Recovery on Scotland’s West Coast
Restoring valuable island habitat has far-reaching effects. Not only do islands become safe havens for nesting seabirds but other wildlife benefit, as well.
Take the lovely Marsh Fritillary butterfly, one of Scotland's most threatened species. Its island home in the Inner Hebridies, Scotland, is already showing signs of renewal less than a year after conservationists set out to rid two islands of rats.
"The absence of rats also has a positive impact on the vegetation, valuable habitats for invertebrates, including the Marsh Fritillary butterfly," said Katherine Snell, an ecologist for the South Scotland reserves who is managing the Oronsay Rat Eradication Project for the Royal Society for the Protection of Birds (RSPB).
"We're incredibly happy to see signs of success so quickly after the field work."
Ghaoideamal and Eilean an Eion
Launched in January 2012, the project involves two small islands, Ghaoideamal and Eilean an Eion (Gaelic for Bird Island), off the west coast of Scotland managed by RSPB. Besides butterflies, the tiny low-lying islands, 7.61 ha and .89 ha respectively, are a sanctuary for Arctic terns, black guillemots, little terns, European otters and grey seals. As many as 1,000 grey seals use the islands to mate and raise their pups between August and December.
Though uninhabited, the islands became overrun with rats, most likely introduced two centuries ago during a period of extensive shipping along Scotland's coast. Like other islands with a shared fate, rats destroyed native flora and decimated bird populations.
Snell, who has 11 years' experience in seabird conservation in Antarctica, the Falkland Islands and Scotland, estimates that rats had colonized the islands entirely. Based on the extensive runs and burrows across the islands, she said populations were exceptionally high.
This project was initiated by Mike Peacock, Reserve Manager for 13 years, and designed and managed by Snell. Fieldwork was conducted throughout the Scottish winters by a small dedicated team of Snell, Peacock (also skipper of the boat), as well as reserve staff and volunteers, and supported by RSPB staff at the Scottish headquarters, including Regional Reserves Manager, Dr. Dave Beaumont.
The project called for a pre-baiting program which encouraged rats to investigate a grid of bait stations, placed at 50 m intervals across the island. Bait stations were filled with muesli bars and dried fruit. Once rats were used to the stations, the team deployed rodenticide bait.
Because the islands are highly sensitive areas for vulnerable non-target species, such as raptors and otters, Snell wanted to use a first-generation rodenticide to protect non-target species.
"The careful management and monitoring of this type of project is critical in order to avoid secondary poisoning of non-target species," she stressed.
Snell contacted Bell's UK representative, Brady Hudson, for an alternative to diphacinone, which is no longer available in the UK. She ultimately settled on a first-generation rodenticide containing coumatetralyl for the majority of the baiting and supplemented it with Bell's CONTRAC BLOX.
"Only small quantities of CONTRAC were needed to target residual rats or for areas that we couldn't access to deploy bait stations in advance, thus inherently mitigating against secondary poisoning," Snell said.
The team wired bait into bait stations, four per ha, and topped it up until no additional bait was taken.
Despite a winter of gale force winds which made boating to the islands difficult, they checked stations regularly - daily when baiting first started and then once every three days - to assess bait uptake and rat activity.
"The deployment of bait was successful and the uptake of bait by rats was good," Snell reported. "CONTRAC proved to be highly palatable with large quantities of bait taken early in the baiting program, but this rapidly diminished to negligible bait-take after ten days.
"No dead rats were found on the surface nor any evidence of rats taken by predatory or scavenging birds," she added.
To monitor rat activity, the team again set up a grid of non-toxic cocoa and wax blocks until the start of the bird breeding season.
Monitoring with wax blocks was concurrent with baiting and will continue each winter and spring until the islands are rat free which requires two years with no rat activity.
After that, permanent monitoring stations will be deployed along the coast to detect any invading rats, using Bell's PROTECTA Bait Stations with wax blocks, and with snap traps used outside the bird breeding season.
Encouraging Signs of Bird Recovery
Now at the one-year mark, things are looking positive and Snell is encouraged by signs of bird recovery.
Before the project, Arctic terns attempted to nest on the islands around the reserve with no apparent success. In the summer of 2012, following the first winter of reduced rat activity, 124 apparently occupied nests were counted, and for the first time, the colony of Arctic terns was able to fledge significant numbers of young from Ghaoideamal.
Also, a pair of little terns nested on the island for the first time in three years.
"This is a fantastic result," Snell said, adding that there are fewer than 2,000 pairs of the beautiful, delicate terns in the UK and numbers in Europe are declining.
"Any safe haven we can provide for these birds to breed is incredibly important."