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FINAL SUMMARY REPORT
Contents
2. Introduction
3. Site Access
5. Control Trial, Western Midlands
7. Control Visits Outwith Trial Areas
8. Efficiency of Control by Shooting, Breeding Season
9. Efficiency of Control by Shooting, Post-breeding and Winter Period
10. Trapping
13. Modelling Population Response to Control
14. Conclusion
1.1 The regional Ruddy Duck Control Trial was established to determine the feasibility, costs and access requirements necessary to reduce the U.K. ruddy duck population to less than 175 birds in ten years. This figure was chosen as representing a 95% reduction in the estimated population of 3,500 at the time of the decision to proceed with regional trials. It was decided at that time that data from regional trials would not provide sufficient information on the population dynamics of ruddy ducks at very low densities to allow any determination of the feasibility, costs and access requirements for complete eradication. The trial took place on Anglesey, in the Western Midlands, and Fife. Limited winter control also occurred in Avon, Leicestershire, and Northamptonshire, and limited breeding season control (by trapping) took place in Gloucestershire.
1.2 A report by the Wildfowl and Wetlands Trust (WWT Wetlands Advisory Service, 2002) suggests that the U.K ruddy duck population was 5,946 in January 2000, with 95% confidence that the total lies between 5,407 and 6,733. A total of 2,651 ruddy ducks were culled between 16 April 1999 and 10 May 2002. Of these, 2,634 were controlled by shooting and 17 by trapping. The total number consists of 751 females, 1,137 males and 763 immature birds.
1.3 On Anglesey the aim of the trial was to reduce the breeding population by a minimum of 70% within three years. The original breeding population of 200 birds was reduced by over 70% within a year and by an estimated 93% within 16 months.
1.4 In the Western Midlands the aim was to reduce the immediate pre-breeding population by the maximum amount possible. Counts on a sub-set of 17 sites showed reductions of 28% in the first twelve months. Counts on a sub-set of 23 sites showed a further 54% reduction in the second twelve months of the trial, giving an overall reduction of 66% in the first two years of the trial.
1.5 The aim of the trial in Fife was to kill the maximum number of the post-breeding population. A total of 216 ruddy ducks were culled in Fife.
1.6 Permission to carry out control of ruddy ducks was sought on a voluntary basis for 153 sites. Of 193 landowners and other interested parties contacted, 58% gave permission for control. Access to carry out control was granted for 52% of the 153 sites. Control by shooting was allowed on 48% of all sites, with control by trapping on a further 4%.
1.7 Effective control proved feasible on breeding sites and on a range of post-breeding and wintering sites. On average 47% of the ruddy ducks present on breeding sites were killed per visit. On post-breeding and wintering sites 1 km. sq. or less in extent, 54% of birds present were shot per visit on average while the comparable figure for larger waters is 19%.
1.8 Modelling suggests that the U.K. ruddy duck population can be reduced to fewer than 175 individuals using year-round control in between four and six years if access is available to the principal wintering sites. The likely cost of this reduction is between £3.6m and £5.4m.
2.1 The ruddy duck (Oxyura jamaicensis) is a native of North and South America and was introduced to wildfowl collections in the United Kingdom in the 1940s. However, a small number of birds escaped from captivity and began to breed in the wild. As the population of wild ruddy ducks in the UK has risen, so has the number of records of ruddy ducks on the European mainland. In 1983 ruddy ducks were recorded in Spain. By 1991 hybrids resulting from crosses between ruddy ducks and the globally threatened indigenous white-headed duck (Oxyura leucocephala) were recorded in that country. The two species hybridize readily, with the ruddy duck possessing the competitive advantage. This threat from the ruddy duck is now widely recognized as the most significant threat to the white-headed duck. The UK appears to be the main source of birds in mainland Europe and in 1992 the government decided to assess the feasibility of ruddy duck control in the UK.
2.2 Initial research into the feasibility of control was carried out by the Wildfowl and Wetlands Trust (Hughes, 1996). The conclusion of this report was that control was feasible but there was a need for verification via a regional trial. The White-headed Duck Task Force accepted this conclusion and the Central Science Laboratory was contracted by the Department of the Environment, Transport and the Regions (DETR) to carry out the work.
2.3 Three areas of the United Kingdom were chosen for the trial - Anglesey, Fife and the Western Midlands (defined as South Cheshire, Staffordshire, Shropshire, West Midlands Metropolitan County, and Warwickshire). In Anglesey and the Western Midlands a combination of breeding and non-breeding season control was carried out. In Fife control was limited to the autumn and early winter.
