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NETWORK International Conference
Integrated Management of Urban Canada Geese
Author: Mr Mark Underhill, Gwent Levels Project Officer, Countryside Council for Wales
Wandsworth Borough Council (WBC) was awarded funding by the European Commission to restore (improve the water quality, landscaping and decrease bankside erosion) three urban park lakes in Wandsworth (Battersea Park Lake, King George's Park Lake and Tooting Common Lake): The London Lakes Project (WBC 1997). The project was divided into six distinct Phases. Phase 1&2 Landscaping; Phase 3 Waterbird Monitoring and Management; Phase 4 Fish Management; Phase 5 Water Quality Monitoring and Management; and Phase 6 Dissemination of Results. WWT Wetlands Advisory Service were contracted to undertake Phase 3, the aim of which was to determine the use of the study area by waterfowl in order to provide advice to project partners to limit the impact of waterfowl on the study sites.
Studies were designed to collect data on all waterfowl present. However, emphasis was placed on the collection of detailed information on Canada Geese (Branta canadensis) as they were perceived as a "problem". Canada Geese can cause problems to wetland site managers in two ways. 1) Goose faeces, when deposited in the water can make a significant contribution to the problem of eutrophication (Manny 1975). 2) Canada Geese are large herbivorous birds and can limit marginal and bankside vegetation through grazing and damage to soil structure through puddling (walking on) bare soil and planted areas on the lake banks (Clark & Jarvis 1978, White-Robinson 1984, Conover & Decker 1991, Harradine 1991, Allan et al. 1995).
Earlier studies of the use of the site by waterfowl confirmed the councils view that Canada Geese potentially contributed to the problem of eutrophication by depositing relative large amounts of phosphorous rich faeces into the lake (Underhill1994). The same studies indicated that Canada Geese spend more time on the lake banks and on the amenity grassland beside the lake, relative to other native wildfowl species, thereby contributing to the problem of bankside erosion. Similarly, other feral and exotic wildfowl, in particular domestic X Greylag Geese and Muscovy, were seen to be in conflict with the projects objectives. These domestic crosses were largely sedentary at Battersea Park (Underhill 1994), and so, although not as numerous as Canada Geese, the grazing and trampling pressure exerted on the banks was continuous throughout the year. In order to meet the water quality and landscaping objectives of the project it was considered necessary by the project partners to reduce the number of Canada Geese and other feral and exotic waterfowl using Battersea Park Lake.
Techniques available to reduce the use of a site; or damage caused by Canada Geese fall into two categories (Allan et al. 1995). Site-based management: (through scaring, use of chemical repellents, physical exclusion and/or habitat management); and population control: (by prevention of egg hatching, shooting, culling at the moult, culling at other times and relocation).
A review of the scientific literature (Allan et al. 1995) and experience from WWT Wetlands Advisory Service, suggested that none of the above methods, used in isolation, was likely to be successful. At the time the London Lakes project was being set up, a new approach to Canada Goose management was being advocated; combining management techniques, tailored to the nature of the site, type of damage occurring and the population biology of the local birds; and termed an Integrated Management Strategy (IMS) (Allan et al. 1995).
The IMS approach had not, as far as WWT were aware, been used in management of Canada Geese. Thus, WWTs work in Wandsworth, provided an ideal situation to test the effectiveness of this approach in a practical demonstration project.
The aim of the work at Battersea Park was to reduce the numbers of Canada Geese using the park through techniques that were economically sustainable and politically acceptable to Wandsworth Borough Council.
Assessing The Use Of Battersea Park By Geese
To devise an IMS for a site or area one first needs to assess what habitat factors were attracting Canada Geese to the site; and how these changed over time (daily and seasonally).
The distribution and behaviour of geese on the site were studied during three separate study periods: breeding season (April-May), moult period (late June-early July), and the non-breeding season (November). These were chosen to sample the birds use of the site at key points during their annual cycle, when it was anticipated they would have very different habitat requirements.
For the purpose of this study, Battersea Park Lake was divided into 54 sectors (Figure 1) determined subjectively by the degree of disturbance, the amount of artificial feeding opportunity and the presence or absence of areas where waterfowl naturally enter and leave the lake. The position of Canada Geese was mapped in relation to the sectors described above at dawn, midday and dusk on four separate dates during each of the three seasons (12 scans per season). An overview of the daily and seasonal variation in waterfowl distribution was calculated as the mean number of Canada Geese in each sector at dawn, midday, and dusk.
