4 Cormorant Management Tools

the intercafe cormorant management toolbox

4 CORMORANT MANAGEMENT TOOLS

Limiting the interaction between 4.1 Scaring Cormorants Away combination. If these deterrents are cormorants and fish can be From A Fishery used in conjunction with highly- achieved in a number of ways, visible human presence, this will each falling into one of four broad The basic philosophy behind increase their overall efficacy but categories of action: techniques to scare birds away may reduce their cost-effectiveness. from a fishery is that cormorants As with many other techniques, 1. Scaring cormorants away from a are startled sufficiently to move to it seems best to operate these fishery. another foraging site by means of deterrents before or as soon as birds 2. Protecting the fish — by auditory, visual or even chemical arrive at a site — thus preventing preventing cormorants from deterrents. Clearly, the effectiveness them from getting used to the area reaching them. of these techniques relies on: (1) as a foraging site in the first place. 3. Altering fish availability to the deterrents being sufficiently Once birds have learned that a site cormorants — by making frightening to cormorants to make is good for foraging or breeding, it a fishery less attractive as a them move elsewhere; and (2) there will be much harder to deter them foraging site. being a ‘better’ alternative site for from coming to it. 4. Reducing overall cormorant them to move to. numbers — for example, by 4.1.1 Auditory deterrents killing cormorants locally to The main drawback of these reinforce scaring at specific techniques is that cormorants A number of commercially sites, killing them more eventually (often quite quickly) produced noise-generating bird intensively, or reducing their realise that they offer no real threat scarers are available — for example, reproductive efficiency. and the birds become ‘habituated’ through local agricultural suppliers. to the noises, sights or smells, These vary considerably in their In addition, under some ignoring them thereafter. However, price and complexity, from simple circumstances cormorant-fishery there is good evidence that birds humming tapes to relatively conflicts can be addressed through are scared consistently by human sophisticated, automatic devices the use of financial or other presence if they perceive that such as gas cannons. A general compensation measures. humans are associated with danger. consideration with all these devices Where this is not the case, the is noise nuisance, and any national The Toolbox aims to summarise birds can sometimes be approached and local controls on their use must information on each category of at close quarters and show no be taken into account. action with regard to the methods apparent fear of man. available, their efficacy, the 4.1.1.1 Gas cannons constraints on their deployment The key to the successful use of Gas cannons are deterrent devices or use, and the relative costs. auditory and/or visual deterrents that produce loud banging noises The aim is to provide a broad seems to be to make them as by igniting a mixture of gas (either overview of the effectiveness of unpredictable as possible by acetylene or propane) and air different management options for changing their location and under pressure. The frequency of different cormorant-fishery conflict frequency of use, and by using detonation can be regulated by situations. a number of techniques in adjusting the gas feed or with an

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Gas cannon. Photo courtesy of Thomas Keller. automatic timing device. Most produced by a cannon is similar to migrating fish such as Atlantic cannons produce a single bang at the noise of a shotgun and causes a Salmon (Salmo salar) smolts, or pre-set, timed or random intervals, startle reflex, thus prompting birds in the vicinity of obstructions or but some devices can produce in the vicinity to take flight. Their barriers in rivers that may cause double or triple bangs, and rotators efficacy is reportedly heightened fish to congregate and hence are available so that the noise can where birds have had prior increase their vulnerability to be aimed in different directions. experience of shooting to kill. predation. Some are regulated by computer to produce a random length of the Gas cannons are widely used The effectiveness of gas cannons volley and with random intervals throughout Europe at aquaculture depends on how they are used, the between volleys, or they may facilities and to protect inland size of the site to be ‘protected’, incorporate light detectors to allow fisheries, particularly at smaller and the availability of alternative the device to be turned off at night. sites. They have also been feeding areas for the birds close deployed at specific locations by. Local conditions, such as A gas cannon is relatively or for particular times at larger wind direction and strength, can expensive and prices vary, sites — for example, to protect also affect the intensity of noise. depending on whether it is fishing gear (e.g. fixed nets), or Cannons are more cost effective electronic or mechanically ignited; to restrict local damage for short, at smaller fishery sites, and the whether it is a single, double or highly sensitive periods. These cost of sufficient numbers to cover multi-bang device; and whether might include the draining and a large area may be prohibitive. features such as a rotator or harvesting of Common Carp Researchers have suggested that mechanical or electronic timer (Cyprinus carpio) ponds, during one cannon can protect 1.3–2.0 ha are fitted. The unexpected noise aggregations of breeding or at aquaculture facilities, if

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‘A cannon firing repeatedly without any variation in timing or direction quickly loses its potential to scare birds’ Vehicle-mounted gas cannon. Photo courtesy of Thomas Keller. reinforced with other techniques. The general consensus of opinion is away by it, especially if they have A survey of catfish(Ictalurus that gas cannons are most effective no experience of shooting to kill. spp.) farmers in the USA indicated when moved every few days, have A cannon firing repeatedly without varying levels of satisfaction with variable firing intervals and are any variation in timing or direction the use of gas cannons to deter deployed in combination with other quickly loses its potential to scare Double-crested Cormorants: scaring techniques. For example, birds. In such circumstances, around 10% of respondents felt placing a cannon in a hide used by cormorants have even been they were ‘highly effective’ and shooters, and frequently moving reported to use gas cannons as about half found them ‘somewhat it between hides, may prolong the perches. Although cannons can be effective’; others regarded them as scaring effects of both the shooting effective if the firing frequency and ‘ineffective’. and the cannon. Gas cannons direction are varied, these scarers employed at fish-rearing ponds in may be socially unacceptable near A simple field experiment carried Israel have also been mounted on residential areas due to public out in the Czech Republic recorded wheeled carriages or on vehicles to concern about noise nuisance, the reactions of cormorants to make them highly mobile, where especially if left to fire at night. the firing of a gas gun. A number their effectiveness is reinforced However, pointing cannons away of cormorant responses were by human presence and shooting. from houses and constructing recorded: (a) no reaction; (b) taking Products are also available that simple straw baffles around them fright; (c) diving; (d) soaring and combine visual and acoustic stimuli allows the devices to be placed at circling; and (e) flying out of the to scare birds — the ‘Rotating approximately half the distance pond. These were found to be Hunter’ consists of two propane of cannons without baffles, with correlated with the distance of the cannons and the metal silhouette of no increase in noise nuisance. As birds from the gas gun. Typically, a person that swivels with the force sounds tend to be heard at greater birds up to 300 m away displayed of each bang. distance at night, gas cannons near an active response (e.g. soaring and human settlements should be turned circling, flying out of the pond), The main reason for cannons off or programmed to stop at night, suggesting that this method would losing their effectiveness is unless Night Herons (Nycticorax be particularly effective on smaller habituation — birds get used to nycticorax) or other nocturnal birds fish ponds. the noise and are no longer scared are also a problem.

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Gas cannons may also have an crackers, screamer shells, whistling also require little manpower — undesirable effect on other wildlife and exploding projectiles, bird these are simply lengths of slow (e.g. birds and mammals) and bangers, flash/detonation cartridges burning fuse with bangers inserted humans (e.g. fishermen or fish farm and flares. These can be fired from at intervals to produce a series of workers), and they may also need modified pistols (with a range of loud explosions at approximately to be located in secure locations approximately 25 m) or shotguns 20-minute intervals. Placing them to guard against theft. One must (range of 45–90 m) and can produce inside clean, empty oils drums also be aware that the cannon noise noise levels of up to 160dB. As the can enhance the noise of the may be mistaken for gunshots, direction and intensity of firing can explosions, but particular care is and it would be prudent to inform be controlled to suit the bird species needed to ensure this is done safely. the police, wildlife rangers and, and location, an advantage of this Weather conditions can affect the in some countries where they may technique is that deterrence can be burning speed of the rope and there be deployed near national borders, targeted and disturbance of non- is also a danger of creating a fire the military about their presence. It target species minimised. Be aware hazard. As with all pyrotechnics, may also be wise to advertise the that both the cartridges and the gun great care must be taken with their use of such equipment widely to require a firearms certificate in some storage and transport. anglers, or others using a site, as countries, and legal restrictions on the loud report may be disturbing to their use may also apply. In some In Israel, some fishermen have those with a nervous disposition or countries, pyrotechnic operators been licensed to use professional certain medical conditions. need to be licensed or carry special fireworks and have also explored insurance. the use of remote-control devices Moreover, in other circumstances to set off pyrotechnics placed at the use of gas cannons may be various locations around fish farms. imprudent. For example, at fish Trials were completed with some over-wintering ponds stocked with success, but this approach was not very large densities of small fish, adopted for widespread use due to the noise of cannons can agitate the relatively high costs and some and stress the fish. At sites in technical problems. A large variety Italy, such stress has reportedly of powerful fireworks are available, caused fish to move, exposing them thereby helping to prevent bird to more environmentally harsh habituation, and many are much conditions and leading to mass less expensive than simple banger mortalities. shells. However, legal restrictions on their use apply in most 4.1.1.2 Pyrotechnics countries. Pyrotechnic devices are widely used as a cormorant deterrent at In a survey of Mississippi catfish aquaculture facilities and to protect farmers, 21 of 281 respondents inland fisheries, particularly at (around 7%) regularly used smaller sites. They produce loud Pyrotechnic rocket. pyrotechnics. Of these, 24% bangs or whistles and emit flashes Photo courtesy of Paul Butt. considered them to be ‘very of light and colour, and they effective’, 57% ‘somewhat can provide a cheaper and more effective’ and 19% ‘not effective’. flexible alternative to gas cannons, Alternative pyrotechnics include Other researchers have reported depending on the level of use bird-scaring rockets — similar variable effectiveness in the use and whether their use introduces to recreational fireworks — and of pyrotechnics against different additional manpower costs. rope-firecrackers. These devices are species of fish-eating birds. This relatively inexpensive (for short- may be partially dependent on the There are a wide variety of noise- term use) and easy to use. The availability of alternative feeding producing cartridges, including shell rope-firecrackers (‘banger ropes’) and loafing areas for birds.

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As with gas cannons, pyrotechnics roosts in the Northern Po Delta and problems of public safety. are not considered effective in Italy, with varying results. They should also not be used in on large bodies of water and They proved useful at smaller situations where there could be habituation can occur rapidly roosts, particularly during the a fire hazard, such as near dry if they are used too frequently. initial establishment period. vegetation. Like gas cannons, Moreover, if they are used in large At a large roost (2,500–3,000 the noises can also have negative numbers they are also unlikely to birds) established 10 years impacts on other wildlife and be cost-effective. Habituation can previously, a large number of humans. be delayed by using pyrotechnics pyrotechnics were deployed on selectively — i.e. infrequently several after-dark occasions, 4.1.1.3 Shooting to scare and at close range, and by varying with reinforcement using a laser Shooting to scare is one of the the type of shell used (whistles, rifle. However, there appeared most widely used techniques bangs, flashes). However, they to be no clear or lasting effects for deterring cormorants at sites can be very effective at smaller in this instance; the financial across Europe and elsewhere. It sites, particularly in combination costs were high and the logistics is one of the few techniques that with mobile, visual scarers, other complicated, and staff motivation is employed at all types of water deterrents, or by occasionally proved difficult during inclement body, from small to large and killing individual cormorants. weather conditions. from inland to coastal, as well as at aquaculture facilities. There Pyrotechnics are often used in Nevertheless, pyrotechnics can are fewer legal restrictions on Israel, in combination with other be an extremely effective and the use of this technique than on techniques, in effective deterrence relatively low-cost, non-lethal shooting to kill (although non- programmes and for effective method of bird scaring. They toxic ammunition must be used dispersal of night roosts. It should are easy to operate, the risks near water bodies in many places), be noted that their effectiveness of habituation are reportedly and in some countries a shooting may be partly due to the presence negligible if their use is licence and appropriate insurance of an active human operative ‘randomised’ as much as possible may be a legal pre-requisite even and, with the exception of rope- (i.e. applied on an ad hoc, as-needs for shooting blank cartridges. firecrackers, pyrotechnics therefore basis at different locations) and represent a fairly labour-intensive they pose fewer safety problems Shooting to scare can be used to method of bird scaring. than shooting. However, their deter birds or reinforce the scaring use should be limited to sites effect of other deterrents, such Pyrotechnics have been used away from residential areas to as human presence, gas guns and to scare cormorants at several avoid causing a noise nuisance pyrotechnics. It is more widely

Verey Pistol. Photo courtesy of Paul Butt. Blanks. Photo courtesy of Paul Butt.

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‘Shooting to scare is one of the most widely used techniques for deterring cormorants at sites across Europe and elsewhere’

