Grackles Wildlife Damage Management

Authors: Michael J. Bodenchuk, David L. Bergman
Publication: USDA-APHIS-Wildlife Services, April 2020

Human-Wildlife Conflicts

• Grackles are numerous in North America, numbering in the tens of millions.
• They cause conflicts by eating crops, spreading pathogens, and causing property damage.
• Management includes dispersal, exclusion, and lethal removal.

Impact on Agricultural Crops & Landscapes

• Grackles damage grains (rice, corn, wheat) and fruits (tomatoes, citrus).
• Common grackles prevalent in peanut areas; sunflowers near wetlands suffer more.
• Great-tailed grackles damage citrus for monoterpenes, affecting fruit quality.
• Droppings alter soil pH; damage ornamental plants and trees.

Livestock and Aquaculture

• Grackles eat livestock feed and spread pathogens like Salmonella.
• They prey on fish in hatcheries and natural ponds.

Structural Damage

• Roosting on powerlines can cause outages.

Human Health and Safety

• Large roosts produce droppings, potentially spreading histoplasmosis.
• Bird collisions with aircraft are a concern.

Nuisance Problems

• Roosts are noisy and can damage property with droppings.
• Grackles may attack if their nests are threatened.

Damage Identification

• Identified through visual and noise observations, and inspection of damaged crops.
• Careful observation is needed to correctly identify the bird species causing damage.

Management Methods

• Integrated Approach: Focus on damage reduction rather than population control.
• Habitat Modification: Pruning trees, managing cattail roosts.
• Exclusion: Netting, porcupine wires.
• Frightening Devices: Pyrotechnics, propane cannons.
• Repellents: Methyl anthranilate (MA), lemon grass oil, garlic oil.
• Toxicants: DRC-1339 used by certified applicators.
• Trapping: Decoy traps, funnel traps, drop nets.
• Shooting: Limited effectiveness, supports hazing.
• Other Methods: Decoy crops, bird-resistant seed treatments, sodium lauryl sulfate for roost control.

Economics

• No nationwide economic estimates; regional studies show significant crop losses.
• Blackbird flocks, including grackles, cause millions in damages annually.

Species Overview

• Common Grackle: Widely distributed, larger than blackbirds, known for noise and large roosts.
• Boat-tailed Grackle: Coastal regions, larger, distinctive calls.
• Great-tailed Grackle: Largest species, adaptable to various habitats.

Legal Status

• Federally protected under the Migratory Bird Treaty Act.
• Control actions allowed under a Standing Depredation Order.

Key Terms

• Granivore: Seed-eating animals.
• Monoterpene: Compounds in plant oils.
• Pyrotechnics: Devices producing loud noise and light.

References

• Various studies and reports cited for crop damage, management methods, and species information.

This summary captures key aspects of the technical series on grackles, including their impact, management strategies, and economic considerations. Always check local regulations before implementing control measures.