Developing an IMS For Battersea Park
The number and distribution of Canada Geese around the lake; and their daily and seasonal variation were use to infer which aspects of the park habitat were attractive to geese (islands for nesting sites, amenity grassland for grazing, supplementary feeding by the visiting public). Subsequently, site-based management (designed to reduce the carrying capacity of the site); and population control measures (to reduce the number of birds using the site, and to limit recruitment); were selected to form an IMS for the park.
Measuring the Success of the IMS
Twice monthly waterfowl counts were undertaken at Battersea Park and nine adjacent parks and open spaces in central London (Regents Park, Hyde Park, Kensington Gardens, St. James Park, Buckingham Palace Gardens, Clapham Common Ponds, King Georges Park and Tooting Common Lakes) from the start of the project in 1994. These counts allowed WWT Wetlands Advisory Service to monitor the number of individual species and species groups in the study area. The effectiveness of the IMS was measured by comparing data from these waterfowl counts before and after the implementation of IMS. Comparisons were made across three groups: Canada Geese, native waterbirds (wildfowl, grebes and rails), and other feral, exotic and hybrid waterbirds (typically Greylag and Mallard type domestic hybrids).
Comparisons were made with peak monthly counts and the mean of the 24 (twice-monthly) counts undertaken in each year (annual mean). The results from Battersea Park were placed in a local population context by comparing them with the summed counts from other local parks (excluding Battersea Park Lake): Hyde Park, Kensington Gardens, King Georges' Park, Clapham and Wandsworth Commons. Counts from Buckingham Palace Gardens and St. James' Park were not used as waterfowl counts were not available for these sites in 1994.
Counts at Battersea Park started in January 1994 and continued until December 1995. Some site management associated with IMS took place during 1994. However, most was undertaken after July when the Canada Geese had left Battersea Park (to winter at other nearby parks). Therefore, "before" and "after" IMS comparisons at Battersea Park were made on count data collected from January-December 1994 "before IMS" and January-December 1995 "after IMS".
NUMBER AND DISTRIBUTION OF CANADA GEESE IN BATTERSEA PARK : 1994
The number of Canada Geese using Battersea Park changed considerably during the year, with the largest concentrations of birds present during the breeding season (average of 209). By the time of the moult, at the end of the breeding season, average numbers had fallen to 125. There was, however, a far more dramatic decrease in numbers between the breeding and winter season when an average of just 16 birds were present.
The seasonal changes in numbers were accompanied by equally dramatic changes in distribution. During the breeding season, distribution was characterised by large numbers of birds on the islands and in the park. In particular, Duck and Heron Island and areas of amenity grassland adjacent to these islands were heavily used (Fig 2). Further examination of the daily patterns at this time indicated heavy use of the islands at midday and dusk; and of the park at dawn and dusk (Fig. 3). There were marked changes in overall distribution at the time of the moult in June and July (Fig 2). Most notably, a reduced use of the park-land areas and a generally more concentrated distribution of birds on open water areas. Daily patterns indicate the most heavy use of parkland only at dawn, with most birds spending the remainder of the day on the open water. Canada Geese, in common with all waterfowl, become flightless for a period of about two weeks at the end of the breeding season, when they moult and then re-grow all their main flight feathers. The distribution of geese during this period probably reflected the reluctance of flightless birds to leave the relative safety of the open water. Few Canada Geese used Battersea Park Lake during the winter (Fig 2). The birds that did use the lake were mainly confined to the water, with no birds seen on the islands and few on the mainland.
INFERRED HABITAT USE AT BATTERSEA PARK
The concentrated use of Battersea Park Lake by Canada Geese during the spring, described above, suggested that the main factor attracting Canada Geese to the site was breeding habitat in the form of large vegetated islands on which the geese nested.
Access to grazing is obviously important to geese. However, unlike many London Lakes which are surrounded by areas of amenity grassland, Battersea Park Lake is surrounded on most sides by shrubberies and mature trees. Thus grazing is limited to areas to the south of the lake and north of Duck Island (Fig 1). These areas lie approximately 50m and 100m, respectively from the lake edge. Access and the vista, back to the water is restricted in both areas, being particularly poor from the south grazing areas.
The real and potential threat to geese from the public and their dogs whilst grazing away from the waters edge was thought to limit access to the main areas of amenity grassland to dawn and dusk during the spring and summer, when it was light for one or two hours before the park was open. The small areas of amenity grassland and restricted times when it was "safe" to graze these areas was probably a factor limiting the number of geese that the site could support. Geese compensated to a certain extent by taking food from the public and this was recognised as an additional attraction to geese.
