Western screech-owl (Otus kennicottii) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Population estimates are almost non-existent for Western Screech-owls, and those that do exist are educated guesses. Being a small nocturnal species, the screech-owl is not often seen nor is it particularly easily surveyed.  Descriptions of the species’ abundance vary. Beginning with the earliest description, Bowles (1906 and 1917 describes the species first as ‘tolerably common’ in northwestern Washington and then ‘by no means common.’ Based on discussions with ornithologists in the 1970s, BC screech owls were described as being of low-medium abundance and having stable populations (Fyfe 1976). More recent discussions of Canadian Western Screech-owl abundance can be found in the previous COSEWIC report (Kirk 1994), as well as Kirk et al. (1995), Campbell et al. (1990) and Kirk and Hyslop (1998). The only Canadian population estimate for the species as a whole given in these sources is a ‘best guess’ of 1,000-2,000 pairs in Kirk et al. (1995). Cannings (1997) estimated that there were fewer than 20 O. k. macfarlanei in the Okanagan Valley in 1996 and Fraser et al. (1999) estimated that there were fewer than 3,000 screech-owls on southern Vancouver Island and the Gulf Islands (=O. k. "saturatus").

Breeding Bird Surveys (BBS) and Christmas Bird Counts (CBC) are potential sources of information on population trends, but are not that useful for Western Screech-owl. The BBS, a daytime survey carried out by volunteers across North America has very limited value for assessing nocturnal species populations. Western Screech-owls were recorded on nine routes between 1966 and 1977, and on another eight between 1978 and 1983, but the increase shown from this data is statistically insignificant because the number of records is too small (Kirk 1994). Downes et al. (2001) continue to indicate that there is not enough Canadian BBS data for statistical analysis for this species. CBCs are more likely to show trends as some participants conduct nocturnal owl counts within their area. Kirk et al. (1995) indicate that there was a significant positive trend in Western Screech-owl numbers continent-wide between 1959 and 1988, but Kirk (1994) hypothesizes that this may be due to increased numbers of people owling rather than a real population increase. Also, the CBC count compiler for White Rock, BC indicates how the presence of a single keen owl observer on that count made a significant difference to the number of owls found (Mackenzie pers. comm., 2001). Examination of two counts in southwestern BC (Ladner and Vancouver) show that Canadian CBC numbers in BC are likely too small for analysis (BirdSource).

Two other sources of information may help to describe populations in the future. The new Bird Studies Canada British Columbia Nocturnal Owl Survey which began in 2000 may become important in elucidating owl trends, but cannot do so yet due to its newness. Secondly, those undertaking Spotted Owl surveys for the British Columbia Ministry of Environment, Lands and Parks recorded all owls during their surveys in southwestern BC. As there is information spanning about ten years it may be possible to get some idea of Western Screech-owl population trends if there are sufficient records of this species.

In the US generally (White 1994) and in Idaho in particular (Belthoff, pers. comm., 2001, Doremus, pers. comm., 2001 and Hayward, pers. comm., 2001) the populations of Western Screech-owls have been described as stable or probably stable.

Coastal Subspecies – Otus kennicottii kennicottii

Campbell et al. (1990) gathered a total of 1,377 historical and recent records of both subspecies of Western Screech-owl in the BC bird atlas. They consider O k. kennicottii to be uncommon to fairly common on the south coast and Vancouver Island and rare to uncommon on the northern mainland. Numerous anecdotal reports and a few reports described below help to elucidate the abundance of this subspecies.

Three recent studies conducted on Vancouver Island show that the species is still relatively common in suitable habitat over unsettled regions of the island (Setterington 1998, Holroyd et al. 2000, Mico and Van Enter 2000). Owls surveys in the Nimpkish Valley which were estimated to cover about 14% of the watershed (about 26,000 ha, but all at lower elevations) found between 61 and 102 individual Western Screech-owls annually between 1995 and 1997 (Setterington 1998). Western Screech-owls were the most common owl species of the five recorded. In Clayoquot Sound, Western Screech-owls were again the most common of five owl species found in breeding season surveys conducted there (Holroyd et al. 2000). In the Campbell River watershed study, screech-owls were the second-commonest species of four, after Northern Saw-whet Owl (Aegolius acadicus) (Mico and Van Enter 2000). At 16 of 60 stations, and at all of their five study sites, the authors recorded Western Screech-owls. A study of unknown scope and date in Pacific Rim National Park that recorded screech-owls on a monthly basis, tallied up to eight screech-owls in January (Holmes, pers. comm., 2001).

