Urban gulls and their management in Scotland: review

This report looks at the ecology of urban gulls in Scotland, the problems they cause, and management solutions.

8 Best practice recommendations for mitigating problems involving urban gull colonies

One of the key aims of this study was to provide, as far as is currently possible, standard 'best practice guidance' for those Local Authorities that feel the need to address problems associated with urban gulls or for which this need may arise in the future. A number of Local Authorities across the UK have put together guidance documents on urban gulls containing information relevant to their local situation (see for example: http://www.south-ayrshire.gov.uk/environmentalhealth/pc-gulls.htm ; http://www.sunderland.gov.uk/public/editable/themes/healthy-city/eh/pest-control/advice-re-herring-gulls.asp ; http://www.scarborough.gov.uk/pdf/herring_gulls/herring_gull_leaflet.pdf ;

http://cardiff.gov.uk/regulatory/EnvPublicProt/pollution/pestcont/seagulls.htm ; http://gloucester.gov.uk/libraries/documents/e.health/ehf23.pdf . However, the scope of such documents varies between Local Authorities and the guidance that is given is generally location specific and based largely on advice from specialist consultants, who may not be advocating it on the basis of effectiveness proved in a scientific manner.

This final chapter first outlines the (substantial) gaps in scientific knowledge in this field that exist to date, which place severe limitations on the level of specific guidance that can be given to Local Authorities or others with a desire to mitigate the problems associated with urban gulls. Next we provide as specific guidance as can be supported by rigorous scientific research on the types of situation in which the various mitigation measures that are available might prove effective, the major limitations of each technique and some specific practical considerations associated with the implementation of each in urban environments in Scotland. Finally, the principal areas of additional research that we feel are of the highest priority currently in the context of urban gull issues are outlined.

8.1 Current limitations on the provision of best practice guidance

At present, a lack of knowledge in several key areas limits the extent to which sound scientific advice can be given on the likelihood of the various mitigation methods achieving their intended aims if implemented. These key areas are as follows:

  • Lack of rigorously monitored studies of mitigation techniques

Our reviewing (Chapter 6) identified very few studies that have attempted to monitor the effects of mitigation techniques on target gull colonies. Of the studies that have been carried out, the majority have either (i) been carried out in more 'natural', non-urban environments (such that the extent to which the effects shown are indicative of the likely effects in an urban setting are unknown), and/or (ii) been insufficiently rigorous in their design or interpretation ( e.g. because several techniques were tried concurrently, because the counting methods employed were not suitable) to allow firm conclusions to be drawn.

  • Lack of information on the ecology and demography of urban gulls

Our reviewing (Chapter 5) identified a dearth of information on the basic biology of urban gulls that is required to allow predictions of the likely wider-scale and longer-term effects of many of the available mitigation techniques. The information that is lacking can be broadly categorised as ecological data (such as diets, foraging ranges, wintering behaviour) and demographic data (survival and reproductive rates, timing of breeding, dispersal, recruitment and population mixing).

  • Lack of information key information on non-urban gulls

Although less of a limitation than the above two areas of knowledge, more information on the reasons behind the declines of 'natural', non-urban gull colonies in the wider countryside in Scotland might very well assist in establishing the reasons for the increased attraction of gulls into urban environments. Although some long-term studies have been carried out on the demography and ecology of gulls at some such colonies in Scotland in the past ( e.g. those on the Isle of May, see Chapter 5 for some key references), the focus in recent years has tended towards other seabird species.

8.2 Guidance for Local Authorities on mitigation techniques

In the following table, we list mitigation techniques that might be considered in Scotland to address problems with urban gulls. We note at the outset that there has been very little rigorous scientific research on the effectiveness of such techniques in general, and almost none on the likelihoods of most techniques being successful within urban environments (Section 8.1 above). Whether a technique is likely to produce the required effect at any given location is likely to depend on a large number of factors, and some of the key considerations are the following:

  • The species of gull involved (as the species differ somewhat in their ecology, see Chapter 5);
  • The seasonality of the problem (breeding season or winter months; i.e. the extent of site tenacity, see Chapters 4 & 5);
  • The scale of the perceived problems ( e.g. ranging from isolated aggression events to widespread fouling/littering/noise problems);
  • The number of gulls involved in the perceived problems;
  • Characteristics of the urban location ( e.g. accessibility of nesting areas, public access, height and nature of buildings).

