Loxahatchee NWR with those of a coastal marsh area (Merritt Island NWR). Forty- 

 five gizzards were obtained at Loxahatchee and 40 at Merritt Island. Overall, 

 89.9% of the food (by volume) was plant matter and 10.0% was animal, but the 

 proportion of plant to animal food and species consumed varied from area to 

 area. At Loxahatchee, 97.3% of the food was vegetable in origin; the most im- 

 portant plants were Tracy's beakrush ( Rhynchospora traceyi - 32.8%), dotted 

 smartweed (29.4%), swamp smartweed ( Polygonum hydropiperoides - 18.2%), and saw- 

 grass ( Cladium jaimaicensis ) . At Merritt Island, only 81.1% of the diet was 

 vegetable. The most important plants here were spiny naiad ( Naias marina - 

 49.2%), shoalgrass ( Diplanthera wrightii - 10.6%), and muskgrass ( Chara sp. - 

 7.3%). Gastropods (6.5%), pelecypods (6.9%), and adult and larval insects 

 (4.6%) were the most important of the animal foods eaten at Merritt Island. 

 Scorched mussel ( Mytilus exustus - 2.9% of all food from both localities), com- 

 mon Atlantic marginella ( Prunum apicinum - 1.5%), and dragonfly nymphs (Libell- 

 ulinae - 1.2%) were the most important individual animal foods (Stieglitz 1972). 



Texas Singleton (1953) reported the contents of 25 stomachs that were col- 

 lected from spring through fall in a rice-marsh area in Chambers County. These 

 birds had consumed 41.8% (by volume) plant matter and 52.8% animal matter. In- 

 sects (32.9%), jungle rice ( Echinochloa colona - 23.8%), and fish (16.2%) were 

 the primary foods taken. The only other foods forming more than 3% of the diet 

 in this sample were gastropods (7.5%), cultivated rice ( Oryza sativa - 6.3%), 

 and wild millet ( Echinochloa crusgalli - 4.8%). Stomachs collected elsewhere 

 in Texas showed a wide variety of foods. Two stomachs collected in a saline 

 habitat in Aransas County were 90% full of widgeongrass ( Ruppia maritima) , and 

 four stomachs collected from February through April in Cameron County contained 

 50% insects, 35% minute snails, and 7% vegetation. The stomach of another bird 

 taken in Calhoun County was almost entirely full of squarestem spikerush ( Eleo- 

 charis quadrangulata ) . 



Feeding techniques and many other aspects of Mottled Duck feeding behavior 

 have not been studied. 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying Stieglitz and Wilson (1968) studied breeding Mottled Ducks for 

 two seasons at the Merritt Island NWR in Florida. In 1966, the first egg was 

 laid on 6 March, the last on 25 June. In 1967, the first egg was laid on 1 1 

 February and the last on 1 7 July. Peak nesting periods were 16-31 March in 1966 

 and 1—15 April in 1967. In both years nest initiation declined in May, and 

 nests found after late May may have been replacement efforts. In Texas, Ober— 

 holser (1974) reported egg dates from 18 March to 21 July; Singleton (1953) 

 stated that nesting occasionally occurred as early as February, but usually be- 

 gan in March, with a peak of nesting in April. 



Mean Clutch Size In their Merritt Island (Florida) study, Stieglitz and 

 Wilson (1968) had data for 78 complete clutches. Clutch size ranged from 5 to 

 13 eggs, with a mean of 9.4; the most frequent clutch size was 10 (22 nests). 

 Clutch size decreased as the nesting season progressed. In a study near Lake 

 Okeechobee, Florida, Beckwith and Hosford (1957) found 8 eggs to be the largest 

 and most frequent number found (4 of 5 nests). Singleton (1953) reported that 



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