78 



NORTH AMERICAN FAUNA 67 



some of the seasonal variations in diet. However, seasonal fluctuation 

 in the abundance of aquatic animal life is apparently the basic 

 explanation. 



The crayfish was the principal food of the King Rail in the rice 

 area, constituting 23 percent (by volume) of the annual diet; it 

 formed 61 percent in spring; 22 percent in summer; 3 percent in fall; 

 and 7 percent in winter. Since crayfish were available the year round, 

 it appears that consumption of this crustacean was influenced as 

 much by the availability of other favored foods as by the abundance 

 of crayfish. Possible seasonal variations in the size, agility, and/or 

 palatability of the crayfish according to age may have been factors 

 bearing upon the extent of seasonal use by the King Rail. 



Another staple food available at all seasons was fish, which com- 

 posed 26 percent (by volume) of the diet in the fall when many fish 

 had become impounded in the shallow borrow pits of drained ricefields 

 and were easy prey for the foraging birds. 



Aquatic insects were important foods, especially certain beetles and 

 waterbugs which were available the year round. Predaceous diving 

 beetles (Dytiscidae) furnished 19 percent of the winter diet. 



Land beetles, chiefly ground beetles (Carabidae), scarabs 

 (Scarabaeidae), and snout beetles (Curculionidae) made up 6 per- 

 cent of the rail's annual food, while grasshoppers (Orthoptera) 

 constituted T percent. 



A wide variety of other insects were taken in small quantities. 

 During the summer and fall they formed 8 percent and 5 percent, 

 respectively, of the food. Among these insects were dragonfly (Odon- 

 ata) nymphs, back-swimmers (Notonectidae), horsefly (Tabanidae) 

 larvae, fall army worms, rice water weevils {Lissorhoptrus simplex) , 

 and rice stinkbugs {Solubea pugnax) . 



Frogs accounted for about 5 percent of the annual diet. 



The King Rail apparently is more of a vegetarian than its salt 

 marsh counterpart, the Clapper Rail. John Oney (1954, p. 23), in 

 studying fall foods of the Clapper Rail along the Georgia coast, 

 found that plant materials constituted only trace items of the Clapper 

 Rail's diet at that season. Martin, Zim, and Nelson (1951, p. 82) found 

 the volume of plant food in the Clapper Rail's diet to be 11 percent in 

 winter, 1 percent in spring, 0 percent in summer, and 3 percent in fall. 

 In the Arkansas area, vegetable matter in the diet of the King Rail 

 made up the following volumetric percentages during the 4 seasons : 

 42 percent in winter, 5 percent in spring, 10 percent in summer, and 

 26 percent in fall. 



Cultivated rice seed was taken in larger quantities than any other 

 plant food, forming 16 percent of the annual diet. Increased consump- 

 tion of rice seed during fall and winter was due in part to the 

 abundance of waste grain left in the stubble. Kalmbach (1937, p. 60), 