used than the use of pyrotechnics possession and operation, the use of treatment phase. An average because live ammunition is often bird-scaring cartridges is probably bird reduction of over 50% was cheaper and more readily available. somewhat limited. reported. However, bird numbers The most commonly deployed recovered to pre-treatment levels weapon is a 12-bore shotgun, Shooting to scare can be an over a period of two to six weeks. although relevant certificates for effective deterrent, and it is To be effective in the longer term, such use may be required. The sometimes the only option available this means that such scaring would safest way to use a shotgun for this on a river or still water to which need to be repeated at regular purpose is to fire blanks, which are the public have access. It has intervals for as long as cormorants available from local gun dealers. been demonstrated in a recent remained in the area. When done This also avoids any possibility study in the UK that shooting to properly (e.g. as birds first arrive), of actions being misconstrued, of scare can reduce the number of and in conjunction with other birds being injured, and of adding birds present at fisheries for the deterrents, this can be highly lead to the ecosystem. duration of the shooting period effective over a long period of time. and for a ‘post-treatment’ period. Live ammunition can also be used, A large-scale experiment was 4.1.1.4 Bio-acoustics, acoustics, but care needs to be taken not to undertaken involving thirteen, ultrasonics and high intensity kill or wound birds, unless the six-week field trials carried out sound appropriate authorities approve over two years at a range of Bio-acoustic deterrents are sonic this. The practice of ‘peppering’ fishery types (including river and devices that transmit sounds with a cormorants with small lead shot stillwater fisheries, stocked and biological meaning — for example, pellets in order to deter them is unstocked sites, and fisheries recorded bird alarm and distress commonly considered inhumane with and without cormorant night calls. Typically, alarm calls are and illegal in most places. A roosts). The experimental design used when birds perceive danger, starting pistol can be used as an involved three treatments: control while distress calls are used when effective alternative to the use of (no shooting), lethal shooting and birds are captured, restrained or a shotgun, although care should non-lethal shooting (at the same injured. Both types of calls are be taken so that others do not intensity). Each six week trial was usually species-specific and can misinterpret this course of action. divided into three two-week phases: cause members of the same species pre-treatment, treatment (when to take flight, but they may also It is also possible to purchase a shooting with blanks was carried elicit a response in other species variety of special bird-scaring out) and post-treatment. Numbers that are taxonomically related or cartridges. However, these of cormorants were then compared which closely associate with the are specially designed to be before and after commencement of call-producing species. fired through a signal (Verey) shooting and between control and pistol sleeved to 12 gauge and shooting sites. Recorded alarm calls are widely not through a normal shotgun. used as bird deterrents, and such Appropriate firearms certificates The results indicated that shooting biologically meaningful sounds may also be required for these. (to kill or to scare) significantly should be more repellent and Furthermore, because of the noise reduced the number of cormorants resistant to habituation than other they make and the restrictions on for both the treatment and post- sounds, although responses vary

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between species (e.g. some species An underwater acoustic system of gull [Larus spp.] are initially (‘Cormoshop’®) has recently attracted to the noise, apparently to been developed and produced investigate). There are reports of the commercially in France, based successful use of broadcast distress on the calls of the Killer Whale calls to deter some species of heron (Orcinus orca). Underwater (Ardea spp.) and Night Heron. loudspeakers, supported by floats However, in trials in Italy and situated 40 cm under the water Israel the broadcast of Night Heron surface, diffuse sound waves into distress calls at night and early in the water to frighten cormorants the morning caused unacceptable when they are diving. Various disturbance to people living nearby. frequencies have been tested and those at 90 kHz — the frequency of Researchers have reported that sounds from a Killer Whale — were locating sources of cormorant found to be most effective. The distress calls is problematic. manufacturers have continued to It was discovered that some revise the frequency settings and commercially-sourced distress calls power output to further improve the trialled in Italy were actually the effectiveness of the device. cries made by nestling cormorants when calling their parents. Further, Initially, the ‘Cormoshop’® it has been noted that the birds system was tested at commercial rarely seem to make distress calls fish ponds in France and feedback anyway. Despite repeated attempts from the pond owners was largely by one researcher to induce and positive. Experience indicated record such sounds from injured that diving cormorants took and captured adult cormorants, flight immediately and stayed and while ringing nestlings, the away from the protected ponds. birds always remained silent. However, the device appeared Nonetheless, trials have been to work only on ponds where that birds habituate to the device carried out in some countries with the fish density was relatively at extensive aquaculture facilities, cormorant distress calls, but the low (<300 kg/ha). At higher fish and it has reportedly proved too results have suggested that the densities the system appeared to be expensive for use at such locations. technique is of short-term use only less effective, possibly as a result The device has been used with and ineffective in the longer term of the cormorant’s dive time to more success at fish ponds used for due to habituation. Similar reports catch a fish being shorter because recreational angling, possibly as a from North America indicate that of greater food availability. The result of the presence of the device distress calls were generally found system reportedly has no adverse being reinforced by regular human to be ineffective against Double- effect on fish behaviour and can disturbance. crested Cormorants, at least over be reliably used under all climatic long periods of time. conditions. However, it requires a Sonic bird scaring systems that reliable electric power source and produce a variety of electronically- The possibility of broadcasting thus may not be applicable at more produced sounds, sometimes cormorant distress calls underwater remote sites. associated with randomly- to enhance their effect (sound activated lights, are also available propagates more effectively Units have mainly been used in commercially. The range of loud underwater) has been considered, France and Belgium, although and sudden noises they produce but it does not appear to have been they have also been deployed at can frighten birds but, as they tested as yet or made commercially sites in Italy and Germany. Initial have no biological meaning, the available. feedback from Belgium suggests risk of habituation is greater. With

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involved. Some reports suggest such devices can deter cormorants, although a proportion of the birds present were reported to dive rather than fly away.

In the Po Delta in Italy and in Sardinia, extensive trials have been conducted with sonic bird- scaring devices to scare cormorants away from their night roosts and to keep birds away from particular areas within extensive aquaculture lagoon systems where high densities of fish are held over winter. Two commercially-available devices were tested. The trials indicated that electronic sounds could be useful, at least in the short term, to deter groups of birds, but appeared to be ineffective against single birds, particularly if these birds were well used to the area. Habituation was seen as a problem and strong winds dispersing the sound away from the desired direction was also considered to have affected the efficacy of the devices.

Evidence indicates that most species of birds do not hear in the ultrasonic range (>20 kHz) so there is no biological basis for using ultrasonic devices and no evidence that such devices deter birds. Ultrasound loses intensity far more quickly with distance than regular sound, so it is usually ineffective outdoors.

High intensity sounds, such as air horns and air-raid sirens, can distress birds and cause them to Sonic bird scaring devices. Photos courtesy of Josef Trauttmansdorff and Paul Butt. leave a site. However, they have a relatively short range and birds static systems, frequent changes mounted) systems that can be used appear to habituate quickly to their in location and adjustment of the in response to bird problems are use. Trials at aquaculture facilities sounds produced can reduce this more effective, though they are also in Israel and Italy with vehicle risk, and mobile (e.g. vehicle- more expensive due to the labour horns and sirens have reportedly

