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Distribution and abundance of Mexican spotted owls

January 1995

January 1995

In book: Mexican spotted owl recovery plan, volume II (pp.14)
Chapter: 1
Publisher: U.S. Fish and Wildlife Service
Editors: U.S. Fish and Wildlife Service

Authors:

Alan B. Franklin

United States Department of Agriculture

Sarah Rinkevich

U.S. Fish and Wildlife Service

Fernando Clemente-Sánchez

Colegio de Postgraduados

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Content may be subject to copyright.

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

CHAPTER 1: Distribution and AbundanceCHAPTER 1: Distribution and Abundance

CHAPTER 1: Distribution and Abundance

of Mexican Spotted Owlsof Mexican Spotted Owls

of Mexican Spotted Owls

James P. Ward, Jr., Alan B. Franklin, Sarah E. Rinkevich,

and Fernando Clemente

Knowledge of the distribution and abun-

dance of Mexican spotted owls can provide

insight into the subspecies’ geographic limits and

habitat requirements. For example, standardized

surveys for northern spotted owls among differ-

ent habitats have provided evidence of the owl’s

affinity for older, densely layered forests

(Forsman et al. 1977; 1987, Thomas et al. 1990,

Blakesley et al. 1992). In addition, distribution

and abundance patterns often provide a founda-

tion for more intensive natural and life history

studies.

For this recovery plan, we gathered and

examined information on the distribution and

abundance of Mexican spotted owls accumulated

through 1993. We used this information to (1)

document historical and current extent of this

subspecies, (2) help formulate recovery unit

boundaries, and (3) provide a template for

landscape-scale analyses.

SOURCES OF INFORMATIONSOURCES OF INFORMATION

SOURCES OF INFORMATION

The quality and quantity of information

regarding the distribution and abundance

Mexican spotted owls varies by source. Histori-

cal accounts exist from museum collections and

anecdotal observations by early natural historians

from throughout the owl’s range (reviewed in

McDonald et al. 1991). These early observations

are useful for documenting the owl’s known

historical range. However, haphazard and fre-

quently unknown methods by which the histori-

cal information was obtained confound any

attempt to infer change in the owl’s abundance

from historical to present time. Modern ac-

counts exist from incidental observations pro-

vided by amateur and professional biologists and

from organized surveys conducted by natural

resource management or research personnel.

Incidental observations are similar in quality to

historical accounts, frequently lacking sufficient

information for estimating population param-

eters or testing empirical hypotheses. However,

when combined with results of planned surveys

incidental observations can be used to document

the current extent of the subspecies’ range.

Results from planned surveys and demographic

studies have provided the best available data on

the owl’s abundance.

Planned surveys for Mexican spotted owls in

the United States have been conducted by land-

management agencies since 1989 and by re-

searchers in Mexico since 1992. Survey protocols

were reviewed in 1990 and a more formal

program was subsequently developed to locate

Mexican spotted owls (USDA Forest Service

1990). Owl demographic studies began in the

Sky Island Mountains of Arizona in 1990

(Duncan et al. 1993), and in northern Arizona

(Olson et al. 1993) and in the Tularosa Moun-

tains of west-central New Mexico in 1991

(Seamans et al. 1993).

To document the current (1990-1993)

distribution of the Mexican spotted owl, we

defined an owl site as a visual sighting of at least

one adult spotted owl or as a minimum of two

auditory detections in the same vicinity in the

same year. Observations prior to 1990 are

considered historical records for the purposes of

this report. The methods and limitations of these

data are discussed further in the White et al.

1995.

HISTORICAL DISTRIBUTIONHISTORICAL DISTRIBUTION

HISTORICAL DISTRIBUTION

We compiled 600 and 35 historical records

of Mexican spotted owls in the United States

and Mexico, respectively (Table 1.1). We refer to

these as records and not as independent sites

because several observations may have been

tallied for the same site. Incomplete information

of the owls’ locations prevented us from assign-

ing each record to an individual site. Thus, these

records cannot be used to estimate historical

abundance and are presented only to show the

approximate extent of the owl’s distribution

before 1990.

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

FS 21 16

BLM 6 10

NPS 34 23

Tribal 20 13

New Mexico State 1 0

Unknown

SubtotalSubtotal

Subtotal

8787

6262

FS 82 97

NPS 13 0

Tribal 0 --

DOD 9 6

Private 8 0

Unknown

57 0

SubtotalSubtotal

Subtotal

169169

169

103103

103

FS 2 8

BLM 0 6

NPS 0 0

Tribal 1 --

Unknown

17 0

SubtotalSubtotal

Subtotal

2020

1414

Table 1.1.Table 1.1.

Table 1.1. Historical records and minimum numbers of Mexican spotted owls found during planned

surveys, and incidental observations by Recovery Unit and land ownership.

