NARRS REPORT

Transcription

1 Amphibian and Reptile Conservation RESEARCH REPORT 13/01 NARRS REPORT Establishing the Baseline (HWM Edition). J.W. Wilkinson and A.P. Arnell ARC Science Team 1

2 ACKNOWLEDGEMENTS The NARRS Report is dedicated to all the NARRS surveyors, too numerous to list individually, who give up their time to conduct the surveys that provide NARRS data. Without them, this would not be possible. SUGGESTED CITATION: Wilkinson, J.W. & Arnell, A.P. (2013) NARRS Report : Establishing the Baseline (HWM Edition). ARC Research Report 13/01. Amphibian and Reptile Conservation 655A Christchurch Road Boscombe Bournemouth Dorset, UK, BH1 4AP PHOTO CREDITS p1, p37, Chris Dresh p17, Chris Gleed-Owen p23, p24, John W. Wilkinson 2

3 CONTENTS Page Contents 3 List of Tables and Figures 4 1. Introduction 5 2. Methods Widespread Amphibian Surveys Widespread Reptile Surveys Metadata Species Data Habitat Descriptors Detecting Future Changes 7 3. Results Metadata Species Occupancy Rates Species Richness Habitat Descriptors Detecting Future Changes Discussion Metadata Species Occupancy Rates Species Richness Habitat Descriptors Detecting Future Changes Summary of Detecting Future Changes The Future of NARRS References 35 3

4 LIST OF TABLES AND FIGURES Table 1. Numbers of results received from unique NARRS survey squares Table 2. Numbers of unique NARRS survey squares grouped by NARRS Area Page Figure 1. The areas by which regional NARRS results were pooled for analyses 9 Table 3. Pond occupancy rates for amphibians by NARRS Area Figure 2. Locations of NARRS amphibian survey squares Figure 3. NARRS squares with Rana temporaria present 12 Figure 4. NARRS squares with Bufo bufo present 13 Figure 5. NARRS squares with Triturus cristatus present 14 Figure 6. NARRS squares with Lissotriton vulgaris present 15 Figure 7. NARRS squares with Lissotriton helveticus present 16 Table 4. Square occupancy rates for reptiles by NARRS Area Figure 8. Locations of NARRS reptile survey squares Figure 9. NARRS squares with Zootoca vivipara present 19 Figure 10. NARRS squares with Anguis fragilis present 20 Figure 11. NARRS squares with Natrix natrix present 21 Figure 12. NARRS squares with Vipera berus present 22 Figure 13. Amphibian species richness 23 Figure 14. Reptile species richness 24 Table 5. Descriptors of amphibian habitat (HSI) 25 Table 6. Descriptors of reptile habitat 25 Table 7. Power analyses of future ability to detect changes in occupancy rate 26 (declines or increases) and sample sizes required to achieve higher power, by species, based on numbers of surveys and occupancy rates from NARRS Table 8. Comparisons of pond occupancy rates. 27 Table 9. Comparisons of reptile square occupancy rates. 29 Table 10. A comparison of HSI scores from four Scottish pond surveys

5 1. INTRODUCTION The National Amphibian and Reptile Recording Scheme (NARRS) began in The scheme uses volunteer-based efforts to monitor and report on the status of amphibians and reptiles. For details of the background to NARRS, and survey protocols, please see and/or Wilkinson & Arnell (2011). The scheme currently operates in Scotland, Northern Ireland, Isle of Man, Wales, England, Jersey and Guernsey. The previous NARRS Report (Wilkinson & Arnell, 2011) presented interim results of the scheme s widespread amphibian and reptile surveys after three years of recording. Here, we present the results of one full survey cycle (six years; ) of randomlyselected (PHASE 1) squares, setting the baseline occupancy rates for widespread species against which future differences can be assessed. For the purposes of detecting changes in survey square occupancy (declines or increases), the period is treated as the first sample, the second sample will be , and so on. The utility and limitations of the present results are discussed in the last section, as well as approaches for the future. 2. METHODS This section contains a brief description of the NARRS methodology. For detailed survey protocols and full background information, please see (PHASE 1) Widespread Amphibian Surveys Amphibian surveyors are asked to identify the pond nearest the south-west corner of their survey square and, where necessary, obtain permission to survey it from the landowner and/or tenant. Letters of introduction are provided if required. Up to four visits are carried out using (i) visual searching, (ii) netting, (iii) night torching and (iv) -sometimes- bottle-trapping, in order to detect the amphibian species present. Bottle trapping is used by very experienced surveyors only, it is included in the protocols as validation research has demonstrated that using all four methods over four survey visits result in the best chance of detecting all species present in a pond (Sewell et al., 2010). Survey conditions (weather etc.), species present and habitat characteristics are recorded. For amphibian surveys, the latter take the form of the Habitat Suitability Index (HSI), developed for use with great crested newt surveys (Oldham et al., 2000). The HSI is also a good indicator of the overall habitat quality of the pond and its surroundings and, as such, is a useful comparative measure for amphibian habitat in general. 5

