114 



The Canadian Field-Naturaust 



[Vol. XXXVI 



past three years; but earlier sporadic observations? 

 are in accord with them, the whole going to show 

 that the average depth to which the snow accumu- 

 lates on the levels above 3,000 feet can be obtained 

 directly from the average lower limit of this lichen 

 on the tree-trunks. Professor Church has shown 

 that snow densities in the same geographical district 

 at the end of the season of accumulation vary only 

 about 10 per cent. A few determinations of 

 density, or even an assimied density obtained from 

 a nearby district of the same general altitude, taken 

 in conjunction with the average limit of the lichen 

 referred to, may not improbably afford sound in- 

 formation sufficient for the preliminary survey of 

 watersheds. 



Usnea barbata is a typical lichen, sub-alpine in 

 character, foliaceous, with a length of about 9 

 inches, and a light green colour, which blackens with 

 age. It has a fruticose thallus. It fruits in the 

 fall, the fruit consisting of small circular discs about 

 a millimeter in diameter. It entirely covers the 

 trunks and branches of the host trees under favour- 

 able conditions. It ranges in altitude from 2,000 

 to 6,000 feet in the mountain district north of 

 Vancouver. It is partial to open slopes, and does 

 not favour thick stands of alpine timber. With the 

 exception of the yellow cedar (Chamaecyparis 

 noofkatensis) it attaches itself to all alpine trees in 

 this district, including the western white pine (Pinus 

 monticola), alpine fir {Abies lasiocarpa), white bark 

 pine {Pinus albicaulis), and mountain hemlock 

 {Tsuga Mertensiana). 



The indications of snow depth from the height at 

 which the lichen growth begins are unreliable below 

 3,000 feet on southern, and 2,500 feet on northern 

 exposures. Some care and experience are necessary 

 in obtaining a trustworthy average height at any 

 point, as shade, exposure, age, and condition of 

 trees give rise to differences which must be dis- 

 counted in certain cases. But this presents no 

 difficulty to an observer with some experience. 



Between May 2nd and May 10th, 1921, which 

 was the period of greatest snow depth on the 

 northern alpine slopes here, measurements were 

 made in different places between the 3,000 and 4,000 

 foot contours. Usnea barbata was found to begin 

 3 feet on an average above the surface of the snow 

 layer. The difference of 3 feet remained constant 

 in dense, thin, and open forest, on grades of varying 

 steepness, and on level rock-benches. The snow 

 depth at 3,000 feet, for example, averaged 8 feet, 

 and the lichen grew to within eleven feet of the 

 ground; at 3,500 feet the snow depth was 15| feet, 

 and the lichen grew on the trunks to 18^ feet from 

 the ground, while at 4,000 feet, with a snow depth 

 of 21 5 feet, the lichen grew down to 24? feet. This 

 difference of 3 feet between the snow depth and the 

 lichen limit was not departed from at any of the 

 200 or more trees where the measurements were 

 taken in the first week of May, although the trees 

 presented great variations in species, size, aspect, 

 and altitude. 



It is not possible as yet to decide whether the 

 limit of the lichen marks the ordinary maximimi 

 depth of snow, the average depth, or a constant 

 difference. The depth of snow on the northern 

 mountains in May, 1921, was about 3 feet less than 

 what is probably the average depth taken over a 

 long series of years, though this greater depth has 

 only been reached once in the last nine years. The 

 very slow growth of the lichen might, however, 

 make it independent of even such slow seasonal 

 changes as this, in which case the beginning of 

 lichen growth may correspond to the average snow 

 depth. But the point seems to be of sufficient 

 practical importance to justify an appeal at this 

 stage to other observers, especially in view of the 

 cosmopolitan character of this lichen. It might 

 also be worth while to direct attention to other 

 species of lichens whose distribution is more limited. 



AN INVASION OF COOTS 



By J. A. MuNRO. 



LATE October usually sees a gathering of 

 Coots at various points on Okanagan Lake. 

 These bands, sometimes numbering a thou- 

 sand or more, remain until spring, feeding over the 

 beds of Polamogetons unless a particularly severe 

 cold snap causes ice to form over their feeding 

 grounds when they move .south until open feeding 

 grounds are reached. Although rarely shot at or 

 disturbed they are usually on the alert and will not 



allow a close approach. Until this winter I had 

 noticed fearless coots on only one occasion. This 

 was at Summerland in the latter part of March, 

 1918, when a flock of forty were observed feeding 

 over a wide mud flat on the lake shore close to the 

 main street of the village where automobiles and 

 wagons were constantly passing. These birds did 

 not even raise their heads when a vehicle or pedes- 

 trian passed within a few yards. 



