In 2005 Natural England (then called English Nature) published a document that offers advice to developers on issues related to reptile survey and mitigation work. The document is still available and includes useful information, including a summary of the critical factors that should be taken into account when selecting a receptor site:
"You should take into account a number of factors when selecting sites, including agreement from the landowner and local interest groups, site safeguard, assurance of long-term favourable management, and access for monitoring. Locating a suitable release site can take many weeks of survey effort, fact-finding and liaison. If no suitable site can be found, then it is possible that the development will be prevented from proceeding in its original form. "
By referencing this booklet, together with books, published papers and various reports, it is possible to propose reptile receptor site selection criteria. Some of these factors will be further discussed in future blog posts. I will then use these criteria to propose a simple scoring system that allows different proposed receptor sites to be compared.
1. Location
Ideally, reptiles should be retained on site or released into an adjacent area of land. When ex situ mitigation exercises are being considered, the location of a proposed receptor site is often influenced by many different factors that may result in animals being moved over much greater distances and this will be discussed in a future blog post.
2. Area
The proposed receptor site should comprise an area that is at least as large as the area of reptile habitat that will be lost to development. If the proposed receptor site is smaller, available (including enhanced) habitat must be of a sufficiently high quality to support the animals being translocated. Ideally, receptor sites should be both larger and include proposals to enhance existing habitat.
3. Existing Habitat
Receptor sites must include habitat that is suitable for foraging, sheltering and protection. Proposed receptor sites that consist of unsuitable habitat are likely to require significant enhancement work before reptile translocation is possible. Habitat enhancement work on such sites can involve considerable effort and it may take several years before the vegetation sward is sufficiently well established to support translocated reptiles. Determining the suitability of habitat for reptiles includes consideration of many different factors and these will be explored in a future blog post.
4. Extant Reptile Population
The proposed receptor site should not support a population of the species to be relocated, but must be capable of supporting such species with appropriate habitat enhancement works. Additional survey work may be required at the proposed receptor site to determine likely presence of species. This is important to ensure that the mitigation works do not result in a net loss of reptile populations. Although it may be possible to translocate small numbers of animals into an existing population, it is important to ensure that a site's carrying capacity is not exceeded. It is also possible that concerns over disease transmission may make such additions to existing populations undesirable.
5. Predators
Reptiles are preyed upon by a wide range of different predators. In some situations the local abundance of a predator could reduce the likelihood of translocated animals establishing a successful population. Species that may be particularly problematic will be discussed in a future blog article.
6. Site Safeguards
The proposed receptor site should not be subject to planning or other threats (including unsympathetic management work) for the foreseeable future).
7. Site Management
The proposed receptor site should be subject to a written, agreed and funded management agreement. The management agreement should include reference to any additional works that are considered necessary to help establish translocated animals.
8. Site Monitoring
The proposed receptor site should be subject to a written, agreed and funded monitoring programme. The time required for monitoring and the extent of monitoring works required are likely to be determined by the size of the reptile population and impacts of disturbance. Proposed objectives will be discussed in a future post.
[update 1/8/2013] Added predators as an additional selection criteria to consider (ref. Gemma Harding 2004. British Reptile Translocations Guidelines for the selection of receptor sites). Some other factors that folks have suggested can be included within criteria 4 - Existing Habitat (e.g. topography, vegetation, temperature, connectivity etc).