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Riv. ital. Orn., Milano, 82 (1-2): 58-65, 30-IX-2013
58
7, Parkside Avenue, Winterbourne, Bristol BS36 1LU. E-mail: pete.rock@blueyonder.co.uk
Abstract – Urban gull populations in Britain and Ireland have grown exponentially since
1969 to something in excess of 100,000 pairs today and could reach 500,000 pairs within ten
years. Pest control has singularly failed to address the issue and will continue to fail until un-
derpinning science reveals why urban gulls are so successful. All deterrence methods so far em-
ployed (and described) are largely based on guesswork and may have introduced further compli-
cations into the issue. In Italy numbers of urban gulls and their attendant problems will certain-
ly grow (possibly exponentially) in the next ten years.
Key words – urban avifauna, Laridae, British Isles, pest control, deterrence methods.
Riassunto – Gabbiani urbani. Perché gli attuali metodi di controllo falliscono sempre.
Le popolazioni di gabbiani urbani (Gabbiano reale nordico, Larus argentatus, e Zafferano,
La rus fuscus) in Gran Bretagna e Irlanda sono aumentate esponenzialmente a partire dal 1969
no a raggiungere oggi qualcosa come 100.000 coppie, e potrebbero raggiungere le 500.000 coppie
in altri dieci anni. Il controllo delle specie infestanti ha sorprendentemente fallito in questo cam-
po e continuerà a fallire, nché con l’appoggio delle conoscenze scientiche non si scoprirà perché
i gabbiani urbani abbiano un tale successo. Tutti i metodi deterrenti nora impiegati (e descritti)
sono in gran parte fondati su congetture e possono aver anche introdotto ulteriori complicazioni
in questo campo. In Italia i numerosi gabbiani urbani e le loro conseguenti problematiche aumen-
teranno di certo (probabilmente in modo esponenziale) nel prossimo decennio.
Parole chiave – avifauna urbana, Laridae, Isole Britanniche, controllo infestanti, metodi
deterrenti.
Introduction
Roof-nesting by the large gulls was virtually unknown in Britain be-
fore the Second World War. There was some minor colonisation by the
early 1960s (
pArsloW, 1967), but in 1969-70 Operation Seafarer identi-
ed signicant numbers of urban sites (60) and a total of 1,310 pairs of
Herring, Larus argentatus, and Lesser Black-backed Gulls, Larus fuscus,
peter roCk
URBAN GULLS.
WHY CURRENT CONTROL METHODS ALWAYS FAIL
59
URBAN GULLS. WHY CURRENT CONTROL METHODS ALWAYS FAIL
nesting on buildings (CrAmp, 1971). Thereafter, urban colonisation was
rapid. By 2004 it was estimated that well over 100,000 pairs were nesting
on rooftops in Britain & Ireland (
roCk, 2005a).
This exponential growth was fuelled by massive food availability -
mostly from newly opened landlls catering for massive increases in mu-
nicipal waste (the beginning of ‘Throw-Away Society’) and particularly
after the 1956 Clean Air Act forbade the burning of refuse on site. The
gull species were, of course, quick to take advantage of this new feeding
opportunity (
pArsloW, 1967) and in the Severn Estuary Region, for exam-
ple, numbers rose by fteen-fold in rural (wild) colonies by the early 1970s
(
mudGe & Ferns, 1980).
As a result of dramatic population increases, it appears that tradition-
al colonies were outgrown and prospective breeders sought out alterna-
tive breeding areas. In short, they began to colonise towns and cities by
the late 1960s and early 1970s. Gloucester, for example, was rst colo-
nised (3 pairs) in 1967 (
oWen, 1967). It now supports 2,700 pairs (roCk,
2007a).
Since the mid-1980’s complaints to local authorities in UK about roof-
nesting gulls have grown in direct proportion to colony sizes. Many local
authorities nowadays receive in excess of 100 complaints annually (
roCk,
2005a). This, in turn, led to increasing Media coverage of the problems at-
tending all urban gull colonies, but with particular emphasis on aggres-
sion. Aggression (especially during the chick-rearing phase), however, is
a far less common subject of complaint than are noise, mess and damage
in that order.
Nuisance is a fact of life in towns with urban gull colonies, but urban
gulls can also have serious nancial consequences for local economies.