In summary, these provided WWT and the site managers with a number of factors that attracted geese to the site (positive factors) and that limited the number of birds that the site could support (negative factors). An IMS for the site would look at the complete range of site and population based management available, selecting those that accentuated the negative aspects and eliminated the positive aspects. Where possible a range of actions addressing various aspects of these factors would be used.
Exclude Geese from the islands
Canada Geese were excluded from all of the islands on Battersea Park Lake by fencing. One metre high, 25mm 20 gauge galvanised chicken wire was erected as close to the water as possible. A gap of 100mm was left underneath the wire to allow other waterbirds access to the islands. Geese were generally reluctant to fly over the fence because there were mature trees and shrubs directly behind the wire. Prior to the placement of the fence, geese simply walked onto the island.
Reduce food availability
Working with the landscape architects the Wetlands Advisory Service were able to achieve five management aims in conjunction with the planned amenity and aesthetic aims of the landscaping.
The first two actions directly reduced the extent of available grazing land. The third reduced the attractiveness of the remaining grassland as geese will preferentially graze areas with good visibility and access to open water on which to escape predators (Conover and Kania 1991). The last two actions reduced the opportunities for the public to feed the geese
The visiting public were discouraged from feeding the geese via a programme of education and public relations.
Adult Culls and Egg-pricking
A total of 154 Canada Geese were culled under Department of the Environment (DoE) licences during May 1994. Prior to the fencing the islands, a total of 66 Canada Geese clutches were prevented from hatching by egg-pricking under DoE license in 1994. Following the fencing of islands during the 1994/95 winter very few geese were able to gain access to the islands. However, in order to maintain zero production at the site egg-pricking was continued under licence, and in 1995 a total of six clutches were destroyed.
THE SUCCESS OF IMS AT BATTERSEA PARK
Up to 332 Canada Geese were counted at Battersea Park Lake during the 1993 breeding season and numbers were approaching that level in May 1994 (Fig. 4). However, before numbers were allowed to reach their natural maximum a total of 154 birds were culled by WBC. This left potentially 108 birds on the site during the breeding season 1994. The remaining management prescriptions for the IMS took place in late 1994, after most of the Canada Geese had left the site for the winter.
Numbers of Canada Geese using the lake were considerably reduced in 1995 compared to 1994 (Fig. 4). The peak count in 1995 was 63, a 76% decrease on the 262 birds counted in 1994. The mean annual count of Canada Geese using the site also fell by 61% from 74 in 1994 to 29 in 1995.
Peak counts within the Battersea Park sub-population also fell from 451 in 1994 to 341 in 1995, as did the annual mean (333-267) (Fig. 4). However, despite the continued egg-pricking and culling programme within the Royal Parks, the reductions in Canada Goose numbers within the sub-population represented only a 20-26% drop, far less than the 61-76% decreases achieved at Battersea Park Lake.
Other Feral and Hybrid Species
Counts in excess of 60 feral and hybrid species were not uncommon at Battersea Park Lake during 1994 (Fig 5), the peak being 85 birds in January 1994. These counts included up to six species of feral or non-native waterfowl (Black Swan, Pink-footed Goose, Brent Goose, Greylag Goose, Canvas Back and Muscovy). However, Greylag Goose and Muscovy hybrids were the most numerous species, accounting for an average 60 and 15% respectively of the monthly totals. These birds undoubtedly contributed to the problem of eutrophication and trampling and 34 Greylag X domestic geese and 6 Muscovys were removed from the site in July 1995. This has had the desired effect of reducing the number of feral and exotic species from over 50 birds to between 10 and 18 at the end of 1995 (Fig. 5).
Counts of feral species at other sites in the Battersea Park sub-population were much more variable than at Battersea Park Lake (Fig 5). This was because most (85%) of these birds were feral Greylag Geese, which unlike the domestic hybrids found at Battersea Park, are able to fly and thus ranged over other sites in the Core Area. The increase in peak feral bird counts in the Battersea sub-population from 96 in 1994 (85 Greylags) to 123 in 1995 (114 Greylags) (Fig. 5) is indicative of the continued spread of Greylag Geese in Central London. The Battersea Park IMS was effective in removing Greylag hybrids from Battersea Park in 1994, and there was no sign of re-colonisation in 1995 (Fig. 5). However, the long-term effectiveness of IMS in the face of a colonising species has yet to be tested.
Counts of native wildfowl, rails and grebes at Battersea Park Lake indicated an increase in both the annual mean (141-190; 35%) and the annual peak count (288-357; 24%) between 1994 and 1995 (Fig. 6). Both dabbling and diving waterfowl numbers increased (Table 1), particularly Mallard (44%), Shoveler (357%) and Tufted Duck (78%).
