Pronghorn, which are plentiful on the Chico Basin Ranch, are one of North America’s most remarkable wildlife species. They are the fastest land animal on the continent, capable of sprinting 60 mph. Pronghorn in western Wyoming also make the longest land migration of any animal in the continental United States, traveling over 300 miles round-trip annually between their summer and winter ranges!
Southeastern Colorado is home to 50% of the state’s pronghorn population. However, biologists know little about their movements in this region. With the help of several landowners, including the Chico Basin Ranch, biologists from Colorado Parks and Wildlife set out to study these incredible animals. In February 2016, we captured and radio-collared 44 pronghorn, including 11 on Chico Basin. For the past year, we have followed radio-collared pronghorn from either an airplane or GPS satellite uploads to study animal movements and herd size. Many pronghorn have stayed close to their capture location. In fact, 13 of the 44 pronghorn, including four radio-collared on Chico Basin, have remained within a 10 mile radius. However, other pronghorn have made substantial movements. Nine have been located more than 30 miles away from their capture location. Some of the most interesting movements have been from animals radio-collared on or near Chico Basin. In fact, a female captured on the Ranch’s northeast side has made the longest movements observed to date. After capture, she travelled north to an area near Ramah and stayed until May. She then crossed Highway 24 and moved northwest, passing close to Elbert. She crossed Highway 83 and travelled north once she hit I-25. Her northern-most location, recorded in June, was halfway between Larkspur and Castle Rock, approximately 60 miles from her capture location. She then returned to southeastern Douglas County, before dying of unknown causes in October. Another animal captured near Chico Basin travelled north 40 miles, crossing Highway 24 near Peyton. She stayed in northern El Paso County from May through October before returning to Chico Basin in November, where she has remained through the winter.
We were also interested in examining herd size changes through the year. Prior to this study, we expected groups to be the smallest in late spring when pronghorn females give birth. After fawns are born in early June, pronghorn herds increase again in July before peaking in mid-winter. As expected, average herd size was lowest in May and June at 6 pronghorn per group. Herd size peaked to an average of 40 pronghorn per group in mid-November, a little earlier than expected. We have learned many exciting things about Chico Basin’s pronghorn during this first year and we plan to continue the study for several years. Besides movements and group size, we want to know more about how long the pronghorn live and whether animals return to the same locations every spring and winter. None of this work would be possible without the assistance of the Chico Basin Ranch and other landowners in southeastern Colorado! Thank you!
By Julie Stiver, Colorado Parks and Wildlife Biologist