The readily calculable costs surround mess clearance (faeces on streets,
masonry, windows, car paintwork, etc), damage repair (air-conditioning
and other roof plant insulation, roong felt and ashing, rain-washed
nests blocking gutters and drains causing ooding, degradation of roof-
ing material, etc), roof maintenance (nest clearance and roof cleaning - a
very expensive operation if this involves many nests) and so on... Even the
costs of responding to complaints can be assessed.
Less easy to calculate are the hidden costs, but it is suspected that
these may be rather more signicant for local economies. For example,
tourists persistently woken before dawn will be reluctant to visit again;
shoppers having to avoid faeces and aggression will prefer to spend their
money at centres where gulls do not breed; sleep-deprived workers will ei-
ther fail to turn up or will produce substandard work and so on...
In the light of the foregoing it is not difcult to understand the growth
of those sectors of the pest control industry specically targeting gulls.
This paper assesses the efcacy of various systems, methods and equip-
ment devised for the purpose of deterring roof-nesting by the large gulls.
60
PETER ROCK
Materials and methods
A plethora of equipment has been devised or adapted for use against
urban gulls.
All of the above methods have the potential to cause urban gulls to re-
locate their breeding effort. However, of these simple methods two in par-
ticular (continual nest removal and roof netting) can certainly result in
forced relocation (see discussion).
Roof netting, originally designed to prevent pigeon access has (with-
out testing) been assumed to be suitable for gulls. This is not the case. In
most urban gull colonies in UK gulls are all too often caught in roof nets
because the mesh size is wrong. Carpal joints are trapped resulting in a
lingering death over several days. The worst observed was in Cardiff in
2004 with 13 dead gulls (
roCk, 2004a).
People feeding gulls in town will always attract attention. This has led
to the anecdotal assumption that gulls breed in town because of feeding
opportunities. Of course, the large gulls never reject such opportunities,
but the primary reason for breeding in town is a safe nest platform. Town
has no predators and little disturbance. Additionally, ambient tempera-
tures in town are 4-6 °C higher than the surrounding countryside (Heat
Islands) allowing urban gulls to breed slightly earlier than those in tradi-
tional, wild colonies (
roCk, 2005a).
Furthermore, the large gulls are capable of ying speeds in excess of
100 kph (
roCk, 2006a) allowing home (feeding) ranges to be greater than
100 km in radius. From research (e.g.
roCk, 2007b), it is clear that the
large gulls forage widely at all times of the year and know their home
ranges intimately. This is a sensible survival strategy because if one food
source becomes unavailable, they will know about others.
The more serious methods require more attention because (in theory)
they can be effective. There are, realistically, only two lethal methods.
These are poisoning/narcotising and shooting. Poisoning has long been
outlawed in UK, but narcotising (and then despatching narcotised gulls)
has been shown to be very effective in reducing breeding numbers in wild
colonies (e.g.
Coulson et alii, 1982; soWter, 2004). However, the colonies
involved were far from the public gaze. In town, such action would be very
public. In Scarborough in 1995 a vociferous, well-connected and articulate
lobby effectively prevented further intervention. The active chemical (Se-
canol) has now been proscribed by DEFRA.
The shooting of gulls in town would require many guns and much time.
In Gloucester, for example, with 2,700 pairs (
roCk, 2007a) this would
mean eliminating a major percentage of at least 7,000 gulls (the breeding
adults plus the non-breeding immatures). Even assuming that the legal
complexities surrounding private property and the use of rearms could
be overcome, this would be quite a task!
61
URBAN GULLS. WHY CURRENT CONTROL METHODS ALWAYS FAIL
Tab. I - Outline of the simplest methods with comment.
Method
Nest Raking
Egg Pricking
Continual removal
of nest material
Signs/Posters
Bird Scarers
Wires & Spikes
Birds of Prey
Roof Netting
Description
Smashing eggs and/or destroy-
ing nests.
Eggs are pricked with a needle
or injected with formalin.
Requires someone to visit roof
daily and remove nest materi-
al as soon as it appears.
Requesting people not to feed
gulls or threatening bye-laws.
(a) Loud bangs, screaming
noises, waving streamers, etc.
(b) Plastic Eagle Owls, Bal-
loons resembling threatening
eyes, etc.
(c) Gull distress calls broad-
cast across urban areas.
(d) Wind-driven, moving struc -
tures - ‘The Spider’ etc.
Tensioned wires/spikes are po-
si tion ed on parapets and other
structures to prevent perch ing
and nesting.
Falconers y birds of prey in
urban areas.
Covering the whole, or part of
a roof so that birds cannot get
to it. Can be very expensive.
Comment
Birds simply rebuild nests and relay eggs.
