REV00636

• Permit No: M1985043
• IBM Index Class Name: Revision
• Doc Name: DESIGNATED CRITICAL HABITAT FOR THE MEXICAN SPOTTED OWL ARTICLE
• Type & Sequence: AM2
• Media Type: D
• Archive: No

w •
Environmental Assessment -Mexican Spotted Owl Critical Habitat Designation 3
January, 2001
Mexico, contains over half of known owl sites. Owls here use a wide variety of habitat types,
but are most commonly found inhabiting mature mixed-conifer and ponderosa pine-Gambel oak
forests. The Basin and Range-East RU encompasses central and southern New Mexico, and
includes numerous parallel mountain ranges separated by alluvial valleys and broad, flat basins.
Most breeding spotted owls occur in mature mixed-conifer forest. The Basin and Range-West
RU contains mountain ranges separated by non-forested habitat. These "sky island" mountains
of southem Arizona and far-western New Mexico contain mid-elevation mixed-conifer forest and
lower elevation Madrean pine-oak woodlands that support spotted owls. The Colorado Plateau
RU includes northem Arizona, southern Utah, southwestern Colorado, and northwestern New
Mexico, with owls generally confined to deeply incised canyon systems and wooded areas of
isolated mountain ranges. The Southern Rocky Mountains-New Mexico RU consists of the
mountain ranges of northem New Mexico. Owls in this unit typically inhabit mature mixed-
conifer forest in steep canyons. The smallest number of spotted owls occurs in the Southem
Rocky Mountains-Colorado RU. This unit includes the southem Rocky Mountains in Colorado,
where spotted owls are largely confined to steep canyons, generally with significant rock faces
and various amounts of mature coniferous forest. The critical habitat units identified in this
designation are all within these RUs.
A reliable estimate of the numbers of owls throughout its entire range is not currently available.
Using information gathered by Region 3 of the FS, Fletcher(1990) calculated that 2,074 owls
existed in Arizona and New Mexico in 1990. Based on more up-to-date information, we
subsequently modified Fletcher's calculations and estimated a total of 2,160 owls throughout the
United States (USDI 1991). However, these numbers are not considered reliable estimates of
current population size for a variety of statistical reasons, and a pilot study (Ganey et al. 1999)
conducted in 1999 estimated the number of owls for the upper Gila Mountains Recovery Unit
(exclusive of tribal lands) as 2,950 (95 percent confidence interval 717-5,183).
Mexican spotted owls nest, roost, forage, and disperse in a diverse array of biotic communities.
Nesting habitat is typically in areas with complex forest swcture or rocky canyons, and contains
uneven-aged, multi-storied mature orold-growth stands that have high canopy closure (Ganey
and Balda 1989, USDI 1991). In the northem portion of the range (Utah and Colorado), most
nests are in caves or on cliff ledges insteep-walled canyons. Elsewhere, the majority ofnests
appear to be in Douglas fir (Pseudotsuga menziesii) trees (Fletcher and Hollis 1994, Seamans
and Gutierrez 1995). A wide variety of tree species is used for roasting; however, Douglas fir is
the most commonly used species in mixed conifer forests (Ganey 1988, Fletcher and Hollis
1994, Young et al. 1998). Owls generally use a wider variety of forest conditions for foraging
than they use for nes[ing/roosting.
Seasonal movement patterns of Mexican spotted owls are variable. Some individuals are year-
round residents within an area, some remain in the same general area but show shifts in habitat