What Is Culling and Why Is It Done?

Bird Cull Definition

Canada Geese
David Merrett/Flickr/CC by 2.0

While it may seem destructive to kill birds, there are valid reasons for many types of bird culls. Each situation should be carefully evaluated by authorized wildlife conservation officers and supervisory authorities, however, and no cull should take place without consideration for non-lethal alternatives.

What Is Culling?

Culling is the organized, systematic segregating of organisms from the rest of the group because they don't possess desired characteristics. To cull means to remove, exterminate, or destroy undesirable populations. For instance, hunters may kill deer to lower the massive deer population in a specific area. Culling is illegal in many states.

When situations are extreme, culling may be necessary under certain circumstances, such as:

  • Rare or endangered birds are being threatened by hybridization. This interbreeding may affect the genetic purity of the species that could lead to genetic extinction if hybridization goes unchecked. This is the case with birds such as the red junglefowl, which is in danger of being lost because of interbreeding with free-ranging domestic chickens in its native range. If the free-ranging birds are culled, the wild birds will have better success breeding together.
  • Local, native populations are at risk from aggressive invaders, such as invasive birds that take over nesting sites or attack native birds. If native species are unable to adapt to the aggression, they may be driven out of an area, and there may be nowhere suitable for them to relocate. In some areas, European starlings are culled for threatening eastern bluebirds in this way.
  • Large bird flocks may be posing threats to other wildlife or humans, often through the spread of disease in excessive feces. In urban and suburban areas where large flocks of pigeons, geese, and ducks may take up residence, this can be a concern, particularly near public parks, schools, or playgrounds. Large flocks may also be hazardous in other ways, such as near airports where they may cause airplane strikes or otherwise interfere with safe operations.
  • Unusual population growth may cause an imbalance in local ecology, disrupting food sources and other essential resources. In such cases, bird irruptions may naturally take place, or culling could be considered to keep a population in check. Proper game bird management for hunting activities can also help keep local bird populations balanced so large scale culling is not necessary.

In general, the term cull is applied only to large scale activities rather than the removal of just a few individual birds.

Birds That Are Often Culled

The most common species to be culled are invasive birds, often because their populations are able to grow unchecked outside their native range without competition or predation that keeps their numbers balanced. Feral birds, such as "wild" chickens or duck hybrids, may also be culled if their numbers grow out of control or if they pose problems in urban or suburban communities. In some cases, native birds that breed excessively without natural limitations on their brood success are also culled, such as Canada geese in urban areas where there are no predators to limit their numbers.

In special cases, even native species may be culled as part of conservation measures to protect more vulnerable species. For example, in breeding areas for the endangered Kirtland's warbler, brood parasites such as brown-headed cowbirds are often culled. By reducing the cowbird populations, Kirtland's warblers have greater breeding success. This is only done after very careful population monitoring, however, and is only undertaken as one part of an overall conservation plan.

How Birds Are Culled

Culling can be accomplished in several ways. Large flocks may be hunted, poisoned, or trapped in different ways, and the birds will be killed in large numbers.

A cull could be more subtle during nesting season when eggs are deliberately damaged to prevent excessive population growth. This may be done by coating eggs with oils or chemicals, or even puncturing the shells so they will not hatch. Eggs may also be removed from nests and replaced with false, dummy eggs for birds to incubate instead. With these practices, the adult, nesting birds are not harmed, but there will be fewer new chicks to join the flock. The overall population will remain stable or may decrease as older birds die but are not replaced with a younger generation.

Many hunting agencies use culling to control game birds by adjusting the hunting licenses issued to coordinate with the desired population control. In years when bird populations are overly large, more hunting is permitted or a greater number of licenses are granted, but licenses can be restricted the next year if the population has not recovered.

The exact method for how a bird species is culled depends on a number of factors. The size of the bird population, the type of species, budgetary resources, how much population control is needed, and other factors are all considered before a cull is planned.

Culling - Good or Bad?

Culling is understandably controversial among birders. In many cases, a cull can be seen as necessary to protect struggling native birds, particularly when invasive birds are to be eliminated. On the other hand, protests are often organized about the effectiveness and humaneness of different bird cull methods. This is especially critical when culling is being used as a short term solution instead of long term population management techniques. Wildlife organizations and government groups need to work together to find the best solutions to manage bird populations effectively, including whether or not culling is one technique to be considered.