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Slow-worm densities: |
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Matt Harris Senior Member Joined: 03 Jun 2003 No. of posts: 196  View other posts by Matt Harris |
Posted: 16 Sep 2004 A consultant's report has quoted slow-worm as reaching densities of 600 - 2000 per hectare, but provided no reference for this. Before I embarrass them by asking where they got this from, has anyone else come across this piece of data, or anything similar on slow-worm densities? Ta. Gwent Amphibian and Reptile Group (GARG) |
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GemmaJF Admin Group Joined: 25 Jan 2003 No. of posts: 2090  View other posts by GemmaJF |
Posted: 16 Sep 2004 It doesn't sound too far out Matt, though I do not know the exact reference it came from. Though similar values are given by Platenberg and Langton in a paper called Slow-worms in Kent:estimates of population density and post-translocation monitoring, this was published in English Nature Science No.27 Reptile Survey Methods. I don't know if Lee Brady could tell you more about this paper and the results. An estimated density of 1050 per hectare is given. Gemma Fairchild, Independent Ecological Consultant |
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Matt Harris Senior Member Joined: 03 Jun 2003 No. of posts: 196 View other posts by Matt Harris |
Posted: 16 Sep 2004 What method did Lee, or anyone else for that matter, use to estimate pop. densities? I know Betty used recognition of individuals from head markings etc, but is there any way of estimating from straight tin data, without individual recognition/marking? Gwent Amphibian and Reptile Group (GARG) |
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calumma Senior Member Joined: 27 Jun 2003 No. of posts: 351 View other posts by calumma |
Posted: 16 Sep 2004 The density estimate of ~1000 slow-worm per ha comes from multiple studies. These include the the work of Nick Smith (1990, MPhil Thesis), Anne Riddell (1996, Diploma in Ecology Thesis) and Betty Platenberg (1999, PhD Thesis). Miguel Vences has also published a paper that estimated slow-worm density on an isolated Spanish population. Extrapolating from his results a density of 960 individuals per ha is achieved. Nick, Anne and Betty used head and chin patterns to recognise individual animals. One thing to be aware of with reptile densities is that although estimated densities can be very high indeed in specific areas, calculated density depends upon the size of the survey area. Although obvious many consultants don't take this into consideration. It is rare for all parts of a site to offer excellent habitat, densities are usually much lower than the quoted figures. Consider the situation of a development site that consists of an arable field with a narrow linear headland. The overall density of reptiles may be very low (if the arable field is included in the estimate). However, the *density* of reptiles within the headland could be very high (yes even 1000 per Ha) - yet the overall *abundance* within the headland may be relatively low. Population estimates and the terminology used to describe them need to be interpreted with a great deal of caution. Beware of consultants who claim the 1000 - 2000 animals per ha as justification for dumping large numbers of animals into a small receptor area. A common tactic by the ignorant or unscrupulous... There is absolutely no way of estimating population density from basic tin data without individual recognition or marking. Statistical models (e.g. capture recapture etc) that control for detectability are required. Lee Brady Kent Herpetofauna Recorder | Independent Ecological Consultant |
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Robert V Senior Member Joined: 06 Aug 2004 No. of posts: 717 View other posts by Robert V |
Posted: 16 Sep 2004 I'd have to agree with you on that one Lee, 100%! I'd be suprised if the actual figure of slow worms in an area of say a Hectare was any larger than 30! That is any given hectare where they are known to thrive. That should cause a stir. R RobV |
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Caleb Forum Coordinator Joined: 17 Feb 2003 No. of posts: 448 View other posts by Caleb |
Posted: 17 Sep 2004 Has anyone collected data on the number of slowworms captured in translocations? This should certainly give a minimum size for the population involved... I can well believe that they do reach densities of several hundred per hectare (in suitable habitat), having seen how many have been removed from some Dorset building sites. |
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calumma Senior Member Joined: 27 Jun 2003 No. of posts: 351 View other posts by calumma |
Posted: 17 Sep 2004 I have data available and slow-worm numbers can easily exceed 1000 animals per ha. I have a site that supports a closed population of slow-worm. The site is about 2 ha in size that has had over 1000 animals removed from it. Not all areas within the site offered suitable habitat and the work remains uncompleted (only ~60% of the site has been cleared to date). Obviously delays in progressing the works cause problems when attempting to calculate density/abundance in schemes such as this, since recruitment into the population may occur. No reptile fence is perfect and animals do breed! Lee Brady Kent Herpetofauna Recorder | Independent Ecological Consultant |
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Matt Harris Senior Member Joined: 03 Jun 2003 No. of posts: 196 View other posts by Matt Harris |
Posted: 17 Sep 2004 OK thanks for your replies Gwent Amphibian and Reptile Group (GARG) |
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nils Member Joined: 18 Jan 2011 No. of posts: 1 View other posts by nils |
Posted: 18 Jan 2011 I was wondering if anyone of you could send me published papers where these slow worm densities are mentioned. I am writing a dutch article about translocation of a slow worm population in the Netherlands. We translocated 151 slow worms out of 1 ha grasland that became a building site (it used to be a developmental site, but building was delayed for years). This number has, as far as I know, never been found in the Netherlands. Only estimations have been made. I am pretty astonished about the numbers you are discussing. I could use some references. Need more information, let me know!
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- Slow-worm densities |