Diet and Nutrition of Northern Pintails Wintering Along the Southern Coast of Texas

Abstract

Most northern pintails (Anas acuta; hereafter pintails) in the Central Flyway winter within the Gulf Coast and adjacent rice prairies of Texas, USA. However, wintering habitat has declined in this region as a result of decreased rice production and changes in land use. Because pintails exhibit high winter site fidelity, more pintails are likely to rely on adjacent coastal habitats during winter as freshwater habitats along the Texas coast disappear. However, few studies have investigated the diet of pintails in estuarine environments. We estimated the composition and quality of the diet of pintails wintering along the lower Texas coast, and we compared our estimates to those for pintails in freshwater habitats. Proximate composition and true metabolizable energy (TME) were estimated for 4 foods in the diet of 253 pintails collected along the lower Texas coast during October‐February 1997–1998 and 1998–1999. Shoalgrass (Halodule wrightii) rhizomes, wigeongrass (Ruppia maritima) seeds, dwarf surf clams (Mulinia lateralis), marine gastropods, and Gammarus amphipods comprised most of the pintail diet. Pintail diets in coastal habitats contained smaller proportions of protein and fat and a large proportion of ash compared to diets of pintails from freshwater habitats. As a result, the diet of pintails wintering along the lower Texas coast provided about half the TME of diets of pintails wintering in freshwater habitats. Because pintails rely on endogenous reserves acquired during winter and spring migration to support egg production, pintails wintering in Texas may experience greater reductions in recruitment and survival if displaced to coastal habitats.

Diets of Lesser Scaup during Spring Migration throughout the Upper-Midwest are Consistent with the Spring Condition Hypothesis

“…Amphipods have higher gross energy, protein, and lipid content than do bivalves and gastropods (Jorde and Owen 1988;Ballard et al 2004); amphipods also have higher true metabolizable energy than do bivalves and gastropods, when consumed by ducks (Sugden 1978;Jorde and Owen 1988;Ballard et al 2004). Furthermore, lipid content of amphipods is highest in late fall and early spring (Mathias et al 1982;Arts et al 1995;Meier et al 2000), whereas lipid content of bivalves and insects generally peak in mid to late summer (Davis and Wilson 1983;Meier et al 2000).…”

“…Furthermore, lipid content of amphipods is highest in late fall and early spring (Mathias et al 1982;Arts et al 1995;Meier et al 2000), whereas lipid content of bivalves and insects generally peak in mid to late summer (Davis and Wilson 1983;Meier et al 2000). Finally, scaup are more efficient at assimilating energy from amphipods than other ducks (see Sugden 1978; Jorde and Owen 1988;Ballard et al 2004), suggesting that scaup are highly adapted for foraging on amphipods. Accordingly, the apparent decreases in the percentage of amphipods in scaup diets during spring migration in Iowa and Minnesota reflects a decrease in forage quality for scaup stopping over in those areas (Anteau and Afton 2006).…”

“…Recent studies have reported very high seed consumption by scaup in the absence of abundant amphipod forage (Smith 2007;Strand et al 2008). Seeds may be consumed by scaup, in the absence of amphipods, to accumulate lipid reserves because seeds can be a good source of carbohydrates and lipids Ballard et al 2004). …”

Does choice of estimators influence conclusions from true metabolizable energy feeding trials?

“…The TME is estimated in feeding trials by correcting the EE of fed birds for EL, which is measured in control birds from which food is withheld. Sibbald (1976) described a TME bioassay for studies of poultry nutrition that has also been used to quantify diet quality for several species of wild waterfowl (Hoffman and Bookhout 1985;Jorde and Owen 1988;Kaminski and Essig 1992;Petrie et al 1997Petrie et al , 1998Sherfy et al 2001;Kaminski et al 2003;Ballard et al 2004). The bioassay employs separate experimental and control birds that are starved for 24 h to clear digestive tracts, after which experimental birds are force-fed a known amount of the test diet, and control birds remain without food.…”

A model for the future: Ecosystem services provided by the aquaculture activities of Veta la Palma, Southern Spain

“…Where E = Energy density of diet items is estimated using the relationship between percentage dry weight of sampled organisms and energy density for invertebrates ( i ) (James, et al, 2012) and for fish ( f ) (Hartman and Brandt, 1995) and literature values for macrophytes ( m ) (Ballard, et al, 2004), D = number of bird days month -1 (mean monthly counts 2004-2011 × 30 days), P = proportion of diet type ( i , f , m ) and Q = assimilation efficiency (80%). Diet type proportions were extracted from the (BirdLife_International, 2014) data base.…”