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proved largely ineffective or devices have a limited range, and from the viewpoint of practicality effective only for short periods. this can be influenced by wind for many sites. Legal constraints These devices can also cause strength and direction, ambient on the use of some of these hearing damage to humans and temperature, and surrounding techniques may apply and licences are generally not recommended features such as buildings. Thus, or permits may well be required for general use. However, sirens they are most effective at smaller for their operation. Local guidance mounted on vehicles can provide sites, or at particular locations at and necessary approvals should an effective combination of human larger sites (e.g. netting stations thus be sought prior to using presence with an audible deterrent, or known predation ‘hot spots’) to these devices. The deployment and they have been used with some address specific, local problems. of audible deterrents should also success in Israel to scare birds at All audible deterrent techniques are take account of appropriate safety fish farms. subject to habituation (birds learn issues (e.g. use near members of that they pose no danger and ignore the public or in the vicinity of Sound transmission from all sonic them), and hence they are more sensitive sites). devices is influenced by ambient likely to be of short-term benefit, temperature, wind direction and generally for weeks or shorter In addition, there will be a reflections from surrounding periods. However, efficacy can be need to guard against the use of features such as buildings, and extended considerably by moving pyrotechnics in situations where this should be taken into account devices regularly or mounting there could be a fire hazard, such when setting up such devices. As them on a vehicle for maximum as near dry vegetation. It might with most methods of bird control, mobility, where they are reinforced also be necessary to consider the using such devices as part of an by human presence, using variable security of the device to minimise integrated approach with a variety firing intervals and by employing the risk of possible theft or of techniques is likely to be more them as part of an integrated vandalism (e.g. by deploying the effective and will help reduce the control strategy alongside other device on an island). risk of habituation. measures. Many audible deterrents require 4.1.1.5 Other sound-producing In general, techniques such as some form of power source, and techniques pyrotechnics and shooting to scare this may render them more difficult Other sound-producing techniques appear to be more effective and and expensive to deploy, and can also be used to deter longer lasting against cormorants perhaps impractical, unless there is cormorants. For example, tapes that than static devices, probably due a supply of electricity or suitable produce a humming or clacking to the reinforcing effect of human batteries that can be re-charged. It sound when they move in the presence and, where this is used, is also important that such devices wind can also be used, and the shooting to kill, as well as the will operate reliably and effectively combination of sound and a visual more flexible and targeted means in what may be extremely variable deterrent can be effective (see in which they are deployed. Such environmental conditions. Section 4.1.2 on visual deterrents). measures also appear to be more effective if birds are exposed to Costs true danger (e.g. due to shooting The price of auditory deterrents 4.1.1.6 Overview of auditory or if hunting is permitted) in the varies considerably and depends on deterrents surrounding area. the complexity of the device itself Efficacy (e.g. from simple humming tapes to Auditory deterrents can be Practicality relatively sophisticated automatic effective against cormorants. The Auditory deterrent devices are devices) and the operating costs. effectiveness varies with the device used widely for a range of bird Static devices such as automatic chosen, the method of use, the scaring purposes. They are gas cannons, bio-acoustic size of the site and the availability readily available, relatively easy deterrents and sonic devices are of alternative foraging sites to to deploy and simple to operate. relatively expensive, and the which the birds can relocate. Such Such deterrents thus rate highly costs involved in trying to apply

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these over a large area are likely bang may be disturbing to those specific areas either deliberately, to be prohibitive. However, once with a nervous disposition or by direct harassment, or indirectly purchased, such devices can be certain medical conditions. through, for example, leisure used over many years and running activities or routine day-to-day costs are relatively low. 4.1.2 Visual deterrents activities. However, frequent or extended periods of human The costs of pyrotechnics or There are a number of relatively presence may be needed for this shooting to scare are relatively simple and inexpensive visual to be effective. Thus, options to low in terms of the materials, in deterrents, mainly used for scaring encourage or extend incidental the short term at least. However, birds from farmland, which can human presence at ‘problem’ sites manpower costs have to be taken be successfully adapted to deter might be considered. into account, particularly if fish-eating birds at fisheries and dedicated staff are used for bird aquaculture facilities. Human presence is also a feature scaring duties, and recurrent costs of many bird deterrent methods, can be high if such deterrents are 4.1.2.1 Human Disturbance and it should be appreciated used repeatedly. Staff costs can be Human activity has been shown to that it is difficult to separate reduced where volunteers or local be consistently effective for scaring the effects of another deterrent stakeholder groups are involved in cormorants away from fisheries (e.g. pyrotechnics) from the bird scaring programmes. and aquaculture facilities, and it effects of human presence. is not constrained on grounds of Cormorants can habituate to Acceptability acceptability to other people as human presence, particularly if The use of auditory deterrents for some other techniques often are. this carries no perceived threat, deterring birds is widely recognised Human disturbance is one of the so the simultaneous use of other and accepted. However, general most widely used techniques for deterrents is advisable. considerations with the use of all deterring cormorants, particularly auditory deterrents relate to their at aquaculture facilities and at The timing of human activity is potential noise nuisance and their fisheries on smaller rivers and important. Cormorants normally indiscriminate impact on non-target stillwaters, and it can be conducted leave their roost before sunrise species. Auditory scarers may be on foot, using vehicles or by and feed most actively just after socially unacceptable in residential boat. Birds can be disturbed from dawn, so human presence needs areas, and they may also have an undesirable effect on other wildlife and humans in the area (e.g. fishermen or fish farm workers). To an extent, the level of possible disturbance can be regulated by the way these devices are used — for example, by pointing them away from houses or constructing simple straw baffles around them. It may also be wise to advertise the use of such equipment widely to anglers, or others using a site, as the loud

‘Timing of human activity Whilst some types of human disturbance will be innapropriate at fisheries, this is a consistently effective method of deterring Cormorants. is important’ Photo courtesy of Paul Butt.

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to be targeted at this time. This motionless devices either provide will be easier where personnel only short-term protection or are live on, or very close to, the site ineffective, as the threat from to be protected, but it may still them is perceived, rather than prove to be costly or impractical. real. Some birds reportedly even Nevertheless, human presence begin to associate the presence over a reasonable period has the of scarecrows with favourable advantage that it will enable an foraging conditions. In a survey accurate count to be made of the of fish hatchery managers in the numbers of birds affecting a site United States, only one of the and, thus, better assessment of the 14 hatchery managers (7%) who extent of any problem. However, it commented on the effectiveness of might be noted that a study in Israel various control techniques said that showed that cormorants shifted scarecrows had a high success rate their main feeding time from early against fish-eating birds; six (43%) morning — when worker presence said they had no effect. was high — to early afternoon, Scarecrow with replica gun and when the workers went to lunch. In a survey of 13 freshwater fish dressed in yellow coat. farms in the Modena district of Photo courtesy of Simon Nemtzov. Although the use of a dedicated Italy, where damage from 11 fish- human scarer is likely to be more eating bird species was reported, expensive than other visual and the owners or managers of four undertaken by people dressed in acoustic methods, these costs can farms reported that human-shaped similar yellow, hooded coats. be offset by a greater reduction in and/or moving scarecrows had losses. Costs can be particularly no effect, three reported success Revolving scarecrows are brightly high if specific working time is for a matter of days and only two coloured devices that spin slowly as dedicated to this activity and other indicated benefits lasting weeks or the wind blows. Some are human- costs are taken into consideration months. shaped, while others consist of a (e.g. fuel costs for vehicles), revolving square, sometimes painted but they can be relatively low To maximise the effectiveness of with large predator eyes (also where human presence involves scarecrows, it is recommended that known as ‘hawkeye’ deterrents). volunteers (e.g. unpaid anglers or they are made to appear life-like, Both designs can be enhanced by hunters). Casual scaring associated possess biological significance, the addition of a mirror that flashes with routine day-to-day activities be highly visible and have their as the device revolves. As these can also be effective and of low location changed frequently to delay devices are wind operated, there cost. However, as with all scaring habituation. Fitting scarecrows is minimal maintenance and these techniques, the success of human with loose clothing or bright devices are relatively inexpensive. scaring is dependent on alternative streamers that move and create feeding areas being available. noise in the wind can also enhance There are many types of automated their effectiveness. Alternatively, scarecrows available for fishery 4.1.2.2 Scarecrows scarecrows might mimic clothes use, most of which have been Scarecrows are a traditional, worn by active human scarers. For adapted from scarers used in widely used method for scaring example, dressing both scarecrows agriculture. The more sophisticated avian pests. These are sometimes and the farmers in bright yellow devices are powered by 12-volt designed to mimic the appearance raincoats with hoods and having the car batteries, and they display and of a predator (e.g. a bird of prey), scarecrows ‘hold’ a black pipe (as a collapse on a controlled-time basis but they are most commonly replica gun) enhanced the efficacy of or with motion detectors. These human-shaped effigies, usually scarecrows at an Israeli aquaculture scarecrows can also be fitted with constructed from inexpensive facility. This scaring was reinforced various extras such as hooters, materials. In general, however, by periodic shooting in the area, sirens and lights.

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Revolving bird scarer — ‘predator eyes’. Photo courtesy of Paul Butt.

The most effective techniques appear to be those that simulate shooting through the use of effigies that suddenly appear from cover. One example is a model of a man with a gun that is attached to a gas cannon in such a way that the effigy appears a few seconds before the cannon is fired. This can also be used for purely visual scaring when simultaneous use of the cannon is inappropriate.

Large (around 5 m high), brightly- Inflatable ‘Scarey Man’ deterrent coloured inflatable ‘men’ have also (top), and inflatable ‘man’ (right). recently been produced, primarily Photos courtesy of Paul Butt and for advertising purposes. This type http://www.immagoinflatables.co.uk/ of device is powered by an air skyguys.html. pump in the base, and it flaps and sways, both in a breeze and due to the continual flow of air through the One drawback is that automated device. The long arms also wave scarecrows can be quite expensive and flap about. The devices are thus to purchase and maintain, and unless highly visible over relatively long the site is secure (e.g. an inaccessible distances, and in the UK they have island) they can be stolen or reportedly been successfully used vandalised. Trials with these against cormorants. A potential devices have had some success in disadvantage, however, is that the reducing the presence of cormorants scarecrows have been reported as inflatable ‘men’ require sources (and herons), but it is commonly ‘ineffectual’ against cormorants of electrical power with which to reported that birds habituate to the at some sites. Regularly changing operate the air pumps. devices quite quickly, and animated the position of such devices is

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recommended to maximise what producing or visual deterrents, effectiveness they may have. or, to improve effectiveness, by ‘Model birds of periodic human activity, especially prey are reported Both static and animated if they are dressed like the scarecrows are commonly used at scarecrows. to be effective aquaculture facilities and fishery sites, particularly smaller ones. The 4.1.2.3 Predator models at scaring major drawback with scarecrows, Model raptors deter birds by cormorants at however lifelike they may be, is that mimicking real birds of prey they do not present a threat that is and creating fear and avoidance some sites’ sufficiently alarming to birds under behaviour in the target species. most circumstances. Consequently, Many potential prey species react over a period of time, birds learn to predator models. However, the predator across Europe, the White- that effigies do not represent an strength of the response varies tailed Eagle (Haliaeetus albicilla), actual threat and begin to ignore between species, and model raptors is absent from many areas where them. To increase the threat and fail to incorporate behavioural cormorants are present. therefore lengthen the time before cues, which may be critical to the habituation, it is recommended induction of fear and avoidance in The flying of live, trained birds of that all these devices are moved the target species. Model birds of prey across bodies of water by a regularly, rather than left in one prey are reported to be effective at falconer might also be used. This place. Moreover, devices should scaring cormorants at some sites. has been tried in Israel. However, not be left in place once cormorants However, there is evidence that although its efficacy was relatively migrate from an area because, the avoidance response to large high, the farmers stopped using the when the birds return, the period of avian predators is, in part, a learned birds due to the very high cost. habituation can be particularly short. behaviour. This may diminish the potential for the wider application While most raptor models are The effectiveness of scarecrows can of this technique against inexpensive and easy to deploy, be reinforced with other sound- cormorants, since its main avian cormorants can rapidly learn that the model poses no threat, become used to its presence and no longer react. The deployment of a Peregrine Falcon model adjacent to cormorant feeding areas in the southern Po Delta, Italy, appeared to be largely ineffective and tends to support this view. Thus, the effectiveness of such models is increased if they can be made to look lifelike, are animated and moved frequently.

Another form of predator model that has been used is that of tethered floats made to resemble the head of a crocodile or alligator. These floats are distributed around the pond and purportedly can deter water-birds from landing on the pond. It is not known whether these Mobile scarecrow dressed identically to local workers and also incorporating have been used successfully against an auditory deterrent device. Photo courtesy of Paul Butt. cormorants.

