The survival of elk calves is the focus of a 6-year, statewide study that will enter its second year in 2020 with continuing support from Pitkin County Open Space and Trails.
Colorado Parks and Wildlife is studying factors that influence elk “recruitment” rates – in other words, the survival of elk calves to adulthood, when they are considered recruited into the herd. Declining ratios of calves to adult elk cows has occurred across much of the state of Colorado, spurring the study to find out why the ratios are in decline. With fewer calves reaching adult status, overall herd numbers are dropping.
CPW is studying two herds in southern Colorado, the Trinchera herd and Uncompahgre Plateau herd, both of which have calf-cow ratios of 25 to 30 calves per 100 cows. These ratios are considered low. The agency is also studying the Bear’s Ears elk herd in northern Colorado, where elk recruitment rates are high – 55 to 60 calves per 100 cows, according to CPW. Locally, the Avalanche Creek herd is on the low side, at 30 to 35 calves per 100 cows. These ratios are based on aerial surveys of elk herds, conducted annually in December through February by CPW to look at population trends among elk herds across Colorado.
The aerial surveys, however, don’t provide a complete picture of what is happening on the ground because different factors can produce the same ratio of cows to calves. For example, high pregnancy rates among cow elk combined with low rates of calf survival could produce the same calf-cow ratio as low pregnancy rates among cows and high rates of calf survival.
In 2019, the first year of the study, adult female elk were captured and collared in March. Wildlife officials assessed body condition of the cows and pregnancy rates. Cows were outfitted with a tracking collar as well as a transmitter that allowed CPW to find and collar calves soon after their birth. Within the Avalanche herd, CPW collared 24 pregnant females. In May and June, the agency collared 26 calves – those born to the 24 collared females, plus two others.
Wildlife officials weren’t sure where the calves would be born and, in fact, some were born in challenging terrain, at 11,000 to 12,000 feet. Nonetheless, researchers were able to reach the newborns quickly and successfully collar the young animals.
This December, as the study heads into its second year, CPW intends to collar an additional 25 animals in the Avalanche herd – specifically, calves that are 6 months old. That would bring the total number of collared 6-month-olds to 51 (including the calves that were collared last spring as newborns). The collaring of additional 6-month-olds will help give CPW higher confidence in its estimate of over-winter calf survival, one of the factors that can help shed light on population trends.
In 2020, CPW is looking to increase its sample size of cow elk to 40 animals in the Avalanche herd, along with 40 to 50 newborn calves.
Pitkin County Open Space and Trails has budgeted $70,000 for tracking collars for the second year of the study after allocating $54,000 for the first year of the work.
The collared cow elk will also play a role in a second CPW study – one that evaluates the impact of human recreation on the demographics and behavioral response of elk. The Avalanche and Bear’s Ears herds are being studied. The effort involves the placement of wildlife camera grids to study elk responses to recreation but the collared elk that are part of the calf-cow study will provide additional information on elk movements that may also provide important insight into the response of herds to recreation. The results of the recreation study will be used to evaluate the effectiveness of existing trail closures in minimizing disturbance to elk.
Pitkin County Open Space and Trails closes a number of its trails and properties to protect wintering elk and other wildlife. The recreation study may shed new light on the best management practices to minimize impacts to elk while maintaining recreational opportunities.
By Pitkin County Open Space and Trails