Review of urban gulls and their management in Scotland: a report to the Scottish Executive

Author(s): Calladine, J.R., Park, K.J., Thompson, K. & Wernham, C.V.

Published: January 2006  

Publisher: Scottish Executive

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This project aimed to: (i) produce the most up to date review possible of the size and distribution of urban gull colonies in Scotland, and whether they have changed in recent years; (ii) review current scientific knowledge of the ecology of urban gulls and the reasons they are attracted to Scottish towns and cities; (iii) review management practices used in Scotland and elsewhere and the scientific evidence for, and specific contexts associated with, their success or failure; (iv) establish the extent of perceived problems associated with urban gulls across Scotland, with specific regard to the perceptions and roles of Scottish Local Authorities; (v) review current legislation and powers related to urban gull issues and their perceived effectiveness; (vi) advise on standard best practice guidance for Local Authorities (the contexts in which certain types of mitigation measure are likely to be effective based on current scientific evidence); and (vii) make suggestions for further research needs on urban gull issues in Scotland. The project did not have a remit to assess the extent to which urban gulls are perceived as a problem by the overall Scottish urban population. Nor did it have a remit to advise whether actions to mitigate urban gull problems should be carried out, or to provide guidance on control for any specific locations.

The aims of the project have been achieved by a combination of: (i) literature searching and review; (ii) face-to-face consultations with representatives from Scottish Local Authorities and experts in the fields of gull research, gull control and legislation; and (iii) a questionnaire survey of every Local Authority in Scotland.

A questionnaire survey (completed largely by Environmental Health Department (or equivalent) representatives for every Local Authority in Scotland) demonstrated that there is a widespread perception within these Departments that problems with urban gulls exist. Of the 32 Local Authorities that completed the survey, 27 reported known local populations of urban gulls and 25 reported problems associated with those populations (based largely on a combination of complaints received from the public, reports from colleagues/Councillors and their own general perceptions). Of the 27 that reported known local urban gull populations, 20 felt that gull numbers within their urban areas had increased in the last 10 years (based on a similar combination of information sources). Also based on the survey, aggressive behaviour (mostly restricted to the breeding season), followed by noise, littering and fouling by droppings (largely during the breeding season but also during the winter months in some areas), were perceived as the greatest problems caused by urban gulls, both in terms of frequency of occurrence and severity. The questionnaire survey and follow-up consultations also provided information on Local Authority perceptions about: the effectiveness of various control methods; waste strategies; reasons for the attraction of gulls into urban areas; and the legislation and powers available to Local Authorities to take action if required. The questionnaire survey was not designed to show the extent to which the Scottish population as a whole perceives urban gulls as a problem: a broader survey of members of the public living and working in urban areas would be required to demonstrate whether a wide-scale problem exists.

Numbers of urban gulls in Scotland were obtained from the Joint Nature Conservation Committee's 'Seabird 2000' survey database (surveys carried out in 1998-2002 plus some additional material), supplemented by information provided directly by Local Authorities and that from other more local sources (local and Scottish Bird Reports, independent reports). For the purposes of this study, we evaluated information from breeding sites classified as 'urban' by JNCC, and also any gulls nesting on the roofs of buildings (with the exception of e.g. derelict buildings on uninhabited islands). Five species of gull have populations in Scotland that breed in urban areas, the current sizes of which have been estimated as (Apparently Occupied Nests): Herring Gull (6,202 AONs); Lesser Black-backed Gull (4,309 AONs); Common Gull (1,656 AONs); Black-headed Gull (1,391 AONs); Great Black-backed Gull (337 AONs). The review discusses in some detail the caveats associated with these estimates and concludes that they may be underestimates, based on: (i) limitations to counting methods (the problems of counting gulls in general, and specifically in urban environments); (ii) a limited number of comparisons between Seabird 2000 and more local survey data; and (iii) the perceptions of some Local Authorities. There are no comprehensive counts available of the numbers of gulls using urban areas outside of the breeding season.