Type of mitigation technique(Report section)

Mitigation technique(Report section)

Contexts for possible effectiveness in urban Scotland

Major biological limitations

Practical application issues

Non-lethal disturbance(6.1)

Sounds ( e.g. distress calls, bangs, sirens,)/pyrotechnics(6.1.1)

  • Clearing gulls from relatively small areas for short periods of time;

  • Moving gulls to alternative sites, particularly non-breeding birds (e.g. disturbance at roosts to deter recruits).

  • Habituation to the scaring method is likely to occur;

  • Less likely to be effective at moving territorial breeding gulls.

  • Frequent changes in the position, time and type of disturbance may improve effectiveness;

  • In urban settings, disturbance methods may disturb humans and other non-target species.

Use of birds of prey(6.1.2)

  • Little rigorous documentation of success available on which to base guidance;

  • Falcons might be used effectively in relatively open areas ( e.g. industrial areas with large flat roofs, landfill sites);

  • Hawks might be useful only to flush pest birds from buildings, which can then be secured;

  • Success less likely with territorial nesting gulls cf landfills and roosts (e.g. at airports and to deter non-breeding birds from recruiting into the breeding population).

  • Choice of bird of prey species is likely to be important depending on context of use;

  • Generally requires intensive work initially and re-enforcement over subsequent years.

  • Training and careful choice of bird of prey species to reduce risk of actual kills of gulls and/or other non-target species;

  • Relatively large areas might be "treated" by birds of prey flying, particularly falcons;

  • Need to start before gulls begin nesting at potential breeding sites;

  • Can be used with sounds / pyrotechnics but regular re-enforcement using bird of prey likely to be necessary;

  • Concerns specific to the urban environment (risks to the public and birds).

Human disturbance (6.1.3)

  • Unpublished information suggests that this may be effective in clearing breeding colonies from urban areas if appropriate access to nesting areas can be achieved.

  • Likely to require intensive work during the breeding season (starting early in the season);

  • Suggested as being less prone to habituation than other scaring techniques.

  • Issues of access to all suitable nest sites;

  • Currently no studies to assess the extent to which any effect in a given year will persist in subsequent breeding season(s);

  • Some persistent individuals/pairs of gulls may require additional methods of removal.

Manipulation of nesting areas(6.2)

Preventing access, landing or nesting(6.2.1)

  • Can eliminate nesting and loafing birds from specific proofed buildings;

  • Need to proof all suitable gull nest sites to reduce effectively numbers nesting in any particular area;

  • Correct design and placement of any devices used is essential.

  • Birds are likely to move to alternative suitable nesting sites nearby.

  • Issues of access to all suitable nest sites;

  • Correct design and placement of devices required for different buildings and gull species (training issues);

  • Periodic maintenance of devices required.

  • Need to minimise risks of entanglement to gulls and non-target species.

Manipulation of nesting substrates(6.2.2)

  • Anecdotal reports of nesting prevented by use of roofs of particular materials or colours but no consistent reports and no rigorous testing documented.

Creation of alternative nesting habitat or relocation of colonies to non-conflict sites(6.2.3)

  • Likely to require: (i) creation of suitable nesting habitat (suitable substrate in a setting that renders nesting areas free from ground predators; see section 6.2.2) in a location away from human interests; (ii) pro-active attraction of the gulls to the area; and (iii) use of suitable methods (see other sections of Table and Chapter 6) to disturb gulls from current breeding locations that are perceived to be problematic;

  • No specific studies to test whether the idea is feasible in the context of urban gull colonies.

  • Requires knowledge of likely distances over which gulls of breeding age would be likely to move if disturbed;

  • Requires knowledge of other likely areas for colonisation (some of which might also result in perceived conflicts with humans).

  • Availability of suitable locations within a suitable distance of existing colonies is critical;

  • Recurrent problems with containing the colonies in non-conflict areas?

Manipulation of food sources(6.3)

Reducing food availability e.g. street litter, waste, people feeding gulls(6.3)

  • Likely to requires widespread co-ordinated effort to eliminate or reduce all food sources within an area (winter problems) and within possible foraging ranges (breeding birds).

