Action Synopsis: Bird Conservation About Actions

Scare birds from fish farms

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One before-and-after study from Israel found that the population of pygmy cormorants in the area increased after birds were scared away from fish farms, possibly due to lower persecution.
  • One of two studies that examined fish stocks found that fewer fish were taken from a farm when heron distress calls were played. The other study, a literature review, found no evidence for the effects of scaring birds on fish stocks.
  • Two replicated studies from Belgium and Australia found that using foot patrols to disturb birds from fish farms did not reduce the number of birds present or fish consumption.
  • Ten of eleven studies from across the world, three controlled, found evidence that playing distress calls or using other acoustic deterrents (some with flashes of light) reduced the number of birds at fish farms, or changed bird behaviours. One of these involved underwater broadcasting. One study found effects were only temporary and five found that birds became habituated to noises. Four studies, one replicated and controlled, two before-and-after, found that acoustic deterrents were not effective in scaring birds.
  • Five of seven studies, one controlled, found evidence that visual deterrents (including inflatable ‘Scarey Man’ scarecrows) reduced the number of birds at fish farms. Three found evidence for habituation to deterrents and three studies found no evidence that visual deterrents were effective.
  • Two studies examined other deterrents, finding that trained raptors were effective but that the effects of helicopters and ultra-light aircraft were either inconclusive or very temporary.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A trial at a fish pond in western Germany in 1976 (Behlert 1977) found that broadcasting the flight call of a grey heron Ardea cinerea during daylight caused herons standing near the pond to take off and deterred flying herons from landing. However, at dawn trials, the majority (ten of 12) of herons were not deterred from landing. Preliminary trials had revealed that distress calls were more effective at scaring herons than heron alarm calls, combined heron and other bird alarm calls or a white-tailed sea eagle Haliaeetus albicilla call.

    Study and other actions tested
  2. A controlled trial in northern Israel in September and October 1978 (Spanier 1980) found that 88% (1,122 of 1,265) of black-crowned night-herons Nycticorax nycticorax feeding at fishpond were scared off when heron distress calls (both adult and juvenile) were played on 12 observation nights. Over the study period there was no apparent habituation to the distress calls, in contrast to when recordings of a gas gun were used, when herons became habituated after only one night (60% of birds remained at ponds after 12 nights). Distress calls also reduced the number of herons perched in nearby trees by approximately 50% and, despite less than 5% of scared herons leaving the area, the scaring significantly reduced fish losses over the study period.

    Study and other actions tested
  3. A replicated trial in the winter of 1962-3 in North Rhine-Westphalia, Germany (Ueckermann et al. 1981), tested the effectiveness of visual and acoustic deterrents on deterring grey herons Ardea cinerea from fish ponds and found that a ‘Flash-Harry’ (wind-powered rotating orange cross on a pole) had no effect, whilst birds quickly became used to streamer bands, broadcasting of bird distress/alarm calls and scarecrows. Shooting guns close to birds proved impractical. This study also investigated the use of netting on ponds, discussed in ‘Use netting to reduce fish loss to birds’.

    Study and other actions tested
  4. A replicated study from Limburg, Belgium, over 49 nights in 1982-3 (Draulans & Van Vessem 1985), found that using foot patrols to disturb grey herons Ardea cinerea from 12 fish ponds did not necessarily reduce fish consumption. Low frequency disturbance (e.g. 3-5 farmer visits/night) caused a significant decrease in heron numbers but became less effective as heron numbers increased. Reduced numbers did not necessarily reduce fish consumption, as maximum predation occurred soon after bird arrival and disturbance mostly discouraged only well-fed birds from returning.

    Study and other actions tested
  5. A 1987 literature review (Draulans 1987) found that there was little evidence that scaring devices at fish farms succeeded in increasing fish stocks/reducing losses. Devices could be classified as visual (scarecrows, flags, reflectors, lights, model etc), acoustic (gun shots, firecrackers and gas cannons) or biological (recordings of distress calls etc). Black-crowned night herons Nycticorax nycticorax were deterred by distress calls but only close to the speaker and no data are presented to support any positive effects on fish stocks. The use of dead birds, model predators and dogs is reported by several authors as almost completely ineffectual. Trained raptors seemed effective but expensive.

    Study and other actions tested
  6. A series of experiments in Flevoland, the Netherlands, in 1981-3 (Moerbeek et al. 1987) found that pistol-fired flash cartridges (detonation after a light flash, or a flash only) appeared the most effective method of deterring great cormorants Phalacrocorax carbo from ponds and scared most birds away (although some alighted on nearby ponds). Gas cannons (producing a bang at regular or irregular intervals) had little effect as birds soon habituated to the noise; an overflying helicopter scared cormorants from ponds but they soon returned (on the day following the 2-day trial large numbers were present). An ultra-light aircraft proved inconclusive.

    Study and other actions tested
  7. A before-and-after trial at 25 fish ponds in a catfish farm over 45 days in February and March 1992 in the Mississippi delta region, USA (Stickley & King 1995), found that using a ‘Scarey Man’ resulted in a rapid decrease in double-crested cormorant Phalacrocorax auritus numbers (320 birds/patrol before treatment vs. 8/patrol for the first seven days after erection and 16/patrol for the whole 46 day experiment). Clothing the devices to resemble marksmen, replacing them with actual marksmen and using propane gas exploders (at up to six Scarey Man positions for 23 days) did not further reduce cormorant numbers.

