Energetics and metabolite profiles during early flight in American robins ( Turdus Migratorius)
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ORIGINAL PAPER
Energetics and metabolite profiles during early flight in American robins (Turdus Migratorius) Alexander R. Gerson • Christopher G. Guglielmo
Received: 23 November 2012 / Revised: 5 April 2013 / Accepted: 13 May 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Although birds use fat as the primary fuel for migratory flights, carbohydrate and protein catabolism could be significant in the early stages of flight while pathways of fatty acid transport and oxidation are induced. The fuel mixture of long distance migrant birds can also be affected by the rate of water loss, where birds catabolize more protein to increase endogenous water production under dehydrating flight conditions. Despite many studies investigating flight metabolism, few have focused on the metabolic response to flight during the switchover to fat catabolism in migrants, and none have examined the effect of ambient conditions on fuel selection during early flight. We investigated the effect of water loss on the metabolic response to short duration flight in the American robin (Turdus migratorius). Birds were flown in a climatic wind tunnel and changes in body composition and plasma metabolites were measured. As flight duration increased, there was a gradual switchover from carbohydrate and protein catabolism to fat catabolism. Plasma metabolite profiles indicate that the mobilization of fat occurred within 20 min of initiating flight. Plasma glucose decreased and uric acid increased with flight duration. Ambient humidity did not affect fuel mixture. Thus, it seems that the utilization of fat may be delayed as migrants initiate flight.
Communicated by G. Heldmaier. A. R. Gerson C. G. Guglielmo Department of Biology, Advanced Facility for Avian Research, The University of Western Ontario, London, ON, Canada A. R. Gerson (&) Department of Biology, University of New Mexico, New Mexico, USA e-mail: [email protected]
Short-hop migrants may exploit high rates of endogenous water production resulting from carbohydrate and protein catabolism early in flight to offset high water loss associated with low humidity. Rapid catabolism of lean body components at the start of a flight also reduces mass quickly, and may reduce energy costs. Keywords Plasma metabolites Flight Bird migration Flight energetics Quantitative magnetic resonance
Introduction Flight is the most energetically demanding form of locomotion (Schmidt-Nielson 1972), and migratory birds are unique among vertebrates in their ability to fuel this highintensity exercise for long durations with fat (Jenni and Jenni-Eiermann 1998; Guglielmo 2010). The use of fat in flight is evidenced by the fact that migratory birds increase adiposity coinciding with migratory periods (i.e., spring and fall; Jehl Jr 1997); these fat stores are depleted after long flights in the wild, and replenished quickly during stopover (Battley et al. 2000; Guglielmo et al. 2005; Guglielmