There seems to be a general consensus that reptiles should be either retained on site or moved into an adjacent area of land. Translocation of reptiles to more distant receptor sites is considered to be a 'last resort' strategy.
Examples of published documents that attempt to provide guidelines for UK reptile translocations have been produced by Herpetofauna Groups of Britain and Ireland (HGBI, 1998), JNCC (Clemons and Langton, 1998), English Nature (Moulten and Corbett, 1999, English Nature, 2004) and Highways Agency (2005).
All organisations emphasise the importance of in situ mitigation within the development site itself. Avoiding impacts is clearly the best outcome for reptiles and can be the cheapest option for developers (particularly when delays caused by capture and relocation work are considered). Of course it isn't always possible for new developments to avoid disturbance. Whilst some form of on site relocation may be possible, things get more difficult when ex situ receptor sites are required. Although Clemons and Langton (1998) make no recommendations over distance, both HGBI (1998) and Highways Agency (2005) recommend that receptor sites should be 'close' to the development. Natural England (2004) seem to accept that receptor sites can be:
some distance away
Translocation of slow-worms from a Canterbury development attempted to follow the HGBI (1998) guidelines and involved the movement of animals to a receptor site located within 1 km (Platenberg and Griffiths, 1999). Can 1 km be considered close? HGBI (1998) attempt to define the distances acceptable for translocations:
at least within the same county or similar administrative area, and the same geology and habitat type
In this context 1 km is very close indeed. But clearly the HGBI (1998) definition is rather broad. What is meant by 'county'? Administrative county? Vice county? What about unitary authorities? 'Kent' includes areas that are governed by Kent County Council. However, the Hoo Peninsula is part of Medway Unitary Authority. Is it wrong to translocate reptiles between Kent and Medway? Since Kent is a large county it includes two vice counties; East Kent (VC15) and West Kent (VC16). Is it acceptable to move animals between vice counties? Both Sheerness and Faversham are located within the same local authority area (Swale). However, Sheerness is situated on the Isle of Sheppy. Is is acceptable to move animals between mainland and island sites, even if they are situated within lthe same local authority?
As a recorder I would prefer that reptiles are relocated to areas within the same recording unit. This would help to ensure that the status of populations are maintained in a manner that does not confound future monitoring work. Recording units could be represented by 1 km squares, 10 km squares or vice counties. However, as I will discuss in a future blog post even this obstacle can be overcome (at least to some extent), providing the donor population and receptor site are clearly recorded and results are made publicly accessible.
Of course reptiles do not recognise such artificial boundaries. Although HGBI (1998) imply that it is acceptable to translocate a population several tens of kilometres from one side of a county to another - what about animals occupying development sites that are situated on the boundary? Would it perhaps be better to relocate these animals to a site that is closer, but located in a different county? Restricting the movement of animals to locations within an administrative area may impose unnecessary constraints on a mitigation project that do not contribute to meaningful conservation outcomes.
In a study that investigated the feasibility of introducing grass snakes into the London Wetland Centre, McGrath (2004) acknowledged that introduced animals should originate from a site that is located:
in the same geographic region
McGrath interpreted this as a site located in:
London and otherwise the south-east of England.
That's quite a large area. McGrath subsequently suggested that since only one sub-species of grass snake is native to Britain:
populations from Britain as a whole could be accepted
McGrath seems to be suggesting that the limit on translocation distance should be defined by genetics. However, I wonder if defining genetic variability by sub species is perhaps too simplistic. The movement of sand lizards between Merseyside and Dorset would I suspect be rather frowned upon, even though the animals are the same (sub) species. In their Sand Lizard Conservation Handbook, Moulton and Corbett (1999) consider translocation and advise:
The animals used should be of the right genetic type for the area. The three different regions ie. Merseyside, Weald and north Surrey and Dorset support populations that appear to be different and these may represent distinct “races”. Therefore any re-introductions must avoid mixing (or the possibility of mixing) of these “races” and where possible should use the stock most appropriate for the site.
