The status of the
Western Screech-Owl
(macfarlanei subspecies)
Megascops kennicottii macfarlanei
in British Columbia
by
Richard J. Cannings
Cannings Holm Consulting
S11 C96 RR1, Naramata, BC V0H 1N0
and
Helen Davis
Artemis Wildlife Consultants
4515 Hullcar Road, Armstrong, BC V0E 1B4
22 March 2007
EXECUTIVE SUMMARY
Species information
The Western Screech-Owl was formerly considered conspecific with the Eastern ScreechOwl both taxa were known as the Screech Owl. The two taxa were split as distinct species in
1983, based primarily on distinctive vocalizations. The subspecies M. k. macfarlanei is resident
in the northern Great Basin from interior of southern British Columbia and western Montana
south to northeast California and northern Nevada.
The Western Screech-Owl is a small owl with ear-like feather tufts and yellow eyes. The
species is generally grey-brown, with fine dark vermiculations on the breast on an off-white
background. Sexes have similar plumage. Females are generally larger and heavier than males
and northern subspecies are larger and heavier than southern subspecies. M. k. macfarlanei is
the largest subspecies of all and is generally paler and greyer than M. k. kennicottii.
Distribution
The Western Screech-breeds in wooded areas at lower elevations throughout much of
western North America. It is resident coastally from southern Alaska south to Baja California
(except Queen Charlotte Islands) and in interior valleys from southern British Columbia south to
central Mexico. M. k. macfarlanei is found east of the Cascade Mountains in British Columbia,
Washington, western Montana, Oregon and Idaho. In British Columbia it has been found from
the Lillooet area east to the Rocky Mountain Trench near Cranbrook. Populations seem densest
in and adjacent to the Okanagan Valley, from where most of the breeding records have been
reported, but nests have been found near Lillooet, Lumby and Creston as well.
The taxonomic affinities of the Western Screech-Owls around Lillooet and Cache Creek
remain uncertain, since those birds likely contact populations of M. k. kennicottii in the Fraser
Canyon and Pemberton Valley but remain largely separated from M. k. macfarlanei populations
in the Okanagan and farther east. For this report, the Lillooet population will be considered M.
k. macfarlanei, since it occupies similar habitats at least.
Habitat
M. k. macfarlanei is strongly associated with riparian habitats; most territories are found
along rivers, creeks and lakeshores with mature stands of black cottonwood, birch or trembling
aspen. Adjacent habitats (e.g. ponderosa pine woodland, pastures) are also used for foraging.
Screech-owls nest in cavities in large diameter trees and often use similar cavities for roosting.
Breeding season sites have been located in BG, PP, IDF and ICH biogeoclimatic zones, almost
all below 1000 m elevation. These habitats have been significantly impacted by development in
the last century and in some areas (e.g. the south Okanagan) only half of the original habitat
remains, and much of that is in poor condition with reduced understory and few mature trees.
Biology
The Western Screech-Owl is nocturnal and non-migratory; pairs are territorial throughout
the year. Home ranges are about 50 ha in size. Nesting begins in late March or April and the
young fledge in late May or June. The clutch size is 3 to 7 eggs. Great Horned Owls and Barred
Owls are suspected to be significant predators. Western Screech-Owls are generalist predators,
feeding on a wide variety of small animals, including mice, shrews, bats, birds, insects, fish,
earthworms and crayfish.
i
Population sizes and trends
The best population estimate for M. k. macfarlanei in British Columbia is 150 to 200 pairs;
there are as yet only 20 known breeding sites. There are no data for population trends, although
habitat loss calculations suggest a decline of at least 50% in the Okanagan Valley over the last
century.
Limiting factors and threats
Habitat loss and degradation is the most significant threat to screech-owls in the British
Columbia Interior. Road mortality, pesticides and increased predation from an expanding Barred
Owl population add to this threat.
