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Mule deer by the number: How CPW calculates wildlife population
Mule deer by the number: How CPW calculates wildlife population
Colorado​'s deer populations have fluctuated greatly in Colorado's history. In 2015, Colorado Parks and Wildlife estimated that there were about 436,000 deer in Colorado. Have you ever wondered how CPW calculates mule deer populations?

Every year, CPW biologists take inventory of wildlife in Colorado. These wildlife managers count a subsection of each species in order to calculate the estimated population, productivity and distribution of wildlife throughout the state.

“Ongoing scientific research and monitoring is essential to conserving Colorado’s wildlife and habitat,” said Andy Holland, CPW’s big game coordinator. “The aerial inventory is a critical part of CPW’s wildlife management.”

This process is part of CPW’s science-based management of Colorado wildlife. Thanks to the funding that comes from hunting and angling license sales throughout the state, CPW has a nationally recognized mammals research section that developed many of the methods now used by CPW managers to inventory big game.

Because it is impossible to count every deer in Colorado manually, wildlife managers use multiple sources of data to inform population models to estimate population size. CPW has been inventorying deer populations, as well as other species such as elk, from the air for over 50 years.  

“For every group of deer that we see, we go through the group and classify each individual animal by whether it’s a buck deer, a doe deer or a mule deer fawn,” explained CPW Terrestrial Biologist Darby Finley. “We use this information to calculate a ratio from the number of bucks and the number of fawns per 100 does. The ratios are part of what we put into our population models to calculate deer numbers.”
The aerial inventory helps CPW understand fawn reproductive rates and set wildlife population goals as well as the number of hunting licenses offered every year. Harvest estimates and survival estimates from CPW’s five intensive mule deer monitoring areas are also important factors used in population models to estimate population size. 

“The information that we’re gathering helps us to estimate the sex and age ratio, which in turn helps us calculate the number of bucks we want to see harvested and the number of does we want to see harvested, or not harvested, in order to meet our population goals,” Finley said. 

The results of these annual inventories are available on the Deer Hunting Statistics​ page under population estimates.​