Woody Allen described feral pigeons as ‘rats with wings’. Roman slaves
fed the birds with predigested bread to fatten them up for the tables of
their masters. Today, most of us regard Columba livia with a mixture of
contempt and fear. Do pigeons spread disease? Do their droppings ruin buildings?
Do their flapping wings startle motorists and cause accidents? The answer
is: we simply don’t know. Perhaps surprisingly, given the abundance of feral
pigeons, research into their habits, the threat they pose to people and
the extent to which they ruin buildings, is relatively scant. Similarly,
little support has been given to ornithological research that might reveal
cheaper and more humane methods of discouraging Columba livia from colonising
our city centres.
These issues recently came together at a conference organised by the
British Ornithologists’ Union in London on feral pigeons. According to organisers
of the meeting, it represented the first attempt, at least in Britain, to
unite the resources of the pest control industry, environmental health officers
and scientists in a broader response to what most people regard as a problem.
Of one thing there can be little doubt: pigeons have been with us for
a long time. Martin Jones of the department of biological sciences at Manchester
Polytechnic explained that the birds in most city centres – from Trafalgar
Square in London to St Mark’s Square in Venice – owe their most immediate
origins to the rock dove, a shy species which in Britain is now confined
to rocky outcrops and cliffs in northwest Scotland and in Ireland to the
western regions. Jones says that while it is difficult to be certain about
the original range of the rock dove, it most likely colonised much of north-west
Britain, southern Europe, the Mediterranean, North Africa, the Middle East
and the Indian subcontinent. As early as Neolithic times, rock doves may
have been captured and kept for food. Certainly, the impact of pigeons is
well recorded. According to Jones, the Bishop of St Paul’s Cathedral in
London complained in the 14th century that people throwing stones at pigeons
were breaking cathedral windows. Samuel Pepys, commenting in his diary of
2 September 1666 about the Great Fire of London, wrote: ‘The poor pigeons
were loath to leave their houses, but hovered about the windows and balconies
until some of them burned their wings and fell down.’
Advertisement
These days, the pigeon is found almost everywhere in the world. The
bird was introduced to North America in the early 1600s, to South Africa
in 1654 and to Australia in 1788. Moreover, flocks of feral pigeons still
attract many recruits from the roosts of pigeon fanciers and racers. Jones
doubts whether many showbirds enter the feral population, but numbers sucked
into feral flocks from the lofts of racing pigeon buffs can reach as many
as 100,000 every year, according to Chris Feare of the Central Science Laboratory
of Britain’s Ministry of Agriculture, Fisheries and Foods.
Despite the abundance of the birds in urban environments, little work
has been done to calculate the cost of remedying the damage to which they
contribute. But the damage to buildings is real. Pigeon droppings contain
acids which eat into soft stone and paint. Infestations of the droppings
produce an unpleasant smell. No national figures exist quantifying such
damage. But Richard Bevan, the pest control services manager at Bristol
City Council, told delegates in London that the cost of cleaning buildings
damaged by these birds is considerable. His estimates suggest that to clear
pigeon droppings from a building a few storeys high may cost anything up
to 1,000 Pounds a week just for the scaffolding to give pest controllers
access to the ledges and windowsills where the birds roost or nest.
According to Bevan, Bristol Council paid 9,000 Pounds in a renovation
programme on a local landmark – the Royal Hotel – to have the facade of
the building cleared of pigeon faeces. Once it was done, the pigeons returned
and the exercise had to be repeated. Eventually, the council had to have
the building ‘pigeon proofed’ for 12,000 Pounds, raising the total cost
to 30,000 Pounds.
Bevan also mentioned the Bristol Bus Company, which each year has to
meet around 100 claims from passengers whose clothes have been soiled by
pigeon droppings descending from the multitude of rafters inside the city’s
bus complex. With dry cleaning costs averaging 3.50 Pounds for a dress and
6 Pounds for a suit, the annual bill for compensation can be up to 1,000
Pounds. And the corrosive action of droppings means that the company has
to repaint its buses frequently – at a cost of 1,200 Pounds for each bus.
