40 



NORTH AMERICAN FAUNA. 



[no. 27. 



The progress of the season at Fort Simpson from March to June, 

 1904, as indicated by the temperatures of successive weeks, is shown 

 in the following table: 



Temperatures of successive weeks, spring of t90Jf, at Fort Simpson, Mackenzie 



River. 



Fourth 



week." 



Average of daily maxima: 



March 



April 



May 



June 



Average of daily minima: 



March 



April 



May 



June 



30.7 

 57.9 

 53.2 

 70.4 



3.3 

 33.5 

 34.5 



48.6 



" The ' fourth week ' includes the last nine or ten days of the month. 



On March 19 a flock of white-winged crossbills, evidently migrants, 

 was seen. On March 28 the first hawk owl of the spring was ob- 

 served, and snow fleas (Achorutes) appeared. About the same time 

 several species of small birds, which had been seen rarely during 

 the winter, appeared in larger numbers. On March 30 the buds and 

 catkins on the willows and alders imparted a brown tinge to the 

 hillsides, where these shrubs were common. On the same date snow 

 buntings, which had been absent since the middle of December, reap- 

 peared. On April 2 many small grayish moths were seen in the 

 woods. On April 17 a mourning-cloak butterfly (Euvanessa) a was 

 seen. By April 18 the snow had nearly disappeared from the fields. 

 Mosquitoes (Culex annulatus) first appeared on April 20, and were 

 biting on April 24, but did not become troublesome until over a 

 month later. The sap of the white birches began to flow freely on 

 April 20. On April 23 a small space of open water was seen near 

 the mouth of the Liard. Frogs were first observed on April 28. 



On April 29 Liard River broke up. Its advancing flood first 

 opened a channel nearly straight across the Mackenzie, forcing the 

 ice with irresistible power up on the opposite bank in immense piles. 

 At the same time a mound 60 or 70 feet in height was formed at the 

 month of one of the channels of the Liard, several immense cracks 

 opened in the white expanse before the post, and the huge sheets 

 were soon broken up. The stupendous amount of force exerted by the 

 river upon the broad expanse of ice, 5 feet in thickness, as with a 

 grinding roar it folds and crushes the mighty sheets like cardboard, 

 reducing them to powder and forcing them aloft in great mounds, im- 



°A lisl of the butterflies of the region 1ms been published by Merritt Gary 

 (Proc. U. S. Xat. Mus., XXXI, pp. 425-457, 1906). 



