About 3500 wild horses and burros are to be removed from the US western rangelands under the tentative Bureau of Land Management fall and winter roundup schedule.
The bureau intends to gather 900 others and release them after administering a long-term contraceptive.
The two biggest operations will be in the Owyhee Complex in Nevada and the North Lander Complex in Wyoming.
In Little Owyhee, in the Owyhee Complex, the bureau intends to capture 858 horses, of which 544 will be removed. Of those released, 118 mares will be treated with a contraceptive. The operation is planned for November and December.
During the same period it will also capture 384 horses from the Snowstorms Mountains, which is part of the same complex. In total, 256 of the animals will be removed, of which 48 mares will receive a contraceptive.
The Owyhee herd management area itself will also be targeted, with 141 captured, 11 ultimately removed, and 45 mares given a contraceptive.
In North Lander, in the Rock Creek herd area, the bureau intends to capture 810 horses and remove 580 of the animals. Of the released animals, the bureau hopes to treat 115 mares with a contraceptive. The operation is set for November.
The bureau, in announcing the schedule, noted the drought-stricken nature of the western rangelands, and said the roundups were needed to bring herd sizes into balance with other rangeland resources and uses.
It said changes to the proposed schedule may occur if range conditions deteriorate more quickly than expected.
Sixty-five of the bureau’s 179 herd management areas have already been identified as areas of concern because of drought and wildfire.
The roundups are set to occur between the start of October and the end of February.
It said additional summer gathers will be held, starting in July 2013, with the specific number of removals and fertility-control applications yet to be determined.
Population growth-suppression techniques will include applying porcine zona pellucida (PZP)-based fertility-control vaccines and adjusting sex ratios in some herds to favor males.
Several gathers may use bait and water-trapping methods, rather than helicopters, to capture the animals, the bureau said.
The bureau estimates about 31,500 wild horses and 5800 burros roam federally managed rangelands in 10 Western states, based on the latest data available.
The tentative gather schedule can be accessed here.