BTO Research Report No. 361
South West London Waterbodies SPA Wildfowl Population Analysis
Authors
A.N. Banks, G.E. Austin & M.M. Rehfisch
A report by the British Trust for Ornithology to English Nature
April 2004
© British Trust for Ornithology
The National Centre for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU Registered Charity No. 216652
CONTENTS
Page No.
List of Tables...... 3 List of Figures...... 3 List of Appendices ...... 5
EXECUTIVE SUMMARY...... 7
1. INTRODUCTION...... 9
1.1 Aims...... 9
2. METHODS ...... 11
2.1 Data and Site Structure...... 11 2.2 Analysis...... 11
3. RESULTS ...... 15
3.1 Site Trends...... 15 3.1.1 South West London Waterbodies SPA...... 15 3.1.1.1 Gadwall ...... 15 3.1.1.2 Shoveler...... 15 3.1.1.3 Tufted Duck...... 16 3.1.2 Regional and National Trends...... 17 3.1.2.1 Gadwall ...... 17 3.1.2.2 Shoveler...... 17 3.1.2.3 Tufted Duck...... 17 3.1.3 Staines Moor SSSI ...... 19 3.1.4 Knight and Bessborough Reservoirs...... 19 3.1.5 Thorpe Park Number 1 Gravel Pit ...... 19 3.1.6 Kempton Park Reservoirs ...... 19 3.1.7 Wraysbury Reservoir...... 20 3.1.7 Wraysbury & Hythe End Gravel Pits (including Yeoveney Lake and County Ditch Lake)...... 20 3.1.9 Wraysbury Number 1 Gravel Pit...... 20 3.1.10 Wraysbury Number 1 Gravel Pit (North)...... 20 3.1.11 Wraysbury Number 1 Gravel Pit (South) ...... 21 3.1.12 Wraysbury II (North) Gravel Pit...... 21 3.1.13 Wraysbury II (South) Gravel Pit ...... 21 3.1.14 Yeoveney Lake...... 21 3.1.15 County Ditch Lake ...... 21 3.1.16 Wraysbury & Hythe End Gravel Pits (excluding Yeoveney Lake and County Ditch Lake)...... 22 3.1.17 Wraysbury & Hythe End Gravel Pits (North & South) and Wraysbury Number 1 Gravel Pits...... 22 3.1.18 ‘All winter months’ Alerts ...... 22 3.2 Timing of Counts...... 40 3.2.1 Staines Moor ...... 40 3.2.2 Knight & Bessborough Reservoirs...... 40 3.2.3 Thorpe Park Number 1 Gravel Pit ...... 40 3.2.4 Kempton Park Reservoirs ...... 40 3.2.5 Wraysbury Reservoir...... 40
BTO Research Report No. 361 1 April 2004 Page No.
3.2.6 Wraysbury & Hythe End Gravel Pits (including Yeoveney Lake and County Ditch Lake)...... 41 3.2.7 Wraysbury Number 1 Gravel Pit...... 41 3.2.8 Wraysbury Number 1 Gravel Pit (North)...... 41 3.2.9 Wraysbury Number 1 Gravel Pit (South) ...... 41 3.2.10 Wraysbury II (North) Gravel Pit...... 41 3.2.11 Wraysbury II (South) Gravel Pit ...... 41 3.2.12 Yeoveney Lake...... 41 3.2.13 County Ditch Lake ...... 41 3.2.14 Wraysbury & Hythe End Gravel Pits (excluding Yeoveney Lake and County Ditch Lake)...... 42 3.2.15 Wraysbury & Hythe End Gravel Pits (North & South) and Wraysbury Number 1 Gravel Pits ...... 42 3.2.16 South West London Waterbodies SPA...... 42
4. CONCLUSIONS ...... 59
4.1 SPA Species Trends ...... 59 4.2 SSSI, Sector Level and Site Combination Trends...... 59 4.3 Timing of Peak Counts ...... 60 4.4 Future Research...... 61 4.5 Specific Conclusions in Relation to Aims...... 61
Acknowledgements...... 63
References ...... 65
Appendices ...... 67
BTO Research Report No. 361 2 April 2004 List of Tables
Page No.
Table 3.1.1 Table of Alerts for 15 site consolidations and the SPA as a whole...... 39
List of Figures
Page No.
Figure 3.1.1.1 Smoothed index for Gadwall on South West London Waterbodies SPA ...... 15
Figure 3.1.1.2 Smoothed index for Shoveler on South West London Waterbodies SPA ...... 16
Figure 3.1.1.3 Smoothed index for Tufted Duck on South West London Waterbodies SPA ...... 16
Figure 3.1.2 National and Regional smoothed GAM trends for Gadwall, Shoveler and Tufted Duck ...... 18
Figure 3.1.3 Staines Moor SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 24
Figure 3.1.4 Knight & Bessborough Reservoirs SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 25
Figure 3.1.5 Thorpe Park No. 1 Gravel Pit SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 26
Figure 3.1.6 Kempton Park Reservoirs SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 27
Figure 3.1.7 Wraysbury Reservoir SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 28
Figure 3.1.8 Wraysbury & Hythe End Gravel Pits (complete) SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 29
Figure 3.1.9 Wraysbury Number 1 Gravel Pits SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 30
Figure 3.1.10 Wraysbury Number 1 Gravel Pit (North). Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 31
Figure 3.1.11 Wraysbury Number 1 Gravel Pit (South). Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 32
Figure 3.1.12 Wraysbury II (North) Gravel Pit. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 33
BTO Research Report No. 361 3 April 2004 Page No.
Figure 3.1.13 Wraysbury II (South) Gravel Pit. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 34
Figure 3.1.14 Yeoveney Lake. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 35
Figure 3.1.15 County Ditch Lake. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 36
Figure 3.1.16 Wraysbury & Hythe End Gravel Pits (SPA sectors only). Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison ...... 37
Figure 3.1.17 Wraysbury & Hythe End North & South and Wraysbury No. 1 Gravel Pits. Site trends (‘Target consolidation’) shown for GA, SV and TU, with regional, national and SPA trends for comparison...... 38
Figure 3.2.1 Staines Moor. Histograms show average counts for all months visited...... 43
Figure 3.2.2 Knight & Bessborough Reservoirs. Histograms show average counts for all months visited ...... 44
Figure 3.2.3 Thorpe Park Number 1. Histograms show average counts for all months visited .....45
Figure 3.2.4 Kempton Park Reservoirs. Histograms show average counts for all months visited...... 46
Figure 3.2.5 Wraysbury Reservoir. Histograms show average counts for all months visited...... 47
Figure 3.2.6 Wraysbury & Hythe End Gravel Pits (complete). Histograms show average counts for all months visited ...... 48
Figure 3.2.7 Wraysbury Number 1 Gravel Pits. Histograms show average counts for all months visited ...... 49
Figure 3.2.8 Wraysbury Number 1 Gravel Pits (North). Histograms show average counts for all months visited...... 50
Figure 3.2.9 Wraysbury Number 1 Gravel Pits (South). Histograms show average counts for all months visited...... 51
Figure 3.2.10 Wraysbury Number 2 Gravel Pit (North). Histograms show average counts for all months visited...... 52
Figure 3.2.11 Wraysbury Number 2 Gravel Pit (South). Histograms show average counts for all months visited...... 53
Figure 3.2.12 Yeoveney Lake. Histograms show average counts for all months visited...... 54
Figure 3.2.13 County Ditch Lake. Histograms show average counts for all months visited ...... 55
Figure 3.2.14 Wraysbury & Hythe End Gravel Pits (SPA only). Histograms show average counts for all months visited ...... 56
BTO Research Report No. 361 4 April 2004 Page No.
Figure 3.2.15 Wraysbury & Hythe End Gravel Pits and Wraysbury Number 1 Gravel Pits. Histograms show average counts for all months visited ...... 57
List of Appendices
Page No.
Appendix 1. Summary table of site names and codes ...... 67
Appendix 2. All counties and administration areas intersecting the EA Thames region...... 69
Appendix 3. Site map of South West London Waterbodies SPA...... 71
Appendix 4. Table of Alerts based on all data from the months September – March, for 15 site consolidations...... 73
BTO Research Report No. 361 5 April 2004 BTO Research Report No. 361 6 April 2004 EXECUTIVE SUMMARY
1. The South West London Waterbodies SPA, which comprises seven SSSIs, is designated for internationally important numbers of wintering Gadwall and Shoveler. It also supports large numbers of Tufted Duck. Over the past decade, however, numbers of these waterfowl have been suggested to decline across the SPA.
2. Explanations suggested for the apparent waterbird declines across the SPA include a change in phenology of some species; human disturbance has also been postulated as a contributory factor.
3. Using Wetland Bird Survey (WeBS) data and WeBS Alerts techniques, trends of Gadwall, Shoveler and Tufted Duck were analysed at the SPA and SSSI level. Each trend was viewed in the context of the national and regional trend of the relevant species.
4. At the SPA level, no declines in any of the species reviewed were found over a period of ten years or more. One ‘Alert’ was fired; this was for Shoveler, which declined by 30% over the last five years of analysis.
5. At the SSSI level, High Alerts for ‘all time’ (generally the period 1989-2000) were fired for Gadwall on three of fifteen site combinations, Shoveler on one site and Tufted Duck on two sites, in response to declines greater than 50%. A number of shorter-term High Alerts (≥50% declines) and several Medium Alerts (≥25% declines) were also triggered at specific sites, with various caveats.
6. Comparison of the timing of peak counts at national and SPA scales revealed little difference in the peak mean count month. The majority of peak counts within the standard index window were made within one month of the comparison peak count.
7. Plotting the peak mean counts across all SSSIs revealed little evidence of shifts in timing of peak counts. Most peak counts occurred inside the standard WeBS index window, therefore apparent declines are unlikely to be due to excluded data.
8. Negative effects of human disturbance on waterbirds cannot be ruled out. Recreational disturbance measured by the Wetlands Advisory Service (2003) at Thorpe Park and Wraysbury II Gravel Pits may have contributed to species declines identified here.
9. Future monitoring of the SPA (and component SSSIs) is recommended to include detailed WeBS Alert analysis, in order to examine whether recent SPA-level negative trends in Gadwall and Tufted Duck mark the beginnings of sustained decline or acceptable fluctuation.
BTO Research Report No. 361 7 April 2004 BTO Research Report No. 361 8 April 2004 1. INTRODUCTION
The South West London Waterbodies SPA consists of seven component SSSI reservoirs, gravel pits and lakes. These include reservoirs at Staines, Kempton Park and Wraysbury, and gravel pits at Thorpe Park and Wraysbury again. The SPA is designated under Article 4.2 of the EU Birds Directive (79/409/EEC) for its internationally important numbers of over-wintering Gadwall Anas strepera and Shoveler Anas clypeata, but also supports important winter populations of Tufted Duck Aythya fuligula.
Over the past decade, it has been suggested that numbers of these waterbirds have declined across the SPA. It is unclear whether these declines are real or represent normal annual fluctuation of the relevant populations. Peak counts recorded at the SPA were reported to be ‘out of step’ with national peak counts (Wetlands Advisory Service 2003). Changes in phenology could reflect climate change (Parmesan & Yohe 2003, Root et al. 2003) and would be of particular relevance to apparent declines in Shoveler and Tufted Duck, as the standard Wetland Bird Survey (WeBS) indices for these species are based on a subset of count months for which numbers are considered most reflective of the stable population (September and October for Shoveler, November through to February for Tufted Duck; Pollitt et al. 2003). A sufficiently large change in phenology could erroneously resemble a species decline, when actually a species was stable or increasing. Large counts could fall outside of the index months and would not be included in standard WeBS indexing. Gadwall are indexed on all months from September through to March and are thus not prone to such an issue.
Recreation has also been cited as a factor that could be contributing to waterbird declines. Activities such as sailing and angling take place on a number of the component sites, and have done prior to SSSI and SPA designation. Evidence for increases in these pursuits is scarce, and recreational pressure is even believed to have decreased in some locations. However, it has been suggested that leisure activity may be involved in the apparent decline of waterbird numbers, particularly on the SSSIs Wraysbury & Hythe End Gravel Pits and Wraysbury No.1 Gravel Pit.
In order to determine whether the three species of duck have declined on the South West London Waterbodies SPA, and across the individual component SSSIs, the WeBS ‘Alerts’ system will be used. This procedure generates smoothed indices of waterbird trends, and can identify changes in site, regional and national level populations (e.g. Austin et al. 2003, Austin et al. 2004). Any declines identified on the SPA will be examined in the context of regional and national species trends, to ensure that apparent site level effects are not merely reflecting wider processes.
1.1 Aims
• To determine whether Gadwall, Shoveler and Tufted Duck on the component SSSIs of the SW London Waterbodies SPA have decreased more than would be expected as a result of ‘normal’ between-year variation, having taken regional and national species trends into account. • To do the same for the SW London Waterbodies SPA and other relevant combinations of SSSIs. • To determine whether the timing of peak counts on the SPA and component waterbodies can serve to explain apparent declines.
BTO Research Report No. 361 9 April 2004 BTO Research Report No. 361 10 April 2004 2. METHODS
2.1 Data and Site Structure
WeBS data
Data from the Wetland Bird Survey were used in the analysis. WeBS is a long-term waterbird monitoring scheme, relying on the monthly counts of thousands of volunteers across the UK. Estuaries and inland waterbodies are included in the ‘Core Count’ programme, whilst Low Tide data is also collected at some tidal sites. WeBS Core Counts were used for all site / species combinations for which data were available during the period 1989/90 (hereafter 1989) to 2000/01 (hereafter 2000). This cut-off date is consistent with the last year for which a WeBS report exists (Pollitt et al. 2003). These data were used to construct annual species indices for the three species under review.
