Mount Baxter 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 Baxter herd is middle of the three, but is contiguous with the Sawmill Canyon herd unit to its immediate north.   Rams readily move across both these two herd units, but ewes exhibit more limited habitat use patterns that are repeated from year to year.  This does not mean that the Mount Baxter herd includes just a single female pattern of habitat use.  In fact, it includes multiple such patterns, but those different patterns overlap considerably on the low elevation winter range that is at the northern end of this herd unit.  

East of the crest Sawmill Creek is the division between the Mount Baxrter and Sawmill Canyon herd unit.  At its lowest elevations in bighorn sheep winter range, that creek has normally supported a thick riparian vegetation of water birch that served as a barrier to bighorn sheep movement.  In 2007 a hot July wild fire burned most of the Mount Baxter herd winter range and some of that water birch barrier, but left most of the winter habitat to the north in Sawmill Canyon intact.  The following winter ewes from the Mount Baxter herd readily moved north across Sawmill Creek looking for grazable forage and mixed with the Sawmill Canyon herd there.  That lasted only until new growth sprouted on their scorched traditional winter range to the south, and ewes from the Mount Baxter herd have not been known to cross that herd unit boundary since.  

Along the crest of the Sierra, summer range of ewes from the Mount Baxter herd extends from Mount Baxter and Acrodectes Peak in the north to Kearsarge Peak and Mount Gould in the south with a western boundary on the upper slopes of the east side of the Rae Lakes drainage.  However, rams from this herd range considerably further west.  In summer they frequently can be found using slopes on either side of the Rae Lakes drainage mostly lower than the ewes, as well as in the 60 Lakes, and Gardiner Basins. 

The Mount Baxter herd has the best combination of summer and winter habitat in the Sierra Nevada.   Summer range used by females is extensive with a great variety of forage resources varying from alpine meadows to large alpine patches of Sky Pilot and Alpine Gold, whose flowers they devour, and a frequently used mineral lick on Baxter Pass.  Their winter range is nutritionally the best in the Sierra Nevada.  It extends further east and lower than other winter ranges (except the Sawmill Canyon herd).  The result is earlier winter greenup of forage species and a richer mixture of forage species.  Together, this amounts to a greater availability of nutrients to sheep.   This is reflected in a higher potential population size that the habitat can support.   In the late 1970s 151 sheep were counted in the Mount Baxter herd, which is 21 more sheep than has been documented in any other herd unit to date.  It was the large size of this herd at that time that allowed a restoration program to be initiated in the late 1970s that restored populations to three areas of the Sierra during 1979-88 using sheep caught from the Mount Baxter herd and moved to vacant habitat.

Similar to other herds in the Sierra, the Mount Baxter declined to about 15% of its former size by the mid 1995 coincident with a period that included 7 drought years in an 8 year period and winter range avoidance that coincided with heavy mountain lion predation.   The Mount Baxter herd was somewhat delayed in re-establishing winter range use and recovering numbers after the turn of the century compared with some other Owens Valley herds.  Its recovery was then capped at less than 40% of its former size during 2006-2011 coincident with another period of high mountain lion predation on winter ranges.  It only began further population growth in 2012 following removal of lions known to be killing these sheep.