The feral pigeon (Columba livia var) and its by-products are very familiar to those involved in building surveying and maintenance, especially those working in city centres.
Many pest control companies offer pigeon control services and many pigeon exclusion systems are marketed. However, there is a general lack of understanding of the problem among management and building professionals. This means that the control techniques used are often inappropriate or misapplied with the result that they are ineffective. This is not an insignificant problem as tens or even hundreds of thousands of pounds can be spent on pigeon-related contracts without proper independent advice or specification and without proper competitive tendering. Such ‘one-off’ measures applying a single technique with no reference to other factors are often doomed to failure. This is because pigeons are living organisms and are able to adapt over time and space to circumvent most measures. As with other biologically based building problems their control requires the application of a continuing strategy of measures to control the combination of environmental factors which favour their activities. This requires some background knowledge and a careful assessment of each case.
The Natural History of the Pigeon
The feral pigeon (Columba livia var) is descended from the wild rock dove which inhabits both inland and sea cliffs around the Mediterranean and along the West Coast of Europe (1). This species was domesticated by the ancient Egyptians and has spread all over the world in many different domestic strains.
The feral pigeon stocks are derived from many different strains of escaped ornamental, racing and domestic stocks but tend to revert to a wild type of colouring and conformation. These birds are well adapted to survive in a modern city environment where the tall buildings provide habitats very similar to the cliff homes of their ancestors. Their natural diet is one of seeds and grains but they easily learn to exploit a large range of processed vegetable and animal products. In all activities that do not involve reproduction, the pigeon is a social bird which will actively seek the company of others in order to rest, preen, and feed. They may therefore form flocks of anything from tens to hundreds of individuals, depending on the available food sources. These flocks develop a set pattern of activity, based around a defined set of feeding, resting and roosting sites. Given an adequate food supply the pigeon can breed throughout the year and a stable pair bond is formed. Preferred nesting sites are dark enclosed areas simulating a cave or a crevice (3). Two eggs are usually produced and incubation is shared. Three broods may be produced by a pair each breeding season and individuals may live as long as thirty years.
The most important factor in pigeon survival is the active promotion of their population by men, for recreational and emotional reasons. This is most significant in the provision of food, and in giving protection from human predation. The uncontrolled increase in populations of feral pigeons resulting from this commensal relationship has produced considerable problems in many city and seaport environments. These can be reduced by appropriate management and public education programs.
Problems Caused By Pigeons
Structural damage, damp and decay
Pigeon activity in and around a building may directly damage the structure as pigeons are capable of lifting roof coverings to force an entry, especially if these are already slightly displaced. This activity can allow significant water penetration into the building and subsequent decay. More seriously, they block rainwater drainage systems with their faeces, feathers and other detritus. This can cause massive water penetration and severe decay problems. Nesting activity is particularly dangerous in this respect as pigeons frequently nest in hopper heads and parapet gutters causing a complete blockage in a very short time. This disruption of drainage and the resultant water penetration is especially damaging in unoccupied buildings where problems are less likely to be detected before major damage has been done. The results of water penetration are also more serious as there may already be serious damp and decay problems in the buildings. Pigeon activity of this sort can thus negate the effect of conservation and remedial work. This represents a considerable waste of time and money and may lead to the degradation and loss of valuable building features.
Detritus and faeces
Pigeon detritus and especially pigeon faeces represent both an aesthetic and a public health problem, particularly in the interior of a building. Pigeon droppings quickly deface finishes both to the inside and outside of buildings and are difficult and expensive to remove.
Noise and disturbance
Though they are actively fed and encouraged by many members of the public, pigeons represent a public nuisance as well as a health hazard. This may be because of disturbance caused by calling or nesting activity in the early hours and by pestering for food.
Fleas and parasites
Pigeons can spread fleas and other parasites into inhabited buildings.
