Lodmoor Common Terns

Lodmoor has become the place in recent years to go and enjoy the mass of Common Terns that arrive there every spring to rear their young. Last week we were very shocked to find out that the whole breeding colony had disappeared from the reserve leaving some very bare islands, sadly with lots of abandoned eggs. There must have been a very good reason for this happening as they spend a lot of energy travelling all the way from the mid Atlantic wintering grounds to come here and breed. So what happened? Toby Branston, our Dorset Ecology Manager takes up the story.

By now many local people would have noticed that the common tern colony from our Lodmoor salt marsh island have disappeared. There appears to have been a mass desertion event overnight on 13 -14^th June which left over 62 nests with eggs abandoned. This event has been much discussed, not least on Dorset O&A with the cause open to some debate. Food resource could be a factor with disturbance to the abundance of their main prey item, sand eels by the cold spring. There is some evidence for this as birds were travelling further into Lyme Bay to fish rather than Weymouth Bay just over the sea wall and the link with low mackerel numbers. Canada geese have, as has been pointed out, increased in recent years on the saltmarsh and disturbance from them may have occurred. Disturbance from mammalian predation (fox, mink or stoat) is thought not to be a likely cause and we have found no evidence of mink presence. Indeed, a combination of factors might have caused a build up of stress to an unacceptable level for the birds which resulted in the drastic action witnessed. Sadly, it is not an uncommon occurrence and the common terns locally have deserted en-mass from the Fleet / Chesil in relatively recent years and formed subsequent new nesting grounds nearby, our islands being one of these some 10 or more years ago. We are hopeful that they may return to the islands next year but in the meantime we shall be looking further into the likely causes.