Above: The huge base of an elk antler. Bulls grow antlers annually from the time they are nearly one year old. When mature, a bull’s "rack" may have 6 to 8 points or tines on each side and weigh more than 30 pounds. The antlers are usually shed in March or April, and begin regrowing in May, when the bony growth is nourished by blood vessels and covered by furry-looking "velvet." Antler growth ceases each year by August, when the velvet dries up and bulls begin to scrape it off by rubbing against trees, in preparation for the autumn mating season or rut. A bull may gather 20-30 cows into his harem during the mating season, often clashing or locking antlers with another mature male for the privilege of dominating the herd group. By November, mating season ends and elk generally move to their winter ranges. Calves weighing 25-40 pounds are born in late May or early June.

Below: Paul holds a mid-sized specimen of an elk antler, with sprawling Lamar Valley in the background. During the winter months, Lamar Valley is home to one of the largest herds of elk in the world. Climate is the most important factor affecting the size and distribution of elk herds here. Nearly the whole park - approximately 2.2 million acres - provides summer range for elk. However, winter snowfalls force elk and other ungulates to leave the greater part of the park. Only the northern, lower-elevation portion of Yellowstone, where temperatures are more moderate and snowfall less than in the park interior, can support large numbers of wintering elk. Annual precipitation, which occurs mostly as snow, averages as high as 75" in the southern, high-mountain plateaus of the park; minimum temperatures there are often well below 0° F, and have been as low as -66° F. In contrast, most of the northern range averages less than 30" of precipitation annually, and winter temperatures are considerably warmer.