191-1] Qrinnell : Mammals and Birds of tin Colorado "Valley 117 



we did not witness such a catastrophe in the few minutes consumed 

 in floating by such places, many trees were on the verge of toppling; 

 the annual mortality from this local condition alone must be large. 

 Evidently the herons have failed to grasp the situation, and cling 

 to old habits, even though these entail considerable annual loss. The 

 area in which this destruction occurs is so small compared with the 

 entire range of the pallid blue heron, and the proportion of the local 

 birds which suffer disaster to their nests is also so small, that the 

 contingency in question has not effected any change in the habits of 

 the birds. 



Ten miles below Ehrenberg, on the California bank of the river, 

 was a colony which was visited on March 30. There were approx- 

 imately thirty nests, one to three per tree, which were unquestionably 

 occupied, besides others in various stages of construction or dilapida- 

 tion. The place had evidently been inhabited for at least one year 

 previously. One nest, situated forty feet above the ground in a cotton- 

 wood, contained three fresh eggs. The time of laying in this region 

 is thus indicated. 



Inspection of the nests of a colony on the Arizona side four miles 

 above Laguna, April 25, showed young perhaps one-third grown. They 

 could be seen from the ground clambering about the nest platforms. 

 Another colony, on the Arizona shore five miles northeast of Yuma, 

 passed May 2, showed young appearing conspicuously above the nest 

 rims, and their hoarse calls were to be heard to a considerable distance. 



Along the whole course of the river, save in the rock-walled box 

 canons, blue herons were almost continually in sight. Their chief for- 

 aging grounds were the mud bars traversed by shallow diversions of 

 the river. The habit of the river of having frequent periods of falling- 

 water, even when, as in the spring, the aggregate tendency is to rise, 

 results in the stranding of many fishes in the shallow overflow's as 

 the water seeps away or evaporates. This frequently recurring supply 

 of fish appears to be the chief source of food of all the species of 

 herons occurring in the region. The stomach of one blue heron con- 

 tained a semi-liquid mass of fish, identifiable from the large-sized 

 scales as carp ; another contained a large catfish. One stomach was 

 empty save for a single grasshopper leg; this gives a clue as to an 

 emergency diet, when the river is rising rapidly. It may be remarked 

 that the opacity of the moving water of the main stream is so complete 

 as effectually to prevent fishing here by piscivorous birds in the usual 

 manner. 



