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Introduction and General Information

  • Control of populations may be required in a variety of situations to avoid overpopulation and/or due to conflict with human activities including agriculture and recreation.
  • Depending on the situation, control measures may include:
  • Preventing/limiting reproduction
  • Limiting access to certain areas (fencing/netting)
  • Scaring/Hazing
  • Environmental manipulation (decreased attractiveness)
  • Relocation
  • Culling

N.B.

  • Many of the methods used for population control are identical to those used in Environmental and Population Management for Disease Control.
  • Use of some forms of population control may be prohibited or restricted by national and international legislation. Information on legal restrictions and requirements for licences should be sought prior to the implementation of control measures. For example in Europe wild birds are protected under the European Union Directive on the Conservation of Wild Birds (79/409/EEC), which in implemented in Britain through the Wildlife and Countryside Act 1981 and in Northern Ireland by the 1985 Wildlife Order (P12.10.w1, P12.6.w4, D13).

"The Canada Goose, like all other birds in Britain, is protected under the EC Wild Birds Directive implemented in the United Kingdom through the Wildlife and Countryside Act (1981). This makes it an offence to capture, kill or injure Canada Geese, to damage their nests or eggs, or to disturb them on a breeding site. Any control technique which involves breaking the protected status of the Geese requires a licence from the appropriate government authority". P12.10.w1:- The Management of Problems caused by Canada Geese - A Guide to Best Practice).

  • Management actions may be required on a regional basis, not just a single affected site: different areas may be used at different times of year, and birds moved from one site may adversely affect another site.
  • Some methods of control, particularly culling, may be opposed by concerned members of the public. Every effort should be made in designing and implementing population control strategies to ensure that all interested parties are kept informed and are made part of the decision-making process.
  • Sound scientific data should be used in designing and implementing population control plans
  • Non-lethal methods of population control should be applied whenever possible.

(B23.17.w3, P12.5.w3, P12.10.w1, P12.6.w4, D13, V.w5)

Waterfowl Consideration GENERAL:
  • Within collections, control of reproduction is an essential part of general management, reproductive management and disease control. Avoiding excess population growth is important to prevent overcrowding with associated overgrazing, erosion, territorial disputes, general stress and as a result of all these, increased disease risks.
  • The major areas of conflict between human activities and free-flying waterfowl requiring population control are in the areas of agriculture, fisheries and recreation.

Agriculture:

  • Mainly geese eating crops.

Fisheries:

  • Goosanders (Mergus merganser - Common merganser) Mergus merganser, and red-breasted mergansers Mergus serrator - Red-breasted merganser (also other fish-eating birds such as cormorants Phalacrocorax carbo - Cormorant) consuming fish.
  • Eiders Somateria spp. and scoters Melanitta spp. consuming mussels.

Recreation:

  • Mainly geese, particularly Canada geese (Branta canadensis - Canada goose).
  • Particularly in urban areas such as parks, also golf courses.
  • N.B. Conflict of interest may occur between people who enjoy the presence of waterfowl in public areas such as parks and those who consider them a nuisance.
  • Problems may include aesthetic considerations (presence of droppings, also feathers while moulting, and noise), human health considerations (potential hazard from droppings) and aggressive behaviour of individual birds.

Aircraft:

  • Risk of bird-strike.

Habitat damage:

  • Bank erosion.
  • Damage to marginal vegetation.

N.B. It is important to remember in developing a control plan for free-flying waterfowl that an integrated approach combining a variety of strategies is likely to be more effective than any one action used alone.

(B23.17.w3, B122, P10.62.w1, P12.5.w3, P12.10.w1. P12.11.w2, D13)

Crane Consideration
  • In general, reproduction rates in cranes in captivity have not been so high as to produce problems with excess populations. However, there are sometimes problems with imbalanced sex ratios or with chicks from prolific pairs. (N19.16.w2, V.w5)
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Restricting Breeding

  • Restricting breeding to limit population growth is most easily applicable to captive birds, but may also be used in the control of free-living birds in some circumstances.
  • N.B. reproductive control methods may have a considerable long term effect on population growth, but are not effective in themselves for short-term population reduction, particularly with long-lived species.
Waterfowl Consideration EGG CONTROL
  • Within collections, waterfowl may be prevented from breeding quite easily in most cases, by removing eggs after they are laid.
  • Replacing removed eggs with dummies for the birds to sit on may be used to prevent double-clutching.
  • Separating females from males may be used to prevent eggs being fertilised.
  • For free-flying birds, consideration of legal restrictions is important before any form of interference with eggs or nests.
  • In the UK, a licence is required for any activity involving disturbance of nests or interference with eggs, as all wild birds are protected under the Wildlife and Countryside Act (1981). Possible methods include:
  • Egg removal.
  • Egg removal and replacement with dummy eggs.
  • Egg pricking.
  • Egg boiling.
  • Coating with mineral oil (liquid paraffin).
  • Whichever method is chosen, it should be applied as soon as possible, preferably immediately after the clutch is completed. Egg removal alone is less effective than other methods for species which may lay a second clutch.
  • N.B. A very high percentage of eggs must be prevented from hatching for effective population control, and the control actions must be repeated each year: "it may need 80% of all of the eggs on a site to be treated for in excess of 8 years before egg control alone will begin to show a reduction in population size." (Allan, 1999 - P12.10.w1:- The Management of Problems caused by Canada Geese - A Guide to Best Practice).

VASECTOMY:

  • An alternative which may be of use for long-term prevention of breeding is vasectomising adult males of breeding pairs. This would be most applicable to species with long-term pair bonds and high site fidelity such as Canada geese (Branta canadensis - Canada goose).
  • As with other forms of egg control, a very high proportion of breeding adults would have to be treated in this way in order for this to be effective as a form of population control.

(B23.17.w3, P10.62.w1, V.w5)

Crane Consideration
  • Restriction of breeding may be required in collections if a particular individual or pair is overrepresented genetically in the population. 
    • Breeding can be restricted quite simply by allowing the pair to lay and incubate but replacing the eggs with dummy eggs.
  • It may be necessary to restrict the breeding of common species in order to ensure that spaces are available for more endangered species.
  • If a pair is genetically overrepresented but good parents, eggs from less-well represented cranes may be given to them to incubate and rear.
  • Older offspring of "over-represented" pairs may be housed outside the core population (in non-breeding situations or with reputable private aviculturists). This provides a "back up" population in the case of catastrophic loss of birds from the managed population.

(J23.27.w2, V.w5)

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Environmental Management & Denial of Access

Depending on the species concerned and the area to be managed, it may be possible to restrict access (e.g. using fencing and netting) or discourage birds from using a site by making it less attractive.
Waterfowl Consideration
Decreasing attractiveness
  • Decreasing the attractiveness of an area to waterfowl may involve e.g.
  • Draining wetland areas / avoiding the creation of waterbodies.
  • Reducing food availability, including discouraging feeding by the public and reducing palatable marginal vegetation.
  • Use of visual barriers between water and grazing areas, to deter geese which prefer a clear line-of-sight between their grazing areas and the safety of water.
  • Making banks steeper.
  • Removing islands (increase water level or physical removal).
  • Use of repellents such as methylanthranilate applied to turf.
  • Appropriate methods may vary depending on factors such as the location, feasibility and cost.
Denial of access
  • Fencing off areas is of limited use for preventing access of birds which can fly. However, fencing has been used successfully to deny access of waterfowl such as Canada geese (Branta canadensis - Canada goose) to e.g. areas of recent plantings during habitat creation operations, and to islands to prevent nesting.
  • N.B.
  • Factors which may affect the effectiveness of fencing include the colour of the materials used: in keeping Canada geese (Branta canadensis - Canada goose) from an area of new plantings, bright orange plastic netting was found to be more effective as a deterrent than otherwise-identical green netting (V.w1).
  • The effectiveness of fencing (which waterfowl can normally fly over, if sufficiently motivated) also may vary depending on factors such as the attractiveness of the site to which access is being restricted and the alternative availability of equivalent resources (e.g. feeding ground, safe nesting sites).
  • For protection of crops, it may be most effective to change cropping patterns, e.g. putting crops which are vulnerable to consumption by waterfowl in fields near roads where disturbance from cars may make the field less attractive, or changing to crops which are not attractive to the waterfowl at the time the waterfowl are present.
  • Protection of limited areas of water (e.g. fish ponds) may be possible using netting.

(B23.17.w3, B122, P12.10.w1:- The Management of Problems caused by Canada Geese - A Guide to Best Practice, P12.11.w2:- Integrated Management of Urban Canada Geese, V.w1, V.w5)

Crane Consideration
Denial of access
  • In limited areas (e.g. gardens) it may be possible to use fencing and/or overhead wires to prevent access by cranes.
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Scaring / Hazing

  • Hazing may be used to keep or disperse birds from an area in which they cause a nuisance or are a potential hazard.
  • In general, the same methods of hazing may be used as described for disease control (see: Environmental and Population Management - Hazing / Dispersal).
Waterfowl Consideration Hazing may be used to keep waterfowl away from an area where they are a nuisance, such as geese from grazing agricultural crops and fish-eating ducks from fishing areas or mussel-growing sites. Hazing may also be used to keep waterfowl from hazards such as toxins (see: Environmental and Population Management - Hazing / Dispersal).

A variety of techniques have been used to haze waterfowl:

  • Aircraft
  • Boats
  • Land vehicles, e.g. all-terrain vehicles (ATV), snowmobiles.
  • Visual - Scarecrows, predator models, lights, balloons, flags, ribbons.
  • Noise-makers - e.g. propane cannon, Breco Buoy, Marine Wailer
  • Pyrotechnics (combined explosion, light and whistling noise)

N.B.

  • No single method used to date is ideally effective or suitable for use in all situations.
  • Combining different methods (e.g. visual hazing techniques and noise-makers), and varying hazing methods (including varying the siting of visual deterrents) may increase the effectiveness of hazing.
  • Effectiveness of hazing, by whatever method, may be increased by using hazing alongside actions to attract waterfowl to alternative locations (e.g. providing waste foods as an alternative to growing crops), and/or by decreasing the attractiveness of the area to waterfowl.
  • Timing of hazing may affect the effectiveness - scaring actions to remove nuisance birds from sites may be most effective if carried out in the early morning.
  • In general, hazing is most applicable where waterfowl need to be kept from an area for a limited amount of time - e.g. from crops prior to and during harvest.
  • The amount of effort and cost required for effective hazing may be considerable and may need to be justified in terms of the perceived benefits in e.g. reducing depredation of crops, or reduced hazard (e.g. risk of birdstrike on aircraft).
  • Many hazing methods may not be useable in populated areas due to their nuisance value for humans.

(B23.17.w3, B122, P10.62.w1, P12.10.w1. P12.11.w2, D13)

Crane Consideration
  • Cranes may be discouraged by hazing from using an area where contaminated feed is known to be present (B36.37.w37, P62.12.w1).
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Reduction of Adult Population

  • Populations may be decreased in the short term, often to a considerable extent, by killing individual animals or by translocating them to other sites.
  • Depending on the species and the terrain, a very high effort may be required to effectively reduce populations.
  • N.B. decreasing population density by decreasing the population e.g. by translocation or culling is likely to be effective only in the short term, as new individuals are usually recruited into the population by reproduction and/ or immigration from other areas.
  • The use of culling in population control of free-living species is frequently controversial, particularly when native species are concerned, the population causing damage/nuisance is rare or endangered and when there is a conflict of interest between different sections of society (e.g. those who like waterfowl present to enhance their local park and those who consider them at best a nuisance and at worst a health risk).
  • It is essential that all interested parties should be kept informed and should be involved in the decision making process. Other options should be explored prior to the use of culling and the decision to cull, or to kill limited number of animals e.g. to enhance the effectiveness of scaring efforts, should be made on the basis of sound scientific data.

(P10.62.w1, P12.5.w3, P12.10.w1. P12.11.w2, D13)

Waterfowl Consideration Translocation:
  • Trapping of moulting (therefore flightless) individuals and moving to a new site has been used in the past to reduce Canada goose (Branta canadensis - Canada goose) populations on sites in the UK and the USA. Problems with this practice for reducing population density include geese returning to their original site once able to fly again, and expansion of population in the new areas, as well as rapid re-expansion of the population at the original site by natural recruitment from the remaining birds. (P10.62.w1, P12.10.w1:- The Management of Problems caused by Canada Geese - A Guide to Best Practice).

Culling:

  • Methods of culling include shooting, and capture for euthanasia.
  • Shooting is most applicable during the open season, which varies between countries.
  • Shooting may not be an option in residential areas.
  • Special exemptions to kill birds may be granted outside the open season: for example in the UK licences may be issued to allow the killing of protected birds to prevent serious damage to fisheries, or to protect crops, but only where there is no other satisfactory solution. Killing under such licenses should be used as an adjunct to other control measures.
  • Trapping is most applicable for waterfowl during the moult, when it may be possible to round up considerable numbers of birds. If they are to be killed it is important to use humane destruction methods (euthanasia).
  • N.B. removing adult waterfowl from a population may be effective only in the short term, as other individuals may move into the vacated habitat.

(P12.10.w1. P12.11.w2, D13)

Crane Consideration --
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Authors & Referees

Authors Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee  

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