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The Influence of Food Density, Flock Size, and Disturbance on the Functional Response of Bewick’s Swans (Cygnus columbianus bewickii) in Wintering Habitats

by Chao Yu 1,2, Lizhi Zhou 1,2,*, Nazia Mahtab 1,2, Shaojun Fan 1,2 and Yunwei Song 3
1
School of Resources and Environmental Engineering, Anhui University, 111 Jiulong Road, Hefei 230601, China
2
Anhui Province Key Laboratory of Wetland Ecosystem Protection and Restoration (Anhui University), 111 Jiulong Road, Hefei 230601, China
3
Department of Resources Conservation and Utilization, Anhui Shengjin Lake National Nature Reserve, Dongzhi 247200, China
*
Author to whom correspondence should be addressed.
Animals 2019, 9(11), 946; https://doi.org/10.3390/ani9110946 (registering DOI)
Received: 30 September 2019 / Revised: 6 November 2019 / Accepted: 7 November 2019 / Published: 10 November 2019
(This article belongs to the Section Wildlife)
Changes in environmental conditions cause animals to adjust their behavioral strategies to survive. We investigated foraging behavior in different habitats of wintering Bewick’s swans. We found that the observed feeding rate was not affected by food density but showed a negative relationship with flock size and disturbance time. Handling time had a negative relationship with food density and flock size, but a positive relationship with disturbance. Searching rate was negatively correlated with food density, flock size, and disturbance time. This provides insight into how wintering waterbirds adapt their foraging behavior in complex environments.
Perceiving how animals adjust their feeding rate under a variety of environmental conditions and understanding the tradeoffs in their foraging strategies are necessary for conservation. The Holling functional response, which describes the relationship of feeding rate and food density to searching rate and handling time, has been applied to a range of waterbirds, especially with regard to Type II functional responses that describe an increasing feeding rate with food density but at a decelerating rate as the curve approaches the asymptote. However, feeding behavior components (feeding rate, searching rate, and handling time) are influenced by factors besides prey density, such as vigilance and flock size. In this study, we aim to elucidate how Bewick’s swans (Cygnus columbianus bewickii) adopt flexible foraging strategies and vary their feeding behavior components in response to disturbance, flock size, and food density. We collected focal sampling data on the foraging behavior of swans that foraged rice grains, foxnut seeds, and tubers in paddy field, foxnut pond, and lake habitats, respectively, in Shengjin and Huangpi lakes during winter from 2016 to 2018. The observed feeding rate was not correlated with food density and displayed a positive relationship with searching rate but negative relationships with handling time, flock size, overall vigilance time, and disturbance time. Handling time was negatively correlated with food density and flock size, yet it increased with disturbance, overall vigilance time, and normal vigilance time. Searching rate was negatively correlated with food density, flock size, and disturbance time. Feeding rate was affected by the combined effects of handling time and searching rate, as well as food density and searching rate. The shape of the observed functional response could not be fitted to Holling’s disc equation. However, the disc equation of the predicted feeding rate of wintering swans was found to be driven by food density. This provides insight into how wintering waterbirds adopt appropriate foraging strategies in response to complicated environmental factors, which has implications for wildlife conservation and habitat management. View Full-Text
Keywords: functional response; feeding rate; handling time; searching rate; vigilance; food item density; flock size; Bewick’s swans functional response; feeding rate; handling time; searching rate; vigilance; food item density; flock size; Bewick’s swans
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Yu, C.; Zhou, L.; Mahtab, N.; Fan, S.; Song, Y. The Influence of Food Density, Flock Size, and Disturbance on the Functional Response of Bewick’s Swans (Cygnus columbianus bewickii) in Wintering Habitats. Animals 2019, 9, 946.

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