20/04/21

Chris Park, Project Development Officer (Environment)

When I used to wear the Conservation Officer's hat for the Trust, it was part of my remit to look for quick wins for biodiversity improvements in the Park. The Common Tern was a bird species that occurred in the Park that at the time didn't have anywhere suitable to nest.  We needed to provide somewhere suitable for them, undisturbed by ground based predators, people, dogs, foxes, badgers, otters, mink, rats etc. 

When I worked at Rutland Water I had made several floating islands for terns which were very successful.  I was given the budget to buy a raft which we did from a company based on the Isle of Wight. We actually purchased two rafts, which we launched and installed on Overton Lake. The first year of installation was amazingly successful and at least 13 pairs of terns nested and we ringed something like 21 chicks, although there were some still many birds on eggs and some chicks too small to ring so the final productivity was probably around 30 chicks. 

The rafts were left in situ over winter and were constantly used and heavily soiled by cormorants. We cleaned the rafts and installed a camera ready for the following spring. Sure enough the terns started to nest again but then something went wrong and they all disappeared and so did the eggs. 

When we compared images of the freshly installed rafts with the rafts a year later it became obvious the rafts had sunk lower in the water.  The company that had made them come back the following spring and stripped the rafts down and refilled the bags of buoyancy material (off cuts from the foam used in US army helmets!). The foam had absorbed a lot of water so the freeboard of the rafts had reduced considerably.  We reinstalled the rafts but they were never used by terns again. When we went out to the rafts to clean off a year's accumulation of cormorant guano that had coated the layer of gravel left for the terns to nest on, we found a midden of Swan Muscle shells, many showing two small puncture holes approximately 30mm apart... the tell-tale indicator of Otter canines.  If Otters could get onto the rafts then the tern wouldn't nest.

From then on, the rafts were regularly used by cormorants as a perch... but not the terns, that they were designed for. So the Trust, removed the rafts. When they were brought to the bank the recycled plastic board they were made from had deteriorated so much that the rafts fell apart so were no longer of use. 

This year, thanks to generous funding from the Mick George Community Fund we have been able to install a new tern raft on Overton Lake. This time we have used two 1.5 x 3m plastic pontoon sections fixed side by side creating a 3m x 3m raft. The framework of angle iron around the sides holds in Perspex sheets which at 500mm height plus the freeboard of the raft gives an effective vertical barrier of 700mm to prevent Otters from climbing on the raft and the tern chicks (should we have any) from falling off.  Unless of course Otters have learnt how to leap like Salmon or Dolphins... Let's hope not!

The new tern raft was installed on Monday 19 April 2021. 

As the boat pulled away from the raft yesterday we watched a tern circling the lake eyeing the raft up. I'm going to be keeping my fingers tightly crossed that we can encourage these lovely birds back to nest in the Park. 

The Tern raft has been made and installed with generous funding from the Mick George Community Fund.