In contrast to its status in western and northern Vancouver Island, the abundance of the species in southeastern Vancouver Island from Victoria to Nanaimo and in the Lower Mainland seems to have declined in the last 20 years. Here, researchers and birders almost all state that within the last decade or two the species had changed from common or reasonably common to very uncommon or locally extirpated. This is the case on the University of Victoria campus, where in 1979 there were 13 pairs on the campus and there are now none (Levesque 2000, Fraser pers. comm., 2001). At six other locations in the Victoria area where the species was present in the early 1980s it is no longer present (Fraser pers. comm., 2001). As well, Hobbs (pers. comm. 2001), although still finding Western Screech-owls in southern Vancouver Island (he was aware of at least 18 locations) believes that they are declining rapidly and is aware of locations where the species once was, but is no longer present. Fraser (pers. comm., 2001) also states that south of Nanaimo at a location where he conducted owls surveys between 1987 to 1998, Western Screech-owls changed from being the most commonly detected owl to rarely encountered. A similar decline appears to have occurred on Newcastle Island (near Nanaimo) where the species has not been seen in five years, and in the Gulf Islands (Fraser, pers. comm., 2001). In the Duncan area, Aldcroft (pers. comm., 2001) also thinks that Western Screech-owls have decreased in the area he is familiar with – in 1984 he felt they were common, but he has not heard one in the last three years despite continuing to look for them.

Darling (pers. comm., 2001) has also studied owls in southeastern Vancouver Island. She has collected 623 historic records of screech-owls over the coastal Douglas-fir zone that runs in a narrow band along the east coast of the island from about Denman Island to the southern tip. This includes records of several owls at one location, as well as records of the same owl at different dates. She also surveyed owls in 1998 and gathered 43 records, although some of these are repeat locations at different dates. She was not able to analyze this data in detail, but did find that in many areas, particularly in urban and suburban landscapes where Western Screech-owls had previously been reported, there were often no longer screech-owls present (Darling pers. comm., 2001).

In the Lower Mainland, similar observations of declining Western Screech-owls numbers have been made. Toochin (pers. comm., 2001) believes that there are only 10 known pairs in Greater Vancouver, and that the decline in numbers began in the late 1980s. Also, as mentioned earlier, the species is no longer present in Campbell Valley Regional Park where they once were (Mackenzie, pers. comm. 2001). Mackenzie believes that they are very rare or perhaps extirpated in the White Rock CBC area. In Burnaby, Clulow (pers. comm. 2001) states that Western Screech-owls have declined almost to the point of disappearance. Three former screech-owl territories in a Burnaby park that he was familiar with have not been occupied for three years and the species is no longer present in other local areas. Also, Western Screech-owls known to be regularly present on the University of British Columbia Endowment Lands in Vancouver, have not been detected for a few years (Cannings, pers. comm., 2001). Finally, on the White Rock CBC, where owling efforts have been relatively constant since 1982, screech-owls have not been recorded since 1996 (Mackenzie pers. comm., 2001). Between 1982 and 1996, the longest gap of time without screech owls was two years. Somewhat contrary to these accounts are the results of Robertson et al. (2000), who surveyed for Western Screech-owls in 26 areas in the Lower Mainland and the coast to the north of that area. The researchers recorded Western Screech-owls in 42% of their surveys, despite the survey sites not being chosen on the basis of being whether they were good screech-owl habitat.

Thus, O. k. kennicottii could be described as relatively common and perhaps stable through much of the coast, especially Vancouver Island away from the south-eastern coast. On the other hand, along the south-easternmost coast of Vancouver Island and in the southwestern portion of the mainland the populations appear to be low and likely decreasing. The status of the species along the long stretch of the upper mainland coast up to the Alaska border is poorly known, although in north-coastal BC around the Kitimat valley, the species is apparently very rare (Horwood pers. comm. 2001).

The total number of O. k. kennicottii in BC could be estimated to be between 3,000 and 10,000 individuals. The upper estimate is based on the fact that there is a large amount of available habitat on Vancouver Island and on the northern mainland coast, and additionally the species seems to be common through much of this area. In the Nimpkish Valley study, Setterington (1998) estimated that the owl surveyors covered only about 14% of the Nimpkish Valley and in that area recorded about 100 owls (though the low-elevation survey routes may have covered most of the good screech-owl habitat in the valley--Matkoski, pers. comm.). Also, even if they are uncommon, as suggested by Campbell et al. (1990), through most of the mainland coast then this could account for several thousand owls, given the large extent of available habitat. Additionally, abundance estimates within study areas are likely underestimated as Western Screech-owls do not always respond to tapes or are not always calling spontaneously. For instance, in the Nimpkish Valley surveyors found owls at 18% of sites in 1995 when sites were visited twice, while in 1996 30% of sites had owls when five visits were made. Mico and Van Enter (2000) recorded 16 screech-owls in their one-season study, and visited each site three times but never got a response from screech-owls on more than one occasion. Finally, Cannings (1997) had to return four times to a known site with screech-owls before he got a response.

