Management History

Past and Current Management Control Methods

There have been many individual projects to control brown-headed cowbirds, the majority including trapping and killing of cowbirds to reduce reproduction and population sizes. Cowbird shooting as well as roost kills have also been utilized. Cowbird trapping has increased nesting success and reduced parasitism rates for some species and is currently used today. Decreasing cowbird abundance in riparian habitats has increased the Least Bell's Vireo's productivity at the local level. Management projects use different methods most appropriate to a specific region, and vary in success rates because of varying abiotic and biotic factors. Below are specific project examples as representations of common methods used and their success.

Cowbird Trapping

The use of cowbird traps is an extremely popular method for controlling cowbird populations. In this project two male and three female live decoy cowbirds were kept in each trap, and water and food were supplied and refilled regularly. In addition, shade was provided by cloth and soil covered a mesh floor to allow for foraging. When cowbirds were captured they were removed from the area and euthanized with carbon monoxide. Out of 15 different traps at four different locations a total of 168 cowbirds were removed in a 3-month time span. In only one of the four locations (the location with the most cowbirds captured) parasitism rates decreased significantly. In the other three locations there was no significant change in parasitism rates. It is unknown why more cowbirds were captured in one area in respect to the others, but it did not depend on number of traps per site. It is expected that continued trapping of the cowbirds would eventually decrease parasitism rates over a long period of time.

Cowbird Shooting

Cowbird shooting is another widely used method to reduce cowbird population size, and is often used simultaneously with trapping. Female cowbirds are lured to an area by playing a recording of another cowbird's call. The area in which the recording is played should not be near the traps, as the cowbirds will not visit traps if they detect human activity. Approximately 247 female cowbirds were removed in one area using this method in combination with trapping. This method is considered effective in small-range, local areas.

Roost Management

Since cowbirds join large flocks of blackbirds during the winter season some projects focus on targeting cowbirds in roosts, however this method is not used very often and is typically only necessary in fragmented landscapes and when cowbird trapping is too expensive a method. Since the roosts contain cowbirds from many different regions, they fail to protect specific host species and have little effect on national cowbird populations.