Eggs are quickly recognised as being non-
viable. Gulls reject them and relay.
This method is completely effective, provid-
ed it is assiduously carried out and that all
parts of the roof are accessible. Comment
below.
These are mostly ignored amongst many
other signs and posters. Every town has
one (or several) people who feed gulls. No
effect. Comment below.
Loud noises are quickly ignored by gulls in
towns full of odd noises.
Plastic and other objects of all types are ig-
nored by gulls. No effect.
These have a temporary effect, but are
quickly recognised and then ignored. Often
they make more noise than gulls and can
be stopped by complaints from residents.
No effect.
Little or no effect. Gulls will place nests
elsewhere and, sometimes, on top of such
equipment.
This creates considerable disturbance
amongst the gulls. However, this does not
deter breeding and may result in injury
to falconer’s bird. More show than effect.
Comment below.
This has some effect, provided netting is
carefully positioned and maintained. If not,
birds will nest on top of it. Well positioned
and erected netting will prevent birds nest-
ing on a particular roof, but will also cause
birds to relocate. Comment below.
62
PETER ROCK
If a gap appears in any niche, it will be lled.
Successful colonies attract more recruits than failing colonies.
There are many other urban colonies supplying recruits to the treated colony.
If pairs fail to breed in any season (or several seasons), it will make no difference to growth
rates in the region.
1
2
3
4
Such an operation would certainly attract considerable Media atten-
tion. Quite apart from the inevitable, unfavourable publicity, in an in-
creasingly litigious society, if buildings or other structures were damaged
or, worse, somebody were shot (or narcotised), due legal (and costly) pro-
cess would be brought to bear. Even though some (discreet) shooting by
individuals and pest control companies is known to occur, local authori-
ties have distanced themselves from such action. It is therefore concluded
that lethal methods would be politically unwise in town.
Currently, the most popular method is to oil, or replace eggs with plas-
tic dummies. Oiling with liquid parafn effectively prevents hatching, but
sand-lled dummy eggs (as used by poultry breeders) are seen as more ef-
cient. In theory, by preventing hatching (i.e. reducing the number of off-
spring in any year), it is believed by adherents that populations will de-
cline. This is wrong.
The gures are these:
Of 100 untreated eggs, approximately 20% can be expected to be un-
successful (hatch failure, edging failure or death very soon after edg-
ing, etc). Statistically, half can be expected to be males/females. Females
can be expected to emigrate whereas males tend to return to their natal
colonies once they are old enough to breed (
roCk, 2005a). And then there
is survival. Survival rates amongst the large gulls are high but, statisti-
cally, only (circa) 45% can be expected to survive to breeding age. Thus:
100 minus 20%=80 x 45%=36 divided by 2=18.
Therefore, if 100 eggs are oiled/replaced, the possibility is that 18 birds
will have been prevented from returning to breed. However, other factors
are also at work.
The gures above and the additional factors serve to negate any hoped-
for reduction in population size and neither will there be any decrease in
the mean annual growth rate. The same gures would also apply to surgi-
cal sterilisation (assuming that these birds survive the surgery).
Egg interventions can have a place in management of urban gulls.
During incubation adult birds are measurably quieter than during oth-
er breeding phases (especially chick-rearing). Therefore, this method is
properly used in sensitive areas such as hospitals, shopping centres, etc.
But, there are other dimensions to egg interventions. In 2004 an egg
63
URBAN GULLS. WHY CURRENT CONTROL METHODS ALWAYS FAIL
oiling campaign took place in Gloucester. In 2005 an 18.6% decrease
in numbers of breeding pairs was observed in the treated areas (
roCk,
2005b). However, a 51% increase in numbers of breeding pairs in another
part of Gloucester was observed in the same year. Similar declines and
increases as a consequence of oiling have been noted in Brest, France (
CA-
diou et alii, 2005).
Further, little is known about divorce amongst gulls. Under normal
circumstances the large gulls pair for life (
CrAmp & simmons 1983). Breed-
ing failure is a cause of divorce, but exactly how many breeding failures
will result in divorce is not known. Amongst Great Skuas, Catharacta
skua, divorce results in females seeking younger, tter males (
CAtry et
alii, 1997) and amongst urban gulls, whilst uncommon, it is increasing-
ly the case that adult females are paired with young males (3cy birds) in
urban colonies in the Severn Estuary Region (
roCk, 2005a). It is possi-
ble that these adult females are divorcees and that perhaps it is only one
breeding failure that has triggered divorce. If this is the case, then inter-
ventions (such as egg oiling) may be responsible for divorce.
