BRANTA — Jeb A. Barzen
Patterns of Nutrient Acquisition in Canvasbacks during Spring Migration
Institution: University of North Dakota, USA
Supervisors: RD Crawford
Details: MSc 1989 (Completed)
Address: The International Crane Foundation, E-11376 Shady Lane Road, Baraboo, Wisconsin 53913-0447 USA (Nov 2005) Email
Subject Keywords: Spring, Migration, Nutrient Reserves, Waterfowl, Energetics
Species Keywords: Canvasback Aythya valisineria
Abstract
Wetlands used by nesting birds have traditionally been considered the only habitats able to influence natality rates. I examined the potential for body reserves (fat, protein, and calcium) acquired on spring staging areas to be used for reproduction. My objectives were to: 1) describe changes in body reserves during spring, 2) examine alternative uses for body reserves in spring migrants, and 3) identify where reserves are acquired.
During spring of 1984 and 1985 I collected 151 canvasbacks (Aythya valisineria) at 3 staging areas: Navigation Pool 19 of the Mississippi River; Navigation Pools 7, 8, and 9 of the Mississippi River; and in the prairie pothole region of North Dakota. An additional 28 breeding birds were collected in the aspen parklands of Manitoba. Pair status was determined prior to collection of each bird and all birds were aged. The influence of body size on body reserve levels was corrected where needed.
Median collection dates occurred just prior to peak canvasback use of each staging area. Masses of ovaries, testes, oviducts, and the largest follicle diameter increased as spring migration phenology advanced. In late migration, ovary and oviduct masses of paired females were greater than in unpaired females. Testes masses of paired and unpaired males did not differ.
Among sites, patterns of change in body reserves did not parallel patterns of change in reproductive tissue. Calcium mass of males and females did not differ among sites regardless of pair status. Protein reserves of paired, breeding females were larger than those of unpaired migrant females. Paired males in North Dakota had higher protein reserves than did paired males at Pools 7, 8, and 9 or Erickson. Protein reserves of unpaired males did not differ among various staging areas. Fat masses of males and females varied greatly among sites during migration but pair status had little influence on them.
Paired females arrived on breeding areas fat. Males had more fat and protein than did females during migration but the opposite was true for Erickson females. Flight ranges, estimated from measured levels of stored fat, could not allow canvasbacks at any staging area to fly non-stop to breeding areas and arrive fat.
Though fat and protein reserves are acquired during spring, wetland habitats located close to breeding areas would more likely influence a reproductive effort than would habitats located farther away. Other factors such as the energetic costs of migration and fasting through inclement weather may require birds to stop frequently during migration in order to re-acquire lost reserves. Protection of key staging wetlands scattered along the entire migration route may therefore directly or indirectly influence natality rates of canvasbacks.