  • Need to know the availability of alternative food sources within the range of the gulls and predict how the individual gulls will respond with respect to the removal of the sources over which the LA has control.

  • Lack of knowledge of gull movement patterns and behaviour in urban environments currently limits use of this potential method (see 8.1 above).

Restriction of breeding success(6.4)

Treatment ( e.g. oiling, pricking, substitution) or removal of eggs or nests(6.4.1)

  • Likely to be effective for removal of particular 'problem pairs' or for localised problem areas;

  • Treatment of eggs may reduce gull aggression levels due to incubation behaviour.

  • To reduce numbers of gulls at any one colony, a high proportion of eggs must be treated or removed;

  • Continued effort likely to be required, although reduced recruitment may reduce the level of effort needed in future years.

  • Time consuming (multiple visits required per breeding season);

  • Little expertise required for nest or egg removal, more care required for egg treatment;

  • Removal of eggs or nest destruction may be faster per site visit than egg treatment but is likely to require more follow-up visits to remove replacement clutches;

  • Issues of access to all nest sites.

Introduction of predators(6.4.2)

  • Not likely to be useful in urban environments in Scotland.

  • Risks to non-target species.

  • Inaccessibility of many nests to predators.


  • Technology not sufficiently developed currently.

  • Specificity of chemical or hormone contraception (potential affects on non-target species);

  • Requirement to treat a large proportion of the gull colony over an extended time period.

  • Technology undeveloped;

  • Time consuming, continuous effort;

  • Attraction of pest species to any "treated" food.

Removal of adult birds(6.5)

Capture and translocation or killing(6.5)

  • May be of utility in removing particular 'problem' nesting pairs as a temporary measure.

  • For translocation, distance is likely to need to be large to discourage return;

  • Replacement by other pairs likely to occur .

Narcotic bait(6.5.1)

  • Isolated nesting areas with restricted public access ( e.g. industrial sites).

  • Density dependent responses ( e.g. earlier and more successful breeding) from surviving individuals may reduce effectiveness;

  • Need to target a large proportion of the colony if the aim is to reduce overall numbers;

  • May reduce recruitment from new birds.

  • Nests must be accessible for placing baits and collecting carcasses;

  • Requirements and conditions for obtaining necessary specific licence are considerable;

  • Training and health & safety considerations.


  • Generally likely to be inappropriate for urban environments;

  • Isolated areas with restricted public access.

  • Density dependent responses ( e.g. earlier and more successful breeding) from surviving individuals;

  • May reduce recruitment from new birds.

  • Training and health & safety considerations; (Police advice and consultation required).

Finally, in this section on 'best practice', we note that all of the potential mitigation measures mentioned above have associated practical, financial and ethical difficulties. For these reasons, prevention must always be better than cure: any practical measures that deter gulls from nesting in urban environments in the first place should be a preferred option in areas that currently do not have problems with urban gulls. These might include consideration of specific building designs that do not favour gulls, or, where possible, planning by Local Authorities to site any essential buildings that might attract nesting gulls (such as industrial areas) away from residential areas in which the gulls might be perceived problematic.

8.3 Future research suggestions

We suggest four major areas that we feel are of highest priority in the field of urban gull problems and their successful mitigation in Scotland. The first two of these research areas are generic, and results from studies elsewhere in the future would shed light on the situation in Scotland, while the last two need to be carried out within Scotland, as follows:

  • Intensive ecological/demographic studies of urban gull colonies

We recommend the initiation of intensive studies at a representative suite of urban sites across Scotland or the UK to investigate basic breeding biology (timing of breeding, breeding success, survival rates and patterns of recruitment and dispersal) and foraging ecology (diets, foraging ranges). Such research would probably require the marking of individual chicks and adult birds, remote telemetry work and assessment of diets by direct ( e.g. regurgitates) or indirect ( e.g. stable isotopes, fatty acids) means. The ideal would be to carry out complementary work at a suite of natural sites in similar geographical areas to provide comparative data and allow assessment of population mixing. We suggest that this work should focus initially on Herring Gulls and Lesser Black-backed Gulls, as these have the largest urban colonies in Scotland (Chapter 4) and are most widely reported as causing problems in urban areas (Chapter 3). A coordinated study that carried out such intensive work in a standardised manner at 4-5 colonies of each species in each habitat (urban and 'natural') across Scotland (or perhaps 7-8 sites across the UK) would provide additional benefits in terms of (i) identifying key differences in ecology and demography between species, (ii) identifying key differences in ecology and demography between those gulls breeding in urban and non-urban situations, and (iii) identifying variation in ecology and demography between sites within a given habitat type that might be related to more local factors ( e.g. proximity to the coast, to landfill sites). Such a study would need to document as many such colony-specific environmental variables as possible and colonies should be selected with the most likely influencing variables in mind. Such a study would need to run for a minimum of 5 years to obtain meaningful information on adult survival rates and between-year variation in demographic parameters, and preferably longer to investigate recruitment mechanisms. The design considerations for this recommendation would be complex, and would also need to consider any current or likely future needs to carry out control measures at the colonies to be targeted.