Number of owl sitesNumber of owl sites

Number of owl sites

1990 - 19931990 - 1993

1990 - 1993

FS 25 34

NPS 3 0

New Mexico State 1 0

Private 4 0

Unknown

SubtotalSubtotal

Subtotal

4141

3434

Number of Number of

Number of

owl recordsowl records

owl records

before 1990before 1990

before 1990

Recovery UnitRecovery Unit

Recovery Unit

Colorado Plateau

Southern Rocky Mountains - Colorado

Southern Rocky Mountains - New Mexico

Upper Gila Mountains

FS 138 424

BLM 5 0

NPS 5 0

Tribal 20 --

Private 1 0

Unknown

104 0

SubtotalSubtotal

Subtotal

253253

253

424424

424

Basin and Range - West

UNITED STATESUNITED STATES

UNITED STATES

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

Coahuila 4 0

Nuevo Leon 4 1

Tamaulipas 0 0

SubtotalSubtotal

Subtotal

600600

600

758758

758

FS 18 111

BLM 1 0

NPS 6 10

Tribal 2 --

FWS 1 0

Private 2 0

SubtotalSubtotal

Subtotal

3030

121121

121

Table 1.1.Table 1.1.

Table 1.1. (continued)

Basin and Range - East

MEXICOMEXICO

MEXICO

Sonora 8 9

Chihuahua 10 8

Sinaloa 1 0

SubtotalSubtotal

Subtotal

1919

1717

Recovery UnitRecovery Unit

Recovery Unit

Number of owl recordsNumber of owl records

Number of owl records

before 1990before 1990

before 1990

Number of owl sitesNumber of owl sites

Number of owl sites

1990 - 19931990 - 1993

1990 - 1993

United States TotalUnited States Total

United States Total

Sierra Madre Occidental - Norte

Sierra Madre Oriental - Norte

Coahuila 2 0

Sierra Madre Occidental - Sur

Durango 2 0

Aguascalientes 0 1

Zacatecas 0 0

San Luis Potosi 1 0

Guanajuato 1 0

SubtotalSubtotal

Subtotal

Sierra Madre Oriental - Sur

Eje Neovolcanico

Jalisco 1 0

Colima 1

Michoacan 1 0

Puebla 1

SubtotalSubtotal

Subtotal

3535

1919

Mexico TotalMexico Total

Mexico Total

Values do not connote numbers of owls nor owl sites because multiple records may exist from the same site through time.

Additional owls are known to exist on many Tribal lands but the exact number is unavailable.

Locations of these records were insufficient for assigning a land ownership.

Additional sightings have been reported from 1994 surveys.

Unverified record not included in totals (see text).

UNITED STATES, continuedUNITED STATES, continued

UNITED STATES, continued

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

The general vicinity of all historical records

is presented in the following section according to

RU and land ownership. This information

should help land managers to identify areas that

may be occupied by Mexican spotted owls.

Historical records for owls in the United States

were compiled from several sources which are

cited below. In contrast, much of the historical

information for Mexico was taken from a com-

prehensive summary by Williams and Skaggs

(1993).

Colorado Plateau Recovery UnitColorado Plateau Recovery Unit

Colorado Plateau Recovery Unit

Prior to 1990, Mexican spotted owls were

recorded from Zion (Kertell 1977, Rinkevich

1991), Canyonlands, Capitol Reef (Sue Linner,

FWS, Salt Lake City Utah, pers. comm.), Mesa

Verde (Reynolds and Johnson 1994), and Grand

Canyon National Parks (McDonald et al. 1991),

Glen Canyon National Recreation Area (Behle

1960), and the Cedar City, Richfield, and Vernal

Districts of the BLM (Behle 1981; Sue Linner,

FWS, Salt Lake City, Utah, pers. comm.). Table

1.1 presents more detail regarding these records.

The physical attributes of these historical owl

sites include steep-sided, narrow-walled, or

hanging canyons. The biotic attributes include

coniferous overstory in canyon bottoms with an

understory comprised by Gambel oak, bigtooth

maple, boxelder, and scattered aspen groves near

water (McDonald et al. 1991).

Historical accounts also place the Mexican

spotted owl on the Kaibab Plateau in Arizona

(Ganey and Balda 1989, North Kaibab Ranger

District, unpublished data), plus many sites in

New Mexico. These sites include Fence Lake

(State), Frances Canyon (BLM), the Zuni

Mountains and Mount Taylor (Cibola NF), and

within the Zuni and Navajo Nations (McDonald

et al. 1991, New Mexico Natural Heritage Data

Base, Nature Conservancy, Albuquerque, NM).

Generally, vegetation types reported for these

areas include montane coniferous forests within

canyon settings. The owl has been observed in

steep-walled canyons with minimal vegetation as

well as in forested, steep-sloped canyons on

Black Mesa and in the Chuska Mountains.

Southern Rocky Mountains -Southern Rocky Mountains -

Southern Rocky Mountains -

Colorado Recovery UnitColorado Recovery Unit

Colorado Recovery Unit

Eighteen historical records of spotted owls

exist within this unit (Webb 1983, Reynolds

1989). Most of these owls were found along the

Colorado Front Range extending northward to

Fort Collins. Two additional observations, one

each from Rio Grande and San Juan National

Forests, plus one from the Southern Ute Reser-

vation were recorded during 1989 surveys

(Reynolds and Johnson 1994; Table 1.1).

