Island design

Islands are an important habitat feature, providing disturbance-free nesting for ducks, waders and terns. They are particularly valuable in providing both an ecological and landscape feature in large-scale waterbodies. There is a legacy of island creation within mineral restoration schemes.

Howevever, while many do offer some ecological benefit, very often they do not fulfil their true potential. This advisory sheet aims to highlight the importance of island design and provide some simple guiding principles.

General Principles

Many previously-restored sites support islands with steep banks that sit high above the maximum water level and thereby become a burden to manage, as in the below pictures. While these islands offer some ecological value, this is limited as the steep slopes restrict access for target bird species and limit opportunities for the colonisation / growth of marginal plants.

Key factors in island design: prevailing wind direction, shape and size, target species, surface preparation and type, access to the islands for management / monitoring

Benefits:

Increased species diversity
Increased breeding success through reduced predation risk
Lower long-term management costs

5 easy principles to creating ecologically-functioning islands:

1. Location

To avoid erosion of the island by wind action, islands should be located in the most sheltered area of the waterbody, which in the UK context is usually the south-west corner. However, limited wave action can be beneficial to help form and maintain a beach of shallow gradient.
Islands can offer enhanced opportunities, particularly for breeding birds, when situated in extensive shallows. However, in mineral restoration sites, this is not always feasible due to lack of infill material. In such cases, create shallows in the immediate vicinity of the island, where possible. Islands can also be enhanced by incorporating shallow ponds within in, thereby increasing foraging opportunities.

2. Island Profile

Islands should be low in profile, with shallow gradients into the water, ideally 1:20 where possible.
However, steep-sided islands with naturally eroding faces may provide important habitat for invertebrates; provide nest sites for kingfisher and occasionally, sand martins.
Where multiple islands are possible, a varied profile will allow some to be fully flooded at least once during the winter, which will assist in arresting vegetation succession and maintain bare areas for ground-nesting birds. Islands that remain above the water level will develop some vegetation cover and provide resting areas for wintering wildfowl.

3. Island Shape

Increase the shoreline length as far as possible with spits and bays, particularly on the sheltered side.

4. Substrate

Naturally vegetated, clay-capped islands will attract wet grassland waders e.g. redshank and lapwing.
Topping islands with gravel will attract ringed plovers and common terns.
To provide extra protection, clay piping / old concrete pipes can be installed, or alternatively, old tyres have been placed on islands at Broom Quarry in Bedfordshire.

5. Follow-up Management

Depending on the height of the island - and therefore if it is subject to annual flooding - the new islands may require regular management, at least annually, in order to maintain their breeding-bird interest. This should be considered during the design, including the practicalities of transporting appropriate equipment to the island to undertake management and the cost implications of this.