EHJ May 2003, pages 132-135
Somehow, roof-nesting gulls have become something of a problem throughout the UK. And Peter Rock argues that the situation looks set to get worse
Almost every town and city in Britain has a population of roof-nesting gulls, and with a growth rate of some 13 per cent a year it won't be that long before all of the UK's towns and cities support growing gull colonies.1 For those living or working in an area which has been colonised by gulls, there are good reasons for complaint. Gulls are noisy, especially during courtship and chick rearing, and they produce large quantities of excrement, some of it deliberately aimed at humans, creating health fears. They build nests in gutters, which invariably get rain washed into down pipes causing blockages, and they are aggressive. Stories about gulls stealing food from the hands of tourists, terrorising workers on roofs and even striking bystanders on the street are time and again reported in various local media.
The upshot of all of this gull activity is, of course, a rising level of complaints to the environmental services departments of most authorities. Once the media becomes involved though (with a cull being the most frequently proposed solution), questions begin to be asked about what is being done about the situation. With this in mind, some clear and pragmatic information on the issues and some practical suggestions seem necessary, if not overdue.
While there are other gull species nesting on rooftops (Great Black-backed Gull, Common Gull and Kittiwake etc) numbers are tiny in comparison to the Herring Gull and Lesser Black-backed Gull. These two closely-related species are large, weigh around a kilo and have a wingspan of some four and a half feet.2 They are also very long-lived birds, with the record being almost 35 years3, and are very good at surviving from year to year (adult mortality is less than 5 per cent). Generally speaking, they breed for the first time at age four. However, in town, third year birds breed commonly - a sign that the colony is expanding.
The breeding season runs from March to the end of July. One attempt is made per season and three eggs are laid. In urban situations, this usually means that pairs will bring off three young each year. Pairing for life adds stability to their breeding patterns and, even if this is only 10 years, a pair could raise 30 offspring. This exceptional breeding success explains the exponential, national growth rate of 13 per cent. It should not be forgotten that to maintain a stable population in any species, including humans, all that is necessary is for each individual to reproduce itself once in its lifetime. Urban gulls are doing far better than this.
The large gulls are supreme opportunists and will take advantage of whatever becomes available. If it is edible, they will eat it. In town, they never turn down the scraps really intended for swans, ducks and pigeons and are expert in robbing these birds of their meals. Ample street lighting is provided to enable them to pick up the discarded take-aways thrown down by late night revellers well before the street cleaners even have a chance to clear up. But, their major feeding takes place out of town and may be some distance away - principally landfills (refuse)4 and green fields (invertebrates).5
Strictly speaking, this issue goes back to before the Second World War with a tiny number of records from small fishing villages.6 The key event though, was undoubtedly the passing of The Clean Air Act in 1956. The Act forbade the burning of rubbish at tips, instead it required operators to cover the tip face with inert material at the end of a day's tipping. It was an open invitation to the gulls and populations rose by fifteen fold by the early 1970s.7 This sudden and massive increase in gull populations resulted in traditional colonies being outgrown. The gulls had to find other breeding grounds and our buildings, from a gull's point of view, are little more than cliff-sided islands.
The gulls soon found urban living to be highly advantageous - there are no predators, very little disturbance on rooftops, and critically, high availability of large food supplies fairly close at hand.8 Growing chicks demand high energy, high protein food - and lots of it.5 Without this quality of food, breeding success would be considerably lower.
The most prominent gull colonies in Britain (those with more than 1,000 pairs) started in the late 1960s and early 1970s. In Bristol, the situation started in 1972 with one pair of Herring Gulls - there are now around 1,200 pairs. Gloucester, with 2,400 pairs9 had three pairs of Lesser Black-backs in 196810 which now dominate all colonies in the Severn Estuary area. Aberdeen, with 3,500 pairs, is the biggest colony in Britain, but colonies of around 500 pairs11,12 are to be found in many places. New colonies are quietly establishing themselves throughout the country, but it is not until these grow to about 50 pairs that they start to impinge on human activity.13
There are two reasons why gulls are unlike all of the other "problem species". First, gulls are not confined to a single centre of activity. They move widely and are perfectly capable of making a round trip of 100km in search of food in only a few hours. Second, they are considerably more intelligent than most and despite the best efforts of pest control agencies to deter or remove them colonies have continued to expand. Thus, it has to be concluded that the vast majority of control and deterrence methods and equipment are ineffective and many of these have been costly mistakes for those who have purchased them.
Plastic Eagle Owls seem to decorate many of our roofs up and down the country. Why is this? The gulls just ignore them! The same goes for streamers and other waving structures, balloons showing large eyes, loud, sudden noises and even fireworks. Spikes in rows, tensioned wires and other wire structures are also ignored.
