Rafts are a useful way of providing island habitat in areas of deep open water, where the depth is greater than 45-50cm. Their purpose is to improve breeding success by providing areas safe from flooding, disturbance or predation.
Artificial rafts come in a variety of designs but due to their engineered appearance do not always blend in well with their surroundings. Floating islands and vegetation rafts are an interesting, alternative option because they are more naturalistic and can provide extra benefits for wildlife above and beyond that of rafts. Please see our advisory sheet for more information on floating islands.
Floating islands and vegetation rafts are a fairly recent concept. Increasingly popular on nature reserves in the UK and beyond, they offer an exciting opportunity for minerals sites with open water and can bring an alternative solution to the use of infill for natural island creation.
Raft design
When designing a raft, there are a number of important factors to consider.
Key Points for rafts:
- They need to float, preferably with the deck just above the water line
- They need to rise and fall easily with the water over the maximum flood range
- They need to be stable, so as not to be tipped or spun by current, waves or wind
- They need to provide a sheltered nesting area, which must be high enough not to be swamped by storm waves
- They need means of access and some protection from waves and current for young birds
- Practical factors e.g. water not excessively deep; lake shore accessible by vehicle, for bringing in boat, raft and materials and for regular maintenance checks.
Anchors
Two anchors per raft are preferable and should be attached to opposite corners of the raft to keep it from swinging in the wind. Anchor to the bottom, not to the shore, to prevent vandalism and to keep rats or weasels from getting to the raft.
Gravel covering
Preferably 15mm-25mm gravel with larger pieces and rocks to provide shelter and give sufficient weight to push a running board down to water level.
Optional removable security fence
These comprise four frames made from 50x50mm planks covered with 25mm chicken wire, bolted along each side and fixed at top corners.
Re- entry system (for chicks falling overboard)
Where raft sides are left open, they should include some protection from waves and currents and a means of access (small wooden ramp) for young birds in case they fall off. Locate the ramp on opposite (lee) side of raft to the mooring ring: running board 3m, 25x150mm plank nailed to bottom of the two lower mainframes. Ramp (1.5m, 25x150mm plank) sloping up to top corner of mainframe, nailed to up-stand edging.
Optional removable security fence
These comprise four frames made from 50x50mm planks covered with 25mm chicken wire, bolted along each side and fixed at top corners.
Maintenance
Remove plant growth each winter. Colonising vegetation which starts to cover the raft can prevent birds from nesting.
Nesting areas
Rafts need to provide a dry, sheltered nest area, which does not attract the attention of crows or other avian predators.
- Tyre nests are being used with great success by breeding terns on rafts at Preston Marina in Lancashire and on islands at Broom Gravel Pits in Bedfordshire.
- Simply fill old (clean) tyres filled with washed gravel and place on islands or rafts to provide a simple yet effective nest area
- Clay pipes or old concrete piping can provide important shelter for young chicks.
Artificial Raft Examples
‘DIY’ artificial tern raft design Otmoor RSPB reserve, Oxfordshire
- Designed using 5 x 210 litre barrels lashed to main frame with rope. Bungs on the barrels sealed to prevent leaking.
- Main frame pieces held together with coach screws
- ‘Flooring’ on top of raft 1800mm x 150mm x 19mm
- 4m x 4m piece of Astroturf used to cover raft
- Large concrete blocks dropped into the reedbed.
- Eyebolts put into the blocks with ropes attached; raft anchored to these.
- The anchor ropes attached to the raft using karabiners and eyebolts so it can easily be unclipped and moved if necessary.
- 800kg of washed gravel placed onto the raft.
- The final raft measured 3m x 3m and weighed about 1000kg. Barrels give enough support: 1 litre of air supports 1kg weight so 5 barrels can support up to 1050kg
- Small electric fence erected around the outside to keep predators off the raft.
Portmore Lough Tern raft, Northern Island
- Recycled plastic with mesh sides, covered with shingle.
- Made from two pontoon sections that have been joined together to create an 8.5m x 4.2m floating platform for nesting terns.
Filcris Recycled Tern Rafts
Design is similar to the model from Moor Green Lakes in Berkshire, restored Cemex sand and gravel site.
- Thick polycarbonate sides are mink proof help protect against predation.
- Newest Filcris raft design allows two or more rafts to be easily joined together using the Tern Raft Fixing Kit:
Further reading
Detailed information on the construction and design of rafts can be found on page 13.
RSPB nesting rafts and how to build them guide.
RSPB raft designs and advice.
Relevant case study
We currently have no case studies for this habitat type. If you know of one and would like it to feature on the site contact us.
The information set out within this advisory sheet in no way constitutes legal or regulatory advice and is based on circumstances and facts as they existed at the time Nature After Minerals compiled this document. Should there be a change in circumstances or facts, then this may adversely affect any recommendations, opinions or findings contained within this document