Mount Williamson Herd Unit
Prior to the negative influences of Europeans, bighorn sheep in the Sierra Nevada were distributed in numerous populations inhabiting the crest and east side of the range from Olancha Peak in the south to the Sonora Pass region. Additionally, there were populations on the Great Western Divide in the Kaweah Peaks and Mineral King region. Following extensive domestic sheep grazing throughout the range and the devastating diseases this brought to the native bighorn sheep, by 1970 the distribution of Sierra bighorn had shrunk to a region west of the town of Independence in the Owens Valley from the George Creek drainage to Taboose Pass. Although once considered to include just two demographic units, this region now is recognized to include three, referred to as herd units. The Mount Williamson herd unit is the southernmost of these native populations. Its members currently are known to range from Tunnabora Peak and Vacation Pass to Symmes Creek, but as recently as the 1970s rams were known to range as far north as Pinyon Creek; and earlier in the twentieth century there is evidence that they utilized Mount Russell and Mount Carillon.
Mount Williamson is the second highest peak in the Sierra Nevada and lies in the middle of this herd unit. Many areas on that mountain have been documented to be used by bighorn sheep over the past four decades. Prior to 1986 these sheep commonly wintered along the base of Mount Williamson from George Creek to Shepherd Creek with the most concentrated used from George to South Bairs Creek. This low elevation habitat was abandoned after 1985 coincident with a period of high mountain lion predation on bighorn sheep in the central and southern Sierra Nevada, and use of this winter range habitat is still lacking. Instead, winter habitat use by these sheep is largely in the Shepherd and Williamson Creeks region. Summer range of females is mostly on the north ridge and the high east side of Mount Williamson from North Bairs Creek to George Creek. They are also known sometimes to use the high open sandy slopes between Mount Barnard and Trojan Peak. In 2009 a radio collared female from the Mount Baxter herd emigrated to the George Creek drainage accompanied by three other sheep from the Mount Baxter herd. Data from her GPS collar showed that these sheep initially traveled yet further south to Mount Langley before returning to the Mount Williamson herd unit. They have remained there ever since, occupying habitat previously not used the Mount Williamson ewes in the George Creek drainage south to and east and west of Vacation Pass. Previous to this colonization, only rams were known to use that most southern habitat.
When the Mount Williamson herd utilized low elevation winter ranges along the base of the escarpment prior to 1986, there were a number of opportunities to develop good winter counts. The three best years for sheep counts during 1978-85 repeatedly put the total population right at 30 – a relatively small size compared with the native herds to the north. Since their abandonment of winter range habitat good direct counts have been difficult to obtain. However, in two consecutive years (2007 and 2008), the summer distribution of these sheep allowed good counts by coordinated groups of investigators. Totals in both years were 28 sheep, suggesting little population change since the counts 2-3 decades earlier. Genetic analyses of DNA extracted from bighorn sheep dropping beginning in 1998 also indicated a similar population size. Despite this small population size, the genetic diversity of this herd is almost that of the much larger native herds to the north. Genetic analyses indicate that gene flow from the more northern herds maintains the genetic diversity of the Mount Williamson herd. The recent immigrants from the Mount Baxter herd are examples if this.
Check out Jane Kim’s Migrating Mural project! The first mural, completed in November 2012, features Mount Williamson itself.