WeBS annual indices are calculated using count data collected between September and March. Within this period, the months for which the numbers of a given species are at their most stable are those used for producing the index, and these months differ between species. Gadwall (GA) are indexed on all seven months, Shoveler (SV) indices are based on September and October counts, whereas the index for Tufted Duck (TU) relies on data from November through to February. A consequence of adopting the standard WeBS indexing months is that, in addition to the breeding season, the passage period is also excluded from analysis, thereby guarding against large transitory fluctuations in numbers. The WeBS Alert system (section 2.2) was employed to quantify declines.
However, to investigate the possibility that changes in phenology could help to explain the apparent declines, data from outside the standard indexing months were also analysed where possible. Some data existed for most species / site combinations, although as Gadwall is indexed on seven months, there were fewer ‘extra’ counts for this species.
Site combinations
Analyses were performed at various spatial scales. Smoothed indices were produced for all three species of duck at the SPA level. Also, trends were created for the same species at the SSSI level (Appendix 1. for list of sites and subsites; Appendix 3. for map of sites). For Wraysbury No.1 Gravel Pits and Wraysbury & Hythe End Gravel Pits, various combinations of component sites were analysed (Appendix 1.).
To compare site trends with regional trends, counts of Gadwall, Shoveler and Tufted Duck made on WeBS sectors across the eastern half of the Environment Agency Thames region were indexed, using all available data spanning the period 1989/90-2000/01. It was not considered appropriate to compare trends at the South West London Waterbodies SPA with Thames region counts in western Britain or at estuarine sites, and so inland sectors in southeastern England were targeted. Appendix 2. illustrates which counties intersect the Thames region, and which were included in the analysis. To compare site trends with national trends, all available data for the same species and years were indexed for Great Britain as a whole.
2.2 Analysis
Full details pertaining to the use of Generalized Additive Models (GAMs) for the calculation of annual waterbird indices and the fitting of smoothed trend curves by the WeBS Alert System are available elsewhere (Leech et al. 2002, Atkinson et al. 2001). An overview is given here.
Annual indices
The index value for a particular winter is the number of birds present in that winter (summed monthly counts) expressed relative to the number of birds present in the base winter, which is arbitrarily set at
BTO Research Report No. 361 11 April 2004 100. The WeBS Alert System assigns the base winter to be the most recent winter in the data being analysed.
Missing values, inevitable with count data, are accounted for by the GAM which fits a model with site, year and month factors. For n years of data, when a GAM model is fitted using (n-1) degrees of freedom the resulting index values are equivalent to those that would have been obtained using the Underhill indexing method (Underhill & Prŷs-Jones 1994), formerly used by WeBS for generating annual indices, except that, unlike that method, poor quality but higher than average counts are excluded and thus not permitted to inflate index values. The latter is essential to ensure that the smoothed trends (see below), which are obligate in their use of GAMs, are based on the same data as the annual indices. Imputation was only used for analysing data at the SPA, regional and national levels. It was not felt appropriate to impute data at the SSSI level or below, as the baseline dataset is too small. Indices were left incomplete where counts were missed at the lowest levels.
When producing the index, average monthly counts were assigned a ‘count quality’. If greater than 50% of the standard indexing months were counted, the count was considered of good quality. Where data existed for less than 50% of the standard count months, the count was considered of lesser quality.
Smoothed GAM trends
Natural temporary fluctuations in numbers, for example those caused by variation in the severity of conditions over the winter period, can differ in size and / or direction from longer-term trends, hindering their interpretation. Extreme values may trigger false Alerts due to misinterpretation of temporary, short-term declines as longer-term trends. Alternatively, long-term trends that may have led to Alerts being flagged could be obscured by short-term fluctuations. In order to avoid such misinterpretations and misidentifications when calculating Alerts, the Alerts System uses GAMs to fit a smoothed trend curve to the annual indices. This it does by a reduction in the number of degrees of freedom available to the GAMs. As the number of degrees of freedom is decreased from (n-1) the trend become increasingly smooth until ultimately with one degree of freedom the smoothed curve becomes a linear fit. The WeBS Alert System adopts a standard (n/3) degrees of freedom to produce a level of smoothing that, while removing temporary fluctuations not likely to be representative of long term trends capture those aspects of the trends that may be considered to be important.
Changes in numbers calculated using values from a smoothed GAM trend are less likely to be due to the effects of temporary fluctuations in numbers, or to errors when sampling, than results produced were annual index values to be used. Thus, using GAMs reduces the probability that a decline from a short-lived unsustainable peak in numbers would be responsible for triggering an Alert.
Alerts
Proportional changes in the smoothed GAM trend in numbers are calculated by subtracting the smoothed GAM trend value at the start of the time-frame from the smoothed GAM trend value in the final winter. Calculated change values are expressed as a percentage of the index at the start of the period. Larger values therefore indicate larger proportional changes in numbers, with positive values equating to relative increases in the numbers and negative values equating to relative decreases over the specified time period. These values are then categorised according to their magnitude and direction. Declines of between 25% and 50% inclusive are flagged as Medium Alerts and declines of greater than 50% as High Alerts. Although they will not promote discussion within this report, increases are sometimes flagged in the appropriate tables. In order to facilitate comparison of decreases and increases in numbers, increases of between 33% and 100% are described as Medium increases, while increases of greater than 100% are described as High increases. This allows for the proportionally greater increase required to return numbers to their former level following a given decrease.
BTO Research Report No. 361 12 April 2004 Alerts were generated over three time frames; the five-year period 1995-2000, the ten-year period 1990-2000, and the ‘all time’ period, running from 2000 back to the earliest date for which data were available (generally 1989). This technique was applied to all sub-SPA sites, and to the SPA itself. Alerts were issued with a caveat if based on average yearly counts of less than 25 birds.
Alerts were based on species trends using the standard WeBS indexing months (Austin et al. 2004). This ensured consistency with other research, allowed sector-level comparison with SPA, regional and national trends, and reduced noise that could be introduced from counts of juvenile birds or passage migrants. However, in response to concerns that peak counts of birds at component sites of the South West London Waterbodies SPA were occurring outside of the standard index window, Alerts were also generated using all available data for all species during the period September - March.
Regional and national comparisons
To compare trends at the SPA and SSSI level with those for the same species at wider spatial scales, statistical procedures recently developed for WeBS Alerts (Banks & Austin 2004) were employed. Binomial models were used to assess the relative proportion of the SPA total held by each SSSI and site combination. This procedure was also used to investigate the proportion of the regional and national totals supported by the SSSI or site combination.
The proportion, i.e. the number of birds counted at a site per year divided by the total SPA, regional, or national number for the year, was modelled by logistic regression. The models were binomial and specified a logit link function. Count values were only included in analysis where coverage was complete.
Output plots were generated for each species / site combination. In this way, the proportion of the region’s birds occurring at a given site could be calculated across years. The 95% confidence limits obtained represent the confidence in the calculation of the proportion as it varies with the total number of birds in the SPA, region or nation, and the between-month variation in the average proportion a site holds in a given winter.
Changes in waterbird numbers are reflected in three possible proportional trends; positive, negative and stable.
Where numbers on a site undergo expansion, and regional trends decline or remain stable, a proportional increase is seen at the site under review. The trend is for estimates to increase with time, with largely non-overlapping confidence limits.
Negative trends in the proportional estimate suggest one of three scenarios, and consideration of species’ regional and site trends can determine which applies. Firstly, the site trend could be in decline while the regional trend increases or remains stable. Thus the proportion at the site becomes smaller as the two trends diverge. Secondly, the site trend could be stable whilst the regional trend increases. Thirdly, both trends may increase, but at different rates. If regional counts were formerly low, a particular site may have held a relatively high proportion of the regional total. If the species in question then expands across the region but remains stable at the site, the relative proportion at the site will decrease. Where a WeBS Alert has been fired, it may be safe to assume the first explanation is more likely.
Plots can also be produced that suggest a species is relatively stable in numbers in comparison to the region, typically where a horizontal line can be drawn between the ranges of all confidence limits. These plots do not signify in which direction the site and regional trends are heading (i.e. increasing, decreasing or stable), merely that they remain consistent to each other.
A spreadsheet was also produced detailing the months in which peak counts occurred for all site / species combinations. This allows visual inspection of how consistent the timing of peak counts is.
BTO Research Report No. 361 13 April 2004
BTO Research Report No. 361 14 April 2004 3. RESULTS
3.1 Species Trends
3.1.1 South West London Waterbodies SPA
In this and all subsequent trend graphs, closed symbols indicate ‘good’ quality count data, whilst open symbols indicate counts based on less than 50% of the standard index months for the species.
3.1.1.1 Gadwall
Across the SPA as a whole, this species has shown a steady increase since 1989 (Figure 3.1.1.1). Numbers peaked in 1998, with a subsequent drop-off in the following two winters. However, despite this recent negative trend, Alerts were not fired for Gadwall across any of the comparison time periods (five year, ten year and ‘all time’), and numbers were still higher in 2000 than in 1995.
Southwest London Waterbodies SPA
800
700
600
500
400
300 Average Count 200
100
0 1990 1995 2000 Winter Gadwall
Figure 3.1.1.1 Smoothed index for Gadwall on the South West London Waterbodies SPA.
3.1.1.2 Shoveler
The smoothed index for Shoveler shows an almost symmetrical pattern. Numbers rose sharply in 1994 after a shallow decline from an average of around 400 birds, and the trend has been for a further period of moderate decline since (Figure 3.1.1.2). However, current population levels are still greater than ten years ago, and those in 1989. The current period of decline is reflected in a Medium Alert being triggered for the five-year time span, this due to a 30% decrease since 1995 (Table 3.1.1). It should be noted that the trend showed a large fluctuation during the period 1993-1995, so it is possible that current apparent declines could be reversed in a relatively short time period. Furthermore, the Medium Alert should perhaps be treated cautiously, as the WeBS Alert system uses a ‘biological filter’ to interpret certain species declines (section 4.1).
BTO Research Report No. 361 15 April 2004 Southwest London Waterbodies SPA
1000
800
600
400 Average Count
200
0 1990 1995 2000 Winter Shoveler
Figure 3.1.1.2 Smoothed index for Shoveler on the South West London Waterbodies SPA.
3.1.1.3 Tufted Duck
In common with Gadwall, numbers of Tufted Duck have increased on the SPA, although at a slower rate (Figure 3.1.1.3). Average counts have risen from below 500 birds in 1989 to over 1,000 in 2000, whilst the ten-year period witnessed a 52% increase in Tufted Duck numbers. Although declines were recorded on some component sites (Kempton Park Reservoirs, Wraysbury & Hythe End Gravel Pits SPA sectors), increases were witnessed on others, often from initially low numbers (Wraysbury Number 1 Gravel Pits - especially South sector, Knight & Bessborough Reservoirs, Wraysbury Reservoir: Table 3.1.1). Since 1995, there has been a small decline (7%), which should be considered within the range of ‘natural’ population fluctuation for the species.
Southwest London Waterbodies SPA
2500
2000
1500
1000 Average Count
500
0 1990 1995 2000 Winter Tufted Duck
Figure 3.1.1.3 Smoothed index for Tufted Duck on the South West London Waterbodies SPA.
BTO Research Report No. 361 16 April 2004 3.1.2 Regional and National Trends
3.1.2.1 Gadwall
At both national and regional levels, Gadwall numbers have increased steadily over the past 11 years (Figure 3.1.2). The number of Gadwall wintering in Great Britain has risen by approximately 3,000 birds since 1989, with record levels recorded each year but 2000/01 (Pollitt et al. 2003). The winter of 2000/01 was therefore slightly unusual, and this is reflected in the regional trend. At this spatial scale, despite evidence of some fluctuation (accounted for by the smoothed GAM), year-on-year increases were also seen, with a period of steep increase from 1997. Counts in 2000 bucked this short-term trend, although numbers were still higher than in 1996.
3.1.2.2 Shoveler
Across Great Britain as a whole, the Shoveler index has remained largely stable over the time period studied (Figure 3.1.2). There is a degree of fluctuation around the smoothed GAM, with three high counts from 1989 – 1991 being followed by three lower counts before a return to 1990 levels. The regional trend has likewise shown fluctuation between years, with declines around 1992 followed by increases in 1994 and 1995 (Figure 3.1.2). Overall, the Shoveler index for the Thames region is fairly stable.
3.1.2.3 Tufted Duck
Tufted Duck indices are very similar at both regional and national scales (Figure 3.1.2). The general trend is for a shallow increase, with limited fluctuation. At the regional level, the index is stable at around 4,000 birds, with an increase of around 400 birds since 1989. Nationally, the trend has shown minimal fluctuation, with a greater relative increase over the same period; it is possible that the wintering population is affected by concurrent increases seen in native breeding Tufted Duck (Crick et al. 2004).
BTO Research Report No. 361 17 April 2004 T eerhRpr o 6 BTO Research Report No.361 A p ril 2004 Gadwall Shoveler Tufted Duck
1400 1400 5000
1200 1200 4000 1000 1000
800 800 3000
600 600 2000 whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
12000 10000 80000 18
10000 8000
Number of birds 60000 8000 6000 6000 40000 whole GB 4000 4000 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
Year
Figure 3.1.2 National and Regional smoothed GAM trends for Gadwall, Shoveler and Tufted Duck.