Faeces and human diseases
The presence of feral pigeons and most especially their faeces represents a potential health hazard to employees and to the general public. This is particularly so when large accumulations of filth build up inside a building. They are commonly carriers of a number of serious human diseases including salmonellosis, psittacosis and pseudo-tuberculosis. Their faeces provide an ideal environment for the growth of the organisms causing such diseases as histoplasmosis, aspergillosis, cryptococcus and listeriosis. Although the risk of infection from pigeons may be relatively low, the diseases are severe and may be life-threatening. Pigeon faeces represent a health and safety hazard for employees who have to remove them or work in their vicinity. They are thus a special problem in the renovation of buildings where large accumulations have been allowed to build up. Dealing with such accumulations can be expensive and time-consuming because of the protective equipment and procedures that may be required.
Health and safety problems are also caused by the build-up of faeces due to the slippery and unsafe footing it provides on walkways and ledges hindering proper maintenance. This may also be a particular problem during building works and renovation.
If measures are not taken to minimise pigeon activity around a building their presence will cause significant problems for building management and maintenance. These problems are both avoidable and expensive to deal with. They can also have an appreciable effect on the cost of renovation work and the time taken to complete a project.
Common Pigeon Control Techniques
Many techniques have been used for controlling pigeons around buildings all of which have advantages and disadvantages (4). Some of the more common techniques currently employed are listed below when considering control options it is useful to distinguish those that reduce pigeon numbers in an area or merely modify their behaviour.
This is the most successful long-term measure for controlling the absolute number of pigeons in an area. During the Second World War, the reduction of food availability dramatically reduced the number of pigeons despite the increase in suitable nesting and roosting sites.
Poisons and narcotic baits
Poisons can provide effective control, especially those producing a period of deranged behaviour before death. This alarms other birds in the flock and they will avoid the location in the future. Narcotic baits are available that stupefy the birds which may then be collected and disposed of by licensed bird handlers. Poisoning of birds is illegal in the UK.
Pigeons may be caught in live traps after a short period of baiting. A large proportion of a flock feeding in a given area can be removed by this technique. Traps require a private area for operation and regular attention from an experienced operator. The problem with this technique and others that involve the removal of birds from an area without reducing the suitability of the environment is that other birds will soon move in from adjacent areas.
Birth control and removal of nest sites
Baits impregnated with birth control agents can be used but have limited uses as decreases in reproduction are made up by increased recruitment of birds from other areas. Removal of nest sites reduces reproduction but more importantly obliges breeding birds to leave the area. Nesting activity is a major source of the detritus blocking drainage around the building.
Shooting using an air gun or .22 garden gun may not significantly affect the pigeon population. However, it is an effective method of scaring the birds away from a location. If carried out regularly at the time birds are settling for the night, it will prevent a roost from being established at that location.
Food supplies rather than predators are the main determinants of pigeon numbers. However, falcons and other raptors are used successfully to clear birds from feeding sites such as airfields. In buildings, the problem often arises from roosting rather than feeding behaviour. When threatened by a raptor, pigeons tend to cower into their roosts rather than fly away. Therefore, the use of trained airborne predators would not be useful in these circumstances. Domesticated carnivores such as mink, ferrets or cats will kill individual birds. More significantly, they will disturb the birds in those areas where they hunt, preventing roosting, resting and nesting.
Bird scarers may be visual, audio, mechanical or a combination (2). They work by producing a stimulus that is perceived as frightening or noxious by the pigeons. Unfortunately, they have proved generally ineffective for this species due to their great adaptability and learning powers. Unless reinforced by actual pigeon deaths, they soon learn to ignore alarming sights and sounds. Appropriate reinforcement may involve killing pigeons and displaying their carcasses. The use of recorded alarm calls is also ineffective in this species, primarily because no true alarm call has been identified but also because when alarmed the rock pigeon tends to sit tight on its perch. The use of noxious stimuli such as loud sirens or explosions often becomes ineffective for similar reasons. These techniques are also unacceptable around occupied buildings due to the disturbance and nuisance they cause to people.