And what of the costs to the National Health Service of mending broken
limbs when pedestrians slip on wet pigeon droppings? According to Bevan,
a broken arm costs between 150 Pounds and 300 Pounds to reset, while a broken
hip may be up to 3,000 Pounds. An ambulance costs around 170 Pounds per
call out. Then there is postoperative care. And aside from the direct costs
of treatment, people with broken bones may lose pay if they are off work.
Altogether, there are around 1 million accidents each year in Britain involving
people slipping, many of them attributable to pigeons.
Clearly the bill for dealing with the damage attributable to pigeons
must reach many hundreds of thousands, even millions, of pounds if these
figures are true for the whole country. yet possibly the greatest fear is
that pigeons – often dishevelled and maimed in appearance – spread disease
and potentially harmful microorganisms. Bevan reports that of 23 outbreaks
in 1984 of Newcastle disease, a disease affecting poultry caused by Paramixovirus,
19 were unequivocally caused by pigeon droppings and infected carcasses
which had contaminated foodstuffs processed into poultry feed. Altogether
that year, farmers had to destroy 820,000 birds to contain the disease.
The cost to insurance companies was 2.2 million Pounds.
But do pigeons harm people? John Cooper, a vet at the Royal College
of Surgeons of England, has studied this problem. Pigeons neither bite nor
scratch. he says that any physical harm is confined to accidents when people
slip on pigeon droppings or when motorists swerve to avoid hitting birds.
In his view, Columba livia may possibly spread infections, transmit parasites
and trigger allergic reactions, but hard evidence to support the idea of
widespread infection is flimsy. Allergens, though, have long been associated
with Columba livia: ‘pigeon fanciers lung’ is one term for allergic alveolitis,
a pulmonary condition associated with repeated exposure to feathers, dust
and other materials from pigeons.
Nevertheless, Cooper’s investigations have established that the birds
carry a wide range of microbes, from bacteria and viruses to fungi and nematodes.
‘Often, a bird excretes a microbe, say salmonella, on one day but not the
next, making detection difficult,’ points out Cooper, who analyses faecal
swabs taken from the birds captured in London. he believes the main routes
of infection are inhalation and ingestion. People might, for example, sniff
in germs from the vapours of droppings, or accidentally swallow traces of
droppings, if they have been feeding the birds.
One of the most worrying infections is avian tuberculosis which, Cooper
says, is ‘increasingly being recognised as an opportunistic infection, particularly
in HIV carriers’. Other possible transmissible parasites include the northern
mite Dermanyssus gallinae, which can cause skin lesions and irritation in
humans. Cooper has found that pigeons carry organisms which cause infections
such as chlamydiosis, a salmonellosis, pseudotuberculosis, and very rarely,
the ones that cause listeriosis, Newcastle disease and staphylococcal infections.
Cooper says that while infection is unlikely, people who suspect that
they are ill through contact with pigeons should watch out for fever, headaches,
diarrhoea and influenza-like symptoms all of which have been reported in
people infected by birds (not necessarily pigeons). He advises people who
fear infection to avoid the birds altogether if possible and to pay close
attention to hygiene – to wash immediately if any contact is made with the
birds or their droppings. Also, people can avoid attracting pigeons by careful
disposal of refuse. Cooper says that people should be particularly wary
of birds that look ill – ones that obviously have diarrhoea, nasal discharges,
nodules and are emaciated.
The most drastic way of eradicating the risk is to cull the pigeons,
but Cooper thinks this inappropriate. ‘It’s easy to push the lever of risk
of disease to justify control, but I don’t think this (course of action)
can be substantiated.’ Instead, he suggests education, minimising contact
with the birds, and encouraging people in urban environments to practise
hygiene when preparing food or handling rubbish.
He advocates further research to investigate the scale of the risk:
‘Very little has been done on the period of carriage of microorganisms,
for example.’ Also, he says, investigators need more experimental material
– such as dead birds from environmental health officers and pest control
agencies. ‘It’s surprising how few people are reported as definitely having
diseases attributable to pigeon infection,’ he says. He could name only
a few references – isolated cases of cryptococcosis reported in North American
medical journals.