3.1.3 Staines Moor SSSI
Site trends for Gadwall and Shoveler at Staines Moor reflect those on the SPA as a whole, and to a lesser extent, the regional and national trends (Figure 3.1.3). Although the SSSI holds only small numbers of Gadwall, and a consistently small proportion as estimated by WeBS counts (hereafter referred to as ‘proportion’) of the SPA total, there has been a steady increase over the past twelve years, with an especially large increase since 1995. Shoveler trends at Staines Moor are very similar to the SPA trend and show similar fluctuation, unsurprising in that a large estimated proportion of the SPA total was counted here. This proportion appears to have substantially declined in recent years, and a Medium Alert was triggered for the five-year period, in common with the SPA trend for the species (Table 3.1.1). Again, interpretation of this decline should include reference to the biological filter (section 4.1)
Tufted Duck at Staines Moor SSSI have shown declines since 1989, with a Medium Alert triggered (Figure 3.1.3, Table 3.1.1). This is in contrast to the increasing SPA trend. The proportion of the SPA and regional totals of Tufted Duck supported by Staines Moor looks to have declined sharply since 1989, with some evidence of a slight upturn in recent years.
3.1.4 Knight and Bessborough Reservoirs
This SSSI does not support large numbers of Gadwall, but the index for this species has steeply risen (Figure 3.1.4). Average counts of Shoveler on the site reached above 200 in 1995, but since that winter have declined consistently. This peak is consistent with the pattern for the entire SPA, and Knight & Bessborough Reservoirs were predicted to hold between 20% and 50% of the SPA total around this time. The rapid decreases since 1995 resulted in a High Alert status being issued in response to a 63% decline (Table 3.1.1), although over this time period, results should be accepted cautiously in context of the WeBS Alerts ‘biological filter’ (section 4.1). The regional trend for Shoveler has been largely stable, reflected in the proportional plot (Figure 3.1.4). As the regional trend has remained fairly constant, so the regional proportion at the SSSI reflects the SSSI trend, suggesting that the SSSI trend cannot be explained by wider species trends. Data for Tufted Duck are variable in availability, but the smoothed trend for the five-year period seems consistent with the SPA trend in that it is downward. However, numbers of Tufted Duck on this SSSI are predicted to reflect only a small fraction of the SPA total.
3.1.5 Thorpe Park Number 1 Gravel Pit
The smoothed index for Gadwall at this SSSI shows a marked contrast to the SPA trend (Figure 3.1.5). Numbers have declined from a peak in 1993, although it should be noted that counts were not available before this date. This resulted in an ‘all time’ High Alert being fired (Table 3.1.1). The proportion of the regional total has changed only minimally since 1995, implying that the sector trend could reflect regional population effects. Counts of Shoveler at Thorpe Park are negligible, never exceeding yearly averages of four birds. The trend for Tufted Duck fluctuates, with the pattern over the last six years of analysis reflecting that for the SPA.
3.1.6 Kempton Park Reservoirs
Gadwall trends at Kempton Park are broadly in step with those at the SPA and regional levels, with steady increases from 1990 to 1998 (Figure 3.1.6). Trends in the last two years of analysis (1999 and 2000) are similar to those across the SPA, marking the possible beginning of a decline. The proportion of Gadwall on the site as a function of the SPA and regional totals appears to be increasing, with little change since 1994. Numbers of Shoveler have increased from a baseline average of no birds to over 60 in the year 2000. However, the total yearly average does not exceed 25 birds and so the >1000% increase (Table 3.1.1) should be treated with caution. Tufted Duck show a clear decline at Kempton Park, both in the smoothed trend (Figure 3.1.6) and the High Alerts fired for all time periods considered (Table 3.1.1). The corresponding proportions of SPA, regional and national levels are all
BTO Research Report No. 361 19 April 2004 modelled to decrease accordingly, although at the regional level, the range of confidence limits suggest that sector-level changes could be consistent with regional patterns, as a horizontal line can be plotted through the range.
3.1.7 Wraysbury Reservoir
Numbers of Gadwall and Tufted Duck counted on Wraysbury Reservoir are fairly trivial in relation to numbers present on other component sites within the SPA, and contribute little to the SPA trend. Yearly Gadwall numbers are very small (usually averaging five or lower), whilst the index for Tufted Duck is fairly stable, with occasional fluctuations (Figure 3.1.7). However, Shoveler numbers at Wraysbury Reservoir were consistently between 20% and 80% of the SPA total for the early 1990s (Figure 3.1.7). This figure is now lower, and High Alerts were triggered for all three time periods reviewed (Table 3.1.1). The period of decline seems consistent with those at the SPA and regional level, and the stable proportion at the regional level implies changes in step with wider changes, although the negative trend is steeper at the sector.
3.1.8 Wraysbury & Hythe End Gravel Pits (including Yeoveney Lake and County Ditch Lake)
The site trend for Gadwall closely follows that of the SPA itself, with continuous increases up to the start of a decline after 1998 (Figure 3.1.8). It is perhaps too early to assess the importance of this apparent decline as over five years Gadwall numbers have still increased. However, as this SSSI regularly holds between an estimated 20% and 80% of the SPA total, close monitoring is required. The site appears to be becoming increasingly important for Gadwall, as the proportion of the SPA total held by this SSSI has increased steadily since 1989. There also appears to be some change in the proportion of Shoveler held by the SSSI, with an increase from no birds in 1989 to an estimate of over 0.2 of the SPA total in 2000, although the trend indicates a degree of fluctuation about the trend line during this time and confidence limits about the proportional estimate are wide. The only Alert at this SSSI was fired for Tufted Duck, with a 46% decline over five years triggering a Medium Alert (Table 3.1.1). The short-term nature of this decline suggests interpretation using the biological filter, but this trend is broadly consistent with the SPA trend, even though short-term declines have been greater at the SSSI level. Also the proportion of the SPA and regional totals held by this SSSI fluctuates from year to year. In 1989 nearly 80% of Tufted Duck on the SPA were estimated to be found at Wraysbury & Hythe End Gravel Pits, although subsequently the population of this duck has increased on other component sites of the SPA, leading to a diminished relative ‘site importance’ of the SSSI for this species.
3.1.9 Wraysbury Number 1 Gravel Pit
Little change is evident in any of the three species trends at Wraysbury Number 1 Gravel Pit SSSI. A five-year Medium Alert was triggered for Gadwall (Table 3.1.1), but the species trend suggests that this was based on a return to stable levels from a short-term peak (Figure 3.1.9), and this level of fluctuation would be allowed for by the biological filter over this time period. The proportion of Gadwall at the SSSI in comparison to SPA and regional levels has likewise remained at a consistently low figure except for two peak years. Shoveler numbers rarely exceed a yearly average count of 20 birds and this site supports relatively few of the Shoveler on which the SPA is designated. The site trend for Tufted Duck resembles the SPA trend, and although there was a moderate ‘all time’ increase, the species appears fairly stable at this SSSI.
3.1.10 Wraysbury Number 1 Gravel Pit (North)
The data for this sector, part of Wraysbury Number 1 Gravel Pit SSSI, are difficult to analyse in depth as the sector has been infrequently counted in isolation. Gadwall and Shoveler numbers have remained low in comparison to other component sectors (Figure 3.1.10). Tufted Duck show some evidence of a
BTO Research Report No. 361 20 April 2004 decline over the past few years of analysis, but there are insufficient data to calculate Alerts (Table 3.1.1).
3.1.11 Wraysbury Number 1 Gravel Pit (South)
This sector is subject to the same limitations as the previous sector. Again, data are lacking to calculate instructive species trends, logistic model predictions or Alerts (Figure 3.1.11; Table 3.1.1). Tufted Duck is the only species counted in average yearly numbers greater than 30.
3.1.12 Wraysbury II (North) Gravel Pit
Available data for this sector, which comprises part of Wraysbury & Hythe End Gravel Pits SSSI, produced smoothed indices that fired two Alerts. Gadwall trends triggered a Medium Alert over five years (the short time period suggesting caution be exercised in interpretation), and a High Alert over ‘all time’ (Figure 3.1.12; Table 3.1.1). Although the smoothed trend is incomplete, and there appears to be fluctuation in the trend, logistic model predictions suggest that the proportion of total SPA Gadwall held at the lake is beginning to decrease. Likewise, a negative trend in the regional proportion estimates intimates that declines are inconsistent with regional trends. Tufted Duck exhibit a similar smoothed index to Gadwall, but it is not justified to calculate Alerts. A zero count was recorded in the year 2000, which theoretically results in infinite change over the time periods used. Again the counts appear to fluctuate, although the relatively stable proportion of Tufted Ducks found at this sector (in all years apart from 2000) imply that this trend may be mirroring the SPA trend. It will be important to monitor whether two years of declines since 1998 continue in later years.
3.1.13 Wraysbury II (South) Gravel Pit
This sector also forms part of Wraysbury & Hythe End Gravel Pits SSSI, but shows slightly different trends to the sector previously analysed. Gadwall trends appear to track those of the SPA and the region, although the proportion of Gadwall at the sector in comparison to the SPA total shows an upward trend (Figure 3.1.13). This suggests that the increasing SPA trend could in part be due to increases at this gravel pit. This sector does not support large numbers of Shoveler, and although the trend is upward, total average yearly counts do not exceed 25 birds, so Alerts should be interpreted with caution (Table 3.1.1). Alerts for Tufted Duck are based on substantial counts, and Alerts were fired for five years and ‘all time’.
3.1.14 Yeoveney Lake
Yeoveney Lake and the following sector, County Ditch Lake, form part of Wraysbury & Hythe End Gravel Pits SSSI but not the South West London Waterbodies SPA. High Alerts were fired for Gadwall, although these should be accepted cautiously owing to the small number of ducks involved (Table 3.1.1). Shoveler numbers fluctuate somewhat at this sector, but the proportion of the SPA total has remained reasonably consistent, indicating that the population is changing in line with the SPA trend (Figure 3.1.14). Alerts were not fired for Tufted Duck at this sector, and the trend seems stable except for one year of fluctuation.
3.1.15 County Ditch Lake
This small component SSSI sector harbours relatively few birds of any of the three waterbird species analysed in this report. Alerts were subject to caveat for Gadwall and Shoveler, on the basis of small numbers (Table 3.1.1). Tufted Duck are stable in their smoothed trend at this site (Figure 3.1.15; Table 3.1.1).
BTO Research Report No. 361 21 April 2004 3.1.16 Wraysbury & Hythe End Gravel Pits (excluding Yeoveney Lake and County Ditch Lake)
Gadwall trends on these gravel pits, which form part of the SPA, resemble the trend for the SPA as a whole, with increases throughout the late 1990s and a drop-off in 2000 (Figure 3.1.16). The index, however, is higher in 2000 than 1995, meaning that no Alerts were fired (Table 3.1.1). The proportion of Gadwall supported by these gravel pits is largely consistent at the SPA level, with some fluctuation. The proportion of the regional total held also fluctuates.
Shoveler have shown steady increases since 1992, and the predicted regional and SPA proportions have increased concurrently (Figure 3.1.16), although numbers are still relatively small in terms of the SPA as a whole. Tufted Duck numbers have declined in the last two years of analysis, triggering a Medium Alert for five years and a High Alert for ‘all time’ (Table 3.1.1). The five-year Medium Alert would be considered within the species ‘normal’ range of fluctuation using the biological filter. The regional proportion of Tufted Duck held at the sector combination remained fairly stable until 1999, implying that changes subsequently are out of step with regional trends. The trend does appear to fluctuate somewhat between years however, so it is perhaps too early to judge whether this is the beginning of a period of decline (Figure 3.1.16).
3.1.17 Wraysbury & Hythe End Gravel Pits (North & South) and Wraysbury Number 1 Gravel Pits
This sector combination shows similar patterns to those at the previous consolidation. Large numbers of Gadwall occur on some of these gravel pits, particularly Wraysbury II (South), and the trend has remained largely stable (Figure 3.1.17). The proportion of the SPA and regional totals supported has also remained consistently high. The Shoveler trend is consistently upward, and the proportion of the SPA total also shows a positive upward trend. Medium Alerts were fired for Tufted Duck for the five- year period and for ‘all time’ (Table 3.1.1). However, as declines appear to have been gradual and shallow, interspersed with occasional high counts, it remains to be seen if the population will show further fluctuation or sustained decline. Also, the five-year trend should perhaps be considered of lesser importance, as the biological filter would prevent Alerts being issued at this time scale for this species. However, as large numbers of Tufted Duck are counted at this sector combination, this situation warrants close monitoring.
3.1.18 ‘All winter months’ Alerts
Alerts based on species trends calculated across all data available for the months September-March appear in Appendix 4. These Alerts are for comparison purposes and should not be taken as accurate reflections of population changes, for reasons presented in section 2.2 (Alerts).
No differences appear between standard and ‘all month’ Gadwall Alerts, as this species is conventionally indexed on the time period September – March. For Shoveler, only one new Alert was fired, a High Alert for all-time at County Ditch Lake (Appendix 4). However, as the average number of birds involved was less than 25, this should not be of great concern.
