Vesper sparrow (Pooecetes gramineus affinis) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

All subspecies

Of the total breeding population of Vesper Sparrows in Canada, Alberta supports an estimated 18%, Saskatchewan, 15%, and the rest of Canada, 14% (Wells and Rosenberg 1999). Using the Partners in Flight total population estimate of 30 million (Rich et al. 2004), there are approximately 14 million Vesper Sparrows breeding in Canada.

Breeding bird survey (BBS) data compiled over the last 40 years show significant declines in 11 states, 12 physiographic strata, the Eastern BBS Region, continental USA, and survey-wide; increases are limited to 3 states and 3 strata, while the other regional trends estimates are close to zero (Sauer et al. 2004). Continent-wide, BBS data indicate a significant annual decline of 0.6% from 1966 to 2003; Christmas bird count data show a similar decline (Sauer et al. 2004).  In Canada, BBS data show a significant annual rate of decline of 0.9% from 1968 to 2002, steepening to 2.5% in the last decade.  Recent (1993-2002) trends for all Canadian Bird Conservation Regions are negative, including significant annual declines of 6.7% in the Boreal Taiga Plains, 8.4% in the Northern Rockies and 7.2% in the Boreal Hardwood Transition.  Vesper Sparrows have become so uncommon in Atlantic Canada that recent declines cannot be calculated, but the trend from 1968-2002 is a significant annual decline of 9.9%.

Coastal Vesper Sparrow

In the late 1990s, researchers estimated that the Canadian Coastal Vesper Sparrow population was five to ten breeding pairs (Fraser et al. 1999). Results from survey efforts in 2002, 2003, and 2004 were consistent with this estimate, with five probable breeding territories documented at the Nanaimo Airport during those years. Searches were also conducted between Mill Bay and Nanaimo and on Gabriola and Saltspring Islands in May and June, 2002 (Beauchesne 2002a) and between Cassidy and Campbell River, and adjacent Gulf Islands, from April to June, 2003 (Beauchesne 2003). No additional breeding localities were identified either year and the Nanaimo Airport remains the only known locality for this species on southeastern Vancouver Island (Beauchesne 2002).  The entire historical range of the subspecies in Canada has a high density of keen birdwatchers who are quick to report any sightings of this rare species.

Coastal Vesper Sparrows are listed by other authors as casual breeders (Cannings 1998) and as occasional local breeders in British Columbia (Campbell et al. 2001). The species has never been recorded on Breeding Bird Surveys (BBS) or Christmas Bird Counts on the coast (Campbell et al. 2001), though BBS routes are not designed to look for rare birds and the species is rarely present in Canada in winter. 

In Washington State, Rogers (2000) estimated that there were approximately 125 singing male Coastal Vesper Sparrows in 1998. However, on San Juan Island, the breeding site closest to British Columbia, only two Vesper Sparrows were located that year (Rogers 2000). No population size estimates could be found for Oregon or California.

This subspecies may never have been common in British Columbia as it was never recorded in large numbers or from more than a few localities. The maximum count of birds at one location during the breeding season is 13 birds in the Cobble Meadows/Cobble Hill region on Vancouver Island in 1978 (Campbell et al. 2001). Because formal surveys of Vesper Sparrow populations were not undertaken historically, trends are difficult to determine. However, the species has disappeared from some historic breeding locations (e.g., Cobble Meadows, Iona Island and the Fraser River valley), suggesting that the population is in decline (Fraser et al. 1999).  Recent counts at the Nanaimo airport suggest the population is more or less stable at that one site.

In Washington State, a decrease in distribution and abundance of this subspecies has also been apparent, although precise historic population data is also lacking for that region (Rogers 2000). The Coastal Vesper Sparrow is currently considered in danger of extirpation in Washington due to habitat destruction (Smith et al. 1997; Rogers 2000).

In Oregon, anecdotal evidence suggests substantial population declines in Coastal Vesper Sparrow have occurred in the last 40-50 years (Altman 2003). There are no available population trend data for the subspecies in California.

Because of the declining population in Washington and the issue of habitat loss in British Columbia, rescue effect is likely minimal at best.