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Body Weight and Composition Changes and Adaptations for Breeding in Wood Ducks

Ronald D. Drobney
The Condor
Vol. 84, No. 3 (Aug., 1982), pp. 300-305
DOI: 10.2307/1367372
Stable URL: http://www.jstor.org/stable/1367372
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Body Weight and Composition Changes and Adaptations for Breeding in Wood Ducks
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Abstract

The weight and carcass composition of Wood Ducks (Aix sponsa) collected in southeast Missouri were analyzed during fall and at specific stages of the reproductive cycle. Males lost 4% of their body weight between fall and spring. Decreases in the weights of digestive organs were primarily responsible for the change. The body weights of hens increased 14% between fall courtship (618 g) and the maximum attained during laying (706 g). Nearly all of the weight gain of females occurred on the breeding grounds and was the result of fat deposition and increases in the weights of the reproductive organs. Body weights of hens decreased 164 g during laying and incubation. Utilization of stored fat for egg production accounted for most of this weight loss. The lack of significant changes in the ash-free lean dry mass of the carcass as well as a change in food habits indicated that the protein requirements for the clutch are obtained by foraging for invertebrates during laying. Weight losses during incubation were small, indicating that hens are able to meet nearly all incubation energy requirements by foraging during inattentive periods. Female Wood Ducks satisfy their nutrient and energy requirements during the reproductive cycle by foraging and the use of endogenous reserves. Adaptations that maximize the use of stored lipids for egg production and facilitate the conservation of endogenous protein and the acquisition of dietary protein enable hens to produce and incubate large clutches of relatively large eggs without significant changes in body protein.

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