Abstract
Riparian habitat makes up a small fraction of the landscape but provides important stopover habitat for migratory birds. Hydroelectric dam operations cause fluctuations in water levels that can change the amount or quality of riparian habitat, which in turn might affect potential fattening rates of migrant birds. Here we used plasma metabolite analysis to estimate variation in fattening rate in relationship to variable water levels associated with reservoir management in four species of neotropical migratory songbirds using riparian habitat at a dam-impacted stopover site in Revelstoke, British Columbia, Canada. Residual plasma triglyceride, our measure of estimated fattening rate, varied systematically with time of day and Julian date and varied consistently among species, but did not vary with age or sex. Controlling for potentially confounding variables, we found no inter-annual variation in estimated fattening rate, even though there were marked differences in water levels among years. Likewise, there was no relationship between daily variation in water levels and estimated fattening rate. Data on feather isotopes (δD), indicative of migratory origin, did not add explanatory power to our models. There was inter-annual variation in plasma glycerol and β-hydroxybutyrate levels and significant, though weak, relationships between these metabolites and water level (higher metabolite levels when drier) that might indicate effects on 'body condition' independent of fattening rate. Our study suggests that, at present, although hydroelectric dam operations influence water levels in the Arrows Lake Reservoir and adjacent riparian habitats, this does not significantly impact fattening rates of migratory passerines using these habitats.
Highlights
Conservation of migratory birds requires research across the entire avian annual cycle to inform potential management and habitat conservation (Faaborg et al, 2010)
Cite as: Wagner DN, Green DJ, Pavlik M, Cooper J, Williams TD (2014) Physiological assessment of the effects of changing water levels associated with reservoir management on fattening rates of neotropical migrants at a stopover site
There was a significant effect of year on body mass in WIWA (F2,148 = 3.78, P = 0.025) and YWAR (F2,189 = 3.81, P = 0.024), the patterns differed in the two species
Summary
Conservation of migratory birds requires research across the entire avian annual cycle to inform potential management and habitat conservation (Faaborg et al, 2010). Resources in lowland, riparian habitats are considered to be especially important for stopovers during migration, in the western USA and Canada. It has been proposed that preservation of stopover habitat is crucial to the conservation of migratory songbirds (Hedenström and Alerstam, 1998; Petit, 2000; Skagen et al, 2005; Martin et al, 2007; Carlisle et al, 2009)
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