Historical owl locations in this recovery unit

occurred in steep-sided canyons. These canyons

are typically broader with walls that are not as

vertical as sites occupied by owls in southern

Utah (Colorado Plateau RU). Northern aspects

of these canyons contain mixed-conifer forest,

while southern aspects contain ponderosa pine

and pinyon-juniper. Canyon bottoms contain

Gambel oak and boxelder. Owl sightings in

southwestern Colorado were generally in can-

yons that cut into mesas covered with pinyon

and juniper. These canyon bottoms contained

mixed-conifer or ponderosa pine-Gambel oak

forests (McDonald et al. 1991).

Southern Rocky Mountains -Southern Rocky Mountains -

Southern Rocky Mountains -

New Mexico Recovery UnitNew Mexico Recovery Unit

New Mexico Recovery Unit

Mexican spotted owls are known historically

(Table 1.1) from private and National Forest

lands in the San Juan, Sangre de Cristo, and

Jemez Mountains, and near Taos and Sante Fe,

New Mexico (Johnson and Johnson 1985,

McDonald et al. 1991). Incidental observations

between 1979 and 1984 established the presence

of the owl at nine additional sites in the Jemez

Mountains, Sante Fe National Forest (Johnson

and Johnson 1985). The owl has also been

observed in Bandelier National Monument and

near Morhy Lake on State lands (Johnson and

Johnson 1985). Historical spotted owl locations

throughout all of New Mexico (including the

Basin and Range - East RU) have been described

as “deep, narrow, timbered canyons with cool

shady places, at elevations ranging from 6,500

[1,982 sic] to 9,000 ft [2,744 m],” (McDonald

et al. 1991, after Ligon 1926).

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

Upper Gila Mountains Recovery UnitUpper Gila Mountains Recovery Unit

Upper Gila Mountains Recovery Unit

Prior to a statewide survey conducted from

1984 through 1988, only one Mexican spotted

owl was recorded from the northern Arizona

(San Francisco Peaks) portion of this RU (Huey

1930). In contrast, several owls were reported for

the National Forest lands in the Mogollon

Highlands of east-central Arizona and west-

central New Mexico (Ligon 1926, Skaggs 1988).

Forests in those reports include the Apache-

Sitgreaves, Gila, and Cibola National Forests

(Table 1.1). A few observations were also re-

corded on BLM land near Bitter Creek, Grant

County and at the Gila Cliff Dwellings National

Monument (NPS), both in New Mexico. Fol-

lowing their survey of Arizona, Ganey and Balda

(1989) reported 69 sites in the Arizona portion

of the Mogollon Rim and in northern Arizona,

including the Coconino, Kaibab, Tonto, and

Apache-Sitgreaves National Forests. Another 44

records exist in the Arizona Heritage Data Base

(Arizona Game and Fish Department, Phoenix,

AZ). However, the latter records are distributed

among habitats similar to those reported by

Ganey and Balda (1989) and include several of

the same sites.

Site characteristics for the historical Arizona

locations (Ganey and Balda 1989) reflect the

features described for other RU’s: mountain

slopes with mixed-coniferous forest, steep-walled

canyons, or ponderosa pine-Gambel oak forest at

elevations ranging from 1,525 to 2,925 m

(5,000 to 9,590 ft). In southern New Mexico,

Skaggs (1988) found cliffs present at 15 of the

18 historical sites which he examined. However,

it is unclear how many of these sites were located

in the Upper Gila Mountains RU. Skaggs (1988)

also noted a well developed understory of

bigtooth maple and Gambel oak dominated by

mixed-conifer.

Basin and Range - West Recovery UnitBasin and Range - West Recovery Unit

Basin and Range - West Recovery Unit

Historical records for Mexican spotted owls

in this RU include observations in the Huachuca

and Chiricahua Mountains during the 1890s

(reviewed in McDonald et al. 1991). These birds

were observed in a foothills-oak woodland and

in a fir tree in Pinery Canyon, respectively. Two

other sightings were recorded in lowland riparian

communities including an owl nesting in cotton-

woods northwest of Tucson in 1872 and near the

Salt River in 1910 (Bendire 1892, Phillips et al.

1964, McDonald et al. 1991).

More recent surveys found the owl occurring

at 84 sites throughout southern Arizona (Ganey

and Balda 1989). Owls were located in rocky

canyons or in several forest types at elevations

ranging from 1,125 to 2,930 m (3,690 to 9,610

ft) in the Atascosa-Pajarito, Santa Rita, Santa

Catalina, Patagonia, Whetstone, Galiuro,

Huachuca, Chiricahua, Pinaleno, Superstition,

Sierra Ancha, Mazatzal, and Bradshaw Moun-

tains, Arizona. Below 1,300 m (4,264 ft), spot-

ted owls were found in steep canyons containing

cliffs and stands of live oak, Mexican pine and

broad-leaved riparian vegetation (Ganey and

Balda 1989). Above 1,800 m (5,904 ft) owls

were found in mixed-conifer and pine-oak

forests. Mid-elevation observations included sites

with Arizona cypress and the other forest types

previously mentioned. The Arizona Heritage

Data Base reports 78 additional records in many

of the same mountain ranges from 1974 to

1989. Historical records on private land include

observations near Animas Peak, Black Bill

Spring, and at the Gray Ranch, in New Mexico

(Skaggs 1988).

