The American crow (Corvusbrachyrhynchos) is one of the most recognizable birds across the United States and Canada. It is widely distributed, breeding in the southern half of Canada and living year-round in almost all of the United States, save some of the drier southwestern deserts. The American crow can be found in a wide variety of habitats as well. Crows are often foundin open woodlands, forests, agricultural fields, woodlots, and even beaches. They also do very well in suburban settings, often being seen in parks, cemeteries, parking lots, and in or around towns.
Crows are opportunistic feeders, eating whatever they are able to find, including insects, earthworms, other small animals, fruit, and grain. They are also known to steal eggs or young chicks from the nests of other birds. Additionally, crowsare excellent scavengers and are commonly seen picking at road kill or foraging among garbage dumps.
The American crow is seldom seen alone and is instead usually found in small loose flocks. Occasionally, flocks numbering in the thousands may be observed. This is especially common in the winter as the crows form large roosting flocks for the night. Large loose flocks of these birds can be seen flying overhead around dusk as they go to gather at their roosting site.
American crows belong to the family Corvidae, which includes jays, ravens, magpies, and nutcrackers. Superficially, the American crow looks very similar to some of the other North American crows and the common raven. One of the best ways to distinguish the American crow from similar corvids is by voice. American crows give a raucous "caw" call that, along with their abundance, large flocking behavior, and conspicuity around humans, attributes to their widespread familiarity. Subtleties in tail shape, build, and bill structure can also help distinguish between species. American crows are black overall, have broad wings, and softly rounded tail feathers.
Crows and other corvids are regarded as some of the most intelligent birds. Crows have been known to use simple tools and there are sophisticated social interactions within flocks.
The U.S. Code of Federal Regulations lists the American crow as a migratory non-game species.It is therefore protected by the Migratory Bird Treaty Act and it is illegal "to possess, transport, or export any migratory bird, or any part, nest or egg of such bird." Federal depredation permits must be obtained to take crows in most cases unless certain requirements are met:either the crows must be actively damaging or about to damage ornamental or shade trees, agricultural crops, livestock or wildlife, or the birds must be in such great numbers that they create a health hazard or other nuisance. While not generally classified asa game species, some states do have established hunting seasons for crows. All state laws should be checked before taking crows as they do not always reflect federal regulation. For example, a state-issued depredation permit is required in Ohio to kill crows outside of the crow hunting season, regardless of circumstance.
American crow populations have generally expanded in size and range over the past few decades. This comes even in the wake of the introduction of West Nile Virus in 1999, in which American crows exhibited the highest death rate of any species.The American crow population was estimated to have been decimated by up to 45%by the virus. Crow populations were able to recover, however, and have been exhibitingan overall increasing trendover the past forty years. Estimates now place the American crow population at 31,000,000.
Another concern in addition to the sheer numbers of American crows is their large scale shift from rural habitat to more urban and suburban ones. Studies have shown that suburban crows have had greater nest success and first-year survivorship than rural ones. This may be due to fewer predators such as great-horned owls and certain hawk species in urban areas. Some scientists believe that the increase in total crow numbers are a direct result of the crows recent exploitation of more urban habitats that were once considered ecological traps.
American Crows have often been regarded as nuisance birds. With their recent expansion to more urban areas, there have been more and more undesirable human-crow interactions. Crows can cause major damage to crops such as pistachios, walnuts, almonds, cantaloupe, tomatoes, peas, pears, corn, beans, and a host of other crops.Crows have also been reported to cause damage to lawns while foraging for grubs or earthworms in large numbers. Additionally, a flock of crows can produce large amounts of malodorous and potentially harmfulfeces.This is especially apparent at roost sites where crows may gather in the thousands each night. The fungal disease histoplasmosis is often a concern in such areas contaminated by bird droppings. The large numbers of birds at roost sites are also noisy and often disruptive to people nearby. Crows have also been implicated in the spread of transmissible gastroenteritis among swine. Lastly, the large flocks of crows can be a serious hazard to aviation. The FAA lists crows and ravens as the 16th most hazardous animal to aircraft using data from 1990 to 2003.
Most experts believe an integrated approach is best when dealing with nuisance crows. Crows are very intelligent and overuse of any one non-lethal method may result in rapid habituation by the crows and decreased method effectiveness. Lethal and non-lethal techniques are outlined below.
Because of crows' success in wide variety of habitats, it is difficult to modify the habitat in any inexpensive way to make it unappealing to crows. However, trees may be covered with netting if they are a common perching or roosting site. The same may be done to small fields if crows are often foraging there. Individual plants may be covered with bags, nets, other exclusion materials, or sticky substances to discourage birds from perching or foraging there. The trees at common roost sites may also be thinned out to prevent large numbers from gathering at that site.
Repellants for crows come in a variety of different types. There are many visual, audio and gustatory/chemical repellants marketed for crow management. The first type, visual repellants, includes putting upscarecrows, effigies of owls or other predators, and reflectors. These methods are often cheap, but may quickly be ignored by crows. It is best to use visual repellants in conjunction with other methods.
Frightening audio or noisemakers are another common type of avian repellant. These include propane cannons, screamer or banger rockets or other pistol-shot pyrotechnics, and the use of recorded distress calls. These methods temporarily scare the birds away from the immediate area. Propane cannons and similar devices emit loud noises, often at set intervals. Some models may rotate to have a greater effective range. Pistol-shot pyrotechnics are small explosives that may be shot from a distance toward the desired target. Shellcrackers are another commonly used pyrotechnic that are fired from 12-gauge shotguns.
Playback of distress calls have proven effective in many species of birds. Crows are highly gregarious and communicate often in their flocks. These distress calls alert to flock to danger and have been effective against crows when repeatedly played as a flock is beginning to roost.
The last type of repellants includes chemical and gustatory repellants. These usually work by causing irritation or pain to the bird when they are exposed to the chemical or if they ingest foods sprayed with it. Some of the more common registered chemical repellants include anthraquinone and methyl anthranilate.
These types of repellants may be sprayed over food/ground, directly toward a target species or specific area, or, in some cases when dealing with waterfowl, over water.
Other Non-lethal Methods
Live-trapping and relocating is not often used for crows in large numbers due to the large costs and amount of labor required. This method may be feasible for small resident groups.
As a last resort, it may be necessary to lethally remove a number of birds. In most cases, lethal actions are not intended to remove every bird in the area, but to remove some and, perhaps more importantly, to condition the others. Audio repellants like propane cannons that resemble shotgun blasts will be more effective if the birds observe the killing of one of their flock members by a shotgun. Occasional killing of birds will help slow the rest of the flock's habituation to non-lethal methods.
It is good to take advantage of crow hunting seasons, where applicable, but in more urban areas, ordinances concerning firearms within city limits or safe distances from buildings may need to be identified and waived. The local authorities should be notified before instituting any shooting program.
Several avicides are also on the market advertising crows as a target species. It is important to be knowledgeable about the active chemicals and their usage before administering avicides. There may be a risk of accidental primary poisoning of untargeted species if used improperly. There should also be no risk of secondary poisoning when avicides are used correctly.