Discussion
Several of the methods described above can result in forcing gulls to
relocate their breeding efforts (most particularly continual nest removal,
netting and egg interventions). It is often the case that local authorities
acting against urban gulls care less about what happens after interven-
tions than about simply getting rid of gulls from their areas of jurisdic-
tion. The large gulls can live for 35 years and if they are deterred from
nesting in one location, they will certainly breed in another, possibly on-
ly as far as the building next door. Questions, therefore, must be raised
about the wisdom of forcing relocations.
Little is known about such forced relocations, but the demolition of
a large warehouse in Bristol in 1997 (
roCk, 2005a) resulted in approxi-
mately 60% of colour-ringed breeding birds relocating to roofs elsewhere
in the colony, but 40%, though they were seen at landlls, roosts and even
abroad, were never found breeding in Bristol. It was not until 2003 (
roCk,
2003) that the rst of these ‘disappeared’ birds was found breeding in
Chippenham - some 32 km from Bristol. Had this bird relocated in 1998 it
would have been one of Chippenham’s rst colonists... It is suggested that
interventions (of whatever kind) are very likely to introduce more com-
plexity into an already complex situation.
To illustrate rapid colonial growth, the Bath colony doubled in size
from 400 to 800 pairs in 6 years (
roCk, 2007c), Gloucester doubled from
1,350 to 2,700 pairs in 5 years (
roCk, 2007a), but Felixstowe, Suffolk,
more than doubled in size from 630 to 1,470 pairs in only 3 years (
roCk,
64
PETER ROCK
2007d). Growth rates, of course, are entirely dependent upon the carrying
capacity of the environment (i.e. food and nest sites).
Town offers limitless nest sites (even Gloucester has ample room for
expansion), but food may become an issue. In line with the European
Framework Directive on Waste (75/442/EEC) and the Landll Directive
(1999/31/EC), Government is acting to reduce waste to landll (Waste
Strategy 2000, National Waste Plan 2003-2020), the requirement being
that municipal waste is reduced to 30% of present levels. Landlls play
an important role within the urban gull issue (
roCk, 2005a), but during
a deterrence trial at Gloucester Landll (
roCk, 2007b) 31% of deterred
gulls did not utilise alternative landlls. These birds were able to nd
food from sources other than landlls, but these sources are unknown. As
landlls receive less organic waste these alternative food sources may be-
come criti cally important (
roCk, 2007b).
If the annual growth rates observed between 1994-2004 (17.6%) are
maintained the urban gull population in Britain & Ireland may exceed 1
million pairs within the next 10 years (
roCk, 2005a), but if not, it is highly
likely that we will see at least 500,000 pairs and urban gulls will far out-
number wild gulls (e.g.
mitChell et alii, 2004).
And what of Italy? Italy has several known urban gull colonies of vary-
ing sizes including Naples, Livorno, Venice, Rome and Trieste where Yel-
low-legged Gulls, Larus michahellis, breed on city rooftops and industrial
units. It is clear that within the next 20 years there will be many more
and some will become large colonies (i.e. more than 1,000 pairs).
Pest control has so far failed to make any signicant impact on annual
growth rates in UK (
roCk, 2005a). It is suggested that this is because, at
best, methods attempt only to address the symptoms and, at worst, are
just guesswork. The considerable expense involved in pest control to date
must, therefore, be viewed as wasted money. Until we understand much
more about why urban gulls are so successful from scientic investiga-
tion, there will be no resolution to the issue, failure will be perpetuated
and money spent to little effect. The question is this: when did we ever
solve any problems without rst knowing, precisely, what we are dealing
with?
Italy, presently, is at the beginning of the urban gull issue with on-
ly small roof-nesting populations. In 2007 Trieste supported circa 350
pairs (
Benussi, 2005). Bristol supported this kind of population in the late
1980s, but in 2004 the Bristol colony stood at almost 2,000 pairs (
roCk,
2004b). All established Italian urban colonies will grow and new towns
will be colonised during the next 10 years. If, as seems likely, exponential
growth similar to that experienced in UK is Italy’s future, this paper car-
ries a warning...
URBAN GULLS. WHY CURRENT CONTROL METHODS ALWAYS FAIL
65
Acknowledgments - I would like to express thanks to Enrico Benussi and Emily Prall for in-
viting me to speak at the 14
th
Italian Ornithological Congress in Trieste and for inviting this pa-
per.
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