Basin and Range - East Recovery UnitBasin and Range - East Recovery Unit

Basin and Range - East Recovery Unit

Historical locations of Mexican spotted owls

occur on lands of several jurisdictions in New

Mexico: the Organ Mountains and near Bitter

Creek (BLM); the Sandia, Manzano, Sacra-

mento, and Guadalupe Mountains in the Cibola

and Lincoln National Forests; and Carlsbad

National Park (Skaggs 1988). The owl has also

been found in Guadalupe National Park and on

private land in the Davis Mountains of Texas

(McDonald et al. 1991, Steve Runnels, The

Heard Natural Science Museum and Wildlife

Sanctuary, McKinney, TX, pers. comm.). One

observation each was also reported on the lands

of the Mescalero Apache and at the Santo

Domingo Pueblo (New Mexico Natural Heritage

Data Base, Nature Conservancy, Albuquerque,

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

NM). Physical and biotic characteristics were

not documented for these various sites. However,

minimal notations describe mixed-conifer forests

on eastern slopes of the Sacramento Mountains

(Skaggs 1988). Canyons were mentioned for

sites near the New Mexico-Texas border of the

Guadalupe Mountains (McDonald et al. 1991).

Sierra Madre Occidental -Sierra Madre Occidental -

Sierra Madre Occidental -

Norte Recovery UnitNorte Recovery Unit

Norte Recovery Unit

More than half of all historical records of

Mexican spotted owls occurring in Mexico have

been reported in this Recovery Unit (Table 1.1).

Owls have been recorded from eight locations in

the State of Sonora prior to 1990. These birds

occurred in the Sierras Pinitos, Azul, de los Ajos,

San Luis, Aconchi, Oposura, and Huachinera

(Williams and Skaggs 1993). The eighth record

was reported from a ridge north of La Mesa,

Mexico. All of these areas are physiographically

and biotically similar to the Sky Island Moun-

tains of southeastern Arizona (Cirett and Diaz

1993). General elevations at or near these

sightings range from 1,950-2,340 m (6,500 to

7,800 ft). Descriptions of sites at or near the

recorded owls vary. Some descriptions include

dense oaks, pine forest, pine-oak woodland,

cliffs, and a spring with alders and sycamores

(Williams and Skaggs 1993).

Ten historical records have been reported

from the State of Chihuahua (Table 1.1). Owls

have been collected, observed, or heard near

Sierra Carcay, Arroyo Tinaja, Pacheco, Sierra

Azul, Colonia Garcia, Sierra del Nido, Rancho

La Estancia, Yaguirachic, Pinos Altos, and

Vosagota (Williams and Skaggs 1993). Eleva-

tions at or near these sightings range from

1,710-2,700 m (5,700 to 9,000 ft). Most of

these observations were made in or near pine-

oak woodlands (Williams and Skaggs 1993).

Owls have also been reported in canyons with

oaks and madrone, and in subalpine forest

comprised of Douglas-fir, true firs, oak, alder,

pines, and chokecherry.

In Sinaloa, one spotted owl was observed

near Rancho Liebre Barranca (Williams and

Skaggs 1993). This area consists of deeply

dissected barrancas with pine and oak forest at

higher altitudes and a mixture of temperate and

tropical forest in canyon bottoms.

Sierra Madre Oriental -Sierra Madre Oriental -

Sierra Madre Oriental -

Norte Recovery UnitNorte Recovery Unit

Norte Recovery Unit

Spotted owls have only been reported from

two sites within this Recovery Unit. Both

records are from the Sierra la Madera of central

Coahuila (Table 1.1). One owl was observed

roosting in a “cliff-lined canyon bottom under a

dense canopy of maples and oaks” in Canada el

Agua (Williams and Skaggs 1993). Another owl

was observed and heard in a “garden-like” arroyo

containing pines, oaks, and madrones (Williams

and Skaggs 1993). Elevations of these observa-

tions were approximately 1,900 and 2,100 m

(6,200 and 7,000 ft), respectively.

Sierra Madre Occidental -Sierra Madre Occidental -

Sierra Madre Occidental -

Sur Recovery UnitSur Recovery Unit

Sur Recovery Unit

Four historical records exist from the States

of Durango, San Luis Potosi, and Guanajuato

(Table 1.1). In Durango, spotted owls have been

observed near Espinazo del Diablo in mixed-

conifer forest and on two occasions in the

Michilia Biosphere Reserve. One of the owls

found in the reserve was observed roosting in a

large oak that was in a cool, wet ravine. The

second owl was found in a pine-oak forest.

Remaining records are of two spotted owls

collected at approximately 2,400 m (8,000 ft)

near Cerro Campanario, San Luis Potosi, and

another that was collected in the State of

Guanajuato (Williams and Skaggs 1993).

