44 On the trail of vanishing birds 



tance. It seemed obvious that these tidal shores were the main 

 source of food for the cranes. However, the narrow fringe of salt 

 flats that lie between the bay shore and the three-foot contour is 

 the habitat in which the birds spend most of their time. These 

 flats are made up of a series of ponds, some of which are elongated 

 in character (they are actually relics of depressions between ancient 

 beach ridges washed out by the changing Pleistocene shorelines), 

 while others are more or less round in shape and isolated. The 

 elongated type are connected with one another by narrow estuaries 

 and with the tidal bays, so that, with a certain wind direction, the 

 tide flows from one end of the pond system to the other, bringing 

 with it the fish and the crabs and other arthropods that are the 

 principle food of the whooping crane. On the other hand, with 

 a prolonged wind in the opposite direction the entire pond system 

 can go dry, forcing the birds to desert it for the shoreline of the 

 bays, where marine life is less concentrated and less easy to secure. 



The isolated, smaller ponds are ephemeral in nature, mere de- 

 pressions or mudholes in the marsh. These depend on the high 

 tides of the autumn season for their quota of food animals. As the 

 winter advances the cranes empty them of this stock, and as the 

 water in the ponds slowly evaporates they become strongly odor- 

 iferous and yellow with algae. There are also large ponds that are 

 a part of the drainage or run-off system of the peninsula, with 

 fresh water pouring in at one end and salt tide at the other. They 

 too have their value to the cranes. 



It was a long and difficult job analyzing the relative merits and 

 deficiencies of these ponds and understanding what makes them 

 tick. Most fortunately for me, preliminary work had already been 

 started by two valued friends, Dr. Gordon Gunter, then head of 

 the Institute of Marine Science of the University of Texas, and 

 Dr. Joel W. Hedgpeth, who was connected with the same institu- 

 tion, as well as with the Department of Zoology of the University 

 of California. Among his many talents, Gordon is an expert on 

 the fishes of the Gulf of Mexico and on salinity problems, while 

 Joel is a specialist on marine invertebrates. Both contributed tire- 

 lessly of their knowledge, in the field and in the laboratory. 



Many cold days had to be faced, wading the ponds, probing in 



