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Stream type influences food abundance and reproductive performance of a stream specialist: the Brown Dipper (Cinclus pallasii)

Hong, Shiao-Yu, Wang, Tsai-Wei, Sun, Yuan-Hsun, Chiu, Ming-Chih, Kuo, Mei-Hwa, Chen, Chao-Chieh
Journal of ornithology 2019 v.160 no.1 pp. 105-115
biomass, birds, breeding season, clutch size, fledglings, floods, food availability, freshwater ecosystems, habitats, macroinvertebrates, models, nests, population growth, predators, reproductive performance, space and time, streams, summer, winter, Taiwan
Avian reproduction and population growth are highly dependent on food availability. Consequently, studies on these variables require accurate estimates of food abundance that may vary in space and time. Dippers (Cinclus spp.) are obligate stream predators in freshwater ecosystems. Although it is well known that dippers are affected by aquatic macroinvertebrate density and proportion of riffle habitat, rarely are these two factors combined to estimate their food availability. We developed a new method to estimate food availability and tested the relationship of food availability with reproduction performance of the Brown Dipper (Cinclus pallasii) in Taiwan from 2013 to 2015. We defined three stream types (stony riffles, sandy runs, and pools) with water depth and benthic substrate. Macroinvertebrate biomass was significantly greater in stony riffles than in sandy runs. We then measured the area of the three stream types in a 400-m stream segment centering on each Brown Dipper’s nest. The area of stony riffles was multiplied by average macroinvertebrate density of each stream to represent food availability in stony riffles of each territory. Response variables on reproductive performance (e.g., laying date, clutch size, fledgling number, and territory length) of each nest were recorded. Linear mixed-effects models showed that food availability estimated using the area of stony riffles was significant correlated with all aspects of reproductive performance of Brown Dippers and was a better predictor than food availability estimated in the total water area. This study also demonstrated that summer floods and winter flows (high or low water level) could influence food availability in the dipper’s breeding season by different mechanisms.