Estimating behavioral multipliers to American black duck and lesser scaup resting metabolic rate to better estimate daily energy expenditure and carrying capacity
Date
2020
Authors
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Publisher
University of Delaware
Abstract
Historic declines of American black duck (Anas rubripes, hereafter black duck) and lesser scaup (Aythya affinis) populations may be the result of multiple factors including resource availability on migration and wintering landscapes. Bioenergetics modeling is used to calculate the carrying capacity of a landscape by estimating energy demand and energy supply. Past estimates of resting metabolic rate (RMR) and behavioral specific multipliers to RMR, physiologic parameters required for calculating energetic demand, are limited and, in some cases, based upon dated past research. I used open-flow respirometry techniques to estimate RMR and behavioral specific multipliers to RMR for captive black ducks (n = 6) and lesser scaup (n = 6) at U.S. Geological Survey’s Patuxent Wildlife Research Center in Laurel, Maryland during winter 2015/2016. RMR estimates for black ducks (357.28 kJ/bird/day) and lesser scaup (381.43 kJ/bird/day) in this study fell within the range of previously published estimates for each species. Behavioral multiplier estimates were different between species and from those reported in previous studies. I found that similarities between multiplier estimates for certain behaviors in each species justified combining behaviors into homogenous groups representing high, medium, low, and extreme low (or RMR) energy behavior classes. I tested the effects of 6 covariates (time of day [AM/PM], presence of live or decoy cohort, food presence [Y/N], weight [g], air temperature [C], and water temperature [C]) on energy expenditure within each behavioral grouping and within each species. Black ducks engaged in “medium” and “high energy behaviors” experienced increasing energetic demand as water temperature decreased, and energetic demand interactively increased with higher energy behaviors. Energy expenditure increased with increasing mass in both black ducks and lesser scaup engaged in “high energy behaviors.” Lesser scaup engaged in “medium energy behaviors” expended more energy in the morning than in the afternoon. Lesser scaup engaged in “high energy behaviors” expended more energy when food was absent than when present. Results from this study technologically improve past estimates, refine estimates derived using allometric equations, simplify the underlying calculations required for bioenergetics modeling and will help improve the accuracy of landscape carrying capacity estimates resulting from those models.
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Keywords
American black duck, Behavioral multiplier, Bioenergetics, Energy expenditure, Lesser scaup, Resting metabolic rate