6 2.2 (PHASE 1) Widespread Reptile Surveys Reptile surveyors use maps or aerial photographs to identify potential reptile habitat in their survey square and obtain permission to visit promising areas as necessary. Up to four visits are carried out using (i) visual searching, (ii) checking existing refugia and (ii) checking artificial refugia (where it has been possible to lay these) in order to detect all reptile species present. Sewell et al., (2012) found that three to four visits resulted in 95% certainty of detecting the widespread reptiles present on a site. The use of refugia can be particularly important in finding slow-worms and, sometimes, snakes. Survey conditions, species present and habitat characteristics are recorded. It is particularly important for reptile surveys to be conducted during appropriate conditions (e.g. of sun and temperature) to maximise detection probability; volunteers are trained in this. A variety of habitat descriptors are recorded in reptile surveys as no equivalent of the pond HSI is currently available for reptiles. In the case of surveys for either taxon, if no pond or reptile habitat exists, or survey permission is refused by a landowner, alternative squares are identified by examining the square immediately to the north of the original and, if necessary, moving around that square in a clockwise direction until a suitable one is found 2.3 Metadata Results from NARRS PHASE 1 surveys were checked for duplicates, which were removed, and then grouped by country or region. These data were further grouped into four NARRS Areas based on latitude: (i) Scotland, (ii) Northern, (iii) Wales and Central, and (iv) Southern. This pooling allows data from areas where few surveys have been conducted to contribute usefully to regional assessments and comparisons. This is desirable in terms of assessing status and trends long-term as well as, potentially, for possible future assessments such as of the effects of climate change. Data for Jersey and Guernsey are not reported here, and will be presented separately. 2.4 Species Data Occupancy rates (of ponds for amphibians, of squares for reptiles) were calculated for each of the widespread species by NARRS Area and overall. Occupancy rates have been adjusted appropriately for those species not occurring in Northern Ireland, the Isle of Man and Scotland. Positive and negative NARRS survey locations were plotted in ArcGIS (v. 10.1) and are shown for both groups and for each species individually (Figs. 2 12). 6

7 Amphibian and reptile species richness by square also was calculated (see 3.3). This is a simple assessment of how many species are found in a square, and is both repeatable and comparable over time. It is theoretically possible for species occupancy rates to remain temporally stable whilst species richness by square changes, thus perhaps indicating a change in habitat characteristics. 2.5 Habitat Descriptors For amphibians, mean HSI and percentages of ponds with good (i.e. scoring >0.7) HSI and bad (<0.3) HSI were calculated for each NARRS Area and overall. Reptile habitat was assessed by quantifying the mean and range of survey route length, on the basis that longer routes are possible in squares with more habitat. Reptile habitat connectivity, isolation and designation status was also quantified. 2.6 Detecting Future Changes Wilkinson & Arnell (2011) presented measures of progress towards the target of achieving 400+ NARRS surveys for both amphibians and reptiles during the first NAARS survey cycle ( ). The target figure of 400 surveys for each taxon was based on estimated species occupancy rates and statistical advice provided by the British Trust for Ornithology during the consultation stage of NARRS (Freeman, 2006). Now, at the end of the first sixyear cycle, we conducted new power analyses of the ability of future surveys to detect changes in occupancy rates (declines or increases) These power analyses use observed species-specific occupancy rates from surveys during and numbers of surveys carried out. Power to detect changes of 20% and 30% in occupancy rates was assessed for all species. Where appropriate, we also used power analyses of surveys with unequal sample size to determine second sample sizes required to detect these levels of change at 80% power. Further explanation is provided in the Discussion. Power analyses were carried out using R statistical software (R Development Core Team, 2012). 7

