230 On the trail of vanishing birds 



others. Samples that we brought back with us indicate that the 

 water in the ponds is almost barren, containing virtually no plank- 

 ton, but mud samples were more interesting. Dr. James B. Lackey 

 of the University of Florida, who analyzed the mud for us, had 

 this comment to make: 



The protein content of the mud is far higher than I would 

 ever expect, and I would judge it to be due to bacteria, blue- 

 green algae and diatoms. It is certainly significant. I expected 

 nitrates and phosphorus to be low because of the paucity of 



organisms, especially green ones, in the water The high 



fat content also amazed me. We finally decided that organisms 

 living in this locality must store up quantities of fat to prevent 

 desiccation by freezing in winter. 



Which is highly interesting when you realize that this entire 

 country freezes solid in winter, the shallow ponds being completely 

 icebound. Yet not only the frogs, snails, and other pond fauna 

 survive, but several species of small fishes, including the brook 

 stickleback. 



In searching on the ground for the actual nest site of the Sass 

 River pair nearest our camp, we came out on the shores of a larg- 

 ish lake where these two birds were first observed on April 30, the 

 Discovery Lake of our maps. It is a much more open area than 

 most of the lakes and ponds of that region, and appeared especially 

 so because of the fact that the water level had dropped perceptibly. 

 There were flat grassy shores, extensive stands of Scirpus, and many 

 partly hidden coves and bays of a marshy character. We found 

 fairly fresh whooping-crane tracks, some of which were evidently 

 the smaller imprints of the young, but we saw no birds. After 

 our first meeting they made a point of keeping clear of us, al- 

 though we heard them, and what were probably other pairs, 

 calling now and then. No doubt on the breeding grounds they have 

 the same rigid territorial setup that we had observed on the 

 Texas marshes in winter. Discovery Lake may typify the best 

 possible nesting habitat for whooping cranes in that region, but 

 this assumption is based chiefly on its open and marshy ap- 