Sierra Madre Oriental -Sierra Madre Oriental -

Sierra Madre Oriental -

Sur Recovery UnitSur Recovery Unit

Sur Recovery Unit

In this Recovery Unit, eight records of

spotted owls have been reported from two States,

Coahuila and Nuevo Leon (Table 1.1). Owls

have been heard and observed on several occa-

sions east of Saltillo, Coahuila. Elevations of

these records are generally higher than other

historical sightings and range from 2,700-3,060

m (9,000 to 10,200 ft). The vegetation at these

sites has been described as oak-pine-conifer

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

woodland or as oak-pine woodland. Cliffs are

present at all sites and chaparral or desert scrub

vegetation can also be seen at two of these sites

(Williams and Skaggs 1993). In addition, two of

the four historical records from Nuevo Leon are

from the mountains east of Saltillo and south of

Monterrey. At one of these sites a spotted owl

was heard calling from an oak-pine-conifer

forest, approximately 2,550 m (8,500 ft) in

elevation. The second was heard calling from an

“oak-pine woodland mixed with Tamaulipan

thorn woodland and scrub and palms on the

canyon cliffs” (Williams and Skaggs 1993). The

elevation at this site was 1,350 m (4,500 ft), the

lowest to be recorded for spotted owls in

Mexico. The remaining two Nuevo Leon records

are from the slopes of Cerro Potosi (Williams

and Skaggs 1993). One female spotted owl was

collected at 2,250 m (7,500 ft) in 1946. Another

owl was heard in 1978 from a pine woodland

near the summit at 3,630 m (12,100 ft), the

highest elevation recorded for a Mexican spotted

owl.

Eje Neovolcanico Recovery UnitEje Neovolcanico Recovery Unit

Eje Neovolcanico Recovery Unit

Only two confirmed records of Mexican

spotted owls exist for the southernmost Recovery

Unit (Table 1.1). Specimens of spotted owls have

been collected from the States of Jalisco and

Michoacan. Two other records from the States of

Colima and Puebla have been published

(Enriquez-Rocha et al. 1993) but have not been

verified (Williams and Skaggs 1993).

In Jalisco, the owls were found on the north

slope of Cerro Nevado de Colima in a park-like

pine forest with broad-leaved oaks, and mesic

ground flora near 2,400 m (8,000 ft) elevation

(Williams and Skaggs 1993). In Michoacan, the

holotype of the subspecies and only existing

State record was collected in 1903 from Cerro

Tancitaro above 1,950 m (6,500 ft). Details

regarding the spotted owls allegedly collected in

Colima and Puebla have not been reported

(Enriquez-Rocha et al. 1993). We mention these

latter records because they suggest possible

extensions of the owl’s range. However, we have

not included them in the totals presented in

Table 1.1.

CURRENT DISTRIBUTIONCURRENT DISTRIBUTION

CURRENT DISTRIBUTION

AND ABUNDANCEAND ABUNDANCE

AND ABUNDANCE

Number of SitesNumber of Sites

Number of Sites

Surveys for Mexican spotted owls conducted

from 1990 through 1993 indicate that the

species persists in most locations reported prior

to 1989. Notable exceptions include riparian

habitats in the lowlands of Arizona and New

Mexico, and all previously occupied areas in the

southern States of Mexico. As a result of planned

surveys, additional sightings have been reported

for all recovery units. New locations will un-

doubtedly be reported following future surveys.

The current known range of the Mexican

spotted owl extends north from Aguascalientes,

Mexico, through the mountains of Arizona, New

Mexico, and western Texas to the canyons of

southern Utah, southwestern Colorado, and the

Front Range of central Colorado (Figures 1.1

and 1.2). Results from planned surveys and

incidental observations conducted during 1990

through 1993 indicate one or more owls have

been observed at a minimum of 758 sites in the

United States and 19 sites in Mexico (Table 1.1).

The greatest concentration of the known

sites in the United States occurs in the Upper

Gila Mountains Recovery Unit (55.9%) fol-

lowed by the Basin and Range-East (16.0%),

and Basin and Range-West (13.6%), Colorado

Plateau (8.2%), Southern Rocky Mountains -

New Mexico (4.5%), and Southern Rocky

Mountains - Colorado (1.8%) Recovery Units.

Thus, fewer owl sites are currently known to

occur north of the Upper Gila Mountains

Recovery Unit (12.7%) than to the south of this

recovery unit (29.6%). In Mexico, the majority

of spotted owls have been documented in the

Sierra Madre Occidental - Norte RU (89.5%).

However, the number of identified sites within a

given RU depends on survey intensity for which

we have little reliable data. Therefore, the per-

centages of sites within a given RU may not

reflect the true relative abundance of Mexican

spotted owls.

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

Number of OwlsNumber of Owls

Number of Owls

A reliable estimate of the number of Mexican

spotted owls throughout its entire range is not

available. Fletcher (1990) calculated that 2,074

owls existed in Arizona and New Mexico in

1990 using information gathered by the FS,

Southwestern Region. McDonald et al. (1991)

modified Fletcher’s (1990) calculations reporting

a total of 2,160 owls in the United States. If one

assumes that all 758 sites included in this recov-

ery plan were occupied by owl pairs, then at least

1,516 adult or subadult owls were known to

exist in the United States and 38 adult or sub-

adult owls in Mexico from 1990 through 1993.

These numbers are not reliable estimates of

current population size because no measures of

bias or precision can be produced. Further, the

amount of survey effort devoted to deriving

these numbers cannot be reliably calculated, nor

is an accurate measure available for areas or

habitats surveyed. Thus, we did not believe it

would be useful to estimate the size of the

Mexican spotted owl population given the

limited quality of data currently available. At

best, our total numbers reported in Table 1.1

represent a range for the minimum number of

owls known to exist during some portion of a

four year period in the United States and Mexico

(777 individuals if each site was occupied by a

single owl to 1,554 individuals if each site was

occupied by a pair).