Existing protection
The Western Screech-Owl (macfarlanei subspecies) was assessed as Endangered in Canada
by COSEWIC and is listed as Endangered in Schedule 1 of the federal Species at Risk Act. In
British Columbia it is listed as an Identified Wildlife species (IWMS xxxx) and is also protected
under the British Columbia Wildlife Act. It is also on the provincial Red List of candidate taxa
for Threatened or Endangered status. The Western Screech-Owl is not listed nor proposed under
the US Endangered Species Act, nor is it listed in the IUCN Red Book, although all owls
(Strigiformes) are listed as a group under Appendix II of CITES (Convention on International
Trade in Endangered Species of Wild Fauna and Flora).
ii
TABLE OF CONTENTS
EXECUTIVE SUMMARY ............................................................................................................. i
SPECIES INFORMATION .............................................................................................................1
Name and classification ...............................................................................................................1
Morphological description...........................................................................................................1
Genetic description ......................................................................................................................1
DISTRIBUTION..............................................................................................................................2
Global range.................................................................................................................................2
Canadian range ............................................................................................................................3
HABITAT ........................................................................................................................................5
Habitat requirements....................................................................................................................5
Habitat trends ...............................................................................................................................6
Habitat protection/ownership.......................................................................................................7
BIOLOGY........................................................................................................................................8
Home Range.................................................................................................................................8
Reproduction................................................................................................................................8
Predation ......................................................................................................................................9
Dispersal ......................................................................................................................................9
Nutrition.....................................................................................................................................10
Adaptability ...............................................................................................................................10
POPULATION SIZES AND TRENDS.........................................................................................10
Search effort...............................................................................................................................10
Abundance .................................................................................................................................11
Fluctuations and trends ..............................................................................................................11
Rescue effect..............................................................................................................................11
LIMITING FACTORS AND THREATS......................................................................................12
EXISTING PROTECTION OR OTHER STATUS DESIGNATIONS ........................................12
ACKNOWLEDGEMENTS ...........................................................................................................14
INFORMATION SOURCES.........................................................................................................14
iii
List of Tables
Table 1. Mean wing chord and mass measurements for two British Columbian subspecies of the
Western Screech-Owl (data from Cannings and Angell 2001). ..............................................1
Table 2. Biogeoclimatic zones, subzones and variants associated with Western Screech-Owl
sites occupied during the breeding season in the British Columbia Interior. ..........................6
Table 3. Loss of Western Screech-Owl habitat in the South Okanagan and Lower Similkameen
valleys. .....................................................................................................................................7
Table 4. Level of Western Screech-Owl habitat securement in the South Okanagan and Lower
Similkameen valleys. ...............................................................................................................7
Table 5. Contents of Western Screech-Owl pellet samples taken from the Shuswap River area
northeast of Lumby ................................................................................................................10
List of Figures
Figure 1. Range of the Western Screech-Owl. .................................................................................... 2
Figure 2. Ranges of the subspecies of the Western Screech-Owl. ....................................................... 3
Figure 3. Locations of screech-owl sightings in the British Columbia interior................................... 4
List of Appendices
[Section and page break]
iv
SPECIES INFORMATION
Name and classification
The Western Screech-Owl (Megascops kennicottii (Elliot)) was formerly considered
conspecific with the Eastern Screech-Owl (Megascops asio); both taxa were known as the
Screech Owl (Otus asio Linnaeus) (AOU 1957). The two taxa were split as distinct species in
1983, based primarily on distinctive vocalizations (AOU 1983). Megascops was considered a
subgenus of Otus (the scops owls) until raised to full generic level in 2003; all screech-owls in
the Americas are now considered to be in the genus Megascops except for the Flammulated Owl
(Otus flammeolus) (AOU 2003).
There have been up to 18 subspecies of Western Screech-Owl described (Hekstra 1982a,
1982b), but recent treatments recognize nine (Cannings and Angell 2001). The subspecies M. k.
macfarlanei was described by Brewster (1891) based on a specimen from Walla Walla, WA. It
is resident in the northern Great Basin from the interior of southern British Columbia and
western Montana south to northeast California and northern Nevada (Cannings 1998), and has
always been recognized as a valid subspecies by the AOU (1957). Coastal birds in British
Columbia belong to the subspecies M. k. kennicottii.
Morphological description
The Western Screech-Owl is a small owl with ear-like feather tufts and yellow eyes. The
species is generally grey-brown, with fine dark vermiculations on the breast on an off-white
background. Sexes have similar plumage. Adults range from 19 to 25.5 cm long, with masses
between 120 and 315 g (Cannings and Angell 2001, H. Davis, unpub. data). Females are
generally larger and heavier than males (Earhart and Johnson 1970, Johnson 1997, Cannings and
Angell 2001). Similarly, northern subspecies are larger and heavier than southern subspecies
(Miller and Miller 1951). M. k. macfarlanei is the largest subspecies of all, with wing chords
about 5% longer and masses about 20% greater than M. k. kennicottii (Table 1). M. k.
macfarlanei is generally paler and greyer than M. k. kennicottii (Bent 1938, Godfrey 1986).
