Atlantic Brant wintering upland field use and bioenergetics
Date
2024
Authors
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Publisher
University of Delaware
Abstract
The need to understand waterfowl energetic demands and habitat use on the wintering grounds is increasingly important for conservation and management. Past research using scan-sampling techniques has produced important estimates of time budgets and daily energy expenditure, but modern technology can increasingly be used to obtain more precise movement data with multiple applications. Atlantic Brant (Branta bernicla hrota) increasingly use upland turfgrass fields, such as baseball fields and golf courses, throughout their wintering range and have undergone massive shifts in their food selection due to population declines caused by a loss of their preferred food, eelgrass, and severe winters. I sought to improve our understanding of Brant wintering ecology with an emphasis on upland turfgrass field use. ☐ I used four years of wintering accelerometry data from 210 telemetered Atlantic Brant throughout New Jersey and New York, USA, to construct time budgets, estimate daily energy expenditure, and quantify habitat use. I also sampled turfgrass fields during the winters of 2021–22 and 2022–23 to explore the importance of field and grass characteristics in determining field use of Atlantic Brant in this urban ecosystem. I used Bayesian hierarchical modeling to quantify differences in daily energy expenditure and habitat use between sexes as well as among months and years. I also explored the effects of environmental and temporal variables on energy expenditure. ☐ I found the extrinsic characteristics of field size and distance to water to have consistently strong effects on field use in all models, while some intrinsic characteristics, such as grass height, live grass mass, clover mass, and carbon–nitrogen ratio had only moderate effects in some models. I found minimal to no effect of the mass of weeds, energy density, or distance to roost on field use. The average daily energy expenditure I calculated (1,238.2 kJ) was lower than in past observational studies, while the amounts of time spent in three behavioral states were comparable. Females had slightly higher average energy expenditure and spent notably more time in flight than males, and there were many notable differences among months and winters. My categorical model of behaviors predicted an increase in flight behavior at lower latitudes and higher tide levels, while a decrease was predicted during periods of rain and higher temperature. I found different trends of habitat use over time than previous studies on Atlantic Brant and found differences among regions to be the strongest driver of differences in habitat use. ☐ I expect these results to help inform future management of Brant in the event of a decline in submerged aquatic vegetation or the Brant population. My improved energy expenditure estimate will allow future studies to more accurately estimate a wintering carrying capacity for Atlantic Brant. Explanations of differences in behavioral time budgets and habitat use will allow managers to consider more detailed effects, such as regional differences within the population and the importance of environmental variables in affecting Brant behavior, energy expenditure, and habitat use.
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Keywords
Bioenergetics, Atlantic Brant, Field use, GPS, Habitat use, Upland turfgrass fields