Author(s): Satoe Kasahara
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Abstract: Avian species have been considered as one of the higher nutrient level organisms in many ecosystems. They use various habitat and diet depending on their preference and resource availability. In the river ecosystem, bird species that prey on fishes and aquatic insect effect on secondary production in the river. Thus, recognizes o f habitat and degree of use by birds is helpful to the understanding of food web and material cycle in the river ecosystem. In this study, I investigated the frequency of appearance of birds in both pool and riffle by automatic shooting camera (Hykecam SP158-J, Hyke, Hokkaido, Japan), and compared the observed bird species and frequency of appearance between two flow environments. We established two study sites that contain two sets of pool and riffle, then we conducted interval photographing in each site four times (May, August, October, January) per year during 2016 and 2017. Interval of photographing was 1 minute and photographing in each season was performed in 24 hours during seven consecutive days. The bird species, the number of birds and behavior of them were recorded from photographs. We also measured flow velocity by the propeller flowmeter in tree point around each camera in 2017. Most recorded bird species by the cameras were ducks that eat mainly plants in common to studied pools and riffles. The frequency of appearance (the number of recorded birds per hour) of ducks was higher in spring and winter than other two seasons, it could reflect the wintering birds. However, the abundance of birds differed between pools and/ or between riffles despite within the site. In pools, birds more appeared on the site with slow flow velocity. Grebes that prey on small fishes were more recorded in pools than riffles while herons, egrets (mainly prey on fishes), and wagtails (mainly prey on aquatic insects) were mo re recorded in riffles. Plovers and sandpipers that mainly prey on aquatic insects recorded only in riffles. As with the case of ducks, the frequency of appearance of these species differed between pools or riffles. For example, Wagtails and shorebirds wer e more recorded in riffle with abundant exposed stones. Our results suggest that riffle provides the foraging and rest site to various bird species while pool provides the habitat for few species. Because the ducks usually forage on a water surface and grebes forage by diving while other birds forage in shallow water from the stone or by walking in the water, the difference of recorded bird species between pool and riffle could reflect of diet and foraging behavior of each species. Possible factors for difference of the abundance of birds between same flow environments could be flow- velocity, the amount of exported stone on the water surface that provides a foothold to bird for foraging and water depth. Thus, accessibility to food and flow velocity were the important factors for the abundance of waterfowl in the river environment.
Year: 2018