Table 2: Environmental determinants proposed to limit free-ranging bighorn sheep populations.

Determinant (subcategories)Geographic distribution of determinantLocations where determinant reportedDie-off attributed to determinant1Selected references

Adverse environmental conditionsNorthern and mountain locationsCaliforniaYes[28]
ColoradoNo[42]
Canadian Rockies, CanadaYes[72]
WyomingYes[43]
Escape terrainRange-wideArizonaNo[83]
Baja California Sur, MexicoNo[84]
MontanaNo[85]
New MexicoNo[44]
Range and migration restriction due to human settlement or activitiesRange-wideAlberta, CanadaNo[86]
ArizonaNo[87]
CaliforniaUnclear2[28]
CaliforniaNo[88]
ColoradoNo[27, 8991]
ColoradoYes[92] (also see [93])
MontanaNo[94]
Free-waterPrimarily arid regionsDesert, generalNo[95]
ArizonaNo[96, 97]
CaliforniaNo[54, 79]
CaliforniaNo[53]
UtahNo[55]

Food quantity
Limited forage and precipitationPotentially range-wideAlbertaNo[59]
ArizonaNo[60, 98, 99]
CaliforniaYes[65]
ColoradoNo[61]
MontanaYes[49]
NevadaNo[50]
New MexicoNo[44, 62]
TexasNo[63, 66]
UtahYes[51]
Plant community successionPotentially range-wideBritish Columbia, CanadaNo[73]
CaliforniaNo[74, 75]
Canadian Rockies, CanadaYes[72, 76]
MontanaNo[94]

Food quality
Protein deficiencyPotentially range-wideColoradoNo[27]
TexasNo[63]
Dietary mineral availabilityRange-wideAlberta, CanadaNo[100]
ArizonaNo[60, 101]
British Columbia, CanadaNo[102, 103]
CaliforniaNo[28]
ColoradoNo[27]
UtahNo[104]
WyomingNo[105]
Selenium deficiencyLocalizedWyomingYes[70]

Competition
Competition for forage-domestic speciesRange-wideAlberta, CanadaYes[106]
ArizonaUnclear2[107]
CaliforniaNo[28, 78]
ColoradoNo[27, 89]
NevadaNo[108]
OregonYes[109]
TexasNo[110]
WyomingYes[111]
Competition for forage-bighorn sheepPotentially range-wideColoradoYes[112]
MontanaYes[113, 114]
Tiburon Island, MexicoNo[3]
WyomingNo[115, 116]
Competition for forage-native ruminant speciesPotentially range-wideCanadian Rockies, CanadaYes[72]
ColoradoNo[27, 89]
ColoradoYes[112]
MontanaYes[117]
MontanaNo[94]
Sierra Nevada, CaliforniaUnclear2[28]
WyomingNo[118]
WyomingYes[111, 113, 119]

Seasonal
Competition for forage-limited winter range (environmental or nonspecific)Potentially range-wideAlberta and British Columbia, CanadaYes[120, 121]
ColoradoNo[42]
Competition for forage-limited winter range (domestic livestock grazing)ColoradoNo[4, 27]
Competition for forage-limited winter range (native ruminant species)WyomingYes[122]
Competition for space (social impacts)Potentially range-wideAlberta, CanadaNo[59, 80]
CaliforniaNo[79]
ColoradoYes[19]
IdahoNo[81]

1Mortality considered to be in excess of baseline levels;
2Mortality in excess of baseline versus endemic disease status was not clear.