NORTH AMERICAN MARSH BIRDS 125 



Most of the sticks used in constructing the nest are of the sage bush. Apparently 

 these nests are very old and have been used for many years, a little bit being 

 added each year in the way of rebuilding and house cleaning. It seems quite 

 remarkable that the young do not injure themselves from the large coarse sticks 

 which form the inner nest, if the same could be called an inner nest. The de- 

 pression of the nests is very slight. The depression starts from the outer edge 

 of the nest and very gradually sinks into the center. 



General Remarks. — On first observation the nests of the great blue heron appear 

 very flimsy, especially the edges, which seem to be very much frayed out and 

 loose. One would think that the storms of a winter would entirely demolish 

 these nests, but on close observation it is found that they are most compactly 

 made, and it is quite evident that the same nests are used from year to year 

 with but very little rebuilding in the spring. One can very easily tell where 

 new sticks have been added, from the fact that they are not sun"! bleached, as 

 are the old sticks in the nest. From seeing the size of the new nests that have 

 been built this year and comparing them with the older nests, one would be very 

 safe in saying that these large old nests are the pioneer homes of these birds and 

 mark their first advent to Great Salt Lake, the date of which we shall omit. 



Eggs. — The eggs are similar to those of the other great bUie herons, 

 The measurements of 44 eggs average 60.1 by 41.9 milHmeters; the 

 eggs showing the four extremes measm-e 68 by 47.2, 63 by 47.7, 51.9 

 by 35.1, and 52.4 by 34.8 millimeters. 



Food. — Referring to the feeding habits of this heron in the lower 

 Colorado Valley, Doctor Grinnell (1914) writes: 



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

 herons were almost continually in sight. Their chief foraging 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 aggre- 

 gate tendency is to rise, results in the stranding of many fishes in the shallow 

 overflows 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 

 occuring in the region. The stomach of one blue heron contained a semiliquid 

 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. 



Behavior. — The tracts of curious, fluffy, buff-colored feathers found 

 on the breasts of herons have long been subjects of speculation as 

 to their function, A popular theory has been that the greasy pow- 

 der, with which these tracts are filled, produces a phosphorescent 

 light which serves to illuminate its surroundings when the heron is 

 fishing at night. Several observers claim to have seen such phos- 

 phorescent illumination in living birds, but it has never been defi- 

 nitely proven that these feather tracts have any luminous qualities. 

 Dr. Alexander Wetmore (1920) has made some interesting studies 

 of this subject in a young Treganza heron, which lead to an entirely 

 different conclusion. He writes: 

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