Description of the Pest
Several bird species may cause serious problems in cole crop production in California.
Horned larks are about 6 to 7 inches long, smaller than robins, but slightly larger than sparrows. They are brown to gray with a distinctive pattern of yellow, black, and white bands on the face and throat. Their name comes from the small tufts of erect, dark-colored feathers behind the eyes of mature males. From a distance, they appear to walk rather than hop, distinguishing them from finches and sparrows. They have high-pitched, distinctive songs and often sing while flying.
Horned larks are classified as migratory nongame birds. They may be controlled under the general supervision of the county agricultural commissioner or under a depredation permit from the U.S. Fish and Wildlife Service.
House finches are highly adapted to human environments. House finches are typically 5 to 6 inches long and feed in small flocks. Male finches have a rosy-red or orange head, rump, and breast with brownish wings and back, and a brown streak on their sides. Females have the brown body and wings, but lack the red or orange coloration.
House finches are migratory, nongame birds, and can only be lethally removed with a depredation permit from the U.S. Fish and Wildlife Service or under supervision of the local county agricultural commissioner.
White-crowned and golden-crowned sparrows cause damage in California. Both are about 6 to 7 inches long. White-crowned sparrows have a distinct pink or yellowish bill, erect posture, gray throat and breast, and a visible crown streaked with black and white. Their call is a clear whistle. Golden-crowned sparrows are similar, except they have no white head stripes. A golden-yellow central crown stripe is prominent with black borders. Their call is three to five clear whistles. Overall, golden-crowned sparrows are less numerous and cause fewer problems than white-crowned sparrows.
Crowned sparrows are migratory, nongame birds, and can only be lethally removed with a depredation permit from the U.S. Fish and Wildlife Service or under supervision of the local county agricultural commissioner.
The house sparrow is a small (approx. 6 inches), stocky songbird with short legs and a thick bill. Male house sparrows have a black throat and white cheeks. The male has a reddish back and black bib, while the female is distinctly brown. The house sparrow is an invasive, exotic species, and as such, can be lethally removed at any time.
Most damage occurs before seedlings have two or three true leaves. Crowned sparrows feed on seedlings and mature plants. Damage to lettuce and cole crop heads will make produce unmarketable.
- Birds can reduce stands in direct-seeded lettuce and cole crop fields by feeding on seeds and young seedlings.
- Seedlings may be nipped off, or small holes may remain in the soil where the entire seedling was pulled out.
Horned larks feed on seeds of wild plants and on insects in open grasslands. They move into lettuce and cole crops when natural forage is scarce or when the lettuce or cole crop is planted closely to their habitat. These birds feed mainly on seedlings (up to 3–4 inches tall) where they nip or completely pull plants out. They feed in flocks and can create bare spots in a lettuce field in a few hours. They tend to feed well out into the field and do not concentrate along fence rows or wooded areas.
In contrast, much of the damage from house finches and crowned sparrows occurs along the field edges where they feed. Although house finches feed primarily along the field edges, they are often seen in open areas and tend to scatter to high, open perches when alarmed.
Natural predators such as raptors and bobcats will feed on some of the smaller bird species, although these numbers mean little for controlling such bird pests.
Always consider habitat modification as a first step for controlling bird pests.
- Look for and eliminate brush or pruning piles, stacks of irrigation pipes, piles of boxes, etc., where birds may rest and nest.
- Consider removing roosting trees along perimeters to reduce bird invasion into fields.
However, there are few situations when habitat modification can be used to control high bird numbers. As such, alternative control methods will likely be needed.
Monitoring and Treatment Decisions
Count birds weekly to help you determine when damage will occur so you can take action early. This is particularly important to reduce damage to fruiting buds and newly sprouted row crops.
- Watch for bird movement into or within the field.
- Keep track of species, numbers, and location if you have had substantial damage in the past.
These records will help you plan control strategies in advance and assess the effectiveness of previous control actions.
Frightening devices can deter some species (e.g., crowned sparrows), but are less effective for others (e.g., horned larks, house finches, and house sparrows).
The most effective way to frighten birds from a field is to use a combination of noisemakers and visual repellents such as mylar streamers and "scare-eye" balloons. For example, scare-eye balloons may be attached to trees or posts that are next to electronic distress call devices. This combination may increase effectiveness over using either approach by itself. For maximum effectiveness, rotate from one type of frightening device to another and do not use one combination of devices for more than a week; otherwise, birds will become used to it.
Common noisemakers include roving patrols of bird bombs and shell crackers. Stationary devices such as gas cannons and electronic distress calls also provide relief. These stationary devices are most effective when you have at least 1 device per 5 acres and when they are elevated above the canopy.
Regardless of the approach used, pay attention to bird responses when using frightening devices. When birds no longer respond negatively to a specific approach, you must switch to a different frightening tactic to continue to scare birds out of the field. At best, an appropriate rotation of frightening devices will control bird pests for a few weeks. Therefore, only use these scare tactics when needed to prevent birds from habituating to these auditory and visual repellents. Additionally, once birds become accustomed to feeding in a field, frightening tactics become much less effective. Therefore, have frightening devices ready to implement before damage occurs so that birds can be deterred right at the onset of damage.
Birds that invade in small numbers, such as scrub jays and magpies, can often be controlled by shooting. Check with California Department of Fish and Wildlife, U.S. Fish and Wildlife Service, and county agricultural commissioner officials before shooting any birds as depredation permits are often needed.
Where permissible, occasionally shooting at a few birds will increase the effectiveness of your noisemaking techniques, especially if noise makers go off at the same times as the actual shots, because birds will begin associating loud noises with the real hazards of firearms.
Trapping can be an effective way to control house finches, house sparrows, and crowned sparrows, especially if conducted over a relatively large area such as several fields. The most effective trap for these species is the modified Australian crow trap.
Successful trapping must take into account the behavior patterns of the birds being controlled. These traps use live birds as decoys to attract additional birds. Therefore, place traps in suitable locations with adequate food, water, shade, and roost locations to keep the trapped birds alive.
Trapping is best carried out by someone experienced with the technique. For house finches and crowned sparrows, trapping must be conducted under supervision of the county agricultural commissioner.
Trapped birds are usually euthanized through the use of a CO2 chamber. Leave some birds alive to serve as future decoys.
Chemical repellents rely on objectionable tastes, odors, or learned aversions to deter birds from consuming or damaging fruit.