Fine, standard large mesh plastic nets are used to exclude pigeons from areas of a building. They may be used in large sections to wall off whole areas or in small strips to prevent pigeon access to individual features. Fixing should be done with stainless steel pins and wires. The colour is generally black to reduce the decay of the plastic by ultraviolet sunlight. Netting is a very effective and economical way of preventing pigeon damage on a building, but may have the following problems: netting may give a hazy appearance to buildings with finely detailed decoration and it may be obtrusive on light or brightly coloured buildings. The use of netting in small sections requires relatively high numbers of fixing points and it has a life of five to ten years. The heaviest gauge netting possible should be used and special attention paid to reinforcing it at edges or attachment points. If this is not done it will soon tear loose. In large areas and in exposed locations the net should be reinforced with stainless steel wire.
The stainless steel wire may be mounted on thin stainless steel brackets via short springs of the same material. These are placed a few inches above ledges at an appropriate height to interfere with landing and take-off by the pigeons. This is especially useful on narrow ledges and very cost-effective where long straight runs of a few metres can be laid. Such wiring is unobtrusive, is easily removed and replaced for maintenance work, and has a life of at least ten years.
Several different systems of stainless steel or plastic spikes are available for fitting to buildings to discourage pigeons from landing. Although some of these are quite effective they suffer from a number of problems; sharp steel spikes are very dangerous to maintenance personnel, litter may become caught on the spikes, build-up of faeces makes them ineffective, their appearance may be unattractive, they are relatively expensive and they may require more fixing points than nets or wires.
A number of adhesive gels are available which are intended to be spread on surfaces so as to make it unpleasant for the birds to perch. These can be effective when fresh. However, they are expensive and lose their effect after a year or so. This means they require regular replacement and are uneconomical in most cases. The gels can also cause damage or fouling problems themselves and can be very difficult to clean off a building once applied. They may be unaesthetic and hazardous for those working on the treated surfaces.
The control of pigeons and pigeon-related problems requires the coordinated application of a combination of measures and attention to detail. Application of single techniques is at best inefficient and is often ineffective. What is required therefore is a careful assessment of the pigeon problem, the ecological factors favouring the pigeons and those factors that could be most cost-effectively controlled. This necessitates a site investigation and some analysis.
A specialist investigation should be carried out to determine the activity of the feral pigeons at the building. Often the most significant problems are not immediately obvious and those which may be causing the most management disquiet may in reality be trivial. The short and long-term consequences of the problem should be assessed and cost so that their relative importance is appreciated.
The next stage is to carry out a detailed study of the ecology of the pigeon population in the area. This should include mapping pigeon numbers and activity around the building through a 24-hour period, and assessing critical factors such as feeding sites, roosting sites, nesting sites and loafing areas.
The factors limiting the pigeon population in the area should be assessed. The most important of these factors is usually the availability of food sources. The proportion of sick and out-of-condition birds in the population and the general condition of the birds should be determined. The effect of current and previous pigeon control measures should be noted. It is important to identify which of the pigeon’s activities are causing the identified problems, for example, the nesting activity causing blocked drains, or roosting causing faecal contamination.
Analysis of data
The results of the investigation of pigeon ecology around the problems building should be analysed in detail. Using the data it is possible to determine which pigeon activities and environmental factors are significant in causing the problems identified. Simple statistical techniques and a graphic representation can be especially useful for this purpose. They are also very useful in demonstrating the problems to the property owner or manager. The next step is to identify the factors limiting the pigeon population, and these limit the problem activities. For example, the availability of safe nest sites may be the critical factor attracting activity around a particular building. Alternatively, the availability of sheltered roosting sites may be crucial. Have factors that can be controlled in a cost-effective manner, and the required works and/or management measures can then be identified.
