Mink control offers brighter future for nesting terns

By Geoff Small and Steve Littlewood (Mull Bird Club)

Tern-ringing-01.jpgCommon tern, Isle of Mull. Photo: Steve Littlewood.

For many years Clive Craik of the Scottish Association for Marine Science has been monitoring terns nesting in Argyll. Some years ago the islands and skerries around Garmony and Glas Eileanan off the shore near Craignure on the Isle of Mull were noted as some of the most significant tern colonies in the UK. Sadly, the ‘alien’ mink on the Isle of Mull devastated them and left the area almost bereft of birds. Various attempts were made to control the mink, but there was only spasmodic success in coordinating and continuing the project, and the number of nesting birds remained at a minimal level. Then, in 2014, the mink populations around Fishnish and Garmony were targeted by Geoff Small for ongoing culling and in 2015 the area north of Craignure close to Glas Eileanan was also intensively trapped by Steve Littlewood and Stephen Sheppard.  It is possible that unverified sites were trapped independently in The Sound towards Glen Forsa as well. In excess of thirty mink have now been removed from the area.

Tern-ringing-03.jpgRinging common and arctic terns on the Isle of Mull. Photo: Steve Littlewood.

On 14th July Geoff and Steve were joined by Clive Craik, Nicholas Watts and Rob Lightfoot for a formal count and ringing of young chicks in the areas. Sites at the Fishnish timber jetty and River Forsa were included in the ringing after being ‘discovered’ as a result of the monitoring. They are unrecorded (new?) colonies. The results and additional monitoring through May and June show a significant nesting resurgence, which encouraged Clive to suggest that the Isle of Mull is once again in line to be Argyll’s premier tern nesting site. Other shore nesting birds also appear to be making a comeback in the monitored areas.

On the day of the ringing there were in excess of 75 active Common Tern nests recorded and 63 chicks ringed, and more than 60 Arctic Tern active nests with 13 chicks ringed. Many birds were noted to be already fledged or too small to be ringed, and perhaps 700-800 birds were observed but not actively nesting.

Despite this success, the mink control is not guaranteed to continue in subsequent years, and it is therefore not a given that the birds will continue to thrive and numbers increase. What we feel we can say at this moment in time is that birds are clearly extremely vulnerable to predation and disturbance but also highly resilient if given a degree of protection. At the end of the day the rich and enviable biodiversity that we tend to take for granted on Mull is very fragile and monitoring and protection are a prerequisite of a healthy future. Hopefully there are lessons to be learned from the intervention on behalf of the terns of Mull. More monitoring of the island’s bird populations would make a useful contribution to that learning.