‘ CATCH-EM-ALIVE-O.’ 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 Azbes was to 
be seen. They cared nothing for the gun, and 
would even dash 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 cottonwood trees 
(Salix scouleriana), together with the alder (Alnus 
oregona), 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.’ 