8 3. RESULTS 3.1 Metadata Table 1. Numbers of results received from unique NARRS survey squares (results from squares surveyed in more than one year have been pooled). English regions are Natural England Regions, see regions/default.aspx Country/Region Total Surveys Amphibian Surveys Reptile Surveys Scotland Northern Ireland Isle of Man Wales England East Midlands East of England London North East North West South East South West West Midlands Yorkshire and Humber TOTAL (all areas) Table 2. Numbers of unique NARRS survey squares grouped by NARRS Area. NARRS Area Total Surveys Amphibian Surveys Reptile Surveys Scotland Northern (NI, IoM, NW, NE, Y&H) Wales and Central (Wal, WM, EM, EoE) Southern (SW, SE, Lon) TOTAL (all areas)

9 Figure 1. The areas by which regional NARRS results were pooled for analyses ( NARRS Areas ). 9

10 Rana temporaria Bufo bufo Triturus cristatus Lissotriton vulgaris Lissotriton helveticus Other Overall amphibian occupancy (all spp.) 3.2 Species Occupancy Rates Table 3. Pond occupancy rates for amphibians by NARRS Area, NARRS Area Species (% occupancy) Scotland 70% 35% <1% 4% 42% <1%* 83% Northern (NI, IoM, NW, NE, Y&H) Wales and Central (Wal, WM, EM, EoE) Southern (SW, SE, Lon) Overall (above areas combined) 67% 48%# 12%# 39% 26%# 0% 87% 60% 35% 15% 43% 16% 0% 86% 48% 22% 18% 29% 24% <1%** 74% 60% 33% 12% 28% 27% <1% 82% # Occupancy adjusted for species not occurring in NI * Alpine newts ** Marsh frog 10

11 Figure 2. Locations of NARRS amphibian survey squares

12 Figure 3. NARRS squares with Rana temporaria present. 12

13 Figure 4. NARRS squares with Bufo bufo present. 13

14 Figure 5. NARRS squares with Triturus cristatus present. 14

15 Figure 6. NARRS squares with Lissotriton vulgaris present. 15

16 Figure 7. NARRS squares with Lissotriton helveticus present. 16

17 Zootoca vivipara Anguis fragilis Natrix natrix Vipera berus Other Overall reptile occupancy (all spp.) Table 4. Square occupancy rates for reptiles by NARRS Area, NARRS Area Species (% occupancy) Scotland 53% 16% 0% 5% 0% 73% Northern (NI, IoM, NW, NE, Y&H) Wales and Central (Wal, WM, EM, EoE) Southern (SW, SE, Lon) Overall (above areas combined) 14% 10%* 17%* 3%* 0% 40% 27% 11% 13% 10% 0% 39% 33% 33% 27% 9% 8%** 61% 35% 22% 22%# 7% 3%** 52% * Occupancy adjusted for species not occurring in NI and IoM ** Includes rare and non-native spp. detected in Southern England # Occupancy adjusted to account for negligible N. natrix records from Scotland 17

18 Figure 8. Locations of NARRS reptile survey squares

19 Figure 9. NARRS squares with Zootoca vivipara present. 19

20 Figure 10. NARRS squares with Anguis fragilis present. 20

21 Figure 11. NARRS squares with Natrix natrix present. 21

22 Figure 12. NARRS squares with Vipera berus present. 22

23 3.3 Species Richness Figure 13. Amphibian species richness. Percentages of NARRS survey squares with 0 5 amphibian species present. (a) Scotland (b) Northern 1% 1% 17% 16% 13% 2% 7% 23% 32% 33% 28% 27% (c) Wales and Central (d) Southern 14% 4% 2% 4% 19% 26% 13% 30% 26% 33% 29% 18% (e) Overall 1% 4% 17% 30% 30% 23