The playing of distress calls and the flying of birds of prey are interesting methods and are plausible. However, while these methods appear to work in the first instance, it is usually not long before the gulls get used to them. They quickly come to recognise the distress call, even when speakers are moved around. Though remaining attentive, they do not allow it to interfere with the serious business of breeding. It is a case of shaken, but not stirred. Birds of prey do intimidate gulls and the gulls will get up into the air because it is safer to be moving than stationary. However, birds of prey can only fly for short periods and, more importantly, there is safety in numbers for a gull colony.
All gull colonies put up with predators in the wild, several of which (Great Black-backed Gulls, Skuas etc) breed right in the heart of seabird colonies and are tolerated. It should also be said that there are towns where Peregrines breed alongside successful gull colonies. As a final word on birds of prey, what happens when the prey turns predator? Records of gulls attacking all sorts of predators are legion and the handlers of birds of prey would be well advised to consider the risks involved in flying their birds.
Egg smashing and nest raking simply result in the gulls rebuilding and relaying. However, continual, daily nest removal throughout the season will effectively prevent gulls from nesting on a roof. This is also true of covering a roof with netting. However, by removing gulls from one roof, you encourage them to move onto nearby roofs. Thus, creating problems for others. At some point in the future, it may result in litigation.
Another option is culling - poisoning, narcotising (and then dispatching the drugged birds) or shooting. Before considering these methods it would be wise to refer to the Wildlife and Countryside Act. Both of the urban gull species are in a special schedule which allows property owners to engage authorised personnel to carry out such services, provided the species involved clearly present a threat to public health and safety, or to aircraft. Nuisance, alone, is not considered to be a reasonable justification. The interpretation of threat, however, leads to a grey area. For instance, though gulls do carry unpleasant pathogens such as salmonella, campylobacter, e-coli etc, it has, so far, not been demonstrated that they are vectors of disease in humans.14
Culling gulls in an urban situation is fraught with all sorts of potential difficulties. For instance, discharging firearms in a built-up area would cause a great deal of concern - and not just to the police. Poisoning would very likely engage the minds of the Health and Safety Executive, not only for operatives, but also for passers-by when moribund gulls fall into the street. Further, the efficacy of culling is dependent on several years' concerted action. During a persistent cull on the Isle of May, it was noticed that young birds were taking up territories previously occupied by adults.15 In other words, if you make a hole in a niche, somebody else will fill it.
But, by far the most difficult situation to deal with would be public reaction. Britain, it is said, is a nation of animal lovers and trying to solve the problem at this serious level would, almost certainly, result in heated debate and, possibly, in direct action. One local authority in the north-east of England was unable to renew its licence to cull, mainly due to the efforts of a strong-willed and articulate lobby of town residents.
What seems to be forgotten in this issue is that, for the gulls, successful breeding is far and away the most important aspect of their lives and that their investment in it is considerable. They will not easily relinquish their grasp on a breeding attempt. Dealing with all manner of threats and avoiding them is thoroughly ingrained in the nature of these birds - they have survived in this way for thousands of years. Were there an easy "cure" to this issue, it would already have been discovered and there would be considerably fewer, or no roof-nesting by gulls at all in Britain - or in the other countries where it occurs. Forming sensible - and sensitive - strategies for the management of urban gulls is going to take time and research.
A very great deal is already known about the ecology of the Herring and Lesser Black-backed Gull, but it has all been derived from traditional, wild colonies. There is almost nothing in the literature about urban gull ecology. This is because, apart from the work carried out by the author, there have been no studies into urban breeding by the large gulls in Britain. Some of the science has already been done and more is planned.
Since 1980, the author has colour-ringed some 5,000 gull nestlings in Bristol and these individually-marked birds have generated in excess of 20,000 post-fledging observations.16 Less than 2 per cent of Bristol-ringed gulls return to the wild to breed. Instead, generally speaking, they return to Bristol once they are old enough to breed (males), or seek out other urban colonies (females). Female gulls ringed in Bristol currently breed in all of the region's urban colonies. By the same token, females from other colonies must be recruiting into the Bristol population and this must also be the case in every other urban colony up and down the country.
What is perfectly clear, therefore, is that the issue of urban gulls is not just a local one, but a regional one. If the problems associated with urban breeding are to be understood and dealt with, regional strategies will have to be formed. This will require regional co-operation between authorities. How should regional strategies be developed? Instead of vainly hoping that pest control agencies will solve all of the problems, the first step must be to get to grips with the facts at a local level - in your authority. Once these are known, there has to be a proper exchange of information and sharing of costs. Stage one, is to accurately assess the number of breeding pairs and the demography of the colony. This assessment will act as a base line from which colonial growth and changes/expansion in the colony can be monitored. It will also clearly demonstrate to all that the problem is being investigated.
