FIVE IMPORTANT WILD-DUCK FOODS. 15 



nearly half of thL> entire food of the 10 vegetarian species of ducks 

 occurring there at the time. This showing is much more significant 

 from the fact that sago pond weed (Potamogeton pectinatus) also was 

 abundant in the lake. The latter plant, in the writer's opinion, is the 

 best all-round duck food ^ in North America, yet at Lake Surprise it 

 furnished somewhat less than 29 per cent of the food of the ducks in 

 comparison with more than 48 per cent supplied by Nymphsea 

 mexicana. 



Thirty-seven canvasbacks collected at Lake Surprise had eaten 

 various parts of this plant to the extent of 71.6 per cent of their diet. 

 This is a second illustration of the unusual phenomenon of the canvas- 

 back's being attracted to shallow water by a highly prized food. 

 Six ring-necked ducks or blackjacks mads more than 91 per cent of 

 their food of this plant, and two southern black ducks (Anas ful- 

 vigula) 98 per cent. The parts eaten are the rootstocks, stolons, 

 tubers, and seeds. Mr. Charles W. Ward has sent us rootstocks 

 of NyTnpJisea mexicana from Avery Island, La., with the information 

 that this plant and wild celery ( Vallisneria spiralis) furnish the bulk 

 of the food of canvasbacks in that locality. 



DESCRIPTION OF PLANT. 



For the purposes of field identification the water lilies of the United 

 States may be divided primarily into two groups according to 

 the shape of the leaf. Two genera, the water shield {BraseniaY 

 and the American lotus, or water chinkapin (Nelumho) ,^ have entire 

 circular leaves with the leaf stalks attached at their centers. The 

 remaining two genera have more or less heart-shaped leaves or a 

 circular or oval leaf with a cleft or sinus from the edge to the point of 

 attachment of the leaf stalk. Of these two genera, one (Nuphar),^ 

 including the spatterdocks or toad lilies, has the top or more of the 

 ovary plainly visible when in flower, the other has the ovary practi- 

 cally hidden b}^ the very numerous stamens. To this last group 

 belongs Nymphsea m-exicana, and it is the only native species of the 

 genus that has yellow flowers. 



Both the leaves and flowers of this species may either float on the 

 surface of the water or stand a few inches above it. The leaves are 

 green above with brown mottlings and vary from greenish to purplish 

 red below with small black markings. The edges of the cleft of the 

 leaf are either somewhat separated or overlapping (fig. 13). The 

 plant springs from an upright rootstock (fig. 14) Which bears some 

 resemblance to an unopened pine cons. The rootstocks vary in size 

 up to 2 inches in thickness and 12 inches in length. The smaller ones 

 (at least up to 1| inches in length, by three-fourths of an inch in 

 thickness) are swallowed by ducks. 



1 See Biological Survey Circular 81, pp. 11-17, for full account. 



2 The seeds, at least, of all these plants are eaten by many kinds of ducks. 



