Issue No. 8, Article 3/May 13, 2005
Why So Much Bird Damage to Early-Planted Corn? How Can It Be Prevented During Replanting?
We have been able to identify several causes for this year's excessive bird damage on early-planted corn. Most of them have been encountered in previous research attempts to minimize this annual problem. What needs to be done during replanting to prevent reoccurrence may be the toughest question.
The two most common blackbirds causing corn plant stand reduction include the common grackle (Quiscalus quiscula) and the red-winged blackbird (Agelaius phoeniceus). Spring planting season is nesting season for blackbirds. Their peak energy and food requirement needs to raise their young coincide with corn crop emergence. They are constantly looking for readily available food.
Insects appear to be the food preference for female blackbirds during nesting because of their high protein content and the ease of feeding to young birds. However, male grackles and red-wings, while eating insects, appear to feed on seeds just as readily.
Nesting habits are also important to know. The common grackle primarily nests in the trees of windbreaks and shelterbelts, including pine tree plantings. The red-winged blackbird nests close to the ground in or near small-grain fields, hayfields, areas with common reed, marshes, and ditches. While nesting, both prefer food sources close to their nesting sites. Planting an attractive food source near a common nesting site always offers a potential for crop injury.
In general this spring, most of these events occurred across Illinois:
- Tillage and corn planting occurred early, interrupting habitat development for insects (common bird food source).
- Numerous cornfields were planted shallow (<2 inches deep) because of cool soil temperatures and adequate moisture. Shallow planting makes the kernels easier for birds to find and pull.
- Planted corn sprouted and began to emerge just before 2 weeks of cold weather returned to prevent further development or decay of planted kernels. This made them an available food supply for foraging birds.
- Weather prevented additional planting to spread out the potential feeding area. Birds learned where the food was and returned time and again to feed.
- Very low moth flight migration into the area prevented the adequate development of an alternative food source for nesting birds. In past years, when armyworms or other insect problems developed, it was easier for birds to use the insects for food.
- Birds had plenty of time to become successful at finding and pulling planted corn kernels for food before warmer weather returned to encourage rapid plant growth. The less time plants take to reach about 4 inches in height, the less time birds have to utilize the kernels for food.
- Seed treatments that enhance early emergence of a corn planting near a primary nesting site seemed to actually concentrate bird depredation into those fields. Birds feed where they first find food and where they can be successful. If surrounding fields had emerged at the same time, the available food supply would have been larger and damage usually diffused across the area.
- No current seed treatment, concentration of the seed treatment, or soil insecticide acted as a deterrent to bird depredation after being in the soil for weeks prior to seedling emergence. No current seed treatments or insecticides are labeled or have been effective in our research at deterring bird depredation of planted corn kernels over an extended period of time when adequate rainfall occurs.
What can be done to help prevent the same stand reduction in the replanting? Our research experience has shown us the following:
- One heavy rain can negate the potential benefit of the use of almost any repellent utilized on the seed or sprayed on the emerging plant. We have several opportunities for a rain of 1/2 inch or more during each spring planting season.
- As soil temperatures increase, deeper planting (~2 inches) can help make birds less successful at getting to the planted kernels, provided the planter slot is closed.
- Warmer soil temperatures will encourage faster emergence and plant growth regardless of the planting depth. This reduces the time for birds to be successful feeding in the field.
- Replanting with a proven early-growth hybrid will also help minimize the amount of available time for bird depredation before plants get 4 inches tall.
- As the season develops, more food sources (insects) usually become available for blackbirds in field borders and small-grain and hay fields. This will naturally diffuse the bird feeding if these areas are not mowed until after good corn crop emergence.
- Any planting practice that reduces the amount of available time for birds to work a corn planting (and be successful) before it reaches about 4 inches tall can reduce the chance for reoccurrence of bird damage.
- Sometimes a field is located so close to a major nesting site that planting a less attractive feeding crop such as soybean may be the best alternative until something else can be done.
Blackbirds, including grackles, are classified as migratory birds and are under the protection of the Migratory Bird Treaty Act, enforced by the U.S. Fish and Wildlife Service (USFWS). Because of the extent of agricultural damage these birds have historically caused, the USFWS has issued a blackbird depredation order, which allows for the control of these birds without a federal depredation permit when they are causing, or are about to cause, damage to agricultural resources. Despite a federal control permit not being needed, these birds are also under state protection. Therefore, a Nuisance Animal Removal Permit is needed from the Illinois Department of Natural Resources (IDNR). You should contact your District Wildlife Biologist or Conservation Police Officer from the IDNR to obtain this permit and a list of accep-table control options. For add-itional information, you may contact USDA's Wildlife Services office in Springfield at (217)241-6700.--Ron Hines