Williamson's sapsucker (Sphyrapicus thyroideus) COSEWIC assessment and status report: chapter 4

Distribution

Global range

The breeding range has been recently summarized by Dobbs et al. (1997). The currently known breeding range is presented in Figure 2 as derived from Dobbs et al. (1997), from Sauer et al. (2004), and from the information summarized under the Canadian Range section. The breeding range is primarily in the mountain ranges of the western United States north to southern British Columbia. It is absent from the central Great Basin ranges of Nevada. There is one breeding population in Mexico in northern Baja California that is disjunct from other populations.

The species is partially migratory, leaving the northern latitudes of its breeding range north of the California border, the area north of the Mogollon Rim in Arizona, and the area north of the mountains in the Santa Fe area in New Mexico. It winters occasionally in southern Oregon, and at lower elevations in California, in southern Arizona and New Mexico, and in the mountains of western Mexico as far south as Jalisco and northern Michoacan, northwest of Mexico City.

Canadian range

The breeding range of the Williamson’s Sapsucker in Canada is entirely within southern British Columbia, where it is a rare summer resident. There are three accidental records for Alberta (Pinel 1993) and three accidental records for Saskatchewan (Godfrey 1986). Two of the Alberta records were from Waterton Lakes National Park, very close to the known range of nataliae, with the other record from Calgary.

The status and range of Williamson's Sapsucker in British Columbia was summarized by Cooper (1995). However, considerable new information on all of the British Columbia populations has been collected or become known since then. The information provided by Cooper (1995) is incorporated into the summary of range and status below, and is cited where it has been used.

There is no zone of contact between the two subspecies in Canada. The most easterly record of thyroideus near Greenwood is approximately 200 km west of the most westerly record of nataliae near Kimberley. There have been no records of Williamson’s Sapsuckers in any season in the area between Greenwood and Kimberley based on the 230 records summarized in Campbell et al. (1990), the additional records in Cooper (1995), any records reported on the southern interior British Columbia birder’s e-mail groups (BCINTBIRD; WKBIRDS; EKOOTENAYBIRDS) from 1997-2004, or any other known sources.

Figure 2. North American breeding range of Williamson's Sapsucker based on Dobbs et al. (1997) and Sauer et al. (2004), and on Gyug (unpublished data) for the Canadian portion of the range.

Figure 2. North American breeding range of Williamson's Sapsucker based on Dobbs et al. (1997) and Sauer et al. (2004), and on Gyug (unpublished data) for the Canadian portion of the range.

Using COSEWIC (2004) definitions, the Total Population refers to all the Williamson's Sapsuckers in Canada, excluding cases of vagrancy. Within the Total Population, COSEWIC defines a population as “a geographically or otherwise distinct group that has little demographic or genetic exchange with other such groups--typically one successful migrant individual or gamete per year or less”. There is no information on genetic exchange of individuals between groups of Williamson's Sapsucker, but it may be relatively low based on the high extent of philopatry, which is based on relatively little information (see Survivorship/mortality section). Based on the known breeding sites, the Total Population has been divided into five geographically distinct populations. These populations are the four populations of subspecies thyroideus: Okanagan-Greenwood, Princeton, Merritt and Hat Creek (west of Cache Creek) and the single population of subspecies nataliae in the Rocky Mountain Trench near Cranbrook. Within these populations, separate locations currently known to be occupied have been identified based on gaps of more than 2 km in known or surmised (based on apparently suitable habitat) breeding locations as suggested for woodpeckers in general by NatureServe (2004). There have been additional breeding locations of Williamson's Sapsucker within the Extent of Occurrence but outside any of the defined populations, but these have not been regularly used, and seem to be only occupied by one pair each.

S. t. thyroideus

The thyroideus subspecies breeds in southern British Columbia (Figure 3) from Lightning Lakes in Manning Provincial Park north to Botanie Creek and Hat Creek (Cooper 1995; Wayne Campbell pers. comm. 2004), east to Scottie Creek (Cooper 1995), Louis Creek (B.C. CDC) and Greenwood (Gyug unpublished data). The Extent of Occurrence of thyroideus based on a minimum convex polygon of all known breeding records is 34659 km² (Figure 3).

I have discounted a 1956 nest record that lacks supporting documentation from northern British Columbia (BC Nest Record Scheme, hereafter BCNRS) about 240 km west of Prince George and more than 500 km north of the next nearest known observation of Williamson's Sapsucker. There have been other extralimital observations of Williamson's Sapsucker cited by Cooper (1995): Carpenter Lake (Jones and Gates 1973), 40 km west of the Hat Creek population, and at Pemberton Meadows in 1984, 90 km west of the Hat Creek population. No breeding activities were cited in these records.

Historically, the range of thyroideus in British Columbia has probably increased to the west and north. Cowan (1938) reported the range to be from the border north to Schoonover Mountain near Okanagan Falls east to Midway, and west to the Similkameen River. By 1970 the range had extended westward to the eastern side of E.C. Manning Provincial Park (Guiguet 1970), and by 1978 birds were breeding within Manning Park (BCNRS; Campbell et al. 1990).

The dates for northward expansion of the range are more difficult to pinpoint. Nesting was observed in one tree for three consecutive years around 1977 about 16 km northwest of Kelowna (Harry Almond pers. comm. 2004, Cooper 1995, Cannings et al. 1987). There is one record of a nest west of Cache Creek in 1969 (BCNRS). The small population at Hat Creek, west of Cache Creek, therefore dates back to the 1960’s at least. Only in the 1990’s were nests reported in the Kamloops area, one of which was still occupied in 2003.

The Area of Occupancy is estimated to be 1016 km².

Figure 3. Extent of Occurrence (black line) and breeding range (shaded area) encompassing all known or suspected breeding sites of Williamson's Sapsucker in British Columbia up to, and including, 2004.

Figure 3. Extent of Occurrence (black line) and breeding range (shaded area) encompassing all known or suspected breeding sites of Williamson's Sapsucker in British Columbia up to, and including, 2004.

The breeding range is not continuous but rather consists of a main population in the area east of Okanagan Lake to the city of Greenwood (Gyug and Peatt 2000; Gyug unpublished data), and three smaller, disjunct populations: near Princeton (Cooper 1995; Gyug unpublished data), Merritt (Cooper 1995; Gyug unpublished data) and Hat Creek (Cooper 1995; Wayne Campbell pers. comm. 2004). There have been occasional breeding records outside of these areas (Cooper 1995; Campbell et al. 1990; Gyug unpublished data). Within the three populations for which there are breeding records with locations precise enough to estimate population continuity (Okanagan-Greenwood, Princeton, and Merritt), the populations were not continuous but were found in separate locations in patches of suitable habitat. The Okanagan-Greenwood population consists of at least 15 separate locations (defined as >2-km gap between known occupied sites). The Merritt population consists of at least three locations. The Princeton population consists of one location known to be currently occupied, and at least two other previously occupied locations.

T. t. nataliae

The nataliae subspecies is limited in distribution in British Columbia to the southeast corner of the province in the Cranbrook area of the Rocky Mountain Trench and the Rocky Mountains. Historically nataliae bred in the Cranbrook area, probably south to Newgate at the U.S. border (Johnstone 1949, Guiguet 1970), but was never very abundant. Specimens or observation records were only available from Newgate and from Cranbrook (Cowan 1938; Munro and Cowan 1947). It was thought the subspecies was in decline or extirpated from British Columbia since there had been no breeding records after 1938 (Johnstone 1949, Campbell et al. 1990) and the reason for disappearance from the 1937-38 breeding site was that the site was logged the following year (Johnstone 1949). Cannings (1997) found no Williamson's Sapsuckers south of Cranbrook to Newgate in 11 days of field searches. However, research for the British Columbia provincial status report (Cooper 1995) turned up sparse records from the intervening years, and a breeding record from south of Cranbrook in 1979, that indicated the subspecies may have continually occupied the Canadian portion of its range. A nesting record from 1999 in the Whiteswan Lake area (Campbell et al. 2000), 70 km north of Cranbrook, confirmed that the subspecies was still breeding in the area, and may have a range larger than previously thought, or may be expanding its range northwards. Cooper (1995) reported sighting records from the Flathead Valley from 1986-1992, and there have been more recent records in the same area in the late 1990’s (Fred Hovey pers. comm. to Ted Antifeau 2003). There was one nesting record from 2004 at Kimberley Nature Park where a female was also seen in 2001 (EKOOTENAYBIRDS 2001-2004).

The Extent of Occurrence of nataliae based on a minimum convex polygon around the approximate locations of these records was 8399 km² (Figure 3).

The range as might be mapped on a distribution map that excludes large areas of unsuitable habitat was about half that size, 4532 km² (Figure 3). There were only 4 known breeding locations from which to estimate Area of Occupancy; a 500-m radius around each of the four sites yielded an Area of Occupancy of 3.1 km². There was one observation, perhaps of a non-breeding bird, reported by Cooper (1995) of a Williamson's Sapsucker at Brisco (Kaiser et al. 1978), 130 km north of Cranbrook.

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