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4.1.2.4 Displaying corpses The deployment of replicas or actual dead individuals in a manner which signals danger to members of the same species can be used as a visual deterrent for many bird species, especially crows (‘corvids’). Reportedly, corpses have to be in good condition to remain effective and, as with other static deterrents, they should be moved frequently to reduce habituation. Efficacy depends on the availability of alternative foraging sites and is enhanced Raptor kite. Photo courtesy of Paul Butt. when it is reinforced with additional deterrent techniques. While this technique is reportedly three-dimensional appearance may place, such balloons have been used highly effective for corvids and further enhance the effect, and large as opportune targets and their use there is some evidence it has been eyespots are considered better than to help deter cormorants has had to effective against egrets (Egretta small ones. Although easy to set up be abandoned. spp.), it is not clear whether or not and move around, balloons can be it deters cormorants. easily damaged in high winds and 4.1.2.6 Kites can deteriorate in sunlight, leading Kites and kite-hawks are The desirability of displaying corpses to a loss of helium and thus height. commercially available, airborne in areas accessed by the general Balloons also need to be checked devices that are meant to act as public may also need to be taken regularly to ensure they cannot break mobile model predators which into consideration in case the corpses free from their moorings and present ‘target’ birds perceive as a threat. raise public concern and complaints. a hazard to aircraft. Their use near Kites commonly bear an image of There are also other considerations aerodromes may be restricted by air a soaring raptor and are tethered if real corpses are used, notably navigation regulations. A cheaper to the ground. Some varieties because of possible pollution arising alternative is to fill the balloons with are secured to a length of line from decomposition, particularly in pressurised air and to hang them (commonly about 80 m), but these fish farm areas, and health and safety from T-shaped poles. only operate in a wind and, once fears about the possible spread of grounded, have to be re-launched avian ‘flu. Balloons, and other visual scaring manually. Alternative models are devices, have been used against tethered to a flexible 13 m pole 4.1.2.5 Balloons cormorants to increase the deterrent and re-launch automatically when Helium-filled balloons are used effect of other physical exclusion the wind starts blowing. The as an inexpensive method of bird devices such as wires and floating ‘Helikite™’ is a cross between a deterrence in agriculture. Their ropes (see 4.2). large helium balloon and a kite, effectiveness can be enhanced by which ‘flies’ above a pole. This has the inclusion of eyespots, consisting Studies indicate that the the advantage that it does not need of a circular pattern that resembles effectiveness of balloons at scaring wind to stay in the air. the general appearance of vertebrate birds varies between species, the eyes. Two circular eyespots arranged eyespot design and with the mode Like balloons, kites and kite-hawks horizontally, each containing of presentation. However, effects can be damaged by strong winds concentric rings of bright colour, are commonly only short-term and and may be difficult to keep up in appear to be the most alarming and birds quickly habituate to them. In the air when wind speeds exceed effective designs. Those that have a some places where hunting takes 8 km/hr. Since they pose no real

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threat to birds, do not behave like raptors, and remain visible for long ‘Lights may be relatively ineffective periods, birds quickly habituate during daylight hours but they may be to these devices. Hence, they are effective only over a small area and particularly useful at night roosts’ for a short period of time. As with balloons, their use near aerodromes may be controlled by air navigation regulations. birds and can produce an avoidance or no success as a depredation response. Lights may be relatively control technique. However, it 4.1.2.7 Radio-controlled model ineffective during daylight hours is known that reflectors can be aircraft but they may be particularly useful effective at deterring cormorants Radio-controlled aircraft have been for deterring night-feeding birds at some sites, particularly in sunny used to scare bird pests since the such as herons, or at night roosts. locations. For example, in Israel, early 1980s. Although mainly used They are easy to deploy and require hand-held mirrors are reported to over airfields, this technique has also very little maintenance, but birds be very effective. As with many been applied at other sites, including will quickly become habituated other deterrent techniques, they are deterring cormorants and herons at and so lights are best used in best combined with other methods fisheries and aquaculture facilities. combination with other deterrent of scaring. For instance, on a For cormorants, experience has methods. They should not be large lake in Greece, mirrors and shown that model aircraft should be deployed where they might cause audible deterrents have been used used to scare birds while they are a visual nuisance to neighbouring successfully to deter cormorants still in the air, as birds already on the properties or near airfields. from sites close to the shore (see water are only encouraged to dive. Case Study No. 1). At larger, land-based fish farms it 4.1.2.9 Mirrors/reflectors has been estimated that one model Mirrors and reflectors work on the 4.1.2.10 Reflective tape aircraft is required for approximately principle that sudden bright flashes Tapes can best be regarded as a every 100 ha. Using a falcon-shape of light produce a startle response combined visual and exclusion aircraft, or a conventionally shaped and so drive birds from an area. deterrent (see Section 4.2.2). A aircraft painted with a raptor design, For example, CD discs are highly wide variety of twines and tapes can enhance the efficacy of this reflective and can be hung on are readily available, including technique. While quite effective, the wires or other objects where they varieties such as Mylar® Tape, use of model aircraft is relatively will move with the wind to deter which has a metal coating on one expensive, labour-intensive, not birds. Rotating, reflective pyramids side that reflects sunlight and also suitable in bad weather and requires have also been developed that produces a humming or crackling skilled operators — training to are powered by a 12-volt battery noise when moved by the wind. become fully competent can take up and deflect light into the air at the Tapes are relatively cheap and to two months angle of the birds’ approach. These easy to deploy, but they can break automatically switch off in the easily in bad weather conditions, In Finland, an attempt to scare dark and will run for several weeks necessitating extra labour for cormorants was made using a between battery changes. Although repairs and, potentially, causing small, wind-driven helicopter rotor inexpensive and easy to put up an unsightly litter nuisance. mounted on a tripod. Although the and relocate, the effectiveness of Good maintenance of the tapes efficacy of the device was not fully mirrors and reflectors as a bird is essential in order to stop gaps monitored, it is thought to have scaring technique is variable. resulting from broken tapes been partially successful. being exploited as entry points In a survey of 336 fish hatchery by birds. Strips of reflective tape 4.1.2.8 Lights managers in eastern USA, eight are often hung from wires that are Flashing, rotating, strobe and reported using tin reflectors of stretched across fish ponds (see searchlights are a novel stimulus to which seven said they had limited Section 4.2.2) to make the wires

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more visible and to increase their directed over distance on specific sure of the precise target and what effectiveness as deterrents. problem birds. Birds are startled the end of the beam will hit. Some by the strong contrast between the lasers can be dangerous at short or Reflective tapes are in regular use ambient light and the laser beam, even large distances, and proper at aquaculture facilities in a number by the bright spot moving toward training and adherence to local of countries (e.g. Germany, Italy them on the ground or in the tree laws is essential. Lasers can blind and UK), and close configuration of and by the actual beam when it people or animals, permanently these tapes can provide successful reflects dust particles and appears or temporarily, and this can also protection, particularly if an as a large ‘stick’ moving toward lead to unexpected accidents (e.g. alternative feeding area is available them. The laser light need not be car crashes) if devices are used nearby. However, since the tapes shone into the bird’s eyes to startle inappropriately. are short-lived, the technique is them, and indeed it is inadvisable to probably best suited to protecting do so. During low light conditions Trials with low power (5 mW) red small areas of high value stock in this technique can be applied very laser (650 nm) guns, such as the the short term. selectively, but at night the light Desman rifle®, in France, Italy beam is visible over a large distance and the UK have demonstrated A cheap source of reflective tape and hence can cause non-selective that cormorants are sensitive is the magnetic tape in old video disturbance. These devices are to this laser light and that these cassettes, since this is highly ineffective in daylight and in misty devices can be effectively used reflective and easily available. or foggy conditions. at cormorant roosting sites. In However, it is inadvisable to use tape from video cassettes with a play length of longer than two hours, as these are made of thinner ‘Birds are startled by the strong (and more breakable) tape. contrast between the ambient light