Tufted Duck, usually indexed between November and February, showed six changes in Alert status using ‘all months’ data (Appendix 4). At two SSSIs, Staines Moor and Knight & Bessborough Reservoirs, the species were subject to High and Medium Alerts respectively, where using standard months no Alerts were fired. As both these new Alerts were over the five-year period, interpretation using the biological filter should be cautious, as these declines may be within the range of ‘normal’ population fluctuation. The High Alert triggered at Staines Moor serves to highlight the problems with indexing across all months. Figure 3.2.1 shows that in 1995, an abnormally high number of Tufted Duck were counted between July and October. This may have been due to a successful breeding season or an influx of passage migrants. The seemingly isolated season of high counts would influence the GAM disproportionately, contributing to the five-year decline identified.
BTO Research Report No. 361 22 April 2004
At four further sector combinations, Tufted Duck trends changed sufficiently to remove or alleviate Alerts fired using standard indexing. The Medium Alerts fired over ‘all-time’ at Staines Moor and Wraysbury II (South), and over five-years at Wraysbury & Hythe End N & S with Wraysbury Number 1 Gravel Pits were no longer triggered with the new data. Similarly, the High Alert issued for Wraysbury & Hythe End Gravel Pits (SPA sites only) changed to a Medium Alert, as the species trend declined by 8% less.
BTO Research Report No. 361 23 April 2004 Gadwall Shoveler Tufted Duck
70 500 400
60 400 300 50 Target 300 40 200 30 200 Consolidation
20 100 100 10
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.0 1.2 0.6
1.0 0.5 Target 0.8 0.8 0.4 Consolidation 0.6 0.6 0.3 0.4 as proportion 0.4 0.2
0.2 0.2 0.1 of SPA 0.0 0.0 0.0
1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.25 0.7 0.16 0.6 0.14 0.20 0.5 0.12 Target 0.10 0.15 0.4 0.08 Consolidation 0.3 0.10 0.06 0.2 0.04 as proportion 0.05 0.1 0.02 0.0 0.00 of Region
Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.018 0.08 0.010 0.016 0.008 0.014 0.06 Target 0.012 0.006 0.010 0.04 Consolidation 0.008 0.004 0.006 0.02 as proportion 0.004 0.002 0.002 0.00 0.000 of GB 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.3 Staines Moor SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 24 April 2004 Gadwall Shoveler Tufted Duck
30 250 140 120 25 200 100 20 Target 150 80 15 100 60 Consolidation 10 40 50 5 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 0.6 0.12
0.5 Target 1.0 0.10 0.4 0.8 0.08 Consolidation 0.3 0.6 0.06 0.2 as proportion 0.4 0.04 0.1 0.2 0.02 of SPA 0.0 0.0 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 0.35 0.06
0.30 0.05 1.0 Target 0.25 0.04 0.8 0.20 0.03 0.6 Consolidation 0.15 0.02 0.4 0.10 as proportion 0.01 0.2 0.05 0.00 of Region 0.0 0.00 Proportion 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 0.06 0.004
1.0 0.05 0.003 Target 0.8 0.04 0.002 0.6 0.03 Consolidation
0.02 0.4 0.001 as proportion 0.01 0.2 0.000 0.00 of GB 0.0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.4 Knight & Bessborough Reservoirs SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 25 April 2004 Gadwall Shoveler Tufted Duck
100 5 140 120 80 4 100 Target 60 3 80 60 Consolidation 40 2 40 1 20 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.40 1.2 0.12
0.35 1.0 0.10 Target 0.30 0.8 0.08 Consolidation 0.25 0.6 0.20 0.06 0.4 as proportion 0.15 0.04 0.2 0.10 0.02 of SPA 0.0 0.05
0.00 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.20 1.2 0.045 0.18 1.0 0.040 0.16 0.035 0.8 Target 0.14 0.030 0.12 0.6 Consolidation 0.10 0.025 0.4 0.08 0.020 as proportion 0.06 0.2 0.015 0.04 0.0 0.010 0.02 of Region 0.005 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.025 1.2 0.0035
1.0 0.0030 0.020 Target 0.8 0.0025 0.015 0.6 0.0020 Consolidation 0.0015 0.010 0.4 as proportion 0.2 0.0010 0.005 0.0 0.0005 of GB 0.000 0.0000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.5 Thorpe Park No. 1 Gravel Pit SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 26 April 2004 Gadwall Shoveler Tufted Duck
120 80 180 160 100 60 140 80 120 Target 100 40 60 80 Consolidation 40 60 20 40 20 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.35 1.2 0.25
0.30 1.0 0.20 Target 0.25 0.8 0.15 Consolidation 0.20 0.6 0.15 0.10 0.4 as proportion 0.10 0.05 0.2 0.05 of SPA 0.0 0.00 0.00
1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.14 1.2 0.08
0.12 1.0 0.06 Target 0.10 0.8
0.08 0.6 0.04 Consolidation 0.06 0.4 as proportion 0.04 0.2 0.02 0.02 0.0 of Region 0.00 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.025 1.2 0.005
1.0 0.020 0.004 Target 0.8 0.015 0.003 0.6 Consolidation 0.010 0.002 0.4 0.005 0.001 as proportion 0.2 0.000 0.000 0.0 of GB
1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.6 Kempton Park Reservoirs SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 27 April 2004 Gadwall Shoveler Tufted Duck
25 300 140
250 120 20 100 200 Target 15 80 150 60 Consolidation 10 100 40
5 50 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 1.2 0.16 0.14 Target 1.0 1.0 0.12 0.8 0.8 0.10 Consolidation 0.6 0.6 0.08 0.06 0.4 0.4 as proportion 0.04 0.2 0.2 0.02 of SPA 0.0 0.0 0.00
1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 1.2 0.05
1.0 1.0 0.04 0.8 Target 0.8 0.03 0.6 0.6 0.02 Consolidation 0.4 0.4 0.01 as proportion 0.2 0.2 0.00 0.0 0.0 of Region Proportion 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.2 1.0 0.0035 0.0030 1.0 0.8 0.0025 Target 0.8 0.6 0.0020 0.6 Consolidation 0.4 0.0015 0.4 0.0010 0.2 as proportion 0.2 0.0005 0.0 0.0 0.0000 of GB
1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.7 Wraysbury Reservoir SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 28 April 2004 Gadwall Shoveler Tufted Duck
500 250 1200
1000 400 200 800 Target 300 150 600 Consolidation 200 100 400
50 100 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
1.0 1.2 1.0 1.0 Target 0.8 0.8 0.8 Consolidation 0.6 0.6 0.6
0.4 as proportion 0.4 0.4 0.2 0.2 0.2 of SPA 0.0
0.0 0.0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.5 1.2 0.40 1.0 0.35 0.4 0.30 0.8 Target 0.25 0.3 0.6 0.20 Consolidation 0.4 0.2 0.15 as proportion 0.2 0.10 0.1 0.0 0.05 of Region 0.00 Proportion 0.0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.07 1.2 0.030 0.06 1.0 0.025 Target 0.05 0.8 0.020 0.04 0.6 0.015 Consolidation 0.03 0.4 0.010 as proportion 0.02 0.2 0.005 0.01 0.0 of GB 0.00 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.8 Wraysbury & Hythe End Gravel Pits (complete) SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 29 April 2004 Gadwall Shoveler Tufted Duck
80 25 300
250 20 60 200 Target 15
40 150 10 Consolidation 100
20 5 50
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.35 0.10 0.25 Target 0.30 0.08 0.20 0.25 0.06 Consolidation 0.15 0.20 0.04 0.15 0.10 as proportion 0.02 0.10 0.05 of SPA 0.00 0.05
0.00 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.12 0.04 0.12
0.10 0.10 0.03 Target 0.08 0.08 0.02 Consolidation 0.06 0.06 0.01 0.04 0.04 as proportion 0.00 0.02 0.02 of Region 0.00 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.016 0.005 0.008 0.014 0.007 0.004 0.012 0.006 Target 0.003 0.010 0.005 Consolidation 0.008 0.002 0.004
0.006 0.003 0.001 as proportion 0.004 0.002 0.000 0.002 0.001 of GB 0.000 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.9 Wraysbury Number 1 Gravel Pits SSSI. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 30 April 2004 Gadwall Shoveler Tufted Duck
40 12 180 160 10 140 30 8 120 Target 100 6 20 80 Consolidation 4 60 10 40 2 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.5 0.04 0.14 0.12 Target 0.4 0.03 0.10 0.3 Consolidation 0.02 0.08 0.2 0.06 0.01 as proportion 0.1 0.04 0.00 of SPA 0.0 0.02 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.18 0.018 0.06 0.16 0.016 0.05 0.14 0.014 Target 0.12 0.012 0.04 0.10 0.010 0.03 Consolidation 0.08 0.008 0.06 0.006 0.02 0.04 as proportion 0.004 0.02 0.01 0.002 0.00 of Region 0.000 0.00 Proportion 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.025 0.0020 0.005
0.020 0.004 0.0015 Target 0.015 0.003 Consolidation 0.010 0.0010 0.002 0.005 as proportion 0.0005 0.001 0.000 of GB 0.0000 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.10 Wraysbury Number 1 Gravel Pit (North). Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 31 April 2004 Gadwall Shoveler Tufted Duck
30 12 200 180 10 25 160 140 20 8 Target 120
15 6 100 80 Consolidation 4 10 60 40 5 2 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.6 1.2 0.20 0.18 1.0 Target 0.5 0.16 0.4 0.8 0.14 Consolidation 0.12 0.3 0.6 0.10 0.2 0.4 0.08 as proportion 0.06 0.1 0.2 0.04 of SPA 0.0 0.0 0.02 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.16 1.2 0.08 0.14 1.0 0.07 0.12 0.06 0.8 Target 0.10 0.05 0.6 0.08 0.04 Consolidation 0.06 0.4 0.03 0.04 as proportion 0.2 0.02 0.02 0.0 0.01 0.00 of Region 0.00 Proportion 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.025 1.2 0.005
1.0 0.020 0.004 Target 0.8 0.015 0.003 0.6 Consolidation 0.010 0.4 0.002 0.005 as proportion 0.2 0.001 0.000 0.0 of GB 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.11 Wraysbury Number 1 Gravel Pit (South). Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 32 April 2004 Gadwall Shoveler Tufted Duck
160 80 600
140 500 120 60 400 Target 100 80 40 300 Consolidation 60 200 40 20 100 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.35 0.35 0.4 0.30 Target 0.30 0.3 0.25 0.25 Consolidation 0.20 0.2 0.20 0.15 0.15 as proportion 0.10 0.1
0.10 0.05 0.0 of SPA 0.05 0.00
0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.25 0.20 0.25 0.18 0.16 0.20 0.20 0.14 Target 0.12 0.15 0.15 0.10 0.10 Consolidation 0.08 0.10 0.06 0.05 0.04 as proportion 0.05 0.02 0.00 0.00 of Region
Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.04 0.030 0.018 0.016 0.025 0.014 Target 0.03 0.020 0.012 0.010 0.015 Consolidation 0.02 0.008 0.010 0.006 0.004 as proportion 0.005 0.01 0.002 0.000 0.000 of GB 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.12 Wraysbury II (North) Gravel Pit. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 33 April 2004 Gadwall Shoveler Tufted Duck
300 50 350 300 250 40 250 200 Target 30 200 150 20 150 Consolidation 100 100 10 50 50
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.7 0.6 0.25 0.5 Target 0.6 0.20 0.5 0.4 Consolidation 0.15 0.4 0.3
0.3 0.2 0.10 as proportion
0.2 0.1 0.05 of SPA 0.1 0.0
0.0 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.35 0.18 0.12 0.16 0.10 0.30 0.14 Target 0.25 0.12 0.08 0.10 0.20 0.08 0.06 Consolidation 0.15 0.06 0.04 0.04 0.10 as proportion 0.02 0.02 0.05 0.00 of Region 0.00 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.05 0.030 0.010
0.025 0.04 0.008 Target 0.020 0.006 0.03 0.015 Consolidation 0.02 0.010 0.004 as proportion 0.005 0.01 0.002 0.000 of GB 0.00 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.13 Wraysbury II (South) Gravel Pit. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 34 April 2004 Gadwall Shoveler Tufted Duck
50 120 250
100 40 200 80 Target 30 150 60 Consolidation 20 100 40
50 10 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.14 1.2 0.16 0.14 Target 0.12 1.0 0.12 0.10 0.8 0.10 Consolidation 0.08 0.6 0.08 0.4 as proportion 0.06 0.06 0.04 0.2 0.04 of SPA 0.02 0.0 0.02
0.00 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.07 1.0 0.08 0.07 0.06 0.8 0.06 Target 0.05 0.6 0.05 0.04 0.4 0.04 Consolidation 0.03 0.03 0.2 as proportion 0.02 0.02 0.0 0.01 0.01 of Region 0.00 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.010 0.8 0.006
0.005 0.008 0.6 Target 0.004 0.006 0.4 0.003 Consolidation 0.004 0.2 0.002 0.002 as proportion 0.0 0.001 0.000 of GB 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.14 Yeoveney Lake. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 35 April 2004 Gadwall Shoveler Tufted Duck
80 20 100
80 60 15 Target 60
40 10 40 Consolidation
5 20 20
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds Number of whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.16 0.12 0.12
0.14 0.10 0.10 Target 0.12 0.08 0.08 Consolidation 0.10 0.06 0.08 0.06 0.04 as proportion 0.06 0.04 0.02 0.04 0.02 of SPA 0.00 0.02
0.00 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.10 0.06 0.040 0.05 0.035 0.08 0.030 0.04 Target 0.025 0.06 0.03 0.020 Consolidation 0.02 0.04 0.015 as proportion 0.01 0.010 0.02 0.00 0.005 of Region 0.000 Proportion 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.016 0.007 0.0030
0.014 0.006 0.0025 0.012 0.005 Target 0.0020 0.010 0.004 Consolidation 0.008 0.003 0.0015 0.006 0.002 0.0010 as proportion 0.004 0.001 0.0005 0.002 0.000 of GB 0.000 0.0000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.15 County Ditch Lake. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 36 April 2004 Gadwall Shoveler Tufted Duck
400 100 1000
80 800 300 Target 60 600
200 40 400 Consolidation
100 20 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.8 0.35 0.5 0.30 Target 0.7 0.4 0.25 0.6 Consolidation 0.20 0.3 0.5 0.15 0.4 0.2 as proportion 0.10
0.3 0.05 0.1 of SPA 0.2 0.00
0.1 0.0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.45 0.18 0.30 0.16 0.40 0.25 0.14 0.35 Target 0.12 0.20 0.30 0.10 Consolidation 0.25 0.08 0.15 0.06 0.20 0.10 0.04 as proportion 0.15 0.02 0.05 0.10 0.00 of Region 0.00 Proportion 0.05 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.07 0.025 0.025 0.06 0.020 0.020 Target 0.05 0.015 0.015 0.04 Consolidation 0.010 0.010 0.03 0.005 0.005 as proportion 0.02 0.000 0.01 0.000 of GB 0.00 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.16 Wraysbury & Hythe End Gravel Pits (SPA sectors only). Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 37 April 2004 Gadwall Shoveler Tufted Duck
500 100 1200
1000 400 80 800 Target 300 60 600 Consolidation 200 40 400
20 100 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 800 1000 2500
800 2000 600 600 1500
400 400 1000 whole SPA
200 200 500
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1400 1400 5000 1200 1200 4000 1000 1000 3000 800 800
600 600 2000 Number of birds whole Region 400 400 1000 200 200
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 12000 10000 80000
10000 8000 60000 8000 6000
6000 40000 4000 4000 whole GB 20000 2000 2000
0 0 0 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.9 0.35 0.7 0.30 Target 0.8 0.6 0.25 0.7 0.5 0.20 Consolidation 0.6 0.15 0.4 0.5 as proportion 0.10 0.3 0.4 0.05 0.2 of SPA 0.3 0.00
0.2 0.1 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.45 0.18 0.35 0.16 0.40 0.30 0.14 Target 0.35 0.12 0.25 0.30 0.10 0.20 Consolidation 0.25 0.08 0.15 0.06 0.20 0.04 0.10 as proportion 0.15 0.02 0.05 0.10 0.00 of Region 0.00 Proportion 0.05 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000
0.08 0.025 0.030 0.07 0.020 0.025 0.06 Target 0.015 0.020 0.05 Consolidation 0.04 0.010 0.015 0.03 0.005 0.010 as proportion 0.02 0.005 0.000 0.01 of GB 0.00 0.000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 1988 1990 1992 1994 1996 1998 2000 Winter Winter Winter
Figure 3.1.17 Wraysbury & Hythe End North & South and Wraysbury No. 1 Gravel Pits. Site trends (‘Target consolidation’) shown for GA, SV and TU, with SPA, regional and national trends for comparison (top four graphs). The bottom three graphs show bird numbers with confidence limits at the site as a proportion of SPA, regional and national totals, as predicted by logistic models.