2.4 The principal objectives of the three-year trial were as follows.
- To monitor the effects of the Control Trial and model its effects on the population to assess whether sufficient ruddy ducks can be killed to reduce the population in the U.K. to less than 175 individuals in ten years. To assess the cost of achieving such a reduction.
- To reduce the immediate pre-breeding population in the Western Midlands by the maximum amount possible; to reduce the breeding population on Anglesey by the maximum possible but by a minimum of 70% within three years; to kill the maximum number of the post-breeding population in Fife.
- To conclude whether compulsory access to land will be necessary to ensure the success of any future national control strategy.
2.5 The trial began in April 1999 and ended in May 2002.
3.1. Permission to carry out control of ruddy ducks was requested for a total of 153 sites, with all but ten being in the Western Midlands or on Anglesey. A total of 193 owners and site users were approached and 58.0% of these gave permission to carry out control. A summary of the responses is given in Table 1. Permission was forthcoming to carry out control on 80 of the 153 sites (52.3%), In seven cases (4.6%) control was to be limited to the use of traps. Permission was gained for many of the most important breeding sites in the trial area and almost all of the most important post-breeding and wintering sites.
Category Permission granted Permission refused No definitive reply received Percentage of positive replies Private individuals 65 24 25 57.5 Private estates 16 2 2 80.0 Companies 13 3 4 65.0 Local government 5 4 4 38.5 Non-departmental public bodies 4 0 1 80.0 Other organisations e.g. angling clubs, Wildlife Trusts 9 7 5 42.9 TOTAL 112 40 41 58.0 Table 1 Summary of responses to request to carry out control of ruddy ducks
4.1 Estimated Initial Breeding Population and Aims
4.1.1 Eighty waters on Anglesey were visited in April 1999 to carry out a count of all the ruddy ducks present on the island at the start of the breeding season and before the start of the Control Trial. The resultant population estimate was around 200 adults. However, monitoring of sites in 2000 showed clearly that immigration of ruddy ducks on to Anglesey occurred during most months, with the exception of those in spring (April, May and June) and mid-winter (January and February). One of the stated aims of the trial was to reduce the breeding population of ruddy ducks on Anglesey by the maximum possible, but by a minimum of 70% within three years. This 70% reduction is thus represented by a remaining population of 60 ruddy ducks.
4.2 Control Measures and Effect on Population
4.2.1 A total of 149 control visits were made on Anglesey and 515 ruddy ducks shot on 17 sites. Breeding season control (defined as 1 March to 31 August) was responsible for 373 birds being shot and a further 142 were shot in the post-breeding/winter period. The total is made up of 158 females, 225 males and 132 immature birds.
4.2.2 In the first year of the trial 322 birds were shot, of which 255 were adults. A count at the end of March 2000 of all the potential ruddy duck sites on the island found a total of only 52 birds. This represented a reduction of 74% on the population in April 1999.
4.2.3 During the second year of the trial, a total of 173 ruddy ducks were culled on Anglesey, including 114 adults. The minimum number present on the island was between late June and late July 2000, when it is estimated that only seven adult females and seven adult males remained. This total of 14 adults represents a 93% reduction from the estimated original breeding population of 200. Control by shooting took place on only three occasions between October 2000 and the end of the trial (with 20 birds being culled) as a trap had been built on the main wintering site and the few birds remaining had to be maintained if the trap were to be tested fully.
4.2.4 A count of the main wintering sites on 16 January 2002 found a total of 41 birds.
5. Control Trial, Western Midlands5.1 Aims of Trial
5.1.1 The aim of the trial in the Western Midlands was to reduce the immediate pre-breeding population of ruddy ducks by the maximum possible.
5.2 Control Measures and Effect on Population
5.2.1 A total of 148 visits with control by shooting were made to 27 sites in the Western Midlands. A total of 1,715 ruddy ducks were culled using this method between May 1999 and May 2002. This total consists of 495 females, 743 males and 477 immature birds.
5.2.2 During the first twelve months of the trial 489 ruddy ducks were culled in the region. After the first year a comparison was made between maximum numbers of adult ruddy ducks present on a total of 17 sites where data was available for both the breeding season in 1999 (April to July) and for the same period in 2000. The results suggested a 28% reduction between years although this reduction was not statistically significant.