4.1.2.11 Flags, rags and streamers and the laser beam’ Flags, rags and streamers, including reflective silver or Mylar® streamers, can be readily deployed The possession and use of lasers one trial in the UK, conducted at fishery and aquaculture sites may be prohibited or restricted during cloudy weather, most of the and — potentially — also at roost by legislation or be subject to a cormorants at a night roost were sites. These are cheap and easy licensing regime, depending on the scared away within 20 minutes, to deploy and can prove effective power of the laser being deployed. and treatment over consecutive deterrents, in the short term at There are growing safety concerns evenings caused the temporary least. Their success depends on regarding the availability and desertion of the roost. alternative feeding, roosting or use of lasers and calls for tighter loafing sites being available nearby. regulation in some countries. Thus, In similar trials in roosts in the the legal aspects of using this northern Po Delta, Italy, birds left 4.1.2.12 Lasers technique should be checked with the roost almost immediately. In As the demand for non-lethal, the local authorities before any Italy, lasers have been successfully environmentally safe methods of laser devices are considered for used against birds in both tree bird scaring has increased, there deployment: laser devices should roosts and bankside areas, has been increasing interest in only be used within the limits of sometimes hundreds of metres the use of lasers to scare birds. appropriate laser safety regulations. from the bank- or boat-based Lasers, particularly ones that work operator. The gun ‘scope’ on laser under low light conditions, are From a safety point of view, guns proved useful to accurately an attractive alternative to other shooting a laser light must be target the laser light, and the use bird scaring devices since they regarded the same as shooting a of a light amplifier also helped to are silent and can be accurately bullet — the operator MUST be enhance the efficacy of the device

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in the dark. It was reported that expensive as the red laser guns had four arms that sprayed a mist lasers were particularly effective (above). However, low-cost, hand- of water over the ponds, reducing at preventing the establishment of held green laser pointers are also visibility and preventing birds from new roosts, especially when used in available with a wide variety of seeing the fish. The spray also conjunction with shooting to scare power levels, and these have been provided shade by diffusing direct techniques. used successfully for bird scaring sunlight, and oxygenated the water. at night roosts in Israel and Italy. The latter technique was not tested Similar findings have been Low power lasers of less then against wading or diving birds, demonstrated at other cormorant 5 mW have fewer legal restrictions, but both methods may be useful night roosts, although in some though these can potentially to deter cormorants, particularly trials the laser gun has been less still cause eye injuries, and can at smaller ponds on fish rearing effective, with some birds failing be effective at ranges of up to a sites. The potential for their use in to leave the roost site (e.g. if the few hundred metres. Green laser protecting larger, irregular water bird is facing away from the light pointers of 20–30 mW are effective bodies may be limited because source), thereby discouraging over larger distances (1–2 km), but of the cost and the practical other birds from leaving, too. usually carry more stringent legal installation difficulties. This reinforces the desirability of restrictions and safety standards deploying a mixture of cormorant than the 5 mW lasers, reflecting the 4.1.2.14 Dyes, colourants and scaring devices and techniques. greater risk that they pose. Green turbidity laser pointers of 50, 100 or even There has been little research into Laser guns are available 200 mW are also available, but the use of dyes or colourants to commercially for avian these are increasingly dangerous deter fish-eating birds, but it is deterrence (e.g. Desman rifle®, and apparently no more effective known that cormorants are visual Avian Dissuader), and some in scaring birds than the less feeders, in part at least, and that manufacturers also provide training powerful ones. It is anticipated that birds can abandon feeding sites in in their use. Other, automatic further controls are likely to be response to changing water quality laser devices have been developed placed on the availability and use conditions such as turbidity (i.e. for deterring birds, particularly of lasers and thus particular care reduced water clarity). Studies have near airfields to reduce the risk is needed to ensure compliance also indicated that the foraging of ‘bird strike’. However, these with local regulations, as well as efficiency of egrets was reduced devices are relatively expensive. to ensure safe usage where this is by increasing the turbidity in trial Due to concerns about the safety appropriate. ponds (obtained by dilution of of such devices for humans, one natural sediment). Thus, some commercially available laser gun 4.1.2.13 High-Pressure Water Jets researchers have suggested that was tested for safety at the UK High-pressure water jet systems such measures might represent a Government’s Defence Evaluation have been successfully tested on cost-effective method for protecting and Research Agency (DERA). Carp ponds in Germany. Aside stocks at fish farms or in ponds This was found to be safe if it from deterring predators and and small lakes, since these could was not pointed at an unprotected making the fish less accessible, be relatively easy to apply in such human eye within a distance of a positive side-effect of this small, confined water bodies. 155 m, although the safe distance technique is that the ponds are also In practice, such an approach was considerably reduced if viewed aerated, an important benefit during may conflict with fish husbandry with binoculars. summer when the dissolved oxygen practices in fish farms (and perhaps in Carp ponds can fall to very low feeding of the fish). Green lasers (530 nm) are also levels. available and tend to be brighter Equally, the practice of deliberately than red lasers of the same power A similar device has also been used increasing turbidity at a site may be level. Green lasers are being in Sweden for protecting circular questionable from an acceptability sold commercially as laser guns fish ponds from gulls and terns viewpoint on biodiversity/ for bird scaring, but these are as (Sterna spp.). This rotating device aesthetic grounds, although the

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presence of benthic (i.e. bottom visibility and how real a threat they required. Simple static scarecrows feeding) species such as Carp at are perceived to present: visual and flags are usually constructed fisheries often has this side-effect, scarers are most effective if they from inexpensive materials, while particularly at small stillwater sites are life-like, move and possess automated devices are relatively where stocking rates are high. biological significance, or if they more expensive, depending on their The potential for using dyes or are associated directly with a real level of sophistication, and devices artificially manipulating turbidity threat. such as some lasers can be costly. as a cost-effective method of Commercial bird-scaring laser guns cormorant control has yet to be Disturbance by humans is regarded can be very expensive, but cheaper, proven. as the most effective visual hand-held laser pointers can be just deterrent, but cormorants can learn as effective. Laser licensing and 4.1.2.15 Dogs to feed during even short periods training costs must also be taken Trained dogs, such as border when humans are absent (e.g. into account. collies, can be used to scare birds meal breaks), especially where away from a site. The efficacy of feeding success can be assured For many visual scarers, manpower such an approach for deterring (e.g. at heavily-stocked fish ponds). costs are low, being mainly cormorants is not known. Studies suggest that human effigies confined to initial deployment, and raptor models may be more periodic checking and, perhaps, 4.1.2.16 Overview of visual consistently effective and longer movement around a site. However, deterrents lasting as bird deterrents than kites, the cost of using dedicated staff for balloons and flags. ‘human disturbance’, or to operate Efficacy a laser gun, may be considerable, As with auditory deterrents, the Practicality particularly if required on a regular effectiveness of visual deterrents Visual deterrent devices are used basis. Manpower costs might be varies with the device chosen, widely for a range of bird scaring reduced where incidental human the method and timing of use, the purposes and most are readily presence at a site can be arranged size of the site and the availability available, easy to deploy and or where volunteers or local of alternative foraging sites for simple to use. Such deterrents thus stakeholder groups participate (see the birds. Typically, fixed visual rate highly from the viewpoint Case Study No. 4 — Slovenia). deterrents are only thought to have of practicality for many sites. an effective range of up to about Regulations may cover the use Acceptability 200 m. As such, these techniques of some visual deterrent devices The use of visual deterrents for will be of limited, if any, use on (e.g. lasers, model aircraft, scaring birds is widely recognised river systems, coastal areas or flashing lights) and/or restrict and, since their impact is usually larger stillwater sites, with the their operation in sensitive areas very localised and non-lethal, they possible exception of localised such as airfields. Local guidance have a high level of acceptability predation ‘hot spots’, or in the and necessary approvals should and are generally not a matter of vicinity of fishing gear. always be sought prior to using public concern. However, such such devices. For more expensive devices are not selective and so All visual deterrents, particularly visual deterrents (e.g. automated may impact on other wildlife, and static ones, are subject to inflatable scarecrows), security this should be taken into account. habituation by cormorants, and should be considered carefully to Some visual deterrents may not hence they are generally of short- safeguard the devices against theft be acceptable in certain locations term benefit (typically days to or vandalism. (e.g. flashing lights or perhaps weeks) as the birds eventually bird corpses near residential areas, get used to them, unless they Costs model aircraft and kites near are moved regularly and used in The costs of visual deterrents airfields, or lasers near roads). conjunction with other deterrents. vary widely, depending on the Particular care is also necessary The effectiveness of visual complexity of the device itself and with all uses of lasers even where it deterrents also depends on their the level of human participation is legal to use them.

