on the cameras – all the action stopped. The cameras stopped picking up otters. Through the summer, activity remained little of nothing at most holt sites and the holts themselves showed little spraint and generally looked abandoned. It seemed that during these more clement months and when cubs were larger, otters were going elsewhere. Perhaps to the extensive areas of rocky, shelving coastline or to the fissures and caves in cliffs. More work would be needed to find this out – beyond the scope and timescale of the project. However, the cameras certainly assisted in identifying this apparent pattern.
Using the method of calculating the population of otters from holt numbers – the island population was estimated at between 16 – 22 animals. By the end of my 8 month study, I observed three otter families and around 6 lone animals. The trail cameras confirmed a further 4 families and a number of individuals, including a young animal that was blind in one eye.
Some great work by Anne and also a testament to how Bushnells can be invaluable within research work, undertaking monitoring that is almost impossible any other way.