On the other hand, the lower estimate of 3,000 individuals takes into account the fact that the population is declining in the south and may be declining to a lesser but unknown degree further north. Certainly the large areas of dense, even-aged young forests produced by clear-cut forestry over the past few decades has lowered habitat quality for this species along the BC coast.

Interior Subspecies – Otus kennicottii macfarlanei

Campbell et al. (1990) describes O. k. macfarlanei as rare to uncommon and local in the central-southern interior and very rare in the west and east Kootenays. Cannings et al. (1987) gave a similar description of the interior BC numbers; they agree with Munro and Cowan (1949) who in the 1940s said that the species was ‘formerly more common in the south than in the north (Okanagan), now scarce everywhere’.

The only comprehensive survey of O. k. macfarlanei in Canada is by Cannings (1997). Throughout appropriate habitat in the interior, he surveyed 250 sites (most only once) in the spring or summer of 1996 and found only 13 sites with Western Screech-owls. Twelve of these were in the Okanagan Valley: eight south of Penticton, and four between Penticton and Kelowna. A thirteenth site was found along the Granby River north of Grand Forks, just outside the Okanagan Valley. He concluded that interior Western Screech-owls seemed to be primarily restricted to the Okanagan Valley, but he felt that there was still the possibility that small numbers of birds may be present in the Nicola, Thompson and Kootenay regions. Since this 1996 study, a few new screech-owl sites have been found in the Okanagan Valley--there are now eight known locations near Kelowna (Charlesworth, pers. comm., 2001, Hobbs, pers. comm., 2001). These may not all be breeding sites. Other recent screech-owl records from the region include 13 road-killed screech-owls that were turned into the South Okanagan Rehabilitation Centre for Owls between 1980 and 2000 (Hobbs, pers. comm. 2001).

Outside of the Okanagan region, O. k. macfarlanei continues to be considered rare to very rare and breeding has never been documented (Beaucher, pers. comm., 2001, Clow, pers. comm., 2001, Howie pers. comm., 2001, Wege pers. comm. 2001) (Table 1). Many of the birds outside of the Okanagan region are thought to be non-breeding, dispersing birds as some of the records are from outside the breeding season (R. Cannings pers. comm. 2001). If this is the case, it seems likely that some owls may be coming from Idaho and Washington, which are closer to the record locations than the Okanagan Valley. West and north of the Okanagan (in an area roughly bounded by Spences Bridge, Merritt, Shuswap Lake and Clearwater) Howie (pers. comm., 2001) is not aware of any confirmed sightings since 1988, although there are four specimens from the 1980s in the southern half of this area. There have also been unconfirmed reports of the species from the Little Fort and Celista areas in the last five years. Although Howie (pers. comm., 2001) feels that the species is very rare and was probably never very common, anecdotal reports suggest that the species may have declined in the last three to four decades. On the other hand, he does note that there are numerous remote unsurveyed drainages where the species may occur.sdxc

Table 1. Recent (post-1980) observations of Western Screech-owl O. k. macfarlanei in Canada east of the Okanagan Valley.
Locations are noted from west to east and are of the town or other location nearest to the sighting. Each record is of a single bird unless noted. If undated, sources are pers. comm. 2001.
Location Date Comments Source
Granby River, north of Grand Forks, British Columbia Spring, Summer 1996 heard both seasons Cannings 1997
Robson, British Columbia January 23, 2001 seen E. Beynon
Castlegar, British Columbia April-May yearly, except not 2001 three to four locations, mainly heard S. Clow
Wynndel, British Columbia February 22, 1998 seen and heard, present two weeks M-A. Beaucher
CrestonValley Wildlife Management Area, British Columbia December 24, 2000 seen M-A. Beaucher
Waterton Lakes National Park, Alberta June 2001 heard, unconfirmed C. Smith
Cypress Hills, Saskatchewan Spring 1992 heard Smith 1996
Cypress Hills, Saskatchewan Spring 1994 heard Smith 1996

Thus, O. k. macfarlanei populations can be considered very small and concentrated in the Okanagan Valley and can continue to be described as rare or very rare. Also, the range of the subspecies may be contracting. Numbers of O. k. macfarlanei are difficult to estimate, but must be at a minimum about 50 individuals and probably more likely in the low hundreds, as it seems probable that not all locations are known.

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