Table 1. Mean wing chord and mass measurements for two British Columbian subspecies of the
Western Screech-Owl (data from Cannings and Angell 2001).
Subspecies
M. k. kennicottii
M. k. macfarlanei
Wing Chord (mm) (mean, N)
males
females
168.4 (42)
174.8 (28)
174.5 (38)
183.1 (30)
Genetic description
1
Mass (g) (mean, N)
males
females
163.5 (4)
183.0 (2)
191.6 (74)
235.5 (105)
No genetic information is available for the Canadian populations.
DISTRIBUTION
Global range
The Western Screech-Owl is restricted to western North America, breeding in most
wooded areas at lower elevations within its range (Figure 1). Resident in south coastal Alaska
and coastal British Columbia (except Queen Charlotte Islands) east to the southern Interior of
British Columbia and south to Baja California, northern Sinaloa, western Chihuahua and through
the Mexican highland through Chihuahua and Coahuila south to Distrito Federal (Cannings and
Angell 2001).
Figure 1. Range of the Western Screech-Owl (from Cannings and Angell 2001).
M. k. macfarlanei is found east of the Cascade Mountains in British Columbia,
Washington, western Montana, Oregon and Idaho (Figure 2). Occasional reports of Western
Screech-Owls from southern Alberta and southwestern Saskatchewan are likely attributable to
this subspecies, but no specimens have been taken.
2
Figure 2. Ranges of the subspecies of the Western Screech-Owl (from Cannings and Angell
2001).
Canadian range
M. k. macfarlanei is resident in the valleys of the southern Interior of British Columbia,
from the Lillooet area east to the southern part of the Rocky Mountain Trench near Cranbrook
(Figure 3). Populations seem densest in and adjacent to the Okanagan Valley, from where most
of the breeding records have been reported. However, nests have also been found in the
Shuswap River valley near Lumby (H. Davis unpub. data), Lillooet (Sawicz et al. 2006) and
Creston areas (Beaucher and Dulisse 2004a).
The taxonomic affinities of the Western Screech-Owls around Lillooet and Cache Creek
remain uncertain, since those birds likely contact populations of M. k. kennicottii in the Fraser
Canyon and Pemberton Valley but remain largely separated from M. k. macfarlanei populations
in the Okanagan and farther east. Screech-owls are very rarely reported from the Nicola and
Kamloops areas. At least one specimen from the Hat Creek area appears closer to coastal birds
in its distinct brown coloration (R. Howie, in litt.), but others are rather grey and long-winged
(R. Cannings, unpub. data). For this report, however, the Lillooet population will be considered
M. k. macfarlanei, since it occupies similar habitats.
3
Figure 3. Locations of screech-owl sightings in the British Columbia interior: blue dots, confirmed breeding locations; red dots, other
breeding season sightings; green dots, nonbreeding season sightings; purple dots, pre-1990 sightings.
4
HABITAT
Habitat requirements
In the British Columbia Interior, Western Screech-Owls are restricted to the lower
elevations of southern valleys. Known sites are associated with Bunchgrass (21.4%), Interior
Cedar Hemlock (12.1%), Interior Douglas-fir (33.6%) and Ponderosa Pine (32.9%)
biogeoclimatic zones (Table 2). In this region they are strongly associated with mature riparian
woodland habitats dominated by water birch (Betula occidentalis), black cottonwood (Populus
balsamifera trichocarpa) or trembling aspen (Populus tremuloides) (Cannings 1997). These
riparian zones are often very narrow, and individuals likely forage in adjacent open forests of
ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) and pastures.
Hayward and Garton (1988) found a similar situation in central Idaho, where Western ScreechOwls were positively associated with riparian habitats and deciduous bottomlands and negatively
associated with coniferous forests (Douglas-fir). Hayward and Garton (1988) also found Western
Screech-Owls used more bunchgrass habitat than other owls in their study area, and were
restricted to the lowest elevations in the study area. Riparian habitats in Hayward and Garton’s
study area had abundant deciduous cover from 4 to 8 m in height. Screech-owls are also
widespread in southwestern Idaho and Montana in valley bottom black cottonwoods (J. Marks
pers. comm.).
