Constructing a 24 hour time-energy budget for American black ducks wintering in coastal New Jersey
Date
2012
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Publisher
University of Delaware
Abstract
American black ducks (Anas rubripes) have sustained a long-term population decline, as part of a larger effort to address this decline managers have sought to estimate the winter carrying capacity of black ducks. Carrying capacity can be estimated bioenergetically through a comparison of food availability and daily energy expenditure. Recently the food availability for black ducks wintering in the mid-Atlantic was estimated. Previous estimates of daily energy expenditure found a disparity between diurnal behavioral observations and predictive allometric equations. Black ducks have long been known to be active nocturnally, however their actual behavior has never been quantified. Therefore my objectives were to 1) quantify black duck behavior during diurnal, crepuscular, and nocturnal periods, 2) estimate the daily energy expenditure of black ducks, and 3) compare methodologies of estimating daily energy expenditure.
I conducted behavioral observations of black duckswintering in coastal New Jersey from Oct–Feb 2009–2011. Black ducks were observed across all four time periods: morning crepuscular, diurnal, evening crepuscular, and nocturnal. Nocturnal observations were made using generation III night vision technology. I collected 11,542 observations of black ducks. Using these observations I constructed a time budget for each period. Black ducks were found toexhibit all behavior states during all periods. However, black ducks exhibited reduced feeding during the morning crepuscular period and reduced flight during the nocturnal period. I modeled the effect of several environmental factors on behavior across all four time periods. Precipitation, temperature, and tide were found to influence black duck behavior across time periods. I investigated the effect of hunting on black duck behavior by comparing behavior across eight categories of spatial and temporal hunting designations. I observed increased feeding during diurnal and nocturnal periods on areas open to hunting when the duck hunting season was closed, while I observed increased resting on areas closed to hunting regardless of whether the hunting season was open. I converted time budgets into estimates of energy expenditure. On an hourly basis, energyexpenditure was lowest during the nocturnal period. I calculated a weighted 24 hr estimate of daily energy expenditure (DEE) by multiplying period specific hourly energy expenditures by the number of hours in each period. Averaged across months, black ducks expended 1,235.65 kJ/bird/day. Using only diurnal observations scaled to a 24 hr period, I estimated DEE to be 1,383.14 kJ/bird/day. I also used a predictive allometric equation which estimated DEE to be 1544.95 kJ/bird/day. Differences in black duck energy expenditure between periods were driven by differences in flight between periods. Flight is the most energetically costly behavior, however it is also the most difficult behavior to quantify. My estimates of flight during the morning crepuscular, diurnal, and evening crepuscular periods were higher than previous estimates, leading to a higher estimate of daily energy expenditure. I observed increased rates of disturbance during the morning crepuscular and diurnal periods, perhaps influencing behavior patterns. The nocturnal period appears to be a time of reduced flight and therefore reduced energy expenditure for black ducks. When estimating the DEE of free-living birds, researchers must carefully evaluate their methodology. I used four different methods of estimating DEE which resulted in three statistically different results. To further reduce the error associated with estimating DEE I recommend future research refine black duck specific resting metabolic rates andimprove methodologies toquantify flight behavior.