Herring Gulls breeding in urban areas are concentrated in the east-coast towns and cities of Scotland from Dundee to Inverness (with more than half the estimated urban population in 1998-2002 present in the City of Aberdeen). Smaller colonies exist across the Central Belt, in Berwickshire, Ayrshire and in Dumfries. The distribution contrasts with that of urban-nesting Lesser Black-backed Gulls; the latter are concentrated currently in the Central Belt, but with substantial numbers also in Dumfries, Ayrshire and Aberdeen. Of the three less abundant urban-nesting species, the largest concentrations of Common Gulls recorded in 1998-2002 were in Aberdeen and along the Cromarty Firth (400+ AOBs each), urban-breeding Black-headed Gulls were concentrated at Dyce (1050 AOBs), and Great Black-backed Gulls at the Nigg Oil Terminal, Cromaty Firth (136 AONs).

Recent trends in the numbers of urban-nesting gulls in Scotland can only be reported in a semi-quantitative manner because of uncertainty over the sites that were checked (and so can be stated with certainty to have had no breeding gulls) during the 1993-95 survey, which additionally included only those gulls nesting on roofs. The level of evidence available suggests that urban-nesting colonies of Herring Gulls, Lesser Black-backed Gulls and Common Gulls in Scotland have all increased in the last decade, with some increases in numbers at existing colonies but also the emergence of new colonies. Less information on urban-nesting Black-headed Gulls and Great Black-backed Gulls is available from previous surveys but it is thought that the occurrence of the small number of substantial urban colonies of each is relatively recent.

The scientific review of urban gull ecology covers the current level of knowledge of mixing of urban and non-urban gulls, breeding success, survival rates, recruitment, food and foraging behaviour, nest site selection and predation pressure, and, where possible, contrasts this information with what is known for gulls breeding in more 'natural', non-urban environments. The reviewing revealed a significant lack of information on most of the basic ecology and demographic parameters for urban gulls in Scotland (see point X). The degree of scientific evidence available is insufficient to confirm any hypotheses for the attraction of gulls into urban environments, but the reasons are likely to be complex and to vary between geographical areas and species of gull.

The scientific review of methods for controlling urban gull colonies covers: non-lethal disturbance methods ( e.g. falconry and broadcasting sounds); methods for preventing access to gulls or deterring them from nesting by changing the nesting substrate; methods for restricting breeding success ( e.g. egg and nest removal, egg oiling); and methods for removing adult birds (trapping and killing). For each technique considered, any scientific evidence to demonstrate success or failure in particular specific contexts is examined rigorously, and the practicalities of applying it in an urban setting evaluated. The reviewing revealed a significant lack of rigorous scientific studies that have tested the success of such control techniques (see point X).

This study reviewed the legislation surrounding the control of urban gull problems, and accessed the perceptions of Scottish Local Authorities of its effectiveness. This report reviews briefly appropriate parts of the legislation governing the protection of wild birds in Scotland (and allowable reasons for derogations), legislation surrounding littering and waste, planning and building, and public health. Some key areas highlighted by Local Authorities that they would like to see investigated further include: the working definition of "public health and safety" in the context of its use to justify actions under General Licences; legislation that can be used to restrict persistent feeders of large numbers of gulls; use of building regulations to enforce gull-proof designs for new buildings; legislation that might allow enforcement of nest removal or gull-proofing on private buildings or access rights to allow Local Authorities to carry out the work.

A lack of knowledge in several key areas currently limits the extent to which sound scientific advice can be given on the likelihood of the various mitigation measures achieving their intended aims if implemented (and hence the extent to which 'best practice guidance' for Local Authorities can be given). In addition, whether a technique is likely to produce the required effect at any given location is likely to depend on large number of factors, including: the species of gull involved; the seasonality of the problem; the geographical scale of the perceived problem; the number of gulls involved; and the specific characteristics of the urban location ( e.g. accessibility of nesting areas, public access to the site). In order to improve best practice guidance, we recommend two types of future scientific research (to be focussed on Herring Gulls and Lesser Black-backed Gulls as priorities): (i) intensive studies of the ecology (diet, foraging ranges) and demography (timing of breeding, breeding success, survival rates, recruitment, dispersal) of urban gulls at a suite of representative urban sites across Scotland (or the UK), and (ii) adaptive management studies with rigorous experimental design to assess the effectiveness of key mitigation techniques. Further details of these recommendations are provided in the report
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