Home ranges of interior screech-owls tend to be centered around nests, and are spaced
regularly along rivers and creeks. However, recently, some screech-owl territories in the British
Columbia Interior have been found in less linear habitats (e.g., nesting in aspen stands with only
minor creeks or seepages); in these habitats spacing may be more complex. In the Shuswap
River drainage, locations of roost trees appeared to define the home range boundaries, as there
were very few non-roost tree radio-locations outside the minimum convex polygon created by
roost tree locations. Home ranges were regularly spaced along the river, each home range
spanning 1.0 to 1.5 km of river frontage.
Nesting and some roost sites are in tree cavities, usually those made by Northern Flickers
or Pileated Woodpeckers in large diameter deciduous trees (though coniferous trees are also
used) such as black cottonwood, trembling aspen, paper birch and water birch. Nest trees can be
any decay class from 2-6. Since cavities are needed for both nesting and roosting, a breeding
territory must contain at least two suitable sites to be useful to a pair of screech-owls.
Open roost sites are used more often than cavities, especially in warm weather.
Preliminary data is available on roost trees used by 6 radio-tagged screech-owls along the
Shuswap River, north of Lumby (H. Davis 2007). . There were 140 radiolocations of owls
roosting on different occasions in 7 different tree species. Roost sites were most frequently found
in western redcedar (Thuja plicata; 78 of 140; 56%), followed by paper birch (Betula
papyrifera), hybrid spruce (Picea glauca x engelmannii), black cottonwood, Douglas-fir,
ponderosa pine and willow shrub (Salix spp.). Male and female screech-owls selected conifer
and deciduous tree species for roosts at different frequencies (χ² = 26.6, df = 1, P < 0.001), with
male owls using conifers (84%) for roosting more than females (58%). Screech-owls used
deciduous trees for roosting primarily when those trees were in leaf. Screech-owls occasionally
5
re-used roost trees; but no owl was found using the same roost tree more than 4 times during
monitoring. Mean diameter of roost trees was 39.4 cm, but was highly variable (range 9 - 292
cm). Screech-owls used roosts throughout their home ranges.
Table 2. Biogeoclimatic zones, subzones and variants associated with Western Screech-Owl
sites occupied during the breeding season in the British Columbia Interior.
Biogeoclimatic
zone/subzone/variant
BG xh 1
BG total
ICH dw
ICH xw
ICH total
IDF dk 1
IDF dk 2
IDF dm 1
IDF dm 2
IDF mw 1
IDF ww
IDF xh 1
IDF xh 1a
IDF xh 2
IDF xh 2a
IDF total
PP xh 1
PP xh 1a
PP xh 2
PP total
Grand Total
Site
s
30
30
14
3
17
2
4
4
2
9
2
16
4
3
1
47
37
3
6
46
140
Percent
21.4%
21.4%
10.0%
2.1%
12.1%
1.4%
2.9%
2.9%
1.4%
6.4%
1.4%
11.4%
2.9%
2.1%
0.7%
33.6%
26.4%
2.1%
4.3%
32.9%
100.0%
Habitat trends
From data presented in SOSCP (2005), about half of the Western Screech-Owl habitat in
the South Okanagan and Lower Similkameen areas has been lost over the last century (Table 3).
Indeed, the primary habitat for screech-owls in this area—mature water birch—has declined by
about 87%. Another important habitat type—cottonwood forests—have declined by about a
third in area. Similar data are not available for the rest of range of the owl in British Columbia,
but it is clear that there has been significant loss of cottonwood, birch and aspen woodlands
throughout southern British Columbia since European settlement occurred in the late 1800s.
These habitats are found along the major rivers and lakeshores where this settlement occurred,
and were the first to be converted to urban and agricultural uses.
Added to direct habitat loss is the degradation of these woodlands through the removal of
the mature trees that are required by the owls for roosting and nesting. Most older cottonwoods
6
and birches in residential and park areas have been removed or drastically cut back to reduce the
hazard of falling trunks and branches. The rich shrub and forb understory of riparian woodlands
are often cleared for suburban gardens and golf courses and regularly cleared and burned by
ranchers to provide more grazing and comfortable shade for their cattle.