Stage two is to identify and assess the importance of local food resources used by the gulls from your colony and other colonies. Typically, these will be landfills, refuse transfer stations, pig farms, chicken waste drilling sites etc. The natural food gathering areas such as green fields and coast/river feeding sites are important and the scavenging areas in town and in the suburbs cannot be left out.
Stage three has to be the precise understanding of the dynamics of urban breeding alluded to above. How, exactly, does it all work? This can be achieved by colour-ringing nestlings, although it will take three to four years (as birds mature into breeding condition) to acquire the necessary results. It has to be nestlings because, unlike adults, only their origin is certain. It will then be possible to calculate patterns of recruitment. This is already happening in Bath and Cheltenham. It is hoped that Gloucester, Worcester and Bridgend will also come on board this year.
With this information in place, identifying the origins of recruits will be relatively straightforward. It will also be straightforward to discover which other towns your colony is supplying. There will be some areas in your authority where breeding activity generates a high level of complaints, the majority of which are about noise. The mitigating strategy in this instance is to sterilise the eggs. Sterilising eggs will, effectively, encourage the adults to incubate rather longer than the normal 28 to 30 days. After this, pairs will abandon the season's breeding attempt. Gull noise is moderate during courtship, but at its highest (along with aggression towards humans) after chicks have hatched. Incubation is a quiet affair and birds are discreet and often rather secretive, too.
Sterilisation involves entirely immersing the eggs in a light mineral oil (such as paraffin oil) and putting them back into the nest. This method is only a palliative. It will not remove the gulls and will need to be undertaken every year. However, it does answer some of the more pressing complaints by significantly reducing noise and it could generate income. Theoretically, it also reduces the number of potential recruits in future years, but by how many would require proper assessment.
Another method, though probably difficult to achieve in most situations, is to paint the roof red. Observations from Bristol City football ground show that prior to stand rooves being painted red, gulls bred, whereas after, breeding stopped. As a postscript, the author has analysed some of his data and the findings are significant. Lesser Black-backed Gulls, traditionally long distance migrants, are nowadays increasingly staying in Britain in winter. Up to 25 per cent of adult birds are doing this. Therefore, the prospect is that instead of having gulls on roofs for just five months of the year, it will be rather longer. Let's get the science done!
Peter Rock has been studying Bristol's roof-nesting gulls since 1980 and throughout this time has been involved in international gull research at a high level. For the last 15 years he has been the co-ordinator for the colour-marking of the large gulls for all of the Bird Ringing Schemes in Europe (Euring). He is the author of several scientific papers on the subject (includingthe Lesser Black-backed Gull pages in the Migration Atlas) and has acted as consultant to various authorities on roof-nesting gulls. Contact by e-mail: firstname.lastname@example.org
The author has applied, in conjunction with Bristol University, for a NERC grant to look into the feeding regimes of urban gulls. If successful, not only will it result in a great deal more knowledge on urban breeding, it will also point clearly at directions for the mitigation and management of urban gulls.
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2. Cramp, S and Simmons, KEL (BWP) (1983) Birds of the Western Palearctic. Volume 3, Waders to Gulls. Oxford University Press, Oxford.
3. Clark, JA, Balmer, DE, Adams, SY, Grantham, MJ, Blackburn, JR, Robinson, RA, Wernham CV, Griffin, BM & Milne, LJ (2002) "Bird ringing in Britain and Ireland in 2001". Ringing and Migration Vol. 21, Part 2, 65-143.
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13. Rock, P 2002 Roof-nesting gulls in Cheltenham. Survey conducted in June 2002. Report to the Department of Environmental Services, Cheltenham Borough Council.
14. Monaghan, P, Shedden, CB, Ensor, K, Fricker, CR and Girdwood RWA (1985) "Salmonella carriage by Herring Gulls in the Clyde Area of Scotland in relation to their feeding ecology". Journal of Applied Ecology 22: 669-680.
15. Coulson, JC (1991) "The population dynamics of culling Herring Gulls Larus argentatus and Lesser Black-backed Gulls L.fuscus". In Perrins CM, JP Lebreton and GM Hirons (eds), Bird population studies. Relevance to conservation and management. Oxford University Press, Oxford.
16. Rock, P (1999) "The efficacy of the colour-ringing system used for Herring Larus argentatus and Lesser Black-backed Gulls L.fuscus in Bristol, 1980-1997". Ringing and Migration 19: 306-310.