Perhaps distinct genetic races are less likely to be prevalent in species such as grass snake that are widely distributed across England and Wales. Grass snakes subsequently introduced to London Wetland Centre originated from Holborough in Kent (Anon 2011) - a site located 50 km away. Other long distance translocations have also been publicised in the media. One such project involved the translocation of several thousand reptiles (multiple species, including adder) from Essex to Wiltshire; a distance of over 150 km. In an attempt to promote good practice, Cresswell et al describe mitigation work involving viviparous lizard and adder along the A74 trunk road near the Scottish Border:
Best practice in this regard dictates that, wherever possible, reptiles should be relocated to locations adjacent to or in the immediate vicinity of their existing home ranges or population centres. Only as a ‘last resort’ should they be moved.
Difficulties in identifying suitable adjacent habitat meant that adder:
would need to be translocated to a suitable ‘receptor site’ some distance from the scheme
The distance to this receptor site is not disclosed.
Since translocation projects have been undertaken that involve the movement of reptiles over large distances, is there still a need for guidelines to recommend local receptor sites? In attempting to answer this question I've reviewed available literature to identify relevant issues. These are listed as positive (+) and negative (-) factors:
Short Distance Translocations
+ Species populations are maintained in the local area.
+ Species with large home ranges are less likely to be displaced.
+ Lower captivity and transport times will help to minimise stress and thus reduce post release mortality.
+ Risk of disease transmission between populations minimised.
- Receptor sites may be unavailable.
- Even if available, there is likely to be less choice possibly resulting in selection of sites that are of a lower quality.
- Homing behaviour of some species could result in animals moving back into areas inappropriately.
Long Distance Translocations
+ Greater choice of high quality receptor sites.
+ Translocations can benefit conservation through targeted (re)introductions.
+ Species with homing behaviour less likely to return.
- Loss of local biodiversity interest.
- Increased risk of inappropriate mixing of unique genetic races.
- Movement of animals into areas with different habitat/geology that may increase dispersal and mortality.
- Increased risk of moving species out of their natural range (even if habitat/geology appears the same).
- Movement of individuals out of their home range may increase risk of homing and dispersal, causing increased mortality through predation, road kill etc.
- Increased stress through longer captivity and greater travel distances.
- Increased risk of disease transmission to new areas.
- Possible unforeseen impacts on species already present at receptor site.
Available information suggests that whilst there may some tradeoffs in choosing local receptor sites, translocating animals over long distances introduces many variables that significantly increase the risk of the translocation failing. The next question is how far is too far?
References
Anon (2011) Reptiles and Development. MKA Ecology.
Clemons, J. and Langton, T (1998) Species translocation. In Herpetofauna Workers Manual, Joint Nature Conservation Committee.
Cresswell, W., Hay, J., Whitworth, R., Head, M. and Penniston, L (2012) Moving lizards and snakes from the path of new roads and improvements: how to get it right. Creswell Associates.
Herpetofauna Groups of Britain and Ireland (1998) Evaluating Local Mitigation/Translocation Programmes: Maintaining Best Practice and Lawful Standards. HGBI Advisory Notes for Amphibian and Reptile Groups.
Highways Agency, (2005) Design Manual for Roads and Bridges Volume 10 Section 4, Part 7, HA 116/05 Nature Conservation Advice in Relation to Reptile and Roads, HMSO, London.
McGrath, A. (2004) Introduction of Grass Snakes to the London Wetland Centre: A Feasibility Study. MSc Thesis. Imperial College London.
Moulton, N. and Corbett, K. (1999) The Sand Lizard Conservation Handbook. English Nature.
Platenber, R.J. and Griffiths, R.A (1999) Translocation of slow-worms (Anguis fragilis) as a mitigation strategy: a case study from south-east England. Biological Conservation, 90, 125 - 132.
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