Even though the risk of infection may be grossly overstated, there is
no doubt that the birds are a serious nuisance in city centres and that
councils are often called upon to tackle the problems. Tony Stephens of
Rentokil Environmental Systems says that in this respect, killing the birds
is always the last resort. The first approach is to depoly harmless techniques
that disrupt the birds’ ability to feed, perch or roost. Possibly the most
ingenious devices for proofing buildings against pigeons are arrays of sprung
metal wires, stretched across window ledges or similar structures where
the birds settle. When the birds land on wires, which are invisible from
the ground, they feel unsteady and fly off again. A similar effect is created
by spreading a special, pasticised gel on roosting or perching surfaces:
the birds feel giddy when they land on the gel and fly off.
Often, explains Stephens, pest control companies exclude pigeons from
roosting sites on buildings by covering features, doors or windows with
tensioned netting. Again, by choosing netting the same colour as the covered
features, the proofing can be made inconspicuous. In some factories and
warehouses, such as granaries, the most practical way to keep pigeons out
is to install access doors that roll up or down rapidly, giving pigeons
little time to enter. Doors made from arrays of long, heavy-duty plastic
strips also deny access to pigeons without obstructing forklift trucks and
other vehicles.
If none of these methods works, then pest controllers will destroy birds
that they have trapped or stupefied with drugs such as trichloroethane.
According to Stephens, both methods require careful and methodical planning.
Stupefying is the only legal method in Britain for controlling birds with
chemicals. Controllers encourage the pigeons to eat food mixed with a strong
narcotic, which knocks them into a deep sleep. The controllers revive and
release the birds of protected species that inadvertently get knocked out
alongside the pigeons. Trapping – often the only way to capture birds in
open public places – relies on detailed surveys, precise planning, the birds
accepting the presence of the traps, and a careful cycle of opening and
closing the traps to catch as many birds as possible without alerting members
of the flock to what is happening. In a successful operation, 70 per cent
of a flock can be captured.
Shooting is normally used only as a last resort. This is carried out,
usually at night, by highly trained marksmen, equipped with specially constructed
air rifles. Their goal is to kill with a single shot, but when a bird in
injured they are ordered to despatch it quickly with a shot to the head
or by twisting the neck, says Stephens.
He says that some other methods had been tried, but with limited success.
They include scaring the birds, which is impractical in towns because loud
booms scare people too. Other ploys including scaring pigeons with recordings
of bird distress calls (pigeons have no distress calls themselves, but respond
to those of other birds), or the calls of predators. This has been tried
while placing stuffed birds of prey on ledges where the pigeons usually
settle. None of these methods, though, works in the long term. Live falcons
and hawks can be a successful deterrent, though they must be used continually
to effect a response. Also, such a predator will ignore any pigeons if it
has made a recent catch.
Killing is always the last resort because many people like pigeons and
find comfort in their companionship. Indeed, pigeon-lovers often disrupt
trapping attempts, either by freeing trapped birds or by otherwise thwarting
operations. Some delegates at the meeting reported finding death threats
in empty traps left overnight.
Chris Feare, the head of bird research at MAFF’s Central Science Laboratory,
believes that with further research it may be possible to establish integrated
approaches that are both more humane and cheaper. He suggests that within
any animal population there is a resource that effectively becomes a limiting
factor, determining the survival and growth of that population. Ultimately,
the size of any animal population depends on four key factors. Two, birth
and immigration, expand local populations. The other two, death and emigration,
decrease local populations. In evaluating how pigeon populations repsond
to the various methods and strategies for control, Feare has found that
only reduction of food achieves the desired effect on birth, death, emigration
and immigration. However, he says, this is only a starting point.
Contrary to popular belief, the pigeon is an intelligent bird and its
flock behaviour is highly sophisticated. Taking this into account, and the
fact that pigeons eat a wide variety of foods, it may be possible to establish
which foods are most crucial to the survival of the pigeons. ‘They eat seeds
in London parks, chew at flowers leaves and other vegetative materials.
But what are the important foods? What are the annual variations in availability?
There may be natural nutrients which limit population growth, and we need
to identify them.’ Feare explains that they may well not be in chips or
beefburgers. ‘We need a study, then if we found which foods were the limiting
factors, we could advise local environmental health authorities about appropriate
hygiene measures.’
Such approaches are more promising, Feare argues, than ‘chemosterilisation’,
a technique promoted by a French company. ‘It’s hard to get birds to take
the bait and when they do, it’s often younger birds who are not breeding
anyway.’ Feare is also concerned that the sterilants work by debilitating
the birds rather than by any effect they have on the gonads.
