' CATCH-EM- ALT VE-0.' 333 



tint, which can be raised or depressed at will. 

 Prior to my finding it in this remote region, it was 

 described as being entirely confined to Mexico. 



About a week had passed away ; the bridge 

 was completed, during which time the female 

 birds had arrived ; and, save a stray one now 

 and then, not a single individual of that numerous 

 host that had gathered round the Ribes was to 

 be seen. They cared nothing for the gun, and 

 would even clash at a dead companion as it lay 

 on the grass ; so I did not drive them away, but 

 left them to scatter of their own free will. 



My next camping-place was on the western 

 slope of the Rocky Mountains, near a lake, by 

 the margin of which grew some cotton wood trees 

 (Salix scouleriana\ together with the alder (Alnus 

 oreqona), and the sweet or black birch (Betula 

 leuta). My attention was called to the latter 

 tree by observing numbers of wasps, bees, and 

 hornets swarming round its trunk. The secret 

 was soon disclosed: a sweet gummy sap was 

 exuding plentifully from splits in the bark, on 

 which hosts of insects, large and small, were re- 

 galing themselves. As the sap ran down over 

 the bark, it became very sticky, and numbers of 

 small winged insects, pitching on it, were trapped 

 in a natural ' catch-'em-alive-O.' 



