Jeb A. Barzen

Date of Award

12-1989

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

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.

EXxring spring of 1984 and 198? I collected 151 canvasbacks fAvthva 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 umpired 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 di' :er 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 jaired 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 bur pair status had little influence on them.

Paired females airived on breeding areas fat. Males had. more fat and protein than did fen ales during migration but the opposite was true for breeding 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 prctein reserves are acquired during spring, wetland habitats located closa to breeding areas would more .ikely 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.

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