Calumma Ecological Services has been working with mhs commercial at a site in Eastcourt Lane (Medway). The location is a classic brownfield site - unmanaged, unloved, full of rubbish and absolutely teeming with slow-worms. Medway Messenger has run a news...
Calumma Ecological Services has been working with mhs commercial at a site in Eastcourt Lane (Medway). The location is a classic brownfield site - unmanaged, unloved, full of rubbish and absolutely teeming with slow-worms.
Medway Messenger has run a news item with a typical catchy title. Happily, they do appear to have reported the facts more or less accurately and at least this time I haven't been misquoted! The article can be read online here. Erin was particularly pleased to have her photo in the paper (again)!
So why is it that slow-worms are so regularly caught up in building works and why do the works so frequently need to be delayed?
Slow-worm Habitat
Slow-worms are completely harmless lizards that live in the topsoil and amongst the roots of vegetation. This 'semi-fossorial' lifestyle means that the slow-worm is better off without legs. Over time, evolution has produced an animal that is sleek, tough and completely legless.
Habitats favoured by slow-worms are usually well vegetated. Typically the vegetation is quite rank and displays a good degree of structural complexity. Often, the ground shows signs of disturbance. Disturbed ground is much easier for slow-worms to burrow into. Habitats that display these two important features include gardens, allotments (disused allotments being particularly important), old churchyards and previously developed land that has subsequently been neglected and reclaimed by nature. Descriptions of the latter are often motivated by the particular interest of the person or organisation who is doing the describing! Such sites may be called wasteland by prospective developers, wildlife areas by conservation organisations and frequently eyesores by local residents! Buglife has more information on the value of such areas for wildlife.
Brownfield sites make ideal homes for slow-worms. The sites may be colonised by animals that live around the edge of the site or from adjacent land (such as gardens). Once the brownfield site has been left for a few years to 'mature', the number of slow-worms that may be found there can be very large indeed.
Slow-worm Populations
Slow-worms can be found in very high densities. Work in SE England by Renata Platenberg and Anne Riddell suggests that in favourable habitat the numbers can be as high as 2000 individuals per hectare. In other areas, slow-worms may be far less abundant with populations often displaying a patchy distribution. The distribution of slow-worm in Kent illustrates this. The species is reasonably well distributed across the county, but relatively few records have been generated in the Romney Marsh and Dungeness area. Presumably, marshland habitats may be simply too wet for an animal that lives in the ground. The pebbles at Dungeness are likely to cause a burrowing animals a great deal of consternation!
Yet slow-worms are found at some locations in this general area (such as New Romney). Survey work undertaken by Calumma Ecological Services has revealed that slow-worm populations within appropriate habitat at such locations can be very large - even though the animals appear to be relatively isolated.
Given the above, it should come as no surprise that slow-worms are frequently found on sites identified for development and that they often occur in large numbers. Clearly, any necessary ecological work will require significant effort that may lead to delays for developers. Not only does the presence of large numbers of slow-worm potentially cause delay, but seasonal activity patterns frequently result in time constraints over when the ecology work can be undertaken.
Slow-worm Activity
In the past animals like slow-worms were referred to as 'cold-blooded'. The term cold-blooded is however rather misleading and reptiles are better referred to as ectothermic. In essence, slow-worms maintain their body temperature through external ('ecto') means - unlike you and I who are able to maintain our body temperature internally (e.g. by eating). How do slow-worms do this? Usually by basking in the sun - or at least by absorbing the sun's radiation through cover objects such as flat stones, under which slow-worms can frequently be found sheltering.
In Britiain, weather conditions can get somewhat chilly during the winter. Ectothermic animals therefore face something of a dilemma. How do you maintain a suitable body temperature when the external conditions are too cold? British reptiles solve this problem by hibernating. Unlike some animals, reptiles don't necessarily spend the whole winter asleep and it is not unheard of for surveyors to encounter basking lizards on sunny winter days. Since slow-worms live in the ground, they may be less inclined to become become during the winter. Certainly there are no records of winter activity for Kent.
Consultants engaged in slow-worm mitigation projects must therefore direct their efforts into those times of the year when the animals are active. This may seem like a reasonable and straightforward task. However, when are slow-worms active? Conventional wisdom suggests that reptiles are active from when they emerge from hibernation (mid March to early April) to when conditions become too cold (late September to end October). There are also likely to be seasonal fluctuations between years that are influenced by local weather conditions. To further complicate matters, survey work may not be very effective during periods of cold weather, during periods of wet weather or during periods of prolonged dry weather.
There are also other issues that many consultants rarely give consideration to:
1. Is it ethical to capture and relocate heavily gravid females (June to September)?
2. Is it appropriate to capture and relocate animals late in the season (September to October), when they are preparing for hibernation?
3. How do ecological consultants overcome problems caused by differences in activity displayed by male and female slow-worms?
The latter point is a particularly difficult issue for those involved in commercial ecological consultancy work. Adult male slow-worms typically emerge from hibernation before females. Survey and/or capture work undertaken early in the season will therefore display a population structure that is heavily biased towards males. In May, this trend reverses. Males tend to become more difficult to find, whilst encounter rates for females increases quite dramatically. Presumably after mating, male slow-worms can reduce their risk of being eaten by a predator by becoming less active - or at least becoming more difficult to find by ecological consultants! Female slow-worms must bask with more frequency to help promote the development of their unborn babies. The artificial cover objects so loved by those undertaking reptile survey work make ideal basking locations for female slow-worms. Survey and/or capture work undertaken between June and September therefore results in a significant female bias. Do the majority of translocated slow-worm populations consist of females? If so, what are the implications for their future survival?!
So when is the best time to undertake reptile survey and mitigation works? The answer to this question is likely to depend upon the species present and the particular local site conditions. One thing is certainly apparent though. Reptile survey and mitigation work is a time consuming activity. Developer's must ensure that sufficient time is programmed into their development timetable so that all necessary work can be completed ahead of proposed building works.
Leaving wildlife surveys to the last minute, will invariably result in a delay.
The Kent Reptile and Amphibian Group has analysed information held on its recording database and produced graphs that illustrate many of the activity trends described above. The graphs are available to interested parties - including consultants who sign up for KRAG's Corporate Membership scheme.