  • Adaptive management studies to assess effectiveness of mitigation techniques

The inclusion of urban gull colonies in long-term non-intervention studies (above) is unlikely to be an attractive option in some areas where a pressing need is felt to carry out some form of mitigation action. We recommend that when such action is to be taken, wherever possible this should be carried out as part of a carefully designed study to assess rigorously the effects of the mitigation measures. Such studies need to follow a number of key principles: (i) baseline counts using an appropriate counting technique prior to the onset of the control work and counts using the same method subsequently (for as many years as is appropriate and at an appropriate spatial scale to monitor the likely effects on numbers of breeding pairs, recruits, dispersal of the birds away from the colony and so on), (ii) the implementation of one control method only at a time (so that any observed effects are not confounded and impossible to interpret rigorously), (iii) careful documentation of the details of the control measure and the urban environment in which it is undertaken (including any environmental changes that take place concurrent with, but not related to, the treatment carried out specifically for gull control), (iv) standardisation in terms of treatment and monitoring with other sites testing the same technique if at all possible (to investigate potential variation in outcomes in relation to site-specific factors), (v) comparable monitoring at reference site(s) for a concurrent period of years if at all possible. The implementation of the intensive studies of the ecology and demography of urban gulls at sites across Scotland (as recommended above) would ensure a suite of representative reference sites for the two key urban gull species with which the findings of local studies of the effectiveness of specific mitigation techniques could be compared. See Walters & Holling (1990) for further background to adaptive management approaches.

  • Perception of urban gulls as a problem in Scotland

The current study was given the remit of focussing on the perceptions of Local Authorities in Scotland regarding gulls in urban areas. Hence our questionnaire survey (Section 2.3 and Chapter 3) was designed to assess specifically the views of Local Authority representatives in Environmental Health Departments or their equivalents, and not the wider public. Our results can be used to conclude that many Scottish Local Authorities do perceive urban gulls as a significant problem but this perception is based only LA perceptions and complaints from those people who have experienced urban gull problems at first hand. Our results do not show the extent to which the urban Scottish population as a whole perceives urban gulls as a problem or give any scientific proof that a wide-scale problem exists. If there is any intention to extrapolate the results of our survey to a wider context, we recommend that a wider-scale survey must be undertaken to assess the opinions on urban gulls of those members of the public living and working in urban areas. Such a survey, if designed correctly, could be used to assess in a more rigorous manner whether the problems associated with urban gulls are truly frequent in occurrence, or whether they actually occur infrequently but attract greater prominence because of their severity or interest from the media. In some situations, this type of study could form a sounder basis for implementing mitigation measures in a climate of public opposition to some forms of mitigation and control. A more detailed appraisal of the databases on complaints held by several Local Authorities in Scotland could form useful background information to aid the design of such a survey.

  • Issues surrounding use of legislation and powers

There is clearly a strong feeling amongst Local Authorities in Scotland that difficulties of interpretation, or omission of certain powers available under existing legislation, limit their ability to mitigate against some problems caused by urban gulls (Section 3.6), and through discussions (largely with Local Authority representatives), we have identified a number of key areas that it would be useful to investigate in more detail (Chapter 7). We sought further advice on some of these issues during the course of the current study but more specific expertise in this field is required to take the discussions further. Therefore, if the Scottish Executive feels that there is a need to provide guidance on the legislation surrounding urban gull problems additional to the level that they provide currently, we recommend that further advice be sought from legal experts. Key areas highlighted by some 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..


Email: Central Enquiries Unit ceu@gov.scot

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