24 Figure 14. Reptile species richness. Percentages of NARRS survey squares with 0 5 reptile species present. (a) Scotland 3% 12% (b) Northern 9% 45% 23% 40% 68% (c) Wales and Central (d) Southern 5% 13% 39% 3% 2% 8% 20% 61% 21% 28% (e) Overall 1% 1% 5% 15% 48% 30% 24

25 3.4 Habitat Descriptors Table 5. Descriptors of amphibian habitat (HSI). NARRS Area Scotland Northern (NI, IoM, NW, NE, Y&H) Wales and Central (Wal, WM, EM, EoE) Southern (SW, SE, Lon) Overall (above areas combined) Mean HSI (range) 0.47 ( ) 0.57 ( ) 0.57 ( ) 0.53 ( ) 0.53 ( ) Ponds with HSI >0.7 Ponds with HSI < % 17.44% 22.06% 6.88% 24.75% 9.90% 20.56% 9.35% 19.61% 10.77% Table 6. Descriptors of reptile habitat. NARRS Area Mean length of survey route (range) Surveys in which reptile habitat was part of larger area of good habitat Surveys in which reptile habitat was isolated* Surveys within protected/ designated areas Scotland 1.66 km ( km) 20.51% 53.85% 8.05% Northern (NI, IoM, NW, NE, Y&H) 1.56 km ( km) 15.63% 65.63% 17.14% Wales and Central (Wal, WM, EM, EoE) 1.47 km ( km) 27.87% 44.26% 33.87% Southern (SW, SE, Lon) 1.88 km ( km) 24.58% 42.37% 33.33% Overall (above areas combined) 1.70 km ( km) 23.18% 48.44% 24.52% * completely isolated or isolated by sub-optimal habitat 25

26 3.5 Detecting Future Changes Table 7. Power analyses of future ability to detect changes in occupancy rate (declines or increases) and sample sizes required to achieve higher power, by species, based on numbers of surveys and occupancy rates from NARRS Values for power to detect are rounded down to the nearest 5%; high power values (above 80%) are highlighted in green. POWER TO DETECT (equal sample sizes, two-tailed, α = 0.1) Size of second sample required to detect change at 80% power (unequal sample sizes, two-tailed, α = 0.1) Size of second sample required to detect change at 80% power (unequal sample sizes, two-tailed, α = 0.2) Species No. of Surveys Occupancy Rate 20% change 30% change 20% change 30% change 20% change 30% change R. temporaria % >95% >95% B. bufo 410* 33% >65% >90% T. cristatus 410* 12% >25% >50% very large very large very large 1560 L. vulgaris 412** 28% >55% >85% L. helveticus 410* 27% >55% >85% Z. vivipara % >55% >85% A. fragilis 304* 22% >35% >65% very large 768 very large 332 N. natrix 217 # 22% >30% >50% very large very large very large 596 V. berus 304* 7% >15% >25% very large very large very large very large * Absent from Iom and NI ** Absent from IoM # Effectively absent from Scotland 26

27 4. DISCUSSION 4.1 Metadata Though participation in NARRS widespread species surveys remains good, the numbers of surveys per year have gradually diminished over the course of the first survey cycle. The practical upshot of this is that the broad goal of generating results from 400+ surveys each, for both amphibians and reptiles, has been achieved for amphibians (412) but not for reptiles (310). Fewer completed surveys reduces the power to detect changes in occupancy rate the status measure which NARRS widespread species surveys informs especially where occupancy of surveyed squares is low (see Tables 3, 4 and 7). Implications are discussed under Detecting Future Changes, below. The spread of surveys carried out is generally very good, with some clusters in the Scottish borders and southern England where there are especially enthusiastic surveyors (Figs. 2 and 8). It is also apparent that some areas of the country are under-represented in NARRS surveys, a factor that can be addressed by continuing to target the gaps with NARRS training events. 4.2 Species Occupancy Rates Amphibian occupancy rates varied only slightly from the period (Table 8) and from Swan and Oldham s earlier (1993) work. Table 8. Comparisons of pond occupancy rates. Species Rana temporaria Bufo bufo Triturus cristatus Lissotriton vulgaris Lissotriton helveticus Pond occupancy (%) Swan & Oldham (1993) Pond occupancy (%) NARRS * Pond occupancy (%) NARRS * N.B. this is a subset of the data for NARRS results are again on the whole slightly higher than in Swan and Oldham s (1993) study, a factor likely attributable to reluctance of surveyors to submit negative results. 27