Habitat protection/ownership
Most of the land where interior screech-owls occur is privately owned or on Indian
reserves. Some suitable habitat is protected in regional and provincial parks, such as
Woodhaven Nature Conservancy in Kelowna, Okanagan Mountain Provincial Park, South
Okanagan Grasslands Protected Area and White Lake Grasslands Protected Area. About 877 ha
(13%) of potential Western Screech-Owl habitat in the southern Okanagan is in conservation
lands (SOSCP 2005, Table 4).
Table 3. Estimated loss of Western Screech-Owl habitat in the South Okanagan and Lower
Similkameen valleys (extracted from SOSCP 2005).
Percentage
1850 (ha)
1995 (ha)
loss
10
10
0%
3198
2128
33%
1997
1962
2%
1926
1973
-2%
6431
775
88%
50
50
0%
13612
6898
51%
Habitat type
Ponderosa Pine - water birch moist fan
Black cottonwood - red osier dogwood floodplain
Paper birch - common snowberry moist gully
Trembling aspen - common snowberry moist
Water birch - red-osier dogwood swamp
Western red cedar - Douglas maple riparian
Totals
Table 4. Level of Western Screech-Owl habitat securement in the South Okanagan and Lower
Similkameen valleys (extracted from SOSCP 2005).
Habitat type
Ponderosa Pine - water birch moist fan
Black cottonwood - red osier dogwood
floodplain
Paper birch - common snowberry moist gully
Trembling aspen - common snowberry moist
Water birch - red-osier dogwood swamp
Western red cedar - Douglas maple riparian
Totals
Total area
available
(ha)
10
Secured
Crown
Land
(ha)
1
Secured
Private
Land
(ha)
2128
1962
1973
775
50
6898
48
433
287
98
0
867
2
1
0
7
0
10
Total
Secured
1
Percent
secured
10%
50
434
287
98
0
877
2%
22%
15%
13%
0%
13%
Nine sites (5 in the Thompson Region, 3 in the Okanagan-Shuswap and 1 in the West
Kootenay) have been proposed as Wildlife Habitat Areas (WHAs) by the BC Ministry of
Environment. If these proposals are accepted, the WHAs will provide protection for designated
screech-owl territories on Crown Land through restrictions on forest harvest and road
construction within a 10 ha core area and 100 ha buffer area.
7
BIOLOGY
The Western Screech-Owl is not a well-studied species; information on social behaviour and
vocalizations and other topics is summarized in Cannings and Angell (2001). However, one of
the more in-depth investigations into the species’ biology has been Davis’ study in the Shuswap
River drainage near Lumby, started in 2005 (Davis, pers. comm. 2007). The Western ScreechOwl is nocturnal and non-migratory; pairs are territorial throughout the year (Cannings and
Angell 2001).
Home Range
Preliminary data from the Shuswap River drainage show 95% UD kernel home ranges of male
screech-owls of 52.5 ha (n=3) and one female of 46.9 ha (H. Davis, unpub. data).
Reproduction
Courtship begins in late January and February with the male calling near the nest; mating
occurs in late March and April. Mates roost in close proximity to each other prior to egg-laying
(H. Davis unpub. data). The incubation period is 26 days and the nestling period 35 days
(Cannings and Angell 2001); most nests in the British Columbia Interior likely fledge in late
May and early June. Only one brood is raised each year, though clutches lost early in the
incubation period are probably replaced.
The Western Screech-Owl nests in tree cavities, most commonly those excavated by
Northern Flickers (Colaptes auratus) or Pileated Woodpeckers (Dryocopus pileatus); it also uses
natural tree cavities such as those formed where branches have broken off a trunk, and nest
boxes. As for all owl species, no material is added to the nest cavity; the eggs are laid on
whatever substrate is present. Once selected, a nest site is often used for several years in
succession (Cannings and Angell 2001).
