The "dog days of summer" have become the "calf days of summer," as the Rocky Mountain Arsenal National Wildlife Refuge recently welcomed two new bison calves into the fold. The first was born on July 29, and the second followed shortly thereafter on Aug. 6. With these two new additions, the bison herd has grown to 29 since coming to the Refuge in March 2007.

At birth, bison calves are typically cinnamon in color weighing 40 - 50 pounds and are traditionally born sometime in April. Why were the first calves of the season so late in coming this year?

"It all stems from their initial arrival. When they moved from the bison range in Montana to Colorado, there were several things that changed for them," said Refuge Manager Steve Berendzen. "It's a new environment, and it took them a while to get acclimated. Once they did, the normal breeding season was already passed."

And why did some calves arrive on a normal schedule in years past but not this year? "Sometimes that's just how it goes," Berendzen said.

As the herd continues to expand, the need for a corral structure to conduct adequate medical testing and monitoring of the herd grows. Construction of the corral is underway, with 200 posts already in the ground and fencing soon to follow.

"It's going real well," said Berendzen. "We hope to have enough of it done to do a trial roundup of the bison next fall."

The corral, which will sit just east of the current bison enclosure area, will be approximately 100 feet by 250 feet and will be made entirely of steel. The target for full completion remains a year or two away.