28 Additionally, though the overall occupancy rate for L. helveticus has reduced a little since Wilkinson and Arnell s (2011) report, it remains higher than that recorded previously. Wilkinson and Arnell (2011) suggest this may be due to the recently-recorded decline in quality of UK ponds (Williams et al., 2010), which may favour the species, better identification of species, or possible survey bias towards areas where palmate newts are common (or a mixture of these factors). Future comparisons of both occupancy rates and HSI scores (Table 5 and below) and efforts to widen the geographic spread of NARRS surveys over time may be enlightening in this respect. Area- and species-specific differences in amphibian occupancy rates can be seen (Table 3 and maps), though these are not discussed in detail here. Of particular note, however, is that the occupancy rates for T. cristatus are the lowest for any widespread amphibian in all NARRS areas and overall. This affects ability to detect changes (see Detecting Future Changes, below) and is particularly important because of the UK s requirement to report on the status of this (still widespread but highly-protected) species to the European Union (EU). The responsibility for this function is now devolved to the country conservation agencies (SNH, NE and CCW), each of which is sponsoring initiatives for T. cristatus in their own right, as are other government agencies. For further details on some of this work, see Arnell and Wilkinson (2011a), Arnell and Wilkinson (2011b), Wilkinson et al. (2011), Wilkinson et al. (in press 2012), Wilkinson and Arnell (in press 2013) and Arnell and Wilkinson (in prep.). A combination of approaches to monitoring and conservation will be required long-term to maintain and enhance the conservation of this species in the UK, and to ensure its reporting needs are met. Reptile occupancy is best compared with earlier NARRS results (from Wilkinson and Arnell, 2011), there being no comparable equivalent to Swan and Oldham (1993) for reptiles (Table 8). Occupancy rates are near-identical (noting that occupancy for N. natrix in the present report has been adjusted to account for its near-absence from Scotland). Number of surveys was, however, rather lower than ideal (see above), affecting the ability of future NARRS surveys to detect reasonable changes in occupancy rate with high power for most reptiles. The occupancy rates presented here for both amphibians and reptiles are baseline values from the first NARRS survey cycle ( ); the frequency with which species are recorded in NARRS surveys being the simplest way of quantifying apparent changes in status (declines and/or increases) based on distribution. The ability to detect such differences and to examine trends over time is species-specific, being dependent on both numbers of survey results returned and species overall occupancy rates. This is again discussed under Detecting Future Changes, below. It is also important to note that NARRS surveys should at present continue to operate over a six year cycle, both (i) to allow 28

29 maximum chance of generating and including a sufficient number of results in assessments and (ii) to allow for high inter-annual differences in detectability due to population fluctuations and weather variability. Indeed, it is assumed (with some justification!) that poor weather conditions, especially over the springs and summers of have contributed to a lower number of returned surveys over this period. This is particularly true for reptile survey results. Table 9. Comparisons of reptile square occupancy rates. Species Zootoca vivipara Anguis fragilis Natrix natrix Vipera berus Square occupancy (%) NARRS * Square occupancy (%) NARRS ** # 7 * N.B. this is a subset of the data for ** Unadjusted # Occupancy adjusted to account for negligible N. natrix records from Scotland 4.3 Species Richness These data are presented here mainly to establish a baseline against which future results can be compared. It is particularly apparent, however, that survey squares are overall much richer in amphibians than they are in reptiles and that reptile surveys yield negative results far more often than do amphibian surveys. This may once again be due to differences in detectability and weather patterns that are hard to quantify, but the effects of which are hopefully smoothed over the course of the six year NARRS cycle. It may also indicate that some negative amphibian results (in particular) have not been submitted. Also of note is the low species richness of NARRS reptile squares in the Northern Area, with no more than 3 reptile species in any square. This is perhaps another indication that greater survey effort is required in particular regions and that NARRS training needs to be targeted there. Unsurprisingly, the Southern Area had highest reptile species richness (see Figs. 13 and 14). 29

