Nutrient Reserves And Diet Of Breeding Mallards And Blue-winged Teal

Mallards (Anas platyrhynchos; n = 339) and Blue-winged Teal (A. discors; n = 213; hereafter teal) were collected from western (1986) and eastern (1987) Saskatchewan grassland and parkland habitats during egg formation to examine body composition, diets and digestive organ size with respect to hypotheses concerning habitat (this study) and the use of body fat (Drobney 1980; Rohwer 1986a; Ankney and Afton 1988). I predicted that ducks breeding in grassland habitats would rely upon more stored body nutrients, whereas parkland ducks would rely more upon dietary nutrients to form eggs. Body composition including fat, protein and mineral reserves and digestive organ sizes and diets (used to index food consumption) did not differ due to habitat in Mallards or teal. Female Mallards breeding at the western grassland site used 60% less body fat during clutch formation compared with females from other sites. Two potential explanations for this are: (A) food resources at this site were annually most predictable so less fat is needed as insurance against bad years or (B) females breeding at this site were unable to build up sufficient fat reserves during spring migration because they were subordinates and were excluded from food resources.;Body protein of female Mallards and teal did not decline as predicted by the protein-limitation hypothesis (Drobney 1980). Body fat declined seasonally among western female Mallards, eastern male Mallards and male teal just initiating RFG, and remained constant among all other samples. These data do not support Rohwer\u27s (1986a) migration-uncertainty hypothesis because arrival in Mallards and teal is likely not synchronous. Agricultural grains (hereafter grains) and seeds were important components in the diet of breeding mallards whereas aquatic invertebrates, especially gastropods and insects, dominated the diet of teal. I argue that because grains were recently introduced, and energy extraction from seeds is likely inefficient, the diet of Mallards and teal support the lipid-limitation hypothesis (Ankney and Afton 1988), that reliance on stored body fat supplements a lipid poor diet.;Body fat acquired prior to arrival, contributed 41% of clutch fat requirements in female teal and 60%-150% in female Mallards. Male Mallards used stored body fat during the egg formation period whereas male teal used fat only prior to this period. Female Mallards from three of four collection sites used stored minerals to supplement dietary calcium intake, ca. 11-13 grams for a 10 egg clutch, enough for about 1 egg, whereas female teal relied upon dietary sources of calcium