(less than 5 ha) from a few centimeters to 

 about one-half meter deep. They are 

 primarily herbivores, and good stands of 

 submerged grasses improve the quality of 

 the habitat. Ruppia maritima 



(widgeongrass) is the preferred food in 

 brackish ponds; Potamogeton pu s i 1 1 u s 

 (pondweed), Najas quadalupensis (naiad), 

 and Lemna spp. (duckweed) in freshwater 

 ponds. In brackish marshes Scirpus olneyi 

 (three-cornered grass), Bacopa monnieri 

 (water hyssop), and Eleochari s parvul a 

 (dwarf spikerush) are desirable foods. 

 Echinochloa walteri (wild millet), 

 fascicularis (sprangletop) , 



Leptochloa 

 Panicum sp 



, (fal 1 panicum) , and other 



annuals that produce abundant seeds are 

 good fresh marsh foods. The succulent 

 roots and tubers of species such as S^. 

 olneyi and Sagittaria platyphyl 1 a (delta 

 duck potato) are also favorite foods, 

 especially for geese. 



It is easy to see why fresh and 

 brackish marshes in the delta support so 

 many dabbling ducks. There are thousands 

 of small marsh ponds in all salinity zones 

 (Table 25), and the dominant plant species 

 in brackish to fresh ponds are considered 

 excellent duck food. Ponds 0.4 - 4 ha in 

 size have the best growth of submerged 

 grasses, possibly because wind-induced 

 turbulence is low in these small ponds. 

 Saline ponds are poorly vegetated (Table 

 26). Because of this and because the 

 plant species of this marsh zone make poor 



duck foods, the saline marshes are rela- 

 tively poor puddle duck habitat. 



Much attention has been focused on 

 the habitat conditions of arctic and 

 subarctic nesting grounds and their in- 

 fluence on the growth of duck populations. 

 Much less attention has been directed 

 toward the importance of wintering grounds 

 for reproductive success. A recent study 

 by Heitneyer and Fredrickson (1931), 

 however, emphasized this important aspect 

 of wintering grounds. They found a direct 

 linear relationshio between winter precip- 

 itation in the Mississippi delta riparian 

 hardwoods (an index of pond number and 

 hence habitat quality) and reproductive 

 success of mallards as measured by the 

 ratio of young to mature mallards. In 

 their multiple regression models both the 

 wintering ground quality index and the 

 numbers of ponds in the nesting area in 

 May and June were significantly positively 

 related to mallard age ratios. The study 

 implies that the quality of deltaic plain 

 marshes may also be important in duck 

 reproductive success. 



In contrast to puddle ducks, diving 

 ducks usually prefer deep water. They are 

 carnivores, diving to depths of over 10 

 meters in some cases to obtain their food. 

 Because of this preference they are usual- 

 ly found in open water and along the 

 nearshore zone. However, they are also 

 known to feed on the vegetation of shallow 



Table 25. Density of ponds and lakes of various size classes in 

 marsh zones along the Louisiana coast in August, 1968 (Chabreck 

 1971a). 



Pond and lake size class 



Marsh zone 



Salt 



Brackish Intermediate Fresh 



(acres) 



0.01 

 0.01-0.10 

 0.10-1.0 

 1.0-10 

 10-80 

 80-640 

 640-3,200 

 3,200-16,000 

 16,000-32,000 

 64,000 



(number per 100,000 acres) 



27,700.2 118,841.7 55,952.2 59,181.2 



16,749.0 62,162.2 45,024.0 47,637.4 



4,702.6 14,139.0 10,432.8 9,796.8 



700.0 



1,376.1 



759.1 1,070.5 



69 