Black cottonwoods seem to be favoured as nest trees, probably because of their tendency
to form large natural cavities. Of five nests located along the Shuswap River drainage in the
spring of 2006 (H. Davis unpub. data), four were in large diameter cottonwood trees (mean dbh
90 cm) and one was in a large paper birch (70 cm dbh). Nest holes ranged from 8 m to 25.5 m
above ground (x̄ = 14.8 m) in trees averaging 33.8 m in height. Cannings (1997) describes three
nest sites from Bellevue Creek in Kelowna; all were in cottonwoods ranging from 55 to 116 cm
dbh (mean dbh 90 cm), the nest holes were 8 to 20 m (mean 16 m) above the ground in trees
about 30 m tall. A fourth Okanagan nest was reported in Cannings et al. (1987) from a
cottonwood stub; the hole was 1.5 m above the ground. A nest found in the Creston area of BC
was in a large trembling aspen (45 cm dbh; Beaucher and Dulisse 2004a).
The female lays 3 to7 eggs (a series of 29 clutches from s. Idaho; mean 4.72 ± 0.84SD;
Rains 1998). The male feeds the female throughout egg-laying, incubation, and brooding
8
periods. After the young are about 3 weeks old, the female will join the male in hunting, and
will also take longer breaks from brooding (Cannings and Angell 2001). The male generally
roosts near the nest, moving closer throughout the nestling period; by fledging time the males are
often roosting within 5 m of the nest site and directly opposite the nest cavity (Cannings and
Angell 2001).
Young fledge at about 35 days of age; fledging mass is about 75 % (Sumner 1929) to
88% (H. Davis, unpub. data) of adult mass. Nest predation is rare; most common cause of
nestling loss is starvation (Cannings and Angell 2001). Juveniles remain in close association
with their parents for the first 5 weeks following fledging. They then begin to wander more and
more outside the ranges of their parents and roost farther away (Belthoff and Dufty 1997). In
Idaho, young birds begin to disperse from their natal territories about 2 months after fledging,
i.e. between late June and early August (Belthoff and Dufty 1995). Survival during this period
has been measured only in s. Idaho, where 35 of 48 fledglings (72.9 %) survived from nestleaving until dispersal (Ellsworth and Belthoff 1997).
Most birds probably begin breeding when 1 year old. Several males banded as nestlings
along the Snake River in southwestern Idaho bred the following spring (J. Marks pers. comm.).
The average number of nestlings in a 2-yr Idaho study was 4.07 (2-5, n = 15; Ellsworth 1997); a
4-yr study in Idaho had average nestling numbers of 4.47 ± 0.89SD (3-6, n=23; Rains 1998).
Twenty-four of 27 nests observed in s. Idaho produced at least 1 fledgling, a nesting success of
89 % (Rains 1998). Lifetime reproductive success averages 5.94 young for females in southern
Idaho (0-34, n = 48), for males averages 6.23 (0-21, n = 30); one particularly productive, living
male has apparently fathered 36 young to date (J. Doremus pers. comm.).
Predation
Great Horned Owls are known to predate Western Screech-Owls in the Okanagan Valley
(R. Cannings unpub. data) and Barred Owls are likely common predators where the two species
overlap in the Shuswap and Kootenay regions. Barred Owl predation is a new experience for
Western Screech-Owl populations, since Barred Owls only arrived in southern British Columbia
in the 1960s (Campbell et al. 1990). Anecdotal evidence suggests that Barred Owl predation is
having a significant impact on coastal screech-owl populations in British Columbia and
Washington, with many observations of Barred Owls flying in when screech-owl recordings are
played, as well as direct observations of predation (T. Angell pers. comm., G. Ryder, pers.
comm., J. Hobbs, pers. comm.). As part of the research study in the Shuswap River drainage, a
Barred Owl was captured when it attempted to prey on a screech-owl decoy (Davis, pers. comm.
2007). In the same study, 2 of 6 screech-owls outfitted with radio transmitters were predated by
unknown raptors (probably Great Horned or Barred Owls).
Dispersal
Ellsworth and Belthoff (1997) found that young screech-owls in Idaho disperse about 60
days after fledging (range 41-97 d, n=35); mean dispersal date 16 Jul (range 25 Jun to 25 Aug).
On average females travel about 3 times as far as males (mean of 14.7 km vs. 5.1 km) in the first
9
3 months of dispersal (Ellsworth and Belthoff 1997). The dispersal period is relatively short,
and individuals settle after about 6 days (Belthoff and Dufty 1997).
Nutrition
Western Screech-Owls are generalist predators, feeding on a wide variety of small animals,
including mice, shrews, bats, birds, insects, fish, earthworms and crayfish (Cannings and Angell
2001). Little is known of their specific diets in the British Columbia Interior except for the
analysis of a sample of pellets from the Lumby area (Table 5, H. Davis, unpub. data).
