Blind Lake's Black Terns

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Blind Lake's Black Terns

By Cameron D. Eckert


Black Tern

Just 25 km east of Watson Lake lies Blind Lake, accessible only by air or an overland hike from the Hyland River. In June, Pam Sinclair, Helmut Grönberg and I explored a variety of locations across southeast Yukon in order to better define ranges of forest bird species in the region. We chose Blind Lake as one of our survey locations simply because it was east of Watson Lake, west of Toobally Lakes and happened to catch our eye on the topographical map. Blind Lake is a shallow land-locked lake and prior to our visit there were no previous reports on the bird life there.

click for detail

We had arranged to use a boat which belonged to a small fish farm on the lake and had been advised to camp close to an interesting marsh at the south end of the lake. On June 16, Helmut and I flew from Toobally Lakes to Blind Lake and were welcomed at the fish farm by Geoff Morrison. While unloading the plane and getting the boat ready Geoff told us about the bird species he typically observes around the lake; Belted Kingfisher, Pacific Loons, Dark-eyed Juncos, scoters, and Black Terns. There are times when the mere mention of a particular bird species can stop a conversation in mid-stream and this was one of those times. Black Terns?

In the Yukon, Black Terns are known only as an extremely rare vagrant. The first documented sighting was of two birds seen on June 3, 1978 at Swan Lake, 20 km northeast of Whitehorse. Since then there have been only two other documented Black Tern sightings in the Yukon.

In response to our sudden excitement over his mention of Black Terns, Geoff explained that up to six Black Terns could be seen over the marsh at the south end of the lake. Perhaps anticipating our thought process he added that Common Nighthawks could also be seen foraging with the terns over the marsh. Within half an hour we were boating to our camp at the south end of the lake. Soon we could make out a beige mass of marsh vegetation at the far end of the lake, and then, becoming clearer as we approached more closely, we could make out small dark shapes dancing over the marsh. Black Terns.

The Black Terns were striking in appearance with a jet black head and body contrasting sharply with a pure white undertail; the tail and back were ashy grey, and the similarly grey wings were neatly trimmed with a thin white line along the leading edge of the inner wing. The legs and bill were reddish-black and the black eye seemed lost in the jet black face until caught by a glint of sunlight.

We were immediately filled with questions about these birds; How many? Are they breeding? What habitats are they using? Over the next three days we carefully explored the marsh and tried to answer these questions. The marsh itself was highly aquatic and consisted of an expansive bed of relatively sparse bulrushes in 1 to 2 meters of water. The marsh had not yet greened up and all the vegetation above the water?s surface was dead. Peering into water we could see this year?s green plants growing up from the bottom of the lake towards the surface. While I have explored many marshes and wetlands throughout the Yukon, I had never before encountered one like this.

On June 17 we paddled our boat into a small opening in the middle of the marsh and sat quietly to observe the terns. We were stunned to find that the number of terns was much higher than was previously known. Our high count was of 44 terns over the marsh. Very quickly we spotted terns sitting on nests throughout the marsh. Carefully scanning the marsh we counted 25 nests. This was not just a case of a few vagrant birds at the edge of their range, this was a major breeding colony.

Black Tern nest

The marsh offered nothing in the way of solid ground and the terns had built their nests on loose floating mats of dead bulrushes. These floating nests seemed to have the advantage of being able to rise and fall with waves rather than being swamped by them. The nests consisted of a shallow cup made of dead bulrushes and contained from 3 to 4 olive coloured eggs mottled with brown. On June 18 we found five more Black Terns and a nest at another smaller but similar marsh at the northeast side of the lake. We only remained at the colony long enough to document the nesting activity and try and determine the size of colony. Like Arctic Terns, the Black Terns seemed quite sensitive to disturbance around their nests.

We also observed a few Arctic Terns on Blind Lake but they did not appear to be breeding on the lake and may have been flying over from the nearby Hyland River. The Black Terns did not feed like Arctic Terns which typically plunge head first into the water in pursuit of small fish. Rather, the Black Terns hawked for insects over the marsh and would occasionally drop in a low hover over the lake and pick insects off the water?s surface. We never tired of watching the lively activities of this graceful tern species.

The breeding colony of Black Terns at Blind Lake establishes a significant northwest extension of this species? known breeding range in North America. The nearest known Black Tern colonies are in the vicinity of Fort Nelson, BC, about 300 km to the southeast (Campbell et.al. 1990). The Black Tern is particularly sensitive to environmental degradation, and populations have declined in many areas in North America. The marshes at Blind Lake provide critical breeding habitat for the Yukon?s only known Black Terns and this precious habitat should be protected.

References

Campbell, R.W., Dawe, N.K., McTaggart-Cowan, I., Cooper, J.M., Kaiser, G.W., and C.E. McNall. 1990. The Birds of British Columbia, Volume 2, Nonpasserines: Diurnal birds of prey through woodpeckers. Royal British Columbia Museum, Victoria, B.C., Canada.


PAJA

This article originally appeared in the Yukon Warbler. Reference as:

Eckert, C.D. 1996. Blind Lake's Black Terns. Yukon Warbler 4(2):10-11.


For more information on other Yukon birding destinations contact:

    Yukon Bird Club
    Box 31054
    Whitehorse, Yukon, Canada, Y1A 5P7

    Email: ybc@yknet.yk.ca

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