Getting rid of cormorants typically involves a combination of deterrence, exclusion, and, in some regulated cases, population reduction methods, often tailored to specific contexts like aquaculture, fisheries, or sensitive ecosystems.
Understanding Cormorant Damage
Cormorants, particularly double-crested cormorants, can cause significant issues, especially in aquaculture and sport fishing areas. Their diet consists primarily of fish, and large populations can deplete fish stocks, damage fishing gear, and leave guano deposits that are detrimental to vegetation and structures. Understanding the extent of the damage and the specific habits of the cormorants in your area is the first step in devising an effective control strategy.
Integrated Cormorant Management Strategies
An effective approach often combines multiple methods to achieve desired results. This is known as Integrated Pest Management (IPM) and typically prioritizes non-lethal methods before resorting to lethal ones, in compliance with all relevant laws and regulations.
Non-Lethal Control Methods
Non-lethal methods aim to deter cormorants from specific areas without harming the birds. These methods are often preferred due to environmental considerations and regulatory requirements.
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Habitat Modification:
- Reduce Perching Sites: Remove dead trees, snags, or structures where cormorants might roost or perch.
- Alter Water Depth: In shallow ponds, increasing depth can make fish less accessible to diving cormorants.
- Vegetation Management: Keep banks clear of tall vegetation that could provide cover for birds or block sightlines.
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Exclusion:
- Netting: Overhead netting is highly effective for protecting ponds and small aquaculture facilities. It can be expensive but offers a long-term solution.
- Fencing: Deterring land-based approach to water bodies.
- Underwater Barriers: Submerged lines or fencing can deter diving birds.
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Harassment and Deterrence: These methods aim to scare cormorants away, making the area less appealing. Consistency is key for these methods to be effective.
- Pyrotechnics: Devices like bangers, screamers, and bird-scaring cartridges can create sudden loud noises to disperse birds.
- Effigies: Placing realistic effigies of predators (e.g., eagles, coyotes) or dead cormorants can sometimes deter birds, but their effectiveness often diminishes over time as birds habituate.
- Propane Cannons: Automatic noisemakers that mimic gunshots, useful for covering larger areas.
- Lasers: Handheld or automated lasers can be used at dawn or dusk to move birds off roosts or out of feeding areas.
- Dogs: Trained dogs, particularly Border Collies, can effectively patrol shorelines and chase away birds.
- Human Presence: Regular human activity in an area can make it less attractive to cormorants.
- Visual Deterrents: Reflective tape, Mylar balloons, or strobe lights.
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Acoustic Deterrents:
- Distress Calls: Recordings of cormorant distress calls can be broadcast to scare them away.
- Predator Calls: Sounds of predators can also be used, though birds can become accustomed to them.
Lethal Control Methods
Lethal control, primarily shooting, is typically considered when non-lethal methods are insufficient or impractical, and only after obtaining the necessary permits from wildlife authorities. Most cormorant species are protected under migratory bird acts in many regions, making permits mandatory for any lethal control actions.
- Shooting: This method allows for a rapid reduction in cormorant numbers.
- Effectiveness: Shooting is most effective on breeding colonies, where large numbers of birds congregate daily.
- Targeting: Open-water shooting and removal at night roosts also can be used to protect specific sites.
- Ammunition: When engaging in shooting for cormorant control, it is recommended to use 12-gauge shotguns with non-toxic shot sized #4 or #6.
Below is a quick reference for common shooting specifications:
Equipment Type | Ammunition Type | Recommended Size | Target Application |
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12-Gauge Shotgun | Non-Toxic Shot | #4 or #6 | Breeding Colonies, Open Water, Night Roosts |
Legal Considerations
Before implementing any cormorant control method, especially lethal ones, it is crucial to understand and comply with all federal, state, and local regulations. In many areas, cormorants are protected under migratory bird treaties, and permits are required for any activities that might harm them or their nests. Consult with your local wildlife agency (e.g., U.S. Fish and Wildlife Service, state fish and wildlife departments) to ensure compliance.
Important Considerations Before Action
- Identify the Species: Ensure the problematic birds are indeed cormorants, as other similar-looking water birds might require different approaches.
- Assess Damage: Quantify the damage to determine if control measures are truly necessary and to justify permit applications.
- Integrated Approach: A combination of methods is often more effective than relying on a single technique.
- Permitting: Always check local, state, and federal regulations regarding cormorant control and obtain all necessary permits.
- Consult Experts: Wildlife biologists or pest control professionals specializing in birds can provide tailored advice and help develop an effective plan.