DensityDensity

Density

The abundance of any terrestrial organism is

more appropriately presented as density, the

number of individuals per unit of area (Caughley

1977), hereafter referred to as “crude density”

(Franklin et al. 1990). Because the Mexican

spotted owl occupies a variety of habitats

throughout its range, ecological density, the

number of individuals per area of usable habitat,

(Tanner 1978) would be a more meaningful

measure of abundance. At this time, rangewide

estimates of either crude or ecological density of

Mexican spotted owls cannot be provided for the

same reasons that population numbers cannot be

estimated reliably.

Two estimates of crude density (D) exist

from studies conducted at either end of the

Upper Gila Mountains Recovery Unit. These

estimates were reported for the Coconino Study

Area (CSA) in northern Arizona and for the Gila

Study Area (GSA) in west-central New Mexico

by Gutiérrez et al. (1994). Density of adult and

subadult owls in both studies was estimated

using a count of individuals divided by the size

of the study area (CSA: 484 km

[187 mi

];

GSA: 323 km

[125 mi

]). Identity of owls was

established by capturing and marking or by

direct observation at daytime roosts when

marking was not possible. Methods were similar

to those reported for northern spotted owls by

Franklin et al. (1990) and Ward et al. (1991) and

resulted only in density of territorial individuals.

Only the 1993 estimates of density (D) are

presented here because the boundaries of the

CSA study area were shifted between 1991 and

1992.

D of Mexican spotted owls in 1993 was

0.120 owls/km

(0.310 owls/mi

) in the CSA

and 0.180 owls/km

(0.464 owls/mi

) in the

GSA. The CSA has more ponderosa pine-

Gambel oak forest (72.6%) and less mixed-

conifer forest (14.4%) than the GSA (22.3%

and 28.5%, respectively; Gutiérrez et al. 1994).

The larger proportion of mixed-conifer may

partially explain higher owl density in the GSA.

For comparison (Figure 1.3a), 1993 density of

California spotted owls in the San Bernardino

Mountains, California (LaHaye and Gutiérrez

1994) was 0.118 owls/km

(0.305 owls/mi

) and

density of northern spotted owls in northwestern

California (Franklin, unpublished data) was

0.272 + 0.004 (SE) owls/km

(0.703 + 0.009

owls/mi

). Survey methods used in these later

two studies were identical to those used in the

CSA and GSA. Naive density estimates, the

number of owls counted divided by study area

size, were used in this comparison (Figure 1.3a)

except for the northern spotted owl population.

In the latter case, a Jolly-Seber model was used

to estimate numbers of owls and an associated

sampling variance. The two density estimators

are similar for spotted owls (Ward et al. 1991).

Combining the CSA and GSA density data

and weighting by area provides an average

estimate of 0.144 owls/km

(0.372 owls/mi

)

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

Arizona and New Mexico where it historically

occurred, nor in historically-documented areas

of southern Mexico. Riparian communities and

previously occupied localities in the southwest-

ern United States and southern Mexico have

undergone significant habitat alteration since the

historical sightings (USDI 1994). However, the

amount of effort devoted to surveying these areas

is poorly known and future surveys may docu-

ment spotted owls. Surveys conducted to relo-

cate spotted owls have been unsuccessful in

northern Colorado near Fort Collins and Boul-

der, where records exist from the early 1970s and

1980s, and in the Book Cliffs of east-central

Utah where owls were recorded in 1958.

The majority of Mexican spotted owls

currently known to exist occur in the Upper Gila

Mountains Recovery Unit. This unit can be

considered a critical nucleus for the subspecies

because of its central location within the owl’s

range and its seemingly high density of owls.

Other areas likely to be important include the

Sky-islands of southeastern Arizona and the

Sacramento Mountains, New Mexico (Basin and

Range RUs). Throughout its range, most (91%)

Mexican spotted owls occur on public land

administered by the FS.

Density estimates of Mexican spotted owls

contrasted among forest types in the Sacramento

Mountains and between two areas in the Upper

Gila Mountains RU suggest that mixed-conifer

supports more owls compared to pine-oak, pine,

and pinyon-juniper forest types. Mexican spot-

ted owl densities reported from three areas are

similar to those reported for California spotted

owls occurring in the San Bernardino Moun-

tains, California and slightly less than the den-

sity of northern spotted owls occurring in

northwestern California.

Limited information inhibits reliable estima-

tion of the absolute number of Mexican spotted

owls. However, it is apparent from current

patterns in distribution and habitat use that the

subspecies is rare relative to other raptors and is

distributed discontinuously throughout its

range. Species existing under such conditions are

considered vulnerable to extirpation (see

Dawson et al. 1987 for discussion relevant to

spotted owls). Although future efforts will

undoubtedly discover additional owls, the extent

within the Upper Gila Maintains RU. However,

this estimate should not be extrapolated to a

larger area because (1) the CSA and GSA were

not randomly selected and (2) studies were not

sufficiently replicated. Both of these problems

could severely bias extrapolated estimates be-

cause the areas studied are not necessarily repre-

sentative samples of the entire recovery unit or

subspecies’ range.

