Biologists are trying to decide whether elk herds at the Rocky Mountain National Park and Wyoming's National Elk Refuge should be limited through birth control.

This summer park biologists and veterinarians tranquilized 34 elk. Seventeen were injected with a contraceptive and the other 17 were treated as controls.

Both sets of animals were fitted with color-coded radio collars, so their movements and behavior could be monitored from a distance.

Park biologist Ryan Monello says preliminary results showed the 17 elk acted no differently from the control animals this fall. In spring, all 17 will be recaptured and tested to see if they gave birth.

If the treatment is shown to be effective, the park will begin the third phase of the study to see whether it can be effective in reducing the growth of a free-ranging herd. But the treatments could be costly.