30 4.4 Habitat Descriptors NARRS amphibian surveys have a very useful additional indicator of status in the HSI (Oldham et al., 2000): a decline in HSI score over time indicates a decline in the quality of pond habitat that may come to lead to changes in occupancy rates for the widespread amphibians, particularly T. cristatus. Baseline regional and overall summaries of HSI score measures are presented in Table 5. Only for Scotland is a direct comparison currently available (Table 10; From Wilkinson and Arnell, in press 2012; in press 2013). NARRS survey HSI data for Scotland is similar to independent surveys from 2010 and 2011 in terms Table 10. A comparison of HSI scores from four Scottish pond surveys. Survey Mean HSI Ponds with HSI >0.7 ARC/SNH GCN survey 2010* % ARC/SNH GCN survey 2011* % ARC/SNH GCN status survey 2012** % NARRS amphibian surveys in Scotland % * Based on ARC Removal Modelling to identify new GCN populations ** Targeted on locations where GCNs had previously been recorded of score, and somewhat lower in terms of the proportion of high scoring ponds (i.e. >0.7). This is because 2010 and 2011 ARC/SNH surveys were targeted on habitats modelled to be most suitable for GCNs (see Wilkinson and Arnell, in press 2012 for modelling and survey methodologies) ARC/SNH surveys, however, were centred on ponds within 1 km radius of previous GCN records, accounting for the higher mean HSI score and much greater proportion of high scoring ponds than in the NARRS surveys. These data are encouraging, for all surveys concerned, with those which are random, more targeted and most targeted with respect to GCNs having increasingly higher HSI scores and proportions of high scoring ponds. This is particularly of interest because areas such as Scotland, with no geographically optimal zones (see Oldham et al., 2000), are at a natural disadvantage as compared to other areas in terms of relative score. The HSI clearly operates effectively in Scotland, however, and Wilkinson and Arnell (in press 2013) demonstrate a significant 30

31 relationship between HSI score and the probability of GCN presence (p<0.001; from logistical regression, data not presented here). Data from other region-wide surveys, including HSI score, will help place the NARRS amphibian habitat surveys in context in future, and are anyway required to elucidate our understanding of the way HSI score varies across Great Britain. There is still as yet no standardized way of qualitatively assessing reptile habitat which can be adapted for NARRS surveys. Data are presented here in the same way as for surveys (Wilkinson and Arnell, 2011). The average length of survey routes across all NARRS areas is fairly consistent at around km per survey. Degree of isolation of reptile habitat, however, varies a lot between NARRS Areas, with the Northern Area having both the fewest surveys where habitat was part of a larger area and the most surveys in isolated habitat. This may be reflected in the reptile species richness results (Figure 14 and discussed above). Between 42% and 66% of all reptile surveys took place in isolated habitat, and this is particularly relevant in light of concerns that this may be an increasingly important factor in reptile population declines. This measure will be directly comparable with results from future NARRS survey cycles, as will proportions of surveys taking place in protected or designated areas. The low proportion of surveys in protected or designated habitat in Scotland and Northern Areas (Table 6) may be an indication that more reptile habitat outside reptile-rich areas of southern England should be designated (with reptiles as a noted interest feature). 4.5 Detecting Future Changes The ability to detect changes in occupancy rates is central to NARRS, particularly for species for which there is no statutory reporting requirement. All Britain s widespread herpetofauna, bar the great crested newt, fall into this category. Assessing the levels of change that can be revealed by NARRS has to be a balance between realistic numbers of surveys and detection of sufficient change to inform conservation prior to serious declines. For example, to rely on achieving 5,000 volunteer surveys over six years would be hopelessly unrealistic, and detection of declines of 50% would be near-useless (and possibly too late)! Our analyses (Table 7) therefore examine the present ability of NARRS surveys to detect changes of 20% or 30% in occupancy rates, from the number of surveys completed Power analyses were two-tailed (i.e. examined the ability to detect both declines or increases) and, for equal sample sizes, used an α-value of 0.1. The value α in this case represents the acceptable probability ( risk ) of recording a change where in fact there was none. For species where existing levels of survey will not detect 20% or 30% changes in occupancy, we additionally used power analyses for unequal sample sizes to 31