In another study, Skaggs and Raitt (1988)

examined the density of Mexican spotted owls

among three forest types in the Sacramento

Mountains (Basin and Range - East RU). Eigh-

teen 23.1- km

(9-mi

) quadrats, six in each

forest type, were surveyed for spotted owls.

Quadrats were classified as pinyon-juniper

woodland, pine, or mixed-conifer forest accord-

ing to the most common tree species within the

quadrat. Owl density averaged across the three

forest types (x = 0.126 owls/km

[0.325

owls/mi

]) was similar to the average estimate

from the two southwestern demographic studies.

When partitioned by forest type, analysis of

these data by the Team showed significantly

higher densities (F = 16.93, df = 2, P = 0.0001)

in the mixed-conifer (x = 0.275 owls/km

SE = 0.046 [0.704 owls/mi

, SE = 0.117]) com-

pared to the pine-dominated (x = 0.080

owls/km

, SE = 0.028 [0.204 owls/mi

SE = 0.073]) and pinyon-juniper habitats

(x = 0.022 owls/km

, SE = 0.036 [0.056 owls/

, SE = 0.038]). Density was not statistically

different between the latter two forest types

(Figure 1.3b). Forest type explained 69.3% of

the variation in owl density using this ANOVA

model. Skaggs and Raitt (1988) showed similar

results using density of sites rather than owl

density.

CONCLUSIONSCONCLUSIONS

CONCLUSIONS

The Mexican spotted owl currently occupies

a broad geographic area, but it does not occur

uniformly throughout its range. Instead, the owl

occurs in disjunct localities that correspond to

isolated mountain systems and canyons. This

distribution mimics most historical locations,

with a few exceptions. The owl has not been

reported along major riparian corridors in

Mexican Spotted Owl Recovery Plan

Volume II/Chapter 1

and total number of this subspecies in the

United States will likely not change in magni-

tude enough to alter this conclusion. The con-

trary is true for Mexico where planned surveys

have begun only recently.

Consequently, current strategies devel-

oped to conserve Mexican spotted owls will be

limited to basic knowledge about the owl’s

distribution. More specific recommendations

will require additional information on the total

population size, population structure, or interac-

tions among subpopulations.

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Article

Full-text available

Jan 2014
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Full-text available

Mar 2018

El búho manchado (Strix occidentalis lucida) es una especie amenazada y poco estudiada en México. En este estudio caracterizamos el hábitat de sus sitios de descanso (reproductivos y no reproductivos) y aleatorios (sitios en donde la especie se distribuye aleatoriamente sin un patrón) en Aguascalientes, Durango y Zacatecas e identificamos las variables físicas y biológicas (hábitat) que seleccionan. Usamos estadística descriptiva y determinamos mediante Regresión de Poisson (ARP) aquellas variables de hábitat que tuvieron un efecto sobre los búhos registrados; asimismo, agrupamos las variables identificadas por el ARP con un análisis de Correspondencia Simple (ACS) y realizamos una prueba de Kruskal-Wallis con el objeto de identificar posibles diferencias significativas entre sitios (descanso y aleatorios). Localizamos en total 29 búhos (parejas, polluelos e individuos solitarios) en 11 sitios de descanso en bosques de encino-pino (63.6%), en laderas con exposición norte y más inclinadas que la de los sitios aleatorios. Los sitios reproductivos estuvieron en una elevación más alta, comparada con los sitios no reproductivos y aleatorios; asimismo, en estos sitios encontramos una mayor densidad de árboles, con árboles usados como percha y árboles muertos (en pie) de dimensiones más grandes, comparados con los árboles encontrados en los sitios de descanso no reproductivos y aleatorios. Sin embargo, sólo la variable densidad de árboles fue diferente estadísticamente (P < 0.05) entre sitios. Las variables de vegetación que se asociaron más a los sitios de descanso del búho manchado fueron la altura del árbol de percha, la cobertura arbustiva y DAP del árbol de percha. Esta información la podemos utilizar en planes de manejo y conservación de la subespecie en México.

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The Mexican spotted owl (Strix occidentalis lucida) is widely but patchily distributed throughout the southwestern United States and the Republic of Mexico (Gutiérrez and others 1995, Ward and others 1995). This owl typically occurs in either rocky canyonlands or forested mountain and canyon systems containing mixed-conifer or pine-oak (Pinus spp. -Quercus spp.) forests, and its distribution mirrors the avail-ability of such areas (Ganey and Dick 1995, Ward and others 1995, USDI FWS 2012). Gene flow is known to occur across this fragmented range (Barrowclough and others 2006), but the mechanisms facilitating gene flow are poorly understood. Natal dispersal between disjunct mountain ranges and populations has been documented for dispersing juvenile Mexican spotted owls (Gutiérrez and others 1996, Arsenault and others 1997, Ganey and others 1998, Willey and van Riper 2000, Duncan and Speich 2002). In contrast, there are no documented records of breeding dispersal (defined as movement of a non-juvenile owl between territories where it had the op-portunity to breed, regardless of whether or not breeding occurred on these territories [Daniels and Walters 2000]) by non-juvenile owls. Thus, the potential role of breed-ing dispersal in gene flow within the range of this owl is unknown. Here, we report the circumstances surrounding recovery of a banded Mexican spotted owl that may represent the first documented case of long-distance breeding dispersal in this owl. We banded this owl on 9 August 1999, in the southern Black Range, New Mexico (fig.1), in conjunction with a study evaluating methods for monitor-ing population trend in Mexican spotted owls (Ganey and others 2004). The owl was identified as a female when banded based on vocalizations (Ganey 1990), and as an adult based on appearance of the retrices (Moen and others 1991), indicating

