The rapid response of plasma metabolites to changes in feeding rate in a small passerine Wilsonia pusilla

Abstract

In order to apply plasma metabolite profiling to assess the quality of stopover habitat for migrant birds it is crucial to know how quickly metabolite concentrations change in response to variation in energy intake rate. We fed live mealworms to Wilson's warblers Wilsonia pusilla at rates designed to mimic a low quality (0.58 wet g/h) and a high quality (0.75 wet g/h) habitat. Plasma concentrations of triglycerides and B‐OH‐butyrate were higher and lower, respectively, on the high feeding rate, but plasma glycerol levels did not differ between feeding rates. Birds were then fed at the low rate for five hours, switched to the high rate and blood sampled at various times after the switch. Plasma triglycerides and B‐OH‐butyrate reflected the increase in feeding rate within 10 and 20 min, respectively. Plasma glycerol did not change significantly following the change in feeding rate. We conclude that plasma metabolite concentrations can change very quickly in response to variation in feeding rate, and thus provide a sensitive index of fueling rates near a capture site.