BTO Research Report No. 361 38 April 2004 T eerhRpr o 6 BTO ResearchReport No.361 A p ril 2004 Gadwall Shoveler Tufted Duck 5-Year 10-Year All Time 5-Year 10-Year All Time 5-Year 10-Year All Time Staines Moor 226 130 158 -43 8 -15 -4 -34 -35 Knight & Bessborough Reservoirs 229* x >1000* -63 x 152 x x 54 Thorpe Park Number 1 Gravel Pit -24 x -61 100* x 0* 31 x 0 Kempton Park Reservoirs -7 382 382 >1000* x ** -80 -80 -80 Wraysbury Reservoir 150* 400* 400* -97 -95 -92 88 -25 76 Wraysbury & Hythe End Gravel Pits1 27 363 588 -22 >1000 >1000 -46 -10 -4 Wraysbury Number 1 Gravel Pits -26 x 0 233* x 567* -2 x 36 Wraysbury Number 1 Gravel Pits (North) x x 22* x x 400 x x -18 Wraysbury Number 1 Gravel Pits (South) x x 7* x x 1000 x x 189 Wraysbury II (North) Gravel Pit -44 x -67 16 x 263 ** x ** Wraysbury II (South) Gravel Pit 93 x 167 371* x 725* -42 x -32 Yeoveney Lake -68* x -63* 109 x >1000 -1 x -1
39 County Ditch Lake 58* x -10* 217* x 138* 9 x -7 Wraysbury & Hythe End Gravel Pits2 35 x 26 91 x 408 -43 x -56 Wraysbury & Hythe End N & S and Wraysbury Number 1 Gravel Pits 16 x 22 125 x 440 -30 x -35 South West London Waterbodies SPA 16 201 388 -30 39 29 -7 52 75
Table 3.1.1 Table of Alerts for 15 site consolidations and the SPA as a whole. Figures are percentage change in smoothed index. A cross appears where data were insufficient for analysis. Figures in italics show Medium Alerts (a decline of 25%-50%), whilst bold figures show High Alerts (>50% declines). All Time refers to the period 1989/90-2000/2001.
*indicates calculations based on a total average count of less than 25 birds, that should be interpreted with caution. ** indicates that an Alert cannot be generated as the initial or final index value was zero. 1Includes Yeoveney Lake and County Ditch Lake. 2Excludes Yeoveney Lake and County Ditch Lake.
3.2 Timing of Counts
Figures 3.2.1 – 3.2.15 show average monthly counts of Gadwall, Shoveler and Tufted Duck. Where possible, these have been plotted for months outside of those used for standard WeBS indexing, to allow analysis of changes in timing of site usage. Plots have been produced for each year, and for each site consolidation (note there are no additional data available at SPA level).
Those species triggering Medium or High Alerts at any site consolidation are discussed below. It should be remembered that all Alerts for all species over the five-year period, and Medium Alerts for Gadwall over ten years, are subject to cautious interpretation, according to the biological filter. The remaining site / species combinations are assumed to show stable or increasing trends and thus there is no need to examine changes in relation to phenology.
3.2.1 Staines Moor
Medium Alerts were fired for Shoveler over five years, and Tufted Duck for ten years and ‘all time’. Figure 3.2.1 reveals little evidence that peak mean Shoveler numbers have consistently shifted to months outside of the standard index months (September and October). A large influx of birds occurred in November 1995, but this is more likely to be an isolated passage movement than a long- term phenological shift.
Apparent declines in Tufted Duck are also unlikely to be due to changes in phenology. Although high numbers of these ducks are counted outside of the standard index months (November-February), the majority of these are in July and August. These are likely to be re-dispersed breeding birds or possibly moult migrants (Wernham et al. 2002).
3.2.2 Knight and Bessborough Reservoirs
Only one Alert was triggered at this SSSI, a High Alert for Shoveler over the five-year period. Peak mean counts tended to be within the standard index window, and there is little consistent trend for earlier or later peak counts (Figure 3.2.2).
3.2.3 Thorpe Park Number 1 Gravel Pit
Gadwall were issued with an ‘all time’ High Alert at this SSSI. As Gadwall is indexed on seven months’ data, there is little scope for additional counts, and Thorpe Park was not counted from April to August (Figure 3.2.3).
3.2.4 Kempton Park Reservoirs
High Alerts were fired for all three time periods for Tufted Duck at Kempton Park. For some years (1990, 1991, 1994, 1995, 1997), substantial counts of Tufted Duck occurred in October, which could reflect earlier arriving migrants from Fennoscandia. However, there are too frequent missing counts to allow accurate comparison, and available data suggest that peak mean counts still fall inside the standard index months (Figure 3.2.4).
3.2.5 Wraysbury Reservoir
High Alerts over all three time periods indicate a potentially serious decline of Shoveler at Wraysbury Reservoir. Occasional large counts were made in November and December (e.g. 1989), which potentially could reflect passage migrants using the SSSI in later months than those used for indexing (Figure 3.2.5). However, there is no long-term pattern of this, and as the SPA trend is largely stable (except over the five-year period), it seems more likely that declines at Wraysbury Reservoir are attributable to re-dispersal within the SPA.
BTO Research Report No. 361 40 April 2004 The ten-year Medium Alert fired for Tufted Duck is not considered likely to be due to a shift in bird movements. Peaks occurring in late summer and early autumn may reflect productive breeding seasons, as more juveniles may be included in WeBS counts.
3.2.6 Wraysbury & Hythe End Gravel Pits (including Yeoveney Lake and County Ditch Lake)
A five-year Medium Alert status was triggered by Tufted Duck at this SSSI. There is no evidence that this is due to a temporal change in peak counts, as the peak occurred within the index months in all years except 1993 (Figure 3.2.6).
3.2.7 Wraysbury Number 1 Gravel Pit
Gadwall, subject to a five-year Medium Alert, were counted in very small numbers or absent outside of the standard alerting months (Figure 3.2.7). The Alert was considered likely to have been triggered by a return to stable levels from a five-year peak. Therefore there is no suggestion that this decline could be due to timing of counts.
3.2.8 Wraysbury Number 1 Gravel Pit (North)
No alerts were fired at this sector, largely due to the patchiness of count data (Figure 3.2.8).
3.2.9 Wraysbury Number 1 Gravel Pit (South)
As above, no alerts were fired at this sector, largely due to the patchiness of count data (Figure 3.2.9).
3.2.10 Wraysbury II (North) Gravel Pit
Five year Medium Alerts and ‘all time’ High Alerts were triggered for Gadwall at this sector. Smoothed trends for the species show fluctuations (Figure 3.1.12), but this is not due to temporal changes; counts outwith the standard index months are small in comparison (Figure 3.2.10)..
3.2.11 Wraysbury II (South) Gravel Pit
Medium Alerts were fired for Tufted Duck at this gravel pit for the five-year period, and for ‘all time’. Figure 3.2.11 suggests that peak mean counts predominately occur within standard index months, with only isolated peaks outside this period.
3.2.12 Yeoveney Lake
The High Alerts issued for Gadwall at Yeoveney Lake should be interpreted parsimoniously, as they are based on average yearly counts of below 25 birds. Figure 3.2.12 displays a trend for relatively large counts in August (where counted). This may represent increased counting of juvenile birds after increases in the native breeding population (Fox 1988, Gibbons et al. 1993).
3.2.13 County Ditch Lake
No alerts were fired at this site, largely due to the patchiness of count data (Figure 3.2.13).
BTO Research Report No. 361 41 April 2004 3.2.14 Wraysbury & Hythe End Gravel Pits (excluding Yeoveney Lake and County Ditch Lake)
Tufted Duck were issued Medium Alert status for the five-year period and High Alert status for ‘all time’, subject to caveats (section 3.1.16). Figure 3.2.14 shows no clear pattern of temporal change, although interestingly the plots for 1999 and 2000 do suggest a drop-off in numbers during the indexed months. It should be noted that the scales differ substantially between these plots, implying that the population size is variable and subject to fluctuation.
3.2.15 Wraysbury & Hythe End Gravel Pits (North & South) and Wraysbury Number 1 Gravel Pits
This sector combination was issued with Medium Alerts for Tufted Duck, again over the five-year and ‘all time’ periods. The wintering population of Tufted Duck usually peaks in December or January, and so there is little reason to suppose that changes in phenology are directly causative of species decline.
3.2.16 South West London Waterbodies SPA
As there are no data available for months outside the standard index window, it was not possible to perform a similar analysis for the SPA. However, it was possible to compare the months in which peak counts occurred with those at the national level. These data are available in a companion spreadsheet (Peak count months.xls).
For Gadwall, five of the 12 years analysed (1994, 1995, 1996, 1998 and 2000) showed that peak counts occurred in the same months at the SPA and national levels. Of the remaining seven years, three SPA peak counts occurred within one month of the national peak.
Shoveler peak counts were made in the same months at the SPA and national levels in nine of the 12 years analysed. This is perhaps unsurprising in that this species is only indexed on two months, September and October.
Six peak counts of Tufted Duck occurred in the same months for both SPA and national scales, with a further four peak counts within one month of each other. Tufted Duck is indexed on four months (November-February) and so there is scope for differences in timing of peak counts in this species.
