Experimental and Ecological Implications of Evening Bird Surveys in Stream-Riparian Ecosystems |
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Authors: | S Ma?eika P Sullivan Kerri T Vierling |
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Institution: | (1) Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID 83844-1136, USA;(2) School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Road, Columbus, OH 43210, USA |
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Abstract: | Stream-riparian ecosystems are dynamic and complex entities that can support high levels of bird assemblage abundance and
diversity. The myriad patches (e.g., aquatic, floodplain, riparian) found in the riverscape habitat mosaic attract a unique
mixture of aquatic, semiaquatic, riparian, and upland birds, each uniquely utilizing the river corridor. Whereas standard
morning bird surveys are widely used across ecosystems, the variety of bird guilds and the temporal habitat partitioning that
likely occur in stream-riparian ecosystems argue for the inclusion of evening surveys. At 41 stream reaches in Vermont and
Idaho, USA, we surveyed bird assemblages using a combination of morning and evening fixed-width transect counts. Student’s
paired t-tests showed that while bird abundance was not significantly different between morning and evening surveys, bird assemblage
diversity (as measured by species richness, Shannon-Weiner’s index, and Simpson’s index) was significantly higher in the morning
than in the evening. NMS ordinations of bird species and time (i.e., morning, evening) indicated that the structure of morning
bird assemblages was different from that of evening assemblages. NMS further showed that a set of species was only found in
evening surveys. The inclusion of evening counts in surveying bird assemblages in stream-riparian ecosystems has important
experimental and ecological implications. Experimentally, the sole use of morning bird surveys may significantly underestimate
the diversity and misrepresent the community composition of bird assemblages in these ecosystems. Ecologically, many of the
birds detected in evening surveys were water-associated species that occupy high trophic levels and aerial insectivores that
represent unique aquatic-terrestrial energy transfers. |
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