Whatever the problems posed by pigeons, there will always be people
who enjoy the companionship of the birds and who may frustrate attempts
to banish or kill them. Bevan of Bristol Council describes one elderly woman
whom he saw feeding a flock of pigeons in the centre of Bristol. The woman,
a pensioner, told him that she fed ‘her birds’ with two loaves of bread
a day and 30 pounds of mixed pigeon corn a week. ‘This means she spends
520 Pounds a year encouraging pigeons to thrive. Assuming that this happens
at, say, 50 locations in the city, then people are spending 26,000 Pounds
each year sustaining a problem that costs the council thousands of pounds
to tackle each year.’
The ultimate irony, he says, is in Trafalgar Square. The Department
of the Environment awards licences to vendors that permit them to sell pigeon
feed to tourists at 20 pence a packet. Westminster City Council has to employ
three men, working a 16-hour shift over a seven-day period, together with
a pedestrian vehicle to wash pigeon droppings from the paved area of Trafalgar
Square three times a week – at a cost of 38,725 Pounds each year.
* * *
Social complexities in pigeon flocks
Pigeons have an undeserved reputation for being stupid. Research has
demonstrated their social sophistication, and their capacity to learn new
behaviour. Louis Lefebvre of McGill University in Montreal is midway through
an investigation of the behaviour of pigeons within established flocks.
In observation of urban flocks containing about 50 birds, he and colleagues
at McGill have made new discoveries about the dynamics of flock behaviour.
Some of their findings may be of value in controlling pigeons. For example,
Lefebvre discovered that, as with rock doves, city pigeons tend to have
two peak times for feeding each day, early in the morning and late in the
afternoon. This information is of obvious value to trappers.
However, Lefebvre found substantial variations between individual birds.
Some always forage at the same site while others invariably visit one in
the morning and another in late afternoon. Also, the flocks are not static
but made up of a mixture of ‘regulars’ (usually around two-thirds of the
flock) and ‘visitors’. But there is considerable turnover within what he
calls the ‘core’ flock. Lefebvre found that, on average, a flock attracts
a new member every five days or so.
Discoveries by Lefebvre’s team relating to the feeding habits of flocks
could also have implications for the success of control strategies. One
particularly important finding was that individual birds show a predilection
for particular foods if several are available at once – for example, when
a mixture of seeds, peas, wheat and corn is fed to a flock.
Lefebvre calls this ‘resource partitioning’, and says that the behaviour
avoids unnecessary competition for food within the flock. It also means
that if doped bait is confined to only one or two kinds of food, it may
knock out only a few members of the flock.
Extending this research, Lefebvre found that if two individual birds
share a particular taste, say corn, one will automatically yield to the
dominant bird if both corn and another kind of food are available. ‘The
dominants move to a food, while the subordinates move away from it,’ he
explains.
Within the hierarchies of flocks there are birds with a marked aptitude
for finding new sources of food or learning new tricks to acquire food.
‘One or two individuals do the searching all the time, while most of the
others simply scrounge,’ he says. Moreover, newly discovered patterns of
feeding are rapidly transmitted through the flock through a process of imitation,
emphasising the capacity within flocks for social learning.
In one experiment, two people threw bread to a flock of pigeons, but
at different rates. One threw bread every 5 seconds, the other every 10
seconds. Lefebvre found that at fist, half the flock went to each person.
But it took just 2 minutes for the flock to partition itself according to
the availability of food, with two-thirds of the flock grouped around the
person throwing the most bread.
When the rates of feeding were reversed, it took the flock just 2 minutes
to readjust, with two-thirds of the birds accumulating around the person
who originally threw the bread less frequently.
‘When food can be shared, only a few individuals learn the new foraging
behaviour; the rest of the flock learns instead which knowledgable birds
to follow. The individuals who learn to search and those who learn to follow
differ from one foraging situation to another, leading to a potential pooling
of skills within the flock.’
Lefebvre says that attempts to control flocks by removing the knowledgable
birds would not work because other birds quickly fill the vacant role. ‘We
are dealing with an extremely complex situation .. if ‘intelligent’ individuals
are removed, news of the vacuum soon spreads.’