5.2.3 During the second twelve months of the trial 739 ruddy ducks were culled, 214 in the breeding season and a further 525 in the post-breeding/winter period. Counts carried out on 23 sites in the breeding season in spring 2001 allowed a comparison between 2000 and 2001. Peak counts for each site gave a total for all of 117 birds in 2000 compared to 54 in 2001, a reduction of 54%. The difference between the medians of the two samples is statistically significant (Wilcoxon's test for matched pairs, P<0.05).
5.2.4 Control in the Western Midlands was curtailed by the outbreak of Foot and Mouth disease during the 2001 breeding season. A total of only fifteen visits were made in July and August 2001 and 40 birds culled. A further 400 birds were shot in the post-breeding and winter periods and 47 in the 2002 breeding season to 2 May 2002.
6.1 Control in Fife was limited to the autumn and early winter and occurred in 1999, (one site) and 2000 (two sites). In 2001, control by shooting was limited to one site only as testing of a trap was taking place on the main post-breeding site. A total of 216 ruddy ducks were culled, all by shooting. This total consists of 33 females, 82 males and 101 immature birds.
7. Control outside Trial Areas7.1 A total of ten control visits were made to sites outside the trial areas in order to fully test methods of control on large wintering waters. A total of ten visits were made to four waters in Avon, Northamptonshire and Leicestershire. A total of 188 ruddy ducks (60 females, 75 males and 53 immature birds) were removed from these sites between 12 December 2000 and 16 February 2001.
7.2 In addition, a total of 17 ruddy ducks were caught and despatched during trapping trials in Gloucestershire in April and May 2002.
8. Efficiency of Control by Shooting, Breeding Season (March to August)8.1 Breeding season control by shooting was carried out on both Anglesey and in the Western Midlands. A total of 249 control visits were made at this time of year.
8.2 On average 47.3% (range 0-100%) of the ruddy ducks seen were shot on each visit, although in almost 15% of control visits no birds were killed. Many of these occurred on Anglesey in the 2000 breeding season when few birds remained and there were fewer opportunities for successful control.
9. Efficiency of Control by Shooting, Post-breeding/Winter Period
9.1 Post-breeding (autumn) control by shooting was carried out in Fife while both post-breeding and winter control was carried out in the Western Midlands and on Anglesey. Four to six Field Officers were usually involved and the birds shot by guns on the bank, or on the larger waters, from boats. With only a few exceptions, shotguns alone were used at this time of year.
9.2 The most effective form of control in terms of numbers killed was shooting at the major post-breeding/wintering sites in the trial area, where it proved possible to shoot up to 80 ruddy ducks per site visit.
9.3 Data from visits to small to medium sized post-breeding/wintering sites (i.e. those less than one square kilometre in extent) showed that on average 53.9% of the ruddy ducks present were shot per visit (range 8% to 92%, Figure 1).
Figure 1 Number of birds killed per visit, post-breeding and wintering sites less than 1 km sq.9.4 Many of the major wintering sites used by ruddy ducks are large reservoirs ranging from 1 km sq. to 12 km sq. in extent. A total of 21 control visits were made to four waters of this size during winter months, although in one case (two visits) shooting was limited to two bays and not permitted in the main body of water. A total of 651 ruddy ducks were shot on such sites. The results from these visits show that a smaller proportion of the ruddy ducks was killed per visit (Figure 2, mean 18.7%, range 1% to 56%). In part this is a reflection of the larger number of birds present on these lakes, but the evidence suggests that, even on these larger waters, effective control is feasible. Experience has shown that the ruddy ducks tend to remain within certain areas, even when shooting has started, and do not disperse across the whole site. This makes control easier as a smaller area has to be covered.
Figure 2 Number of birds killed per visit, post-breeding and wintering sites greater than 1 km sq.
10.1 Winter and Post-breeding Trapping
10.1.1 A funnel trap was tested in winter 2001/2002 on Anglesey. Although between 20 and 54 ruddy ducks were present close to the trap on the days it was tested, none were caught. Typically the birds flew in small groups towards the main part of the water and away from the trap when any attempt was made to herd them.
10.1.2 A trap similar in design to that on Anglesey was largely completed on a reservoir in the Western Midlands in autumn 2001. However, structural problems with the dam and low autumn rainfall meant that the water never reached normal levels and was well below those required to test the trap.10.1.3 Another trap was built and placed in a bay regularly used by ruddy ducks at the main post-breeding site in Fife in September 2001. Over a period of 20 days, no ruddy ducks were caught.