A comprehensive remedial programme should be developed using the results of the investigation and analysis described above. This must take into account the management and use of the building as well as aesthetic and financial constraints. Only rarely will it be possible to eliminate a pigeon population or to totally exclude pigeons from a building. In most cases, a percentage reduction in pigeon numbers or the control of a particularly damaging activity is all that is required. Appreciation of this fact and the presentation of achievable targets to the building owner or manager will prevent disappointment. The early definition of acceptable limits to pigeon activity will also prevent the overuse of particular techniques where the law of diminishing returns can result in wasted resources and defaced buildings.
Specialised control and exclusion techniques
A combination of specialist techniques should be chosen to take into account their limitations as described above. Care and attention to detail in specification and application are essential, or even the most suitable techniques or products will be inefficient or ineffective. For example, the positioning of wires can be critical and a single faulty attachment point in a net system can make it useless. Similarly, the side effects of each protection technique on other aspects of the performance of the building must be equally carefully dealt with. For example, nets or spikes may trap rubbish, fixing points may allow water ingress or accelerated erosion of surfaces, and most products will restrict access by maintenance personnel.
Blocking up of internal cavities, for example, roof spaces, without due regard to the provision of suitable ventilation, may result in condensation and damp-related decay problems.
Damage control measures
It is often cost-effective to take steps to limit the damaging effects of pigeon activity and this can often be easier than controlling the pigeons themselves. To this end, hopper heads and secret gutters draining the roof surfaces should be cleared of all pigeon detritus. They should then be protected from future blockage with ‘sausages’ of crushed chicken wire or secured with mesh grills. In either case, provision should be made for clearing any debris that accumulates. The provision of adequate access facilities and safety points for clearing pigeon-affected areas is also important.
Routine inspection and cleaning
The building should be routinely inspected for pigeons, fresh faeces, nesting materials and pigeon-related problems such as blocked roof drainage systems. The building should also be checked for building defects that could allow pigeon access to the interior of the roof spaces. Any detritus should be cleaned off the structure and any defects should be repaired as necessary. Such a program would require a minimum of monthly inspection. Again, the provision of adequate access and equipment is very important.
A continuous and vigorous policy of food restriction should be applied around the building. This should involve the elimination of refuse and litter by regular cleaning, the use of pigeon-proof refuse containers, and public education to discourage voluntary feeding. This is the most important measure in any pest control strategy.
Responsibility for aspects of the control of the pigeon problem must be specifically included in the programs for the management of the cleaning and maintenance of the building. This will require appropriate budget provisions to be made. Overall responsibility for pigeon management should be given to an individual manager and relevant accounts kept so that the cost of pigeon damage and its prevention can be assessed. In addition, the overall pigeon problem in the area should be assessed annually as part of the building management program in order to assess the efficiency of the program. Usually, such a program would be the responsibility of those managers responsible for cleaning, but there may be advantages in making pigeon control a Health and Safety responsibility in order to increase its priority.
- The control of feral pigeons is a management problem which requires the continuous application of a number of measures over a period of time.
- Control is unlikely to be achieved by the application of a single product or technique.
- The most important measures to be taken are often general maintenance and management works.
- The total elimination of pigeons and their associated problems is unlikely to be cost-effective or even achievable.
- Efficient pigeon control requires that the extent and nature of the problem should be defined before any action is contemplated.
- Goals should then be set that are acceptable and achievable within the resources available.
- It is important to monitor the effectiveness of any measures taken and to take further actions as necessary.
As in all building remedial work, the key factors are independent investigation and advice, careful specification, competitive tendering, a holistic approach, and continued monitoring (5).
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Kreds J R, ‘Bird Scaring’, 1980 in ‘Bird Problems in Agriculture’, Wright E N (Ed), BCPC Publications, London
Goodwin D, ‘Behaviours’, 1983 in ‘Physiology and Behaviour of the Pigeon’ A & S.M (Ed), Academic Press, London
Howard M and Oldsbury D ‘Pest birds: The role of building and design and maintenance’, 1991 Structural survey 10 No 1 p38-44
Hutton T C, Lloyd H and Singh J, ‘The environmental control of timber decay’, 1991 Structural survey 10 No 1 p5-20