FOOD HABITS OF SHOAL-WATER DUCKS. 6 



plants, paying less attention to the seeds, while the mallard feeds 

 indiscriminately on both or even shows some preference for the 

 seeds. In fact, in respect to the quantity of foliage taken, the gadwall 

 and the baldpate are different from all other ducks thus far examined 

 by the Biological Survey. They are also more purely vegetarian, 

 their diet including a smaller percentage of animal matter than that 

 of any of the other ducks. 



For a determination of the food habits of the gadwall 417 stomachs 3 

 were available. These were from 19 States and Canada, and their 

 collection extended over a period of 31 years. Only 24 were taken 

 during the five months from April to August and their contents 

 were not included in computing the average percentages, so that 

 the results thus obtained apply only to the fall and winter months. 



Considerably more animal food is taken in summer than in winter, 

 owing, of course, to the fact that more is available at that time of' 

 year. The percentage of animal food for the summer months is 

 higher also because there are included in the averages analyses of 

 numerous stomach contents of ducklings, which feed to a great 

 extent upon insects. All of the 11 stomachs collected during the 

 month of July (9 from North Dakota and 2 from Utah) were of 

 young ducklings. A computation of the average contents of this 

 series produced the following results: Water bugs, 56.18 per cent; 

 beetles, 7.09; flies and their larvae, 2; nymphs of dragonflies and 

 damselflies, 0.27; other insects, 2; total animal food, 67.54 per cent. 

 Pondweeds, 12.55 per cent; grasses, 5.09; sedges, 2; water milfoils, 

 0.55; smartweeds, 0.09; miscellaneous, 12.18; total vegetable food, 

 32.46 per cent. 



Of the remaining 13 stomachs collected in summer, all but two 

 were from mature birds. Their contents averaged 11.17 per cent 

 animal food and 88.83 per cent vegetable; 5.28 per cent, or nearly 

 half the animal food, consisted of snails. Thus it will be seen that, 

 so far as can be judged from the contents of such a limited number 

 of stomachs, the summer food of the adult birds does not differ 

 greatly from their winter food. 



A rather large proportion of the total number of stomachs (131) 

 was from birds taken in Louisiana. These furnished the bulk of the 

 collections for November, February, and March, but averaged much 

 the same as those from the other States, the principal items con- 

 sisting of sedges, pondweeds, Sagittaria tubers, grasses, some culti- 

 vated rice, and mollusks. Arkansas contributed 57 stomachs; 

 Utah, 53; North Carolina, 30; North Dakota, 22; and Florida, 20; 

 the remainder being scattered. 



s Seventy-six of these were examined by W. L. McAtee. 



