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USGS2002

True metabolizable energy of moist-soil seeds

Habitat objectives for migrating and wintering waterfowl are often established by converting population energy demands into an equivalent measure of foraging habitat. In some areas, seeds produced from moist-soil plants provide a significant proportion of the energy available to waterfowl. To accurately establish habitat objectives for migrating and wintering waterfowl, managers must estimate seed production from moist-soil plants and have information on metabolizable energy (ME) of moist-soil seeds. Although methods for estimating seed production have been developed, ME has been determined for few natural seeds. We determined true metabolizable energy (TME) of 10 moist-soil seeds commonly consumed by wintering and migrating ducks. TME estimates were similar (P>0.05) for hairy crabgrass (Digitaria sanguinalis; 3.09 kcal/g), little hairy crabgrass (D. ischaemum; 3.10 kcal/g), pigweed (Amaranthus spp.; 2.97 kcal/g), yellow foxtail (Setaria lutescens; 2.88 kcal/g), fall panicum (Panicum dichotomiflorum; 2.75 kcal/g), curly dock (Rumex crispus; 2.68 kcal/g), and wild millet (Echinochloa crusgalli; 2.61 kcal/g), but less (P<0.05) for beakrush (Rynchospora corniculata; 1.86 kcal/g), paspalum (Paspalum laeve; 1.57 kcal/g), and nodding or curltop ladysthumb smartweed (Polygonum lapathifolium; 1.52 kcal/g). TME values determined for moist-soil seeds in this study will allow managers to accurately estimate carrying capacity of waterfowl habitats.

Wildlife Society Bulletin↗

USGS1999

Precocious breeding by yearling Giant Canada Geese

Many species of waterfowl are capable of breeding as yearlings. In the subfamily Anserinae, however, reproduction normally does not commence until individuals reach two to four years of age (Rohwer 1992). Most published accounts indicate that Canada Geese ( Branta canadensis ) conform to the pattern typically found in other geese, deferring reproduction as yearlings and initiating breeding when birds are two years of age or older (Hanson 1962, Brakhage 1965, Bellrose 1980, Moser and Rusch 1989). The few documented exceptions (Brakhage 1965, Cooper 1978, MacInnes and Dunn 1988) suggest that the likelihood of a successful breeding attempt is higher for yearling males than females and that when early breeding occurs, one member of the pair is often at least two years old. Only two records of nesting attempts by yearling female Canada Geese have been published (Hall and McGilvrey 1971, Mickelson, 1975). In each case, the female produced some fertile eggs but deserted the nest before the eggs hatched. The observations noted above demonstrate that reproduction by yearling Canada Geese is physiolog ically possible for both sexes, but they also raise a number of interesting questions regarding why most individuals defer breeding during their first year. Energetic or nutritional constraints, and the inability of yearlings to secure and successfully defend a territory, are likely physiological (Elder 1946) and social (Brakhage 1965) impediments to early breeding From an evolutionary perspective, reduced reproductive success of yearlings relative to adults, and increased mortality associated with early breeding. also may contribute to deferred sexual maturity in waterfowl (Rohwer 1992).

The Auk↗