Rafts

Floating rafts can be provided for nesting and loafing sites in locations where the water is too deep for island construction, or where there is no suitable material available. Rafts have the advantage that their use by birds is not affected by changing water levels, but they lack the sheltered shallow margins associated with islands. Rafts can be vegetated, for use by wildfowl, or covered with shingle for terns. Tern rafts have been particularly successful in attracting terns to sites which lack natural breeding habitat. Rafts are not usually visited by predatory mammals, and so can be safely situated fairly close to shore.

Factors to consider

It is difficult to make rafts quite as effective as islands, because several conflicting requirements must be reconciled. These include:

1. The ability to float, preferably with the deck just above the water line.
2. The ability to rise and fall easily with the water over the maximum flood range.
3. Stability, so that the raft is not tipped or spun by currents, waves or wind.
4. A dry, sheltered nest site which does not attract the attention of crows or other avian predators. The nest areas must be above the level of storm waves.
5. Means of access and some protection from waves and currents for young birds.
6. An appearance which does not detract from natural surroundings.

Design of rafts

Many different designs have been tried over the years. Strength and buoyancy are essential, together with very firm anchorage. Constructing a large raft is not an easy undertaking, and the logistics of construction, getting it to the site and anchoring it must be carefully thought out. Rafts designed only for breeding are better brought ashore during the winter to reduce damage. Rafts used for loafing during the winter will need cleaning of guano if they are to remain attractive to nesting birds.

Materials

Timber rafts tend to absorb water and sink, although pine or other light wood floats better than heavy timber. In most cases additional floats must be used.

Very small rafts can be floated with 4.5 litre (1 gallon) plastic containers or similar. Slightly larger rafts will stay afloat with 22 litre (5 gallon) drums. Rafts in the range of 1.2-1.8m (4-6′) in dimension require close-cell polystyrene blocks, or scraps or polystyrene beads in watertight containers. Polystyrene blocks need holding in place with galvanised netting or strips.

Normally two anchors are preferable to one, attached to opposite corners of the raft to keep it from swinging in the wind. However, large rafts in deeper open water may be better with only one mooring point, which allows the raft to align itself downwind, rather than being buffeted by cross winds. Anchor to the bottom, not the shore, to prevent vandalism and keep rats or weasels from getting to the raft. Anchors can be made from concrete blocks, concrete filled containers or other heavy items.

One method is to secure a length of chain with rocks or other heavy items in a polythene tub or similar, and then fill with concrete. After setting, the anchor can be turned out of the mould and the chain attached. The anchor shown weighs about 50kg (1cwt) and is suitable for smaller rafts. Anchors for larger rafts may need to be made from two or more weights joined together, to avoid the anchor becoming too cumbersome to be easily positioned. The design below uses concrete anchors in buckets each 250mm (10″) high and 300mm (12″) diameter, connected in pairs with lengths of chain. The shackle for the mooring rope is attached to the point where the chains cross.

The anchor rope can be 20mm polypropylene rope, 19mm flexible steel wire rope or chain. Ship’s chandlers can supply suitable ropes, shackles and other fittings, and any coastal sailing club or fisherman will have advice to offer on the subject of secure anchorage and techniques for lowering anchors into position. Make sure that all connections are robust so that no parts can be lost. Normally the anchor is the cheapest part of the construction, but is a nuisance to replace. Chains and steel ropes are expensive. It may be a good idea to secure a buoy to the rope as shown, so if the raft does come adrift, the anchor and rope are retrievable. Terns or other birds are likely to use the buoy for perching. Take advice on the most suitable length of anchor rope for the local conditions. If it’s too short, the raft may drag the anchor along the bottom in stormy conditions. Three rafts or more anchored in a string will need additional anchorage. If you plan to bring the raft ashore over winter, use a coupling to the raft which is easy to disengage, and if there isn’t already a buoy in position, secure one to the rope before you detach the raft to avoid disaster!

Vegetation

Wader and tern nesting rafts should be bare of vegetation, and surfaced with gravel or shingle contained within a rim. On wildfowl and diver rafts vegetation can be planted to improve appearance and provide nesting cover. To supply sufficient water for plant growth, either a generous depth of turf is needed, or some means by which water is wicked up onto the raft. Rafts of anchored floating vegetation are also feasible (see below).

Nesting boxes

Nesting boxes and duckling ramps can be added to the raft as required. Dutch nesting baskets are designed with an open weave which allows the nesting duck to see in all directions, and an entrance which funnels to about 150mm (6″) to keep away avian predators. Secure the baskets to the raft, at least 1.2m (4′) apart, and facing away from each other. Place a lining of dead grass inside each basket to encourage nesting.