BTO Research Report No. 361 42 April 2004 Gadwall Shoveler Tufted Duck
120 1200 4000 100 1000 3000 80 800 60 600 2000 1989 40 400 1000 20 200 0 0 0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 40 1990 400 1000 20 200 0 0 0 t g ct n r n p c b l p n r y Jul u a p u Jul e u ct A Sep O Nov Dec J Feb Mar A May J Aug Se Oc Nov De Jan F Mar Apr Jun J e O Apr 4000 120 May 1200 Aug S Nov Dec Ja Feb Ma Ma Jun 100 1000 3000 80 800 2000 60 600 1991 40 400 1000 20 200 0 0 0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 4000 120 1200 100 1000 3000 80 800 60 600 2000 40 1992 400 1000 20 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 1993 40 400 1000 20 200 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Nov Dec Ja Fe Mar A J J u Oct eb A Ma May A Se No Dec Jan F Mar May Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 1994 40 400 1000 20 200 0 0 0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 4000 120 1200 100 1000 3000 80 800 60 600 2000 1995 40 400 1000 20 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 4000 120 1200 100 1000 3000 Number of birds Number 80 800 60 600 2000 40 1996 400 1000 20 200 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 1997 40 400 1000 20 200 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 1998 40 400 1000 20 200 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 4000 120 1200 100 1000 3000 80 800 2000 60 600 1999 40 400 1000 20 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 4000 120 1200 100 1000 3000 80 800 60 600 2000 2000 40 400 1000 20 200 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.1 Staines Moor. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
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140 250 600 120 200 500 100 400 80 150 300 60 No data 100 No data No data 1989 40 200 50 20 100 0 0 0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 600 140 250 120 500 200 100 400 150 80 300 60 No data No data No data 100 200 1990 40 20 50 100 0 0 0 t g ct n r n p c b l p n r y Jul u a p u Jul e u ct A Sep O Nov Dec J Feb Mar A May J Aug Se Oc Nov De Jan F Mar Apr Jun J e O Apr 600 140 May 250 Aug S Nov Dec Ja Feb Ma Ma Jun 120 500 200 100 400 150 80 300 60 No data No data No data 100 200 1991 40 50 20 100 0 0 0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 600 140 250 120 500 200 100 400 150 80 300 60 100 200 1992 40 50 20 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 600 140 250 120 500 200 100 400 150 80 300 60 100 200 1993 40 100 20 50 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Nov Dec Ja Fe Mar A J J u Oct eb A Ma May A Se No Dec Jan F Mar May Jun 600 140 250 120 500 200 100 400 150 80 300 60 100 200 1994 40 20 50 100 0 0 0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 600 140 250 120 500 200 100 400 150 80 300 60 1995 100 200 40 20 50 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 600 140 250 120 500 200 Number of birds Number 100 400 150 80 300 60 100 200 1996 40 20 50 100 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 600 140 250 120 500 200 100 400 150 80 300 1997 60 100 200 40 100 20 50 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 600 140 250 120 500 200 100 400 150 80 300 60 100 200 1998 40 20 50 100 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 600 140 250 120 500 200 100 400 150 80 300 60 1999 100 200 40 20 50 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 600 140 250 120 500 200 100 400 150 80 300 60 2000 100 200 40 100 20 50 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.2 Knight & Bessborough Reservoirs. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 44 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul O J A J J Oc J A Jun J u u A Sep N Dec Feb Mar May Aug Se N De Feb Mar Ma A Sep O Nov Dec Ja Feb Ma Ap Ma J
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1992 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1993 60 6 50 40 4 20 2 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v p J Au S O De Jan Fe Mar Apr Jun Jul A S Oct Dec Ja Fe Mar A J J u Oct eb Nov Ma Nov May A Se No Dec Jan F Mar A May Jun 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1994 60 6 50 40 4 20 2 0 0 0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1995 60 6 50 40 4 20 2 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 200 180 18 160 16 140 14 150 Number of birds Number 120 12 100 10 100 80 8 6 1996 60 50 40 4 20 2 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1997 60 6 50 40 4 20 2 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1998 60 6 50 40 4 20 2 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 1999 60 6 50 40 4 20 2 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 200 180 18 160 16 140 14 150 120 12 100 10 100 80 8 2000 60 6 50 40 4 20 2 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.3 Thorpe Park Number 1. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 45 April 2004 Gadwall Shoveler Tufted Duck
250 120 300
200 100 250 80 200 150 60 150 100 No data No data No data 1989 40 100 50 20 50 0 0 0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 300 250 120 250 200 100 200 80 150 150 60 No data 100 100 40 1990 50 50 20 0 0 0 t g ct n r n p c b l p n r y Jul u a p u Jul e u ct A Sep O Nov Dec J Feb Mar A May J Aug Se Oc Nov De Jan F Mar Apr Jun J e O Apr 300 250 May 120 Aug S Nov Dec Ja Feb Ma Ma Jun 250 200 100 200 80 150 150 60 100 100 1991 40 50 50 20 0 0 0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 300 250 120 250 200 100 200 80 150 150 60 100 100 40 1992 50 50 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 300 250 120 250 200 100 200 80 150 150 60 100 100 1993 40 50 50 20 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Nov Dec Ja Fe Mar A J J u Oct eb A Ma May A Se No Dec Jan F Mar May Jun 300 250 120 250 200 100 200 80 150 150 60 100 100 1994 40 50 50 20 0 0 0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 300 250 120 250 200 100 200 80 150 150 60 1995 100 100 40 50 50 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 300 250 120 250 200 100 Number of birds Number 200 80 150 150 60 100 100 40 1996 50 50 20 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 300 250 120 250 200 100 200 80 150 150 60 1997 100 100 40 50 50 20 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 300 250 120 250 200 100 200 80 150 150 60 100 100 1998 40 50 50 20 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 300 250 120 250 200 100 200 80 150 150 60 1999 100 100 40 50 50 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 300 250 120 250 200 100 200 80 150 150 60 2000 100 100 40 50 50 20 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.4 Kempton Park Reservoirs. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 46 April 2004 Gadwall Shoveler Tufted Duck
30 700 500 600 25 400 20 500 400 300 15 300 200 10 1989 200 100 5 100 0 0 0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 500 30 700 25 600 400 500 20 300 400 15 300 200 10 1990 200 100 5 100 0 0 0 t g ct n r n p c b l p n r y Jul u a p u Jul e u ct A Sep O Nov Dec J Feb Mar A May J Aug Se Oc Nov De Jan F Mar Apr Jun J e O Apr 500 30 May 700 Aug S Nov Dec Ja Feb Ma Ma Jun 25 600 400 500 20 300 400 15 300 200 10 1991 200 100 5 100 0 0 0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 500 30 700 25 600 400 500 20 300 400 15 300 200 10 1992 200 100 5 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 600 30 700 25 600 500 20 500 400 400 15 300 300 1993 10 200 200 5 100 100 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Dec Ja Fe Mar A J J u Oct eb A Ma Nov May A Se No Dec Jan F Mar May Jun 500 30 700 25 600 400 500 20 300 400 15 300 200 1994 10 200 100 5 100 0 0 0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 500 30 700 25 600 400 500 20 300 400 15 300 200 1995 10 200 100 5 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 500 30 700 25 600 400
Number of birds Number 500 20 300 400 15 300 200 10 1996 200 100 5 100 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 500 30 700 25 600 400 500 20 300 400 15 1997 300 200 10 200 100 5 100 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 500 30 700 25 600 400 500 20 300 400 15 300 200 1998 10 200 100 5 100 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 500 30 700 25 600 400 500 20 300 400 15 300 200 1999 10 200 100 5 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 500 30 700 25 600 400 500 20 300 400 15 300 200 2000 10 200 100 5 100 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.5 Wraysbury Reservoir. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 47 April 2004 Gadwall Shoveler Tufted Duck
1200 400 2500
1000 2000 300 800 1500 600 200 1000 1989 400 100 200 500 0 0 0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1000 400 1990 100 500 200 0 0 0 t g ct n r n p c b l p n r y Jul u a p u Jul e u ct A Sep O Nov Dec J Feb Mar A May J Aug Se Oc Nov De Jan F Mar Apr Jun J e O Apr 2500 1200 May 400 Aug S Nov Dec Ja Feb Ma Ma Jun 1000 2000 300 800 1500 600 200 1000 1991 400 100 500 200 0 0 0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 2500 1200 400 1000 2000 300 800 1500 600 200 1000 400 1992 100 500 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1000 1993 400 100 500 200 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Nov Dec Ja Fe Mar A J J u Oct eb A Ma May A Se No Dec Jan F Mar May Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1000 1994 400 100 500 200 0 0 0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 2500 1200 400 1000 2000 300 800 1500 600 200 1000 1995 400 100 500 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 2500 1200 400 1000 2000
Number of birds Number 300 800 1500 600 200 1000 400 1996 100 500 200 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1997 1000 400 100 500 200 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1000 1998 400 100 500 200 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 2500 1200 400 1000 2000 300 800 1500 600 200 1000 1999 400 100 500 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 2500 1200 400 1000 2000 300 800 1500 600 200 1000 2000 400 100 500 200 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.6 Wraysbury & Hythe End Gravel Pits (complete). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 48 April 2004 Gadwall Shoveler Tufted Duck
160 100 140 0.0 80 120 -0.2 100 60 80 -0.4 60 No data 40 No data No data 1989 -0.6 40 20 20 -0.8 0 0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun 160 100 140 0.0 120 80 -0.2 100 60 80 No data No data -0.4 No data 60 40 -0.6 1990 40 20 20 -0.8 0 0 -1.0 p t c b l r p v n r e u p ct n y ct b p Jul Oc Jan Apr Jun J e Jul ug O a e 160 Aug Se Nov De F Mar May 100 Aug S O Nov Dec Ja Feb Ma Apr Ma Jun A Se No Dec J F Mar A May Jun 140 0.0 80 120 -0.2 100 60 80 No data No data -0.4 No data 60 40 -0.6 1991 40 20 -0.8 20 0 0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 500 160 100 140 400 120 80 300 100 60 80 200 60 40 1992 40 20 100 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 500 160 100 140 400 120 80 100 60 300 80 200 60 40 1993 40 20 100 20 0 0 0 l t u g p c c b y n b n l g p v r J e Jul ug ep pr u u p Au S O Nov De Jan Fe Mar Apr Jun A S Oct Nov Dec Ja Fe Mar A J J u Oct eb A Ma May A Se No Dec Jan F Mar May Jun 500 160 100 140 400 120 80 100 60 300 80 200 60 40 1994 40 20 100 20 0 0 0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 500 160 20 140 400 120 15 100 300 80 10 200 1995 60 5 40 100 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 500 160 100 140 80 400
Number of birds Number 120 100 60 300 80 200 60 40 1996 40 20 100 20 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 500 80 100 400 60 80 60 300 40 1997 40 200 20 20 100
0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 500 160 100 140 400 120 80 300 100 60 80 200 60 40 1998 40 20 100 20 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 500 160 100 140 400 120 80 100 60 300 80 200 1999 60 40 40 20 100 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 500 160 100 140 400 120 80 100 60 300 80 200 60 40 2000 40 20 100 20 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.7 Wraysbury Number 1 Gravel Pits. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 49 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 140 35 20 30 120 25 15 100 20 80 10 15 60 40 1992 10 5 5 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 60 12 2.5 10 2.0 50 8 1.5 40 6 1.0 30 4 0.5 20 1993 0.0 2 10 -0.5 0 0 -1.0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul Oct Jan A Jun J Oc J A Jul u a e u A Se No Dec Feb Mar May Aug Se N De Feb Mar Ma Jun A Sep O Nov Dec J F Mar Ap May J
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1995 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 350 60 25 300 50 20
Number of birds Number 250 40 15 200 30 150 10 20 100 1996 10 5 50 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 200 25 20 180 20 160 15 140 15 120 10 100 1997 10 80 60 5 5 40 20 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 250 40 10 8 200 30 6 150 20 4 100 1998 10 2 50 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 250 35 14 30 12 200 25 10 150 20 8 15 6 100 1999 10 4 50 5 2 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 100 140 14 120 12 80 100 10 60 80 8 60 6 40 2000 40 4 20 20 2 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.8 Wraysbury Number 1 Gravel Pits (North). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 50 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 140 40 20 120 30 15 100 80 20 10 60 40 1992 10 5 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 140 5 0.2 120 4 0.0 100 3 -0.2 80 2 -0.4 60 1993 1 -0.6 40 0 -0.8 20 0 -1 -1.0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul Oct Jan A Jun J Oc J A Jul u a e u A Se No Dec Feb Mar May Aug Se N De Feb Mar Ma Jun A Sep O Nov Dec J F Mar Ap May J
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1995 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 250 50 8 200 40 6 Number of birds Number 30 150 4 20 100 2 1996 10 50 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 300 60 8 50 250 6 40 200 30 4 150 1997 100 20 2 10 50 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 140 40 10 120 8 30 100 6 80 20 4 60 1998 40 10 2 20 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 200 50 10
40 8 150 30 6 100 20 4 1999 50 10 2 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 350 50 20 300 40 15 250 30 200 10 150 20 2000 100 5 10 50 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.9 Wraysbury Number 1 Gravel Pits (South). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 51 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 600 180 35 160 30 500 140 120 25 400 100 20 300 80 15 60 200 1992 10 40 100 20 5 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 500 200 30 25 400 150 20 300 100 15 200 1993 10 50 100 5 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 250 80 40 200 60 30 150 40 20 100 1995
20 10 50
0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 350 140 40 120 300