    Study and other actions tested
  8. A 1995 review assessed effectiveness of techniques used to prevent double-crested cormorant Phalacrocorax auritus predation at aquaculture facilities in the Mississippi delta region, USA (Mott & Boyd 1995), and concluded that there was little good evidence for what worked and what did not. Pyrotechnics, human effigies, gas cannons, and live ammunition have been used with varying degrees of success in frightening cormorants, but the authors warn that birds can become habituated to them.

    Study and other actions tested
  9. A replicated trial in New South Wales, Australia (Rowland 1995), found that hanging gill nets in fish ponds and using harassment patrols to deter cormorants Phalacrocorax spp. from fish farms was not effective. This study is discussed in ‘Use in-water devices to reduce fish loss from ponds’.

    Study and other actions tested
  10. A replicated, controlled, paired sites study in winter-spring 1991 at four pairs of catfish farms in the Mississippi delta region, USA (Stickley et al. 1995), found a 71-99% reduction in double-crested cormorant Phalacrocorax auritus numbers following the deployment of six ‘Scarey Man’ devices for 10-19 days. However, signs of habituation became apparent (reduced flush success) within the trial period at three sites.

    Study and other actions tested
  11. A before-and-study in May-June 1993 at a trout-rearing farm in Colorado, USA (Andelt & Hopper 1996), found a 48% reduction in  black-crowned night heron Nycticorax nycticorax numbers following the broadcasting heron alarm/distress calls for 11 days (pre-treatment average 77 birds; treatment 40; post-treatment 69). However, numbers and the proportion remaining increased from nights over the treatment phase, indicating habituation. Great blue heron Ardea herodias numbers were unaffected (pre-treatment 15; treatment 13; post-treatment 16. Herons were counted during six pre-treatment (12-13 to 18-19 May 1993), five treatment (21-22 May to 31 May-1 June 1993), and five post-treatment (1-2 to 11-12 June 1993) nights. Calls were broadcast through each night of the 11 day treatment period: 15-sec sequences of night heron calls followed by 14 min without calls, then a similar sequence of great blue heron calls.

    Study and other actions tested
  12. A series of before-and-after trials in trout farms in Colorado, USA, in 1990-2 (Andelt et al. 1997), found that pyrotechnics were effective at decreasing the number of black-crowned night-herons Nycticorax nycticorax and great blue herons Ardea herodia at farms. Firing pyrotechnics for 14 consecutive nights was more successful than doing so for seven nights. Frightening every fifth night was unsuccessful. Rotating lights did not reduce the number of attempted or successful fish captures. ‘Scarey Man’ reduced heron numbers during the first four nights but numbers of both species subsequently increased substantially to night 18, indicating habituation.

    Study and other actions tested
  13. A controlled, replicated before-and-after experiment in January-April and October 1998, and March 1999, in Argyll, Scotland (Ross et al. 2001), found that an underwater playback system (UPS) was effective in deterring common eider Somateria mollissima from feeding on mussels Mytilus edulis at farms on two sea lochs (47-80% fewer birds feeding after use of the UPS; 2-37 birds feeding before use). Underwater recordings of an approaching ‘scare boat’ (scaring by boat being a conventional deterrent method) were played via an underwater loudspeaker, and also a ‘control’ i.e. playback of an unassociated sound. Average return time of eiders after chasing by boat also increased significantly, suggesting that effectiveness was strengthened by UPS.

    Study and other actions tested
  14. Replicated ex situ experiments in Ohio, USA (Dolbeer et al. 2002), found that µ10mW, 633nm laser did not repel brown-headed cowbirds Molothrus ater or European starlings Sturnus vulgaris from a perch over three trials with stationary and moving laser beams treating a randomly selected perch. Effectiveness of a 68mW, 650nm laser in dispersing starlings and rock doves Columba livia from perches, and Canada geese Branta canadensis and mallard Anas platyrhynchos from grass plots was also tested. Starlings did not disperse when targeted with the beam, doves dispersed only in the first 5 min of six 80 min treatment periods. An average, 96% of individual geese in six groups of four birds, dispersed from laser-treated plots during 20-min periods (23 replicates). Mallard dispersed (average 57% of individuals) during 20-min treatment periods, but habituated to the beam after about 20 min. 

    Study and other actions tested
  15. A before-and-after study in northern Israel (Nemtzov 2005) found that pygmy cormorants Phalacrocorax pygmeus relocated away from colonies near fish farms during 1999-2002, following the use of gas cannons and pyrotechnics to scare birds before the start of nesting in winters between 1999-2000 and 2002-3. Between 1998 and 2004, the overall number of cormorant nests in the area increased from 60 to approximately 110 (reaching a high of approximately 155 in 2001), possibly due to greater reproductive success with lower levels of persecution following relocation.

    Study and other actions tested
  16. At four sites around Lake Como, Italy, a controlled replicated experiment (Gagliardi et al. 2006) found that none of three deterrents (gas cannon detonations, fire crackers and shooting near birds) were effective or practical in deterring great crested grebes Podiceps cristatus from areas with commercially important common bleak Alburnus alburnus shoals. Grebe behavioural response was recorded during 3-h observation periods when deterrents were or were not, in use. Cannons had little effect. Crackers and shooting caused significant behavioural changes (less time feeding, resting and preening, and more time swimming) compared to control periods, but grebe numbers were only temporarily reduced in the vicinity.

    Study and other actions tested
Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

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Bird Conservation
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