Table 5. Contents of Western Screech-Owl pellet samples taken from the Shuswap River area
northeast of Lumby (H. Davis, unpub. data).
Taxon
Meadow vole (Microtus pennsylvanicus)
Vole spp. (Microtus spp.)
Deer mouse (Peromyscus maniculatus)
unidentified rodent
Shrew (Sorex spp.)
Unidentified bird
Cedar Waxwing
Ruffed Grouse
Beetle (Coleoptera)
Bat (Chiroptera)
Cricket/grasshopper (Orthoptera)
Total items
No. of items
8
5
6
1
4
3
1
1
21
1
3
54
Percent
14.8%
9.3%
11.1%
1.9%
7.4%
5.6%
1.9%
1.9%
38.9%
1.9%
5.6%
Adaptability
Western Screech-Owls can adapt easily to the presence of humans and are common
residents in some suburban habitats (outside the British Columbia Interior) where nest site and
prey availability requirements are met (Cannings and Angell 2001). They readily use nest boxes
when natural cavities are not available.
POPULATION SIZES AND TRENDS
Search effort
Before 1990 there were no targeted surveys for Western Screech-Owls in the British
Columbia Interior. Indeed, before 1970, there were few attempts to locate owls at night at all in
10
this area. Cannings (1997) searched for screech-owls throughout the southern Interior of British
Columbia between 5 April and 16 September 1996, using a playback protocol at 250 sites. In
2001, Hobbs (2002) revisited many of Cannings’ sites in the Okanagan and found two more in
Kelowna. This study was followed by in 2002 by Tripp (2003), who conducted 108 playback
surveys at 93 sites in the Okanagan Valley. In 2003, Mylymok and Hobbs (2003) surveyed 250
sites in the Okanagan, Boundary and West Kootenay regions. More thorough Kootenay surveys
were done in 2003, 2004 and 2005 (Beaucher and Dulisse 2004b, Dulisse and Beaucher 2006);
they report on 607 call playback surveys at 392 sites. Through three different research projects,
H. Davis (unpub. data) has conducted surveys at 193 sites, most revisited several times, in the
north Okanagan and southeast Shuswap region in 2004-2006. Sawicz et al. (2006) carried out
234 surveys in the Thompson-Nicola region and 480 in the Okanagan region in 2006.
Hausleitner et al. (2007) searched for Western Screech-Owls along transects in the Carpenter
Lake, Seton Lake and Goldbridge areas along the northwestern edge of M. k. macfarlanei range
in 2006.
The British Columbia Nocturnal Owl Survey (e.g. Cannings 2006) has been monitoring
owls along 34 to 56 routes (each 10 to 30 stops long) in the southern Interior of British Columbia
annually since 2000. Surveys are carried out by volunteers in March each year and no playback
is used.
Abundance
To estimate the number of known Western Screech-Owl territories in the Interior of British
Columbia, we assembled 418 sighting records and assigned the locations of each to unique sites.
We considered owl sightings made within about 300 metres of each other to be at the same site.
Considering only sightings made since 1990 during the breeding season (March through July),
there is a total of 140 different sites, based on a sample of 282 sightings. Since screech-owl
home ranges are larger than 300 metres in radius ( see discussion of home ranges above; H.
Davis, unpub. data), this number of sites is liberal, i.e. some neighbouring sites may represent a
single territory. On the other hand, there are very likely more sites yet undiscovered, so 150-200
pairs could be considered a reasonable estimate of the breeding population of M. k. macfarlanei
in British Columbia. However, breeding has been confirmed at only 20 sites.
Fluctuations and trends
No direct population trend data are available, but calculations showing a loss of 50% of
riparian habitat in the 1900s in the south Okanagan (SOSCP 2005) suggest a serious population
decline in that core area. Historical records of screech-owls in the British Columbia Interior are
rather sparse, so no estimate of direct loss of territories can be made. Screech-owls have not
been relocated at five sites where the species was detected in the breeding season before 1990.
Rescue effect
There are Western Screech-Owls in Washington, Idaho and Montana that could provide a
rescue effect for a declining British Columbia population, but the status of the American
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population is unknown. Also, if habitat loss is the primary threat to the Canadian population,
any rescue effect would be nullified.
