Factors Affecting Foraging Microhabitat Selection by Wading Birds at an Artificial Weir
2016
Renken, Rachel C. | Thompson, Jeane A. | Maccarone, Alan D.
To better understand how wading birds select among microhabitats that show spatial heterogeneity, a concrete weir located at the terminus of the Little Arkansas River in Wichita, Kansas, USA, was divided into patches based on water depth. Black-crowned Night-Herons (Nycticorax nycticorax; n = 396), Great Egrets (Ardea alba; n = 54), Snowy Egrets (Egretta thula; n = 36), and Great Blue Herons (Adrea herodias; n = 30) were observed for 60 hr from 10 June-29 July 2015. The total number of individuals was recorded, as was species-specific patch use, feeding activity, and aggression. Only time of day and water depth predicted the number of birds at the weir (R ² = 0.52). Wading bird species differed in capture efficiency, mean prey size, and patch use. Great Blue Herons and Black-crowned Night-Herons mainly captured larger fish below the weir, Snowy Egrets captured mostly smaller fish along the weir edges, and Great Egrets captured both large and small fish. Mean fish length differed by patch and ranged from 2.8–11.9 cm. Total aggression correlated with the number of large fish caught but not with total fish; per capita aggression correlated with the number of birds. Electrofishing showed a non-uniform spatial distribution of fish numbers and biomass. Species-specific foraging patterns reflected patterns of water depth, fish distribution, and aggression.
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