Number of birds Number 100 30 250 80 200 20 60 150 100 1996 40 10 20 50 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 1600 180 80 160 1400 140 60 1200 120 1000 100 40 800 1997 80 600 60 400 40 20 20 200 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 800 700 40 600 600 500 30 400 20 400 300 1998 200 10 200 100 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 1200 120 140 100 120 1000 80 100 800 80 60 600 60 1999 40 400 40 200 20 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 200 60 35 50 30 150 40 25 20 30 100 15 2000 20 10 50 10 5 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.10 Wraysbury Number 2 Gravel Pit (North). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 52 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 180 250 8 160 140 200 6 120 150 100 4 80 100 60 1992 2 40 50 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 350 160 18 140 16 300 120 14 250 100 12 10 200 80 8 150 60 1993 6 100 40 4 50 20 2 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 250 250 25
200 20 200
150 15 150
100 10 100 1995
50 5 50
0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 250 140 25 120 20 200 Number of birds Number 100 150 80 15 60 10 100 1996 40 5 50 20 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 500 500 35 400 30 400 25 300 300 20 1997 200 15 200 10 100 100 5 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 500 350 20 300 400 250 15 300 200 10 150 200 1998 100 5 100 50 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 180 500 20 160 400 140 15 120 300 100 10 80 1999 200 60 5 40 100 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 180 500 80 160 400 140 60 120 300 100 40 80 2000 200 60 40 100 20 20 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.11 Wraysbury Number 2 Gravel Pit (South). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 53 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul O J A J J Oc J A Jun J u u A Sep N Dec Feb Mar May Aug Se N De Feb Mar Ma A Sep O Nov Dec Ja Feb Ma Ap Ma J
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1992 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 140 60 20 120 50 15 100 40 80 30 10 60 1993 20 40 5 10 20 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 160 40 20 140 30 15 120 100 20 10 80 60 1995 10 5 40 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 140 70 120 120 60 100
Number of birds Number 50 100 80 40 80 60 30 60 1996 20 40 40 10 20 20 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 350 80 80 300 60 60 250 200 40 40 150 1997 100 20 20 50 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 140 35 35 30 30 120 25 25 100 20 20 80 15 15 60 1998 10 10 40 5 5 20 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 140 60 250 120 50 200 100 40 150 80 30 60 1999 100 20 40 10 50 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 160 25 40 140 20 30 120 15 100 20 80 10 60 2000 40 5 10 20 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.12 Yeoveney Lake. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 54 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul O J A J J Oc J A Jun J u u A Sep N Dec Feb Mar May Aug Se N De Feb Mar Ma A Sep O Nov Dec Ja Feb Ma Ap Ma J
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1992 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 140 60 140 120 50 120 100 40 100 80 80 30 60 60 1993 20 40 40 10 20 20 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g p v r l p t v c y r u p u o an pr g ct n b n Jul A Se Oct Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u a e u No May N Ma A Sep O Nov Dec J F Mar Ap May J 140 25 8 120 20 6 100 15 80 4 10 60 1995 2 40 5 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 100 30 16 25 14 80
Number of birds Number 12 20 10 60 15 8 40 10 6 1996 4 20 5 2 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 100 30 16 25 14 80 12 20 10 60 15 8 1997 40 10 6 4 20 5 2 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 140 350 8 300 120 6 250 100 80 200 4 150 60 1998 100 2 40 50 20 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 180 70 25 160 60 20 140 50 120 40 15 100 30 80 1999 10 60 20 5 40 10 20 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 100 35 35 30 30 80 25 25 60 20 20 15 15 40 2000 10 10 20 5 5 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.13 County Ditch Lake. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 55 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 600 350 35 300 30 500 250 25 400 200 20 300 150 15 200 1992 100 10 100 50 5 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 700 350 50 300 600 40 250 500 200 30 400 300 150 20 1993 100 200 10 50 100 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 400 300 50 250 40 300 200 30 150 200 20 1995 100 100 50 10 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 600 250 50 500 200 40 Number of birds Number 400 150 30 300 100 20 200 1996 50 10 100
0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 2000 600 100 500 80 1500 400 60 300 1000 1997 40 200 500 100 20 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 1000 1000 50
800 40 800
600 30 600
400 20 400 1998
200 10 200
0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 1400 500 140 1200 400 120 100 1000 300 80 800 600 200 60 1999 40 400 100 20 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 300 600 100 500 250 80 400 200 60 300 150 40 2000 200 100 100 20 50 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.14 Wraysbury & Hythe End Gravel Pits (SPA only). Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 56 April 2004 Gadwall Shoveler Tufted Duck
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 No data -0.4 No data -0.4 No data 1989 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t l t r v n b n u p c c y u g p c v c b y Jul ec pr u J e eb J u e p Aug Sep Oct No D Ja Fe Mar A May J Aug S O Nov De Jan F Mar Apr Ma Jun A Se O No D Jan Fe Mar A Ma Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 -0.6 -0.6 1990 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g n r n p t c b l r u ct a p u e u p ct n y Jul O J A J Jul Oc Jan Apr Jun J e A Sep Nov Dec Feb Mar May Aug Se Nov De F Mar May Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 No data -0.4 No data No data -0.6 1991 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 g v n r n l p t v c y l r r u ct o a p u u o an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May N Ma A Sep Nov Dec Ja Feb Ma Ap Ma J 800 400 80
300 60 600 200 40 400 1992 100 20 200
0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 1000 400 140 120 800 300 100 600 80 200 60 400 1993 100 40 200 20 0 0 0 l g p t c b y n b n l r u e c ug ep pr u u g p v J O Jan Apr Jun Jul Oct Ja A J u eb p Au S Nov De Fe Mar Ma A S Nov Dec Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun
0.0 0.0 0.0 -0.2 -0.2 -0.2 -0.4 -0.4 -0.4 1994 -0.6 -0.6 No data -0.6 No data No data -0.8 -0.8 -0.8 -1.0 -1.0 -1.0 l t g p v r u p v c y g n r n Jul u p o an pr ct b A Se Oct No Dec Jan Feb Mar A Jun J Aug Se Oc De J Feb Mar A Jun Jul u O a e u May N Ma A Sep Nov Dec J F Mar Ap May J 700 350 60 600 300 50 250 500 40 200 400 30 150 300 1995 100 20 200 50 10 100 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J O Ja Ap J Jul Oc Jan Ap J e A Sep Nov Dec F Mar Ma A S Nov De F Ma May J Aug S O Nov Dec Ja Feb Ma Apr Ma Jun 1000 300 60 250 50 800 Number of birds Number 200 40 600 150 30 400 100 20 1996 200 50 10 0 0 0 l p n b r y g t c b r r n l t u e ct e u ep e u u p c c n y J Aug S O Dec Ja F Ma Apr Jun Jul A S Oc De Jan F Ma Ap J J e O eb Nov Ma Nov May Aug S Nov De Ja F Mar Apr Ma Jun 2500 700 100 600 2000 80 500 1500 400 60 1997 300 40 1000 200 20 500 100 0 0 0 l g p t c b y t v n b n r u e c c ec pr u g p v n b p J Au S O De Jan Fe Mar Apr Jun Jul Aug Sep O D Ja Fe Mar A J Jul u Oct a e Nov Ma No May A Se No Dec J F Mar A May Jun 1200 1200 60 1000 50 1000 800 40 800 600 30 600 1998 400 20 400 200 10 200 0 0 0 g v n r n l p t c y l r u ct o a p u u an pr u g ct n y n Jul A Sep O Dec J Feb Mar A J J Aug Se Oc De J Feb Mar A Jun J u O u N May Nov Ma A Sep Nov Dec Ja Feb Ma Apr Ma J 1600 600 160 1400 500 140 120 1200 400 100 1000 300 80 800 600 1999 200 60 40 400 100 20 200 0 0 0 l g n b r y n g t c b r r n l t r u u ct e u u ep e u u p c n y J A Sep O Dec Ja F Ma Apr J Jul A S Oc De Jan F Ma Ap J J e O Nov Ma Nov May Aug S Nov Dec Ja Feb Ma Apr Ma Jun 600 700 100 600 500 80 500 400 60 400 300 300 2000 40 200 200 20 100 100 0 0 0 l g p t c b y v n b n r u e c ec pr u g p v b J O Jan Apr Jun Jul Oct Ja A Jul u e p Au S Nov De Fe Mar Ma Aug Sep No D Fe Mar May J A Se Oct No Dec Jan F Mar A May Jun Month Month Month
Figure 3.2.15 Wraysbury & Hythe End Gravel Pits and Wraysbury Number 1 Gravel Pits. Histograms show average counts for all months visited. A blank corresponds to an unvisited month. Standard index months: GA – Sept-March; SV – Sept-Oct; TU – Nov-Feb.
BTO Research Report No. 361 57 April 2004 BTO Research Report No. 361 58 April 2004 4. CONCLUSIONS
4.1 SPA Species Trends
Smoothed indices for Gadwall, Shoveler and Tufted Duck were generated for the SPA as a whole. Long-term trends indicate that all three species are increasing in the SPA. During the period 1989- 2000, Gadwall showed a 388% increase, Shoveler a 29% increase and Tufted Duck a 75% increase. At the SPA level, Gadwall show a steady increase before a downturn in 1999. A similar trend is seen at the regional level, whilst the drop-off is less pronounced at the GB level. SPA, regional and national trends for Shoveler are broadly similar, with some fluctuation about a reasonably stable trend line. Tufted Duck go against regional and national trends only in the last two years of analysis; it is impossible to tell at this stage if this is ‘natural’ fluctuation or the beginnings of a real decline. Of the time periods analysed, the only Alert issued was for Shoveler over a five-year period. This Alert status agrees broadly with a recent study of the same SPA (Wetlands Advisory Service 2003), although the reported declines in Tufted Duck were not supported by our analysis; a small decline of 7% since 1995 should be considered within the ‘normal’ range of fluctuation.
It should be noted that the WeBS Alert system now incorporates a ‘biological filter’ to compensate for false Alerts triggered by species prone to natural fluctuation within ‘healthy’ populations (Austin et al. 2004). Short-term (i.e. five-year) Medium and High Alerts for Shoveler would be subject to this caveat, as they would for the other two species analysed, on the basis of known ‘normal’ population fluctuation within the short-term period. Medium Alerts for Gadwall over ten years should also be cautiously interpreted for the same reason. The long-term trend for Shoveler certainly seems to fluctuate between years, with decreases possibly associated with cold winters (Kirby & Mitchell 1993), and so the apparent five-year decline in this species should be interpreted cautiously.
4.2 SSSI, Sector Level and Site Combination Trends
It should be noted that as the SPA trends for all species were stable or increasing over the ‘all time’ period, declines at these component sites were counterbalanced by increases at other sites. This could represent re-dispersal within the SPA, or influxes of birds from other sites. However, it is possible that local issues such as eutrophication or disturbance could be leading to this redistribution.
No site or site combination triggered Alerts in all three species. However, Alerts of particular note were fired for two sites: Wraysbury Reservoir and Wraysbury II (North) Gravel Pit. At the former, declines of over 90% were recorded for Shoveler over all time periods reviewed. This is of particular concern given that between 1990 and 1996, the estimated proportion of the SPA total held by this site was between 20% and 50%. However, applying the biological filter, short-term declines should be treated cautiously. Furthermore, as the SPA trend seems largely stable, longer-term declines could be related to re-dispersal within the SPA. Declines in Gadwall and, although Alerts could not justifiably be calculated, Tufted Duck at Wraysbury II (North) are consistent with the findings of the Wetlands Advisory Service (2003). Although the Medium Alerts for Gadwall over five years should be interpreted parsimoniously, the ‘all time’ High Alerts for the same species is of concern; proportional plots imply that regional species trends do not explain those at the sector. However, similar declines are not recorded at either the SPA or relevant SSSI level, and therefore it is possible that birds may have redistributed at a wider spatial scale, or that birds formerly using the gravel pit have been compensated by influxes to other component SSSI and SPA waterbodies. Human disturbance, predominantly shore-based activities, was found to increase through the winter at Wraysbury II (Wetland Advisory Service 2003), which would be expected to affect the trends of Gadwall and Tufted Duck more than Shoveler, as the latter is indexed early in the winter. Gadwall numbers may be partially compensated by increases at Wraysbury II (South), where the proportion of the SPA total held increased concurrent to the opposite trend at Wraysbury II (North); indeed, trends at Wraysbury & Hythe End SSSI, of which these two lakes are components, do not reveal declines in Gadwall numbers. Tufted Duck appears to be in long-term decline at both component sectors, but only short- term decline at the SSSI level.
BTO Research Report No. 361 59 April 2004
Potential causes of declines at Wraysbury Reservoir are somewhat unclear, as the waterbody is likely used as a loafing area only, and is subject to little recreational disturbance (birdwatchers being considered to be the sole pressure). It may be that Shoveler formerly using the site to loaf have moved elsewhere, or that temporal use of the reservoir has altered. Nocturnal counts of Shoveler are relatively high at some component sites of the SPA (Wetlands Advisory Service 2003), so it could be that birds move in to use the reservoir at night, when they are not counted by WeBS. This behaviour could be indicative of the birds avoiding any diurnal disturbance. Alternatively, proportional plots suggest that changes are in step with regional trends. Therefore effects at wider spatial scales (e.g. poor breeding season, harsh winter conditions) may contribute to the measured local effects.
‘All time’ High Alerts for Gadwall were also fired at Thorpe Park and Yeoveney Lake (although this site Alert issued with a caveat because of small numbers of birds). Declines were found at Thorpe Park by the Wetlands Advisory Service (2003), which could in part be attributable to human disturbance such as water-sports, bird watching or dog walking. 40% of birds left the site in response to a disturbance event, although high levels of human disturbance were not recorded in the sectors most frequently used by Gadwall. Also, restrictions are imposed on the usage of the Thorpe Park Gravel Pit by watercraft and fishermen during the wintering period (late October to mid-March), so this factor may have relatively minor impact. Furthermore, proportional plots suggest that sector-level trends could be consistent with regional trends for the species, at least for the past six years of analysis.
