Damage
Grackles can cause several types of damage. As they are scavenging birds, large numbers can be found at dumpsites, food courts and other human areas where food is present. The resulting amount of fecal matter creates unsanitary conditions and can result in physical damage from the uric acid. They are also an agricultural pest bird because they will eat small seedlings and damage crops.

Control
There are numerous products and techniques available to combat nuisance grackles. Like fellow members of the blackbird family, noisemaker units such as the Bird-Gard, Bird Squawker and Bird Wailer units projecting natural distress calls and frightening sounds (selection of units depends on size of area to deter birds as well as severity of problem) plus visual scare products like Scare Eye Balloons, Octopus, Flash Tape and the Avikite can be used to move them from a site. If they are too entrenched to be scared away, exclusion using 1-1/8" Stealth Net or Bird-Shock electrical track on ledges will be necessary. Grackles are too nimble for traditional mechanical ledge products. Fogging a roosting winter flock with ReJeX-iT irritant has also shown some success.

Nesting
Grackles build a bulky yet dense nest of twigs, grasses or weeds lined with feathers, rags or dried grass. The nest may be held in place with a foundation of mud or cow dung. Grackles will nest in a variety of places from willow swamps, dense brush to tall trees with trees being the most common. Boat tail grackle nests will seldom be seen more than twenty miles from the coast.

Breeding
Grackles breed during the spring. They usually lay four to five eggs in a single brood for the year. Common grackle eggs are a pale green to light brown with purple and dark brown streaks and blotches. Boat tailed grackles have lighter blue to grayish eggs with dark streaks and blotches. The eggs take 14 days to incubate with the young being able to fly about three weeks later.

Cycles
Grackles have a definitive seasonal behavior. They nest and breed as one pair or in small groups in the spring time. In the fall, the birds will fall to form large colonies with the juveniles first forming the groups and later joined by the adults. These large colonies can number in the thousands. In colder, northern climates the flock will migrate south, while southern birds will stay put or move into a more urban location. These flocks will usually take over several trees or urban dwellings for their evening roosting. In the winter, their feeding site may be quite far from their roosting spot, making trapping or baiting difficult.