LIMITING FACTORS AND THREATS
Habitat loss and degradation is considered the most important factor limiting the screechowl population in the British Columbia Interior. The availability of tree cavities for nests and
roosts is a critical component of any screech-owl territory, so the loss of large, mature trees in
riparian habitats has reduced the suitability of much of the valley bottom habitats. These trees
are often removed, especially (and ironically) so in parks where public safety is an issue, since
mature cottonwoods in particular are considered a windfall hazard. The clearing of shrub
understories from these riparian woodlands is also widespread, a practice that undoubtedly
reduces the quantity and diversity of small prey suitable for screech-owls.
It has been suggested that forestry operations negatively affect screech-owl habitat on the
British Columbia coast both by the removal of habitat through timber harvesting and through the
removal of dead trees and snags which serve as potential nest cavity trees (Darling, pers. comm.,
2001, Fraser, pers. comm., 2001). Yet, the relationship between Western Screech-Owls and
forestry operations has not been closely studied. Forest fires, perhaps like logging, may also
temporarily remove habitat for interior populations (Hayward, pers. comm., 2001).
Roads also contribute to deaths of screech-owls. Up to six road mortalities have been
documented in one year in the South Okanagan and the actual total is likely much higher when
undocumented incidents are factored in. This level of mortality could have a significant impact
on a small population. Other studies have also documented the impact of road kills on screechowls (Hatler et al. 1978).
Barred Owls are negatively affecting Western Screech-Owl populations along the Pacific
coast (Elliott 2006) and probably in the southern Interior of British Columbia as well. These two
species do not come into contact with each other very often in the Okanagan Valley, but along
the Shuswap River and throughout the Kootenays they share valley bottom habitats. See
Predation above.
EXISTING PROTECTION OR OTHER STATUS DESIGNATIONS
The Western Screech-Owl (macfarlanei subspecies) was assessed as Endangered in Canada
by COSEWIC (COSEWIC 2002) and is listed as Endangered in Schedule 1 of the federal
Species at Risk Act. In British Columbia it is listed as an Identified Wildlife species (IWMS
xxxx) and is also protected under the British Columbia Wildlife Act. It is also on the provincial
Red List of candidate taxa for Threatened or Endangered status.
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The Western Screech-Owl is not listed nor proposed under the US Endangered Species
Act, nor is it listed in the IUCN Red Book, although all owls (Strigiformes) are listed as a group
under Appendix II of CITES (Convention on International Trade in Endangered Species of Wild
Fauna and Flora). Appendix II species are not necessarily threatened with extinction, but may
become so without careful control of trade.
The ranks below have been assigned to the species or subspecies by Nature Serve (2001),
where:
1 = Critically imperiled because of extreme rarity (5 or fewer extant occurrences
or very few remaining individuals) or because of some factor(s) making it
especially vulnerable to extirpation or extinction
2 = Imperiled because of rarity (typically 6-20 extant occurrences or few
remaining individuals) or because of some factor(s) making it vulnerable to
extirpation or extinction
3 = Rare or uncommon (typically 21-100 occurrences); may be susceptible to
large-scale disturbances; e.g. may have lost extensive peripheral populations
4 = Frequent to common (greater than 100 occurrences); apparently secure but
may have a restricted distribution; or there may be perceived future threats
5 = Common to very common; demonstrably secure and essentially ineradicable
under present conditions
The species as a whole is ranked G5 on a global scale, N5 within the United States and
N4 within Canada. Rankings from adjacent states for the species are: Alaska S3?B, Washington
S5, Idaho S4, Montana S3S4. Megascops kennicottii macfarlanei is considered apparently
secure by NatureServe (T4) and critically imperiled in Canada (N1); there are no state or
province rankings for this subspecies other than in British Columbia, where it is ranked S1.
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ACKNOWLEDGEMENTS
We would like to thank Gord Currie of Pope & Talbot, Ltd. for providing funding for this
report. Jared Hobbs of the BC Ministry of Environment, the guru of screech-owls in the BC
Interior, facilitated the production of the report and provided many thoughtful comments. Leah
Ramsay of the BC Conservation Data Centre produced data summaries and relevant past reports.
Jakob Dulisse and Marc-André Beaucher contributed information and opinions on the status of
this species in the Kootenay region.
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