High Alerts for Shoveler, in addition to those at Wraysbury Reservoir, were triggered at Knight & Bessborough Reservoirs. However, as this was over the short-term period, this trend may be considered within the range of ‘normal’ fluctuation (if the biological filter was used).
Tufted Duck showed declines consistent with High Alert status for all time periods reviewed at Kempton Park Reservoirs. Although the numbers of this species did not exceed a proportion of 15% of the SPA total, the declines of 80% are potentially serious. Wraysbury & Hythe End Gravel Pits (SPA sectors only) showed a 56% decline in Tufted Duck over ‘all time’, also enough to trigger a High Alert. However, the species trend fluctuated somewhat, so judgment on the longevity of the decline should perhaps be reserved. Proportional plots for both sector combinations indicate that the estimated proportions of the regional totals are consistent, implying that these trends are within the range of regional-level population change. Recreational disturbance is not considered an issue at Kempton Park Reservoirs, but could be at Wraysbury & Hythe End Gravel Pits.
Long-term Medium Alerts are also of concern and were triggered for Tufted Duck at Staines Moor, Wraysbury II (South) and Wraysbury & Hythe End (North and South) with Wraysbury Number 1 Gravel Pits.
Changes in bird numbers may be related to any substantial changes in water levels at the various component SSSIs. Shoveler numbers at a reservoir in southeast England were significantly negatively correlated with increasing water depth, whilst Tufted Duck were significantly positively correlated with the same changes in water levels. Gadwall showed no significant correlation (Banks, unpublished data).
4.3 Timing of Peak Counts
Using standard WeBS indexing months, it was possible to examine whether peak mean counts at the SSSI level and below occurred in different months between years. This would have been of particular concern if the peaks had occurred outside of the window in which species indices were created. For the SPA, no additional counts were available outside of the indexing period, and problems with site consolidation restrict simple combination of the component SSSI data; however, from the indexed SPA, national and regional trends it is possible to compare whether species trends are ‘in step’.
BTO Research Report No. 361 60 April 2004
Comparing the months in which peak counts occurred at the SPA and national scales, there was little pattern of major difference. 67% of Gadwall peak counts at the SPA were made in the same month or one month either side of the national peak counts, whilst the figure was 83% for Tufted Duck. As Shoveler is indexed on only two months, comparisons of timing are restricted, but 75% of peak counts coincided at SPA and national levels. It should be noted that the functioning of WeBS Alerts should not be affected by variation in timing of peak counts within the standard index months, as the monthly averages are themselves averaged into a yearly mean count to produce the annual species index. Shifting in timing of peak counts would only be problematic if peak counts began to appear outside of the months used for indexing.
At the SSSI level and for site combinations, there is little evidence that seasonal phenology can serve to explain species declines at any of the sites reviewed. Increases in counts of ducks before the first index month (September) are likely to be due to successful breeding seasons or mass moult migrations. Few site / species combinations revealed peak mean counts outside of the months upon which the species are indexed, and therefore it seems safe to assume that the standard index months incorporate the majority of the peak count months.
4.4 Future Research
Further monitoring of the SPA is recommended, to assess whether the High Alert issued for Shoveler over five years marks the beginning of a period of sustained decline. Additional recent downturns in the trends of Gadwall and Tufted Duck may represent ‘normal’ fluctuations or the beginnings of real declines. Specifically the application of WeBS Alerting procedures to the data would allow objective and consistent analysis of the long-term waterbird trends. This monitoring will be carried out as part of the standard WeBS Alerting procedure for Gadwall and Shoveler.
Additional counts on the component sites within the SPA during months outside of the standard index months would allow greater precision in the analysis of potential phenological changes and temporal shifts in peak counts. However, encouraging enough counters to obtain these data may prove difficult.
Finally, detailed research at the component SSSIs issued with species Alerts in this report may help to explain any causative factors behind the long-term declines at sites. For instance, information on water levels, vegetative growth and chemical composition could prove useful, as would further quantification of recreational disturbance. Furthermore, assessment of movements of wildfowl both within component sites of the SPA and to areas beyond the SPA boundaries would facilitate greater understanding of waterbird trends. Colour ringing schemes and / or radio tracking of individuals could prove beneficial.
4.5 Specific Conclusions in Relation to Aims
• Smoothed trends for all three species examined did not show any long-term declines at the SPA level. One Medium Alert was fired, for Shoveler over five years, but this should be interpreted with caution as the WeBS Alert system biological filter suggests that such variation is within the range of ‘normal’ variation. • At the SSSI / sector combination level, High Alerts for ‘all time’ were fired for Gadwall on three sites, Shoveler on one site and Tufted Duck on two sites, in response to declines greater than 50%. Various shorter-term High Alerts and several Medium Alerts were also triggered at specific sites. • Various caveats should be considered during interpretation. Short-term Alerts for all three species, plus ten-year Alerts for Gadwall, are subject to caution according to the WeBS Alert biological filter, which accounts for ‘acceptable’ population fluctuations. Also, declines should be viewed in the light of SPA and (where applicable) SSSI trends.
BTO Research Report No. 361 61 April 2004 • Histograms of the occurrence of peak mean counts across all SSSIs revealed little evidence of shifts in timing of peak counts. Most peak counts occurred inside the standard WeBS index window, therefore apparent declines are unlikely to be due to excluded data. • Calculation of the timing of peak mean counts at SPA and national levels showed that within the standard indexing months, there was little difference between timings of peak counts over the period assessed. • Although not directly inferred from this report, negative effects of human disturbance on waterbirds cannot be ruled out. Recreational disturbance measured by the Wetlands Advisory Service (2003) at Thorpe Park and Wraysbury II Gravel Pits is a consideration in interpreting species trends at these waterbodies.
BTO Research Report No. 361 62 April 2004 Acknowledgments
We wish to thank Sam King at English Nature for project guidance. We are very grateful to Niall Burton for comments, and Heidi Mellan for secretarial support.
WeBS is a partnership between the British Trust for Ornithology, The Wildfowl & Wetlands Trust, Royal Society for the Protection of Birds and the Joint Nature Conservation Committee (on behalf of English Nature, Scottish Natural Heritage, Countryside Council for Wales and the Environment and Heritage Service in Northern Ireland. Data used in this report would not have been collected but for the sterling efforts of the counters involved.
BTO Research Report No. 361 63 April 2004 BTO Research Report No. 361 64 April 2004 References
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BTO Research Report No. 361 66 April 2004 Appendix 1. Summary table of site names and codes. Sites in italics are excluded from the SPA.
SSSI WeBS Subsite WeBS Grid code Reference Staines Moor King George VI Reservoir 23102 TQ0473 Staines Reservoirs: North Basin 23106 TQ050736 Staines Reservoirs: South Basin 23107 TQ053727 Knight & Bessborough Knight & Bessborough 23118 TQ121681 Reservoirs Thorpe Park No. 1 Gravel Pit Thorpe Park: 1 23717 TQ030680 Thorpe Park: 7 23712 TQ026685 Thorpe Park: 6 & 9 23718 TQ025684 Kempton Park Reservoirs Kempton Reservoir East 24103 TQ118708 Redhouse Reservoir 24104 TQ121702 Wraysbury Reservoir Wraysbury Reservoir 23101 TQ025745 Wraysbury & Hythe End Gravel Wraysbury II (North) Gravel Pit 28209 TQ010738 Pits Wraysbury II (South) Gravel Pit 28210 TQ008733 Yeoveney Lake 28717 TQ018732 County Ditch Lake 28716 TQ019732 Wraysbury No. 1 Gravel Pits Wraysbury I Gravel Pit (North) 28207 TQ002750 Wraysbury I Gravel Pit (South) 28208 TQ005745
BTO Research Report No. 361 67 April 2004 BTO Research Report No. 361 68 April 2004 Appendix 2. All counties and administration areas intersecting the EA Thames region. Those areas included in analysis marked ‘Y’, those excluded marked ‘N’.
County District Included? Bedfordshire South Bedfordshire N Bracknell Forest Y Buckinghamshire Aylesbury Vale Y Buckinghamshire Chiltern Y Buckinghamshire South Bucks Y Buckinghamshire Wycombe Y Essex Brentwood Y Essex Epping Forest Y Essex Harlow Y Essex Uttlesford Y Gloucestershire Cheltenham N Gloucestershire Cotswold N Gloucestershire Tewkesbury N Greater London Barking & Dagenham Y Greater London Barnet Y Greater London Bexley Y Greater London Brent Y Greater London Bromley Y Greater London Camden Y Greater London City of London Y Greater London City of Westminster Y Greater London Croydon Y Greater London Ealing Y Greater London Enfield Y Greater London Greenwich Y Greater London Hackney Y Greater London Hammersmith & Fulham Y Greater London Haringey Y Greater London Harrow Y Greater London Havering Y Greater London Hillingdon Y Greater London Hounslow Y Greater London Islington Y Greater London Kensington & Chelsea Y Greater London Kingston upon Thames Y Greater London Lambeth Y Greater London Lewisham Y Greater London Merton Y Greater London Newham Y Greater London Redbridge Y Greater London Richmond upon Thames Y Greater London Southwark Y Greater London Sutton Y Greater London Tower Hamlets Y Greater London Waltham Forest Y Greater London Wandsworth Y
BTO Research Report No. 361 69 April 2004 Appendix 2. Continued.
County District Included? Hampshire Basingstoke & Deane N Hampshire East Hampshire N Hampshire Hart Y Hampshire Rushmoor Y Hampshire Winchester N Hertfordshire Broxbourne Y Hertfordshire Dacorum Y Hertfordshire East Hertfordshire Y Hertfordshire Hertsmere Y Hertfordshire North Hertfordshire N Hertfordshire St Albans Y Hertfordshire Stevenage Y Hertfordshire Three Rivers Y Hertfordshire Watford Y Hertfordshire Welwyn Hatfield Y Luton N Northamptonshire Daventry N Northamptonshire South Northamptonshire N Oxfordshire Cherwell N Oxfordshire Oxford N Oxfordshire South Oxfordshire N Oxfordshire Vale of White Horse N Oxfordshire West Oxfordshire N Reading Y Slough Y Surrey Elmbridge Y Surrey Epsom & Ewell Y Surrey Guildford Y Surrey Mole Valley Y Surrey Reigate & Banstead Y Surrey Runnymede Y Surrey Spelthorne Y Surrey Surrey Heath Y Surrey Tandridge Y Surrey Waverley Y Surrey Woking Y Swindon N Thurrock N Warwickshire Stratford-on-Avon N West Berkshire N West Sussex Chichester N West Sussex Crawley N West Sussex Horsham N West Sussex Mid Sussex N Wiltshire Kennet N Wiltshire North Wiltshire N Windsor and Maidenhead Y Wokingham Y
BTO Research Report No. 361 70 April 2004 Appendix 3. Site map of South West London Waterbodies SPA. Component SSSIs numbered by WeBS codes, as outlined in Appendix 1.
North
BTO Research Report No. 361 71 April 2004 BTO Research Report No. 361 72 April 2004 T eerhRpr o 6 BTO ResearchReport No.361 A p Appendix 4. Table of Alerts based on all data from the months September – March, for 15 site consolidations. Figures are percentage change in smoothed ril 2004 index.
GADWALL SHOVELER TUFTED DUCK FiveYear TenYear AllTime FiveYear TenYear AllTime FiveYear TenYear AllTime Staines Moor 226 130 158 -32 45 45 -63 -24 -27 Knight & Bessborough Reservoirs 229* x >1000* -72 x 22 -36 x 42 Thorpe Park Number 1 Gravel Pit -24 x -61 400* x x 21 x -7 Kempton Park Reservoirs -7 382 382 336* >1000 ** -73 -75 -75 Wraysbury Reservoir 150* 400* 400* -91 -92 -95 -23 -40 -6 Wraysbury & Hythe End Gravel Pits1 27 363 588 5 386 750 -34 0 24 Wraysbury Number 1 Gravel Pits -26 x 0 50* x -21* -7 x 31 Wraysbury Number 1 Gravel Pits (North) x x 22* x x x x x x Wraysbury Number 1 Gravel Pits (South) x x 7* x x 60 x x 88 Wraysbury II (North) Gravel Pit -44 x -67 7 x 33 -25 x -56
73 Wraysbury II (South) Gravel Pit 93 x 167 100* x 367* -34 x -15
Yeoveney Lake -68* x -63* 127 x 257 -1 x 3 County Ditch Lake 58* x -10* 180* x -59* -10 x -20 Wraysbury & Hythe End Gravel Pits2 35 x 26 36 x 100 -28 x -48 Wraysbury & Hythe End N & S and Wraysbury Number 1 Gravel Pits 16 x 22 32 x 32 -21 x -29
Shaded figures indicate changes in Alert status when compared with standard Alerts. A cross appears where data were insufficient for analysis. Figures in italics show Medium Alerts (a decline of 25%-50%), whilst bold figures show High Alerts (>50% declines). All Time refers to the period 1989/90-2000/2001.
*indicates calculations based on a total average count of less than 25 birds, that should be interpreted with caution. ** indicates that an Alert cannot be generated as the initial or final index value was zero. 1Includes Yeoveney Lake and County Ditch Lake. 2Excludes Yeoveney Lake and County Ditch Lake.
BTO Research Report No. 361 74 April 2004