32 examine the number of surveys that would be required to detect these levels of change with 80% power, using α-values of 0.1 and 0.2. A power level threshold of 80% was adhered to throughout as values of power below this are considered unacceptable. On a species by species basis (from Table 7): Rana temporaria has a high occupancy rate in NARRS surveys. Small changes (<20%) in occupancy by this species would be detected at >95% power with current survey sample size. Bufo bufo, L. vulgaris, L. helveticus and Z. vivipara have moderate occupancy rates in NARRS surveys. Current survey sample sizes would not detect 20% changes in occupancy at 80% power, but 30% changes in occupancy would be detected at >85% power. Triturus cristatus has a low occupancy rate in NARRS surveys, though this is no lower than might be reasonably expected (see Swan and Oldham, 1993; and above). Current survey sample sizes will not detect useful levels of change in occupancy rate at anything other than low power. An unacceptably large second sample size (many thousands of surveys) would be required to remedy this in the second NARRS survey cycle. Even detection of 30% change in occupancy with a less rigorous α=0.2 would require over 1,500 surveys Anguis fragilis and N. natrix have low-medium occupancy rates in NARRS surveys. Detection of useful levels of changes in occupancy have only lower power, and the size of the second sample would need to be very large to improve that situation. For both species, however, only several hundreds of second sample surveys would be needed at α=0.2. Though it is useful to examine how power improves with different sample sizes, we consider that α=0.2 is unacceptable, as well as that the probability of achieving several hundred more reptile surveys per NARRS cycle is currently unlikely. Vipera berus has only a very low occupancy rate in NARRS surveys. This is probably sufficient to raise concerns about the conservation status of the species in GB without quantifying declines (in the absence of earlier occupancy estimates). This low occupancy rate (7%) means that power to detect useful changes in occupancy are at low power only or would require huge numbers of surveys in the second sample. 32

33 4.5.1 Summary of Detecting Future Changes NARRS surveys as they stand have a high power (>85%) to detect real changes in species occupancy rates (of 30%) for R. temporaria, B. bufo, L. vulgaris, L. helveticus and Z. vivipara, and can be used as a way of quantifying status for these species. Cohen (1988) suggests that changes in the order of 30% are useful in measuring small effect size. Current numbers of surveys, assuming similar numbers of survey results are submitted , are, however, insufficient to reveal changes in occupancy rate for the other species. In the case of A. fragilis and N. natrix, approximately 25% more NARRS reptile surveys (i.e. nearer the initial goal of 400) would be required in future survey cycles in order to bump up sample sizes to a level of power where any perceived changes in occupancy could be accepted. This should remain a goal of NARRS and increasing the number of reptile surveys from across GB should be a priority for the second survey cycle period. Though NARRS alone cannot quantify status in T. cristatus, we hope that occupancy rates based on NARRS surveys as described here, plus country-based efforts to quantify status, e.g. in Scotland (Wilkinson and Arnell, in press 2013) and England (the Pondnet pilot scheme; see can be used additively with greater combined power than any individual scheme. Ways of capturing and incorporating data from local and consultancy surveys into status assessments for T. cristatus should also be explored. Current efforts by government agencies to meet EU monitoring demands should take more account of the huge amount of invaluable data generated by volunteers in schemes such as NARRS, and at a local level, and this should be explicitly included in efforts to assess status and monitor trends. Very low occurrence in NARRS surveys of V. berus is indicative of the requirement for positive conservation for this species and the need for better monitoring. This will elaborate trends and hopefully reveal causal factors in perceived adder declines. We recommend the urgent expansion and development of the Make the Adder Count programme (see to achieve this. In light of the findings of the present report, however, we also recommend that additional means of quantifying the status of all the widespread reptiles, and qualitatively assessing their habitats, be identified and implemented as soon as possible The Future of NARRS We repeat here our gratitude to the hundreds of volunteer NARRS surveyors, without whom the present report would not exist. NARRS survey squares which are randomly-allocated to surveyors near their postcode (PHASE 1 surveys) will continue in 2013 and beyond, and we encourage continued participation! Both individual surveyors and ARGs can still get involved 33