10.2 Breeding Season Trapping
10.2.1 A total of fourteen traps on three breeding sites in Cheshire and Gloucestershire were tested in April and May 2002. A total of 17 ruddy ducks were caught (twelve males and five females) on one site only, during a total of 226 trap days over the three sites.
10.3 Conclusion
10.3.1 The testing of traps on post-breeding and wintering sites failed to catch any ruddy ducks and the results suggest that trapping is unlikely to succeed in catching large numbers of birds.
10.3.2 Breeding season trapping proved successful on only one of three sites. It proved to be much less efficient than control by shooting, with a greater risk of non-target casualties (Section 12), but may prove an effective alternative to shooting on sites where this is not possible.
11. Effect of Artificial Decoys and Calls11.1. A trial was carried out on five sites in the Western Midlands in June and July 2000 with the aim of testing the effectiveness of pre-recorded male ruddy duck display calls and a combination of calls and artificial decoys (one of each sex) in attracting ruddy ducks closer to Field Officers.
11.2 Analysis of the results suggests that the use of artificial decoys and calls together may attract birds closer, but not within effective shotgun range (30m) or rifle range (100m). However, the use of the call only attracted a number of birds within effective shotgun range and proved to be an effective aid in controlling birds.
12.1 A total of six non-target species were shot during the trial. The total consists of two female tufted ducks (in September 1999 and November 2001), and one juvenile long-tailed duck (in November 2000) shot in error, and three incidents where birds flew into the line of fire (a swallow and two coots in April 2000, February 2001 and January 2002 respectively).
12.2 In addition to the birds mentioned above, a coot was killed by a dog collecting shot ruddy duck corpses in September 2000. Seven young mallard chicks and possibly an immature black-headed gull died after entering traps in April and May 2002.
12.3 The seven non-target species killed during control by shooting represent a non-target percentage of less than 0.3 during shooting operations. The eight non-target casualties lost during trapping represent a non-target percentage of 47 during trapping operations.
13. Modelling Population Response to Control13.1 A stochastic Monte Carlo simulation model was constructed to project the national ruddy duck population from January 2000 under a variety of strategies. Variables included efficacy per person (by how much each member of staff could reduce the national population by per year), numbers of staff, and changes in population growth rate. The mean time taken to reduce the U.K. ruddy duck population to less than 175 birds is between three and seven years. The model predicts that, given adequate site access, there is an 80% certainty that numbers can be reduced to the required level in between five and seven years.
14.1 The success of control on breeding, post-breeding and various sizes of wintering sites has led to a significant reduction in ruddy duck numbers regionally. Control using firearms was effective while trapping was ineffective in catching large numbers of birds. The scale of these reductions and the effort required to secure them suggest that the reduction of ruddy duck numbers to less than 175 individuals nationally is feasible within ten years. Population modelling suggests that year-round control would be the most effective approach. An assessment of the effect of the Control Trial on the national population suggests that there is an 80% probability that the population can be reduced to fewer than 175 birds in between five and seven years at a total cost of £3.9m to £5.5m.
14.2 The Control Trial has shown that access for the purpose of controlling ruddy ducks by shooting can be negotiated on a voluntary basis for around 50% of ruddy duck sites. There are likely to be in the region of 1,000 breeding sites nationally, but the birds concentrate in large numbers on a limited number of sites during the post-breeding and winter periods. Access to these concentrations (approximately 40 sites in total) would be crucial to the acceptable progress of an eradication scheme.
Central Science Laboratory
York. YO41 1LZ
7 June 2002
REFERENCESHughes, B. 1996. The Feasibility of Control Measures for North American Ruddy Ducks Oxyura jamaicensis in the United Kingdom, June 1996. Report to the Department of the Environment, Contract Number CRO 123
WWT Wetlands Advisory Service, The Winter Status and Distribution of Ruddy Ducks in The U.K. 1966/67-1999/2000, March 2002. Report to the Department of the Environment, Food and Rural Affairs.
Further information regarding ruddy ducks can be found at the following links:
- The feasibility of control measures for North American ruddy ducks Oxyura
jamaicensis in the United Kingdom.
http://www.defra.gov.uk/wildlife-countryside/scientific/ruddy/index.htm
- White Headed Duck Task Force - Recommendations for action within the UK
to conserve the globally threatened White-headed duck.
http://www.defra.gov.uk/wildlife-countryside/whd/index.htm
Published 26 July 2002
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