Williamson's sapsucker (Sphyrapicus thyroideus) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

The Williamson's Sapsucker, Sphyrapicus thyroideus, is a medium-sized woodpecker. Unique among woodpeckers, the male (mostly black and white) and the female (mostly black and brown) exhibit strikingly different plumage. There are two recognized subspecies, S. t. thyroideus and S. t. nataliae, both of which occur in Canada. However, there are no distinctive morphological features known that can reliably separate individuals of the two subspecies, so the subspecies have not been assessed separately in this report.

Distribution

The breeding range of Williamson's Sapsucker is in the mountains of western North America from southern British Columbia to the southern United States, and northern Baja California in Mexico. All breeding records in Canada are from British Columbia.  In British Columbia, thyroideus breeds from Manning Provincial Park near the U.S.A. border, north to the Lytton, Cache Creek and Kamloops areas, through the Okanagan Highlands and east as far as Greenwood. The nataliae subspecies is found in the Rocky Mountain Trench north to Cranbrook, Kimberley and Whiteswan Lake, and in the Flathead River valley. There is no zone of overlap of the subspecies in Canada.

Habitat

In the United States, Williamson's Sapsucker breeds in coniferous mountain forests at middle to high elevations. In Canada, the majority (80%) of the breeding records have been in, or within 200 m of, Western Larch forests at elevations of 1000 to 1400 m. A smaller proportion (up to 10%) of the breeding adults may be found in Ponderosa Pine forests and Trembling Aspen groves adjacent to Ponderosa Pine or Western Larch forests, generally at elevations of 800 to 1100 m. Suitable habitat in Western Larch forests is defined by the presence of large (>70 cm Diameter-at-Breast-Height or DBH) veteran (>200 yr old) Western Larch nesting trees that have typically survived many fires and have extensive heartrot making them suitable for cavity excavation, coniferous sap well trees (usually medium-sized 20-50 cm diameter-at-breast-height Douglas-fir), and large trees infected with carpenter ants. Seventy to ninety-nine percent of the diet that the adults feed to nestlings is ants, mainly carpenter ants, gleaned from the surface of decaying trees.

Biology

Williamson's Sapsuckers are migratory birds, only found in Canada during the breeding season, generally late March to September. Breeding home range sizes in Canada in Western Larch habitats are on the order of 17-54 ha, much larger than those reported from Ponderosa Pine and Trembling Aspen habitats in Colorado and Arizona, which were on the order of 4-11 ha, but which were determined by different methods, i.e., the maximum distance from the nest at which the male will respond aggressively to conspecific intruders. Maximum density in Canada is 3.17 pairs/km² in old-growth Western Larch forests. This is the highest density reported for the species from census areas at least 100 ha in size. High densities previously reported elsewhere have been derived from very small plots that probably do not yield valid density estimates.

Population sizes and trends

Total Population size of Williamson's Sapsucker in Canada is estimated at 430 breeding adults in five populations. The largest population, making up 85% of the estimated Total Population, is the Okanagan-Greenwood population, with much smaller populations in the Princeton, Merritt and Hat Creek areas. Population size of the nataliae subspecies in Canada is estimated at only 10 breeding adults.

There are no quantifiable trends in population numbers because the species is relatively rare, detected too infrequently in most areas on Breeding Bird Surveys (BBS), and there have been no previous population estimates prior to this assessment. Only in Oregon was there enough data (26 routes, abundance >1.0 per route per year, and low variance) to provide a reliable estimate of trends from BBS routes where Williamson's Sapsucker numbers have been decreasing at an annual rate of 3.3% from 1980 to 2003.

Based on decreases in suitable habitat the thyroideusOkanagan-Greenwood population is likely declining. There is no known population trend for the nataliae subspecies.

Limiting factors and threats

The principal limiting factor to the species is availability of suitable habitat (old-growth Western Larch) which is being reduced by timber harvesting and land clearing. Only 19.5% of the 594 km² main Area of Occupancy of the Okanagan-Greenwood population was considered suitable habitat as of the early 1990’s. This amount has decreased since then to about 15% in 2004. Timber harvesting is proceeding at the rate of about 1% of this land per year, the majority of which is targeted at the same older forests used by Williamson's Sapsuckers. Estimated habitat loss from logging over the next 10 years is up to 53% of the current habitat. Without some considerations for habitat conservation, suitable habitat for the largest population of this species in Canada may be almost entirely gone for this population in as little as 20 years.

Special significance of the species

The species is of interest because of its markedly different male and female plumages. The possible advantages and causes of this adaptation have not been studied. The species is an indicator species of old-growth Western Larch forests in southern British Columbia, the only habitat in which it is relatively common in Canada. Williamson's Sapsucker is a priority species for Partners in Flight in the Great Basin (Partners in Flight British Columbia and Yukon 2003) and for the Canadian Intermountain Joint Venture (2003). It is also a Species of Continental Importance in the Intermountain West Avifaunal Biome, designated by Partners in Flight.

Existing protection

The species is protected under the Migratory Bird Convention Act and the British Columbia Wildlife Act. However, there is no protection of the species’ habitat. It is not considered Identified Wildlife under the British Columbia Forest and Range Practices Act (which now is only applied to certain COSEWIC-designated species), so does not qualify for any special protection from timber harvesting. Less than 2% of known breeding sites are in protected areas of any sort.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The Committee meets to consider status reports on candidate species.

Definitions (November 2004)

Species

Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)**

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)***

A species for which there is insufficient scientific information to support status designation.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.