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Article

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Wilson Bull

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We analyzed landscape characteristics surrounding Mexican Spotted Owl (Strix occidentalis lucida) nest and roost trees in Arizona at three spatial scales: one circular plot of 201 ha (800-m radius) and two 400-m-wide “ring” plots between 800 m and 1,600 m from each nest or roost tree. The percentages of vegetation types were significantly different between 51 owl and 51 random areas only within the 201-ha circular plots. Owls selected both mature and young mixed conifer forests that had high canopy closure (≥55%) more than expected based on availability. Owls selected pine (Pinus spp.) and pine-oak (Quercus spp.) forests in proportion to availability. Forty-one percent of all nests and roosts were located in mixed conifer forests, even though this forest type covered only 5% of the study area. Pine and pine-oak forests covered 78% of the study area, and 59% of nests and roosts were located in these forest types. The only forest type in which we did not locate nests and roosts was mature open canopy ponderosa pine (P. ponderosa) forest. Owls occupied areas of predominantly younger forests, but only if residual large (≥45.7 cm dbh) trees were present. Indices of landscape structure did not differ significantly between owl and random areas. Future management of Mexican Spotted Owls in areas of moderate topographic relief should focus on retention of mature forests, especially mixed conifer stands with canopy closure ≥55%. Residual large trees, especially Gambel oaks (Q. gambelii), are important microhabitat components in younger forests.

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Using conventional sampling methods, unbiased, precise estimates of the number of individuals in a population can be difficult to obtain for rare, secretive species. We used a Leslie regression model (ARM) to estimate the number (N"0) and the variance of the number (V[N"0]) of adult and subadult Northern Spotted Owls in a territorial population from direct counts within a 292 km^2 study area. Estimates of N"0 from day counts were more accurate and precise and more robust to fluctuations in survey effort than estimates from night counts. ARM estimates from day counts were not significantly different from two different maximum-likelihood estimates and required 30-64% less effort. These findings suggest a less costly method for statistically comparing Spotted Owl abundance between spatial or temporal units.

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We estimated densities of northern spotted owls (Strix occidentalis caurina) over 4 years using intensive surveys of marked individuals on a 292-km2 study area in northwest California. For the 4-year sampling period, estimates from empirical and Jolly-Seber methods were in close agreement, yielding a crude density of 0.235 owls/km2 (95% CI = 0.214-0.256) and ecological densities of 0.544 (95% CI = 0.495-0.592) and 0.660 (95% CI = 0.601-0.719) owls/km2 of suitable habitat, using 2 definitions of suitable habitat. Increases in density over the 4 years were attributed to population processes, such as immigration, rather than internal increases within the sampled area. Densities in our area were relatively high when compared with other populations. Our study design should be useful for making geographic and habitat comparisons and for monitoring spotted owl populations. Estimates from our study and the U.S. Forest Service indicate a 60.0-82.5% reduction of current spotted owl populations on at least 1 National Forest under current management plans by the U.S. Forest Service.

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Article

Full-text available

May 1989

Distribution and habitat use of Mexican Spotted Owls (Strix occidentalis lu- cida) in Arizona were studied from 1984-1988. Owls were widely but patchily distributed throughout the state except for the arid southwestern portion. Distribution of the owl cor- responded with distribution of forested mountains and canyonlands within the state. Owls occurred either in rocky canyons or in any of several forest types, and were most common where unlogged closed canopy (> 80%) forests occurred in steep canyons. Several forest types provided these habitat characteristics in southern Arizona, and owls occurred in all of them. Only unlogged mixed-conifer forest provided these characteristics in northern Arizona, and most owls (67%) were found in this forest type in northern Arizona. Many owls in northern Arizona (54%) were located in areas where timber harvest was either occurring now or was planned in the next 5 years. Owls could not be located at 27% of the historic sites resurveyed, indicating that population levels may have declined in Arizona.

Mexican spotted owl habitat characteristics in Zion National Park

Article

Jun 1996

We studied Mexican spotted owl (Strix occidentalis lucida) distribution, density, and habitat characteristics in Zion National Park from 1989-1991. We found 28 owls (12 pairs and 4 single males) at 16 different locations throughout the park. Estimated crude density ranged from 0.018-0.042 owls/ km2 while estimated ecological density ranged from 0.216-0.738 owls/km2 over 3 years. Owls were associated with narrow canyons that usually contained a water source. Spotted owls used canyons that had greater absolute humidity and more vegetation strata than canyons selected at random. The geomorphology of these canyons may provide conditions compensatory to the complex forest structure associated with the owl elsewhere within its range by providing cool roosts and nest sites.

The Birds of Arizona

Article