34 (squares will be issued during February 2013) and information will soon be easier to find via a revamped and simplified NARRS website (due for release in March 2013). In 2013 we are also introducing the opportunity for NARRS surveyors to conduct PHASE 2 surveys. These will be at fixed locations known to contain a population of at least one of the widespread herpetofauna species. PHASE 2 surveys are open to anyone, but may be particularly suitable for those managing protected or designated areas (from Country Parks to National Parks) and who would like to monitor the herpetofauna present, as well as contributing to the national scheme. The methodology for NARRS PHASE 2 is identical to PHASE 1 except that the emphasis should be on multiple within-year visits to the same site in order to generate counts for the species present. In this way, we hope to gain additional data on population fluctuations (for example of amphibian populations over time) and trends that will augment PHASE 1 results. NARRS PHASE 1 will also continue, and it is crucial that participation levels in the scheme are maintained or improved upon. Finally, we suggest that relatively small (but sustained) amounts of statutory funding, for example to employ a person to spend time arranging access permissions and to pay expenses for volunteers to cover geographical gaps, would quickly boost the numbers of completed surveys. This would in turn improve dramatically the power of the NARRS surveys to detect changes and therefore to provide evidence informing conservation. 34

35 5. REFERENCES Arnell, A.P. and Wilkinson, J.W. (2011a) Pilot modelling to inform determination of Favourable Conservation Status for the great crested newt. CCW Contract Science Report No Arnell, A.P. and Wilkinson, J.W. (2011b) predictive modelling of key herpetofauna species in North Wales. CCW Contract Science Report No Arnell, A.P. and Wilkinson, J.W. (in prep.) Spatial conservation status modelling of the great crested newt in and north-east Wales. CCW Contract Science Report. Cohen, J. (1988) Statistical power analysis for the behavioural sciences. Lawrence Erlbaum, Hillsdale, New Jersey. Freeman, S.N. (2006) Herpetological surveys: Power analyses based upon a proposed National Survey Scheme. Unpubl. BTO report to the NARRS Steering Group. Oldham, R.S., Keeble, J., Swan, M.J.S. and Jeffcoate, M. (2000) Evaluating the suitability of habitat for the great crested newt (Triturus cristatus). Herpetological Journal 10: R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN , URL Sewell, D., Beebee, T.J.C. and Griffiths, R.A. (2010) Optimising biodiversity assessments by volunteers: The application of occupancy modelling to large-scale amphibian surveys. Biological Conservation 143: Sewell, D., Guillera-Arroita, G., Griffiths, R.A. and Beebee, T.J.C. (2012) When is a specied declining? Optimizing survey effort to detect population changes in reptiles. PLoS ONE 7(8): e Swan, M.J.S. and Oldham, R.S. (1993) Herptile sites Volume 1: National Amphibian Survey final report. English Nature Research Reports No. 38, Peterborough. 35

36 Wilkinson, J.W., Wright, D., Arnell, A.P. and Driver, B. (2011) Assessing population status of the great crested newt in Great Britain. Natural England Commissioned Report NECR 080. Wilkinson, J.W., Wright, D., Arnell, A.P. and Driver, B. (in press 2012) Elaborating the distribution of the great crested newt in Scotland. SNH Commissioned Report. Wilkinson, J.W. & Arnell, A. (in press 2013) Enumerating status metrics for the great crested newt in Scotland (2012). SNH Commissioned Report Williams, P., Biggs, J., Crowe, A., Murphy, J., Nicolet, P., Weatherby, A., Dunbar, M. (2010) Countryside Survey: Ponds Report from Technical Report No. 7/07 Pond Conservation and NERC/Centre for Ecology and Hydrology, 77pp. (CEH Project Number: C03259). 36