30 



The Canadian Field-Naturalist 



[Vol. XXXVI 



weight. They rose in a body, crossed the lake 

 in a compact flock, and did not appear again. 



Apparently they leave their breeding ground at 

 Swan Lake after the young are fully fledged and 

 seek new feeding grounds. While I was driving 

 past the lake on July 23rd, 1915, a large flock of 

 moulting adults and juvenals accompanied by an 

 equal number of Redwings was seen in a row of 

 trees along the roadside. From there they flew 

 to an open grassy hillside, evidently hunting for 

 grasshoppers. It was with keen expectation, 

 therefore, that I looked forward to the following 

 summer when I could hope to find them at home 

 on their breeding ground. 



In the chorus of bird voices that greeted my 

 ears on reaching the marsh, the harsh, unmusical 

 mating song of the Yellow-head was the most 

 insistent. The males clung to the swaying tules 

 within a few yards of the shore and when disturbed 

 would fly to the top of the nearby willows, while 

 the females kept hidden in the tules for the most 

 part. Preceding the rasping song, there is a 

 plumage display that shows off the contrasting 

 black and yellow to the best advantage. In this 

 rather grotesque performance the shoulders are 

 elevated, the head lowered and the feathers puffed 

 out, greatly exaggerating the performer's size. 

 Then the unpleasant bray comes as if ground out 

 by main strength, and, at the conclusion, the bird 

 collapses into his sleek handsome self again. 



On this date, May 16th, nest-building had start- 

 ed, but no nests containing eggs were discovered. 

 On June 5th, a dozen nests containing from two 

 to four eggs and several others with nestlings were 

 found. The Yellow-heads nested in small groups 

 of three or four pairs each, often close to a pair 

 of Redwings, with whom they seemed to dwell on 

 neighbourly teims. The Yellow-heads' nests 



were slightly larger than those of the Redwings 

 and were invariably lined with flat pieces of tule 

 f bre, which always served to distinguish them, as 

 the Redwings used coarse grass for lining. They 

 were firmly woven in a clump of stiff brown tules 

 of the previous year's growth and generally 

 fa?,tened to the stoutest part of the stalks, one to 

 two feet above the surface of the water. The 

 eggs showpd a wide vaiiation in size, shape and 

 markings. 



No attempt was made at taking a census, but 

 it would be safe to place the breeding population 

 at thi ty pairs. Two years later, on June 22nd, 

 this was at least doubled. Nests with fresh eggs 

 and others with nestlings of various ages were found. 



Northwestern Redwing: Agelaius phoeniceus 

 caurinus. These are the commonest birds at 

 the lake and they raise two if not three broods 

 during the season. On May 15th were found 

 nests containing fresh eggs and others containing 

 young, from the naked stage to those almost ready 

 to fly. On June 8th conditions were much the 

 same and fresh eggs were noted as late as June 

 22nd. The nests are in no way different from 

 those of the type form and the eggs show the same 

 wide range of size and markings. 



Interior Tule Wren: Telmatodytes palustris 

 plesius. The globular loosely woven nests of 

 this species were a feature of every patch of 

 tules, and the tireless little architect was always 

 to be seen or heard. The occupied nests were 

 softly lined with buUrush-down, and the eggs 

 were piled one on top of another. The unlined 

 cock-nests outnumbered the occupied ones in the 

 proportion of six to one. Often three or four were 

 seen within a few yards, probably all built by 

 the same bird as an outlet for his superabundant 

 energy. 



THE MOUNTAIN BEAVER {Aplodontia riifa) 



By Kenneth Racey 



The following notes have been made during the 

 past three years and have now been combined in 

 this paper in the hope they may prove interesting 

 and assist in fuller knowledge regarding a curious 

 and little known animal, the mountain beaver, 

 sewellel, boomer or ground log, as it is variously 

 known. 



Large and increasing colonies of these creatures 

 are to be found within a comparatively short 

 distance of Vancouver, where they live in peace 



1921. 



*Read before The Vancouver Natural History Society. 



and quietness, seldom disturbed or indeed seen 

 by man, owing to their being nocturnal in habit, 

 coming out at dusk to feed and retiring again to 

 their burrows at daybreak. 



Resembling the muskrat at first sight, but 

 without the long bare tail, they are not easily 

 mistaken for any other animal. The fur resembles 

 more closely that of the true beaver {Castor fiber) 

 than that of the muskrat, {Ondatra zibethica). 

 As a matter of fact, the mountain beaver, although 



not closely related to any existing rodent, is 



ft- 



allied to the squirrel tribe. The ears are sma^/^ 



V^J 