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4.1.3 Chemical deterrents these reasons they are difficult Individual birds learned to avoid to apply effectively outdoors, Brown Trout (Salmo trutta), the Chemical taste repellents are especially in large areas such as fish treated species, but continued to eat quite widely used for reducing the growing areas. In addition, most are other species of fish, and this effect impact of pest birds in agriculture relatively expensive. Furthermore, lasted for seven months - the entire and forestry, as well as a means of methyl anthranilate can be toxic duration of the trial — without deterring birds from perching on to aquatic fauna and may not be reinforcement. buildings. Such techniques have sprayed near water bodies unless it not been widely tested against is in a special formulation designed Clearly, applying such a technique fish-eating birds, but they may for this purpose. in the wild presents significant have some potential. Chemical difficulties and would not be repellents fall into two broad Despite these drawbacks, chemical appropriate at sites on cormorant categories: primary repellents and repellents have been used effectively migration routes, due to the secondary repellents. Primary to deter birds, including cormorants, extensive turnover of the birds. repellents are avoided upon first from large areas, such as airports. However, it might have potential at exposure because they smell or The repellents are typically applied some sites where birds demonstrate taste offensive or cause irritation. using a fogger machine; in some local feeding-site fidelity and Secondary repellents are not places the foggers have been where there is a need to protect immediately offensive, but they attached to motion detectors so a particular species of fish. cause illness or an unpleasant that they only spray chemical when Considerable further work would experience following ingestion. The flocks of birds approach, to avoid be required to develop an effective bird links this negative experience habituation and to reduce costs. method for delivering the chemical to the taste of the treated food and The potential of applying repellents to the target birds. will avoid this food in future. Due as a very thin surface film, in to their toxicity, and concerns about order to deter birds from entering Because of the complexity and adverse effects on the environment, particular water bodies, has also drawbacks of using chemical the use of chemical repellents is been investigated. Research in this repellents for deterring birds usually tightly regulated. area is believed to be ongoing. outdoors, and the associated controls on their use, it is A number of chemicals (such as Most bird deterrent chemicals do important that all aspects, potential methyl anthranilate, dimethyl not impact mammals, and mammal repercussions and regulations anthranilate, cinnamide, deterrents such as hot-sauce are considered carefully before anthraquinone, adirachtin, (capsaicin) are ineffective against commencing any programme to use 4-aminopyridine, methiocarb, birds due to differences in their them against cormorants. and caffeine) have been proven nervous systems. Nevertheless, 4.1.3.1 Overview of chemical as effective deterrents against many people dislike the smell deterrents different bird species. Some of of some of these chemicals, these substances are registered as especially the sickly-sweet, grape- Efficacy bird repellents in the USA, but they like smell of methyl anthranilate, The efficacy of chemical are not authorised for use in many so it should not be sprayed near deterrents will be highly variable other countries and few chemicals settlements. depending on which chemical are believed to be registered for is used on which species and use in Europe. In addition, not Trials have also demonstrated on the mode of delivery. While all of them have been tested on that conditioned taste aversion proven to be effective for captive cormorants. (a subconscious association cormorants fed on dead fish, safe between taste and a feeling of and effective chemical repellents Chemical repellents are generally illness experienced after ingesting have not been developed to a level most effective on surfaces or treated food) can be successfully where they can be recommended indoors, and animals usually induced in captive cormorants fed for use in fishery or aquaculture habituate to smells quickly. For on dead fish dosed with carbachol. applications at the current time.

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Practicality fixed permanently. At other sites, be possible to make it difficult, Chemical deterrents are most such as off-shore fish farm cages, or impossible, for cormorants effective on surfaces and in anti-predator netting can be hung to land on, or take off from, the enclosures, and they are more in curtains underwater to prevent water’s surface. Although certain difficult to apply outdoors. The diving birds reaching fish stock spacings of these wires appear practicalities of administering in the mesh ‘bag’ of the cage. In to be more effective than others, repellents to cormorants and/or larger water bodies, complete there is considerable scope for water bodies require considerable exclusion is far more difficult experimentation at fishery sites. further work before the technique and may well be impractical. At could be recommended for wider such sites it may be possible to 4.2.1 Netting enclosures use. take advantage of the fact that cormorants generally require Complete enclosure of a site with Costs quite long distances for take-off netting is undoubtedly the most Most chemical deterrents are and landing. By positioning wires effective option for preventing expensive, although fogging or ropes across waters it may predation by fish-eating birds, machines can reduce the amount of chemical needed. However, in large areas the costs can be prohibitive.

Acceptability Chemical deterrents that do not harm (but only deter) wildlife are generally very acceptable as a non-lethal method to stakeholders. However, the use of potentially harmful chemicals in the environment does raise acceptability issues and requires mechanisms to ensure that substances could be administered to cormorants without a risk of lethal poisoning, or threatening other bird and other, non-target wildlife species. Thus, any possible human health or environmental implications would have to be taken into account to ensure any such techniques did not have adverse effects.

4.2 Protecting The Fish — Exclusion Techniques These tools involve excluding the birds from the fish. Not surprisingly, the techniques work best when fish are concentrated in relatively small areas. Thus, they are ideal for land-based ponds or raceway fish farms Netting enclosures at fish farms. where netting enclosures can be Photos courtesy of Bruno Broughton and Thomas Keller.