Nesting baskets can also be placed on stilts, away from overhanging branches along which rats could gain access. Where water levels can be controlled, the lowest part of the basket should be 200-300mm (8-12″) clear of the water. Where levels cannot be controlled, the baskets must be well above the normal level.

Vegetation rafts

A simple but effective technique is to make rafts of floating vegetation. Mats of emergent vegetation, up to about 30 sq m in area, can be cut from the sides of lakes and meres, and floated into open water. The raft is then secured by stakes about 2m (7′) long, driven through the vegetation and into the lake bottom, which allow the rafts to rise and fall with changing water levels.

In sheltered locations at Leighton Moss, Lancashire, rafts have lasted over 10 years. The vegetation, mainly yellow flag (Iris pseudacorus), is cut annually in late summer, and stakes are replaced as required. A wide range of waterfowl use the rafts for breeding and loafing. Vegetation rafts are not sufficiently robust for exposed locations. The design below, half-way between a raft and an island, is based on existing clumps of emergent vegetation.After constructing the floating framework, add more turf as needed to give the whole thing a semi-solid flooring. The emergent plants will grow through to provide secluded nest sites for duck.

Floating nest

This design, described by Little (1971), and successfully used on the River Ray, near Oxford, provides a safe nesting site in flowing water. Chick survival is best where the floating nest is sited on a quiet backwater with gently sloping banks, so that when a chick leaves the nest, it can get to shore and climb out despite the current.

Construction procedure:

1. Drive a suitable length of 50mm (2″) diameter steel pipe into the river bed to provide an anchor pole on which the floating nest can rise and fall.
2. Cut out a circular platform from marine plywood, and cut a hole in the centre to fit over the anchor pipe. Screw on three boards to make a frame for the floats.
3. Strap three 4.5 litre (1 gallon) plastic containers to the frame, one each side.
4. Form a superstructure of three metal struts, joined at the top to a ring which forms the bearing on which the nest rises and falls on the pipe. Cover with netting. The mesh holes should be small enough to keep out rats, but leave a 150mm (6″) diameter entrance to one side.
5. If the platform tends to spin in the current, attach a rudder to the floats to keep it properly orientated. The entrance should face the nearest bank.

Timber rafts

Simple log rafts

Logs or old telegraph poles can be used to make simple rafts. Place mud or straw between the logs, together with rhizomes of marginal plants. Without additional support the timbers will float fairly low in the water, and should support a good growth of vegetation. Secure half-drums or other nesting boxes as required.

Telegraph pole raft

The following design is for a vegetated timber raft, suitable for use by nesting waterfowl. Rafts of this type have survived over 10 years’ use in fairly exposed conditions at the RSPB reserve at Fairburn Ings, Yorkshire.

The basic framework is made of two telegraph poles with six timber spacers, covered with 25mm (1″) chicken wire to hold the vegetation. Polystyrene blocks between the spacers provide flotation.

1. Position the telegraph poles on a suitable flat surface close to the water. Using 75mm (3″) coach screws, attach the spacers in the positions shown.
2. Using proper lifting techniques, and taking care not to twist the structure, lift one pole and roll the structure over. Attach the polystyrene blocks with fencing wire, and secure the top spacers with coach screws. Fix the wire mesh to cover using fencing staples. Attach mooring rings to the telegraph poles.
3. Float the raft into shallow water, and plant with clumps of marginal vegetation.

Vegetated timber raft

This design has been used successfully at the Great Linford gravel pit reserve in Buckinghamshire.

1. Make a framework of 150 x 25mm (6 x 1″) boards, to give an area of 1.2 x 1.8m (4’x6′).
2. Secure 25mm (1″) galvanised mesh across the bottom, with diagonal boards as shown to give rigidity to the structure.
3. Turn the raft over, and fill the middle section with polystyrene blocks. Cover with boards to make a floor, and construct duckling ramps.
4. Float the raft into shallow water, and fill the margins with blocks of marginal vegetation.

Tern raft

Tern rafts require a covering of bare shingle, small shelters to give shade for chicks and protection from predators, and access ramps for any chicks that fall overboard. The design shown below is 3 x 3m (10’x10′), and can support up to ten nests. The mesh fence prevents ducks from gaining access. Further details are given in Burgess, Neil D and Becker, Dusty B (1989).

Welded rafts

This design uses welded steel flotation tanks secured by steel girders. Mechanical assistance will be required to get it into the water. The vegetated platform, supported by mesh, floats just above water level, and provides nesting sites for wildfowl.