This increase in use of Battersea Park Lake by native wildfowl was not duplicated across other sites in the sub-population where the peak count fell from 594 to 456, a drop of 23%. The annual mean also fell, though not quite so dramatically from 366 to 342 birds (7%) (Fig. 6).
The results of the waterfowl monitoring at Battersea Park Lake and other sites in the study area indicate that the IMS has been an unprecedented success. Canada Goose numbers have been reduced by 61-76% and other feral and exotic birds by 60-79%. Over the same period the there has been a 24-35% increase in the use of Battersea Park Lake by native waterfowl. Comparison with the number of birds on sites outside the park indicate that in all cases the trends in Battersea Park have been the reverse of trends elsewhere. In other words, the management put in place at Battersea Park has effectively reduced the use of the site by feral and exotic species in the face of increasing problems at other nearby sites.
The effectiveness of IMS is further demonstrated by the lack of success of ad hoc management at other sites in the Core Area. Discussions with managers of the Royal Parks indicate that egg-pricking and in most cases, adult culls have been taking place at Hyde Park, St. James Park and Buckingham Palace Gardens, throughout the course of this project (S. Richards and D. Clarke pers. comm.). Furthermore, fences erected around the islands on lakes at Wandsworth Common and Tooting Bec in 1995, have been totally ineffective in reducing either the use of the site, or indeed the islands themselves by geese (J. Allan pers. comm.). These anecdotal observations, provide further evidence that single management options applied in isolation are ineffective in reducing the use of a site by Canada Geese. The single options described above were part of the components the Battersea Park IMS. This adds further credence to the theory of IMS, demonstrating that the whole (integrated strategy) is more effective than the sum of its constituent parts.
A further important note to the IMS at Battersea Park is that Canada Goose numbers have been reduced without recourse to further culls. The open nature with which management has been carried out, the lack of culls, the increase in abundance and diversity of native waterfowl and the improved aesthetic value of the site has resulted in a more positive perception by the local public to the councils management of the park.
The work described has demonstrated that there are solutions to the Canada Goose problem that do not require continued economic input other than management involved with site maintenance. In this sense they are considered to be economically sustainable by WBC. This combined with the lack of a need for ongoing culls, means that the solutions are also politically acceptable.
This study has shown that reducing Canada Goose numbers through IMS at a site level is possible. More work is now required to validate this technique across a wider range of sites, used in different ways and in different seasons.
Allan, J.R., Kirby, J.S. & Feare, C.J. 1995. The biology of Canada Geese (Branta canadensis) in relation to the management of feral populations. Wildlife Biology. 1;3: 129-143.
Clark S.L. & Jarvis R.L. 1978. Effects of winter grazing by geese on yield of rye grass seed. Wildlife Society Bulletin. 6: 84-87.
Conover M.R. & Kania G.S. 1991. Characteristics of feeding sites used by urban-suburban flocks of Canada Geese in Connecticut. Wildl. Soc. Bull.. 19: 36-38.
Conover M.R. & Decker D.J. 1991. Wildlife damage to crops: perceptions of agricultural and wildlife professionals in 1957 and 1987. Wildl. Soc. Bull. 19:46-52.
Harradine J. (Ed.). 1991. Canada Geese: problems and management needs. British Association for Shooting and Conservation, Rossett.
Manny B.A., Wetzel R.G. & Johnson W.C. 1975. Annual contribution of carbon, nitrogen and phosphorous by migrant Canada Geese to a hardwater lake. Verh. Internat. Verein. Limnol. 19: 949-951.
Underhill, M.C. 1994. London lakes rehabilitation project. Phase 3: waterfowl management. End of year report 1994. Unpublished WWT Wetlands Advisory Service report to Wandsworth Borough Council.
Underhill, M.C. & Hughes, B. 1997. London lakes rehabilitation project. Phase 3: waterbird monitoring and management. Final technical report 1994. Unpublished WWT Wetlands Advisory Service report to Wandsworth Borough Council.
WBC. 1997. An approach to urban lake restoration. Proceedings of the London lakes project conference: March 1997. WBC, Wandsworth.
White-Robinson R. 1984 . The ecology of Canada Geese in Nottinghamshire, and their importance in relation to agriculture. Ph.D thesis, University of Nottingham.
Table 1: The change in mean annual count of native waterfowl at Battersea Park Lake following the application of IMS (1994-1995).
WWT Wetlands Advisory Service
Tel: 01453 890333 Ext. 274
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