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Vaseux Lake Bird Observatory

August 20, 2010

With daily high temperatures hovering around 36°C (97°F) it’s hard to remember that summer is almost over at this latitude.  Many birds are already drifting south towards winter homes in California, Mexico or Argentina, part of the annual cycle that has been turning for millennia.  A small, and much more recent, cog in that annual cycle is the opening of the Vaseux Lake Bird Observatory.

Vaseux Lake, with McIntyre Bluff in the right background

The name is perhaps a bit misleading, possibly conjuring up images of towers and telescopes.  What it is in reality is a band of dedicated birders, a screened tent (essential to ward off the impressively dense mosquito population), a cluster of 14 mist-nets and some alarm clocks that get the team up early each morning from early August through mid-October.  And a spectacular site in the Okanagan Valley, a rich woodland of birch and alder along winding river oxbows set amidst high rock bluffs, arid grasslands, green vineyards and the lake itself.

Vaseux Lake is one of 25 migration monitoring stations in the Canadian Migration Monitoring Network (there are three others in British Columbia—Rocky Point at the south end of Vancouver Island, Tatlayoko Lake on the west Chilcotin Plateau, and Mackenzie on the west side of the northern Rockies).  The primary goal of these stations is simple—to assess the populations of birds migrating through Canada.  These populations are also monitored to some extent by other programs such as the Breeding Bird Survey and the Christmas Bird Count, but migration monitoring fills in some important gaps.  Many species breed too far north to be counted easily during the breeding season, and many winter too far south to be found on Christmas Bird Counts.  But all these birds have to migrate through southern Canada in spring and fall, and birders and bird biologists have come up with ingenious ways of counting them as they go by.

The grandfather of migration monitoring stations in North America is the Long Point Bird Observatory.  This station has been counting migrants along the north shore of Lake Erie since 1960.  Its programs gradually expanded over the years to include nation-wide efforts such as Project FeederWatch and the Canadian Lakes Loon Survey, and in the 1990s it morphed into Bird Studies Canada. One of the main goals in setting up Bird Studies Canada was to promote a network of migration monitoring stations across the country.

Bander Doug Brown in the banding tent at Vaseux Lake

The 25 stations that now form the Canadian Migration Monitoring Network are all managed and funded by local groups (the Vaseux Lake operation is run by the Okanagan Similkameen Conservation Alliance, with most of its funding coming from the Canadian Wildlife Service and the Baillie Birdathon).  Each site differs slightly in its setup, and of course the bird populations it encounters, but the protocol for counting the birds is basically the same across the country.  During migration each station sets out mist-nets that catch many of the songbirds that are moving through shrubs and small trees.  A daily census counts birds that miss the nets, and miscellaneous observations are thrown into the mix as well.  At the end of each morning session, daily totals are estimated for each species recorded, based on the number of birds netted, seen, or heard.

Most of the effort goes into the mist-netting operation, since it provides valuable information that is otherwise impossible to gather.  The birds are harmlessly extracted from the nets every 15 or 20 minutes, carefully measured, banded and released.  The measurements include data on the age of the bird (whether it was born that year or is an adult (“after hatch year” in the lingo of banders).  This age data creates a quick index of the breeding success of each species that year, based on the ratio of young to adults.  Birds are also examined to see how much fat they are carrying (easily seen through the thin skin at the base of the neck—between the two arms of the wishbone).

A long-term commitment is essential to any effort aimed at monitoring bird populations.  Regular monitoring began at Vaseux Lake in 1994, but the station started operating at its present site in 2001.  So this is its 10thyear of comparable counting, and hopefully we can start calculating meaningful population trends for some species when the data are in from this season.  You can download the report of trend analyses from other stations published online here.

The careful observation of birds results in other discoveries, too.  One interesting finding is the presence of many local birds that apparently move down from adjacent mountainsides into the valley-bottom riparian woodlands in late July.  Species such as Swainson’s Thrush, Nashville Warbler and Orange-crowned Warbler leave their breeding and natal territories at higher elevations to take advantage of the rich feeding opportunities essential for their post-breeding moult.  They skulk in the bushes, gobbling caterpillars and other bugs, grow their new feathers and put on a healthy layer of fat before flying south.  These birds are very inconspicuous in late summer, and it was only the systematic banding program that revealed this tactic.

Black-capped Vireo, 27 September 2008, Vaseux Lake Bird Observatory

We also encounter rarities of course, something that spices up the often monotonous work of a bander .  On August 27, 2008 a Prothonotary Warbler was netted at the station.  Bander Doug Brown thought that this bird—normally found in southeastern North America—would be the highlight of the season until a month later when he pulled a Black-capped Vireo out of a net.  This species has a very limited breeding range on the Edwards Plateau of western Texas and is listed as Endangered in the United States.  Why it flew north to British Columbia is anyone’s guess, but it was only the second of its kind to be found in Canada.

The Vaseux Lake Bird Observatory is open every morning in August, September and the first half of October.  It is located on the west side of Hwy. 97, 3 km south of Okanagan Falls and 1 km north of Vaseux Lake.  Park by the wire gate and walk down to the banding tent.  Bander Doug Brown welcomes all visitors and would be happy to show you how the birds are banded.  Please don’t bring your dog along, thanks.

All migration monitoring stations across Canada use volunteers for much of their work.  If you’d like to volunteer, let me know.  You’ll learn a lot about birds!

Postscript:  To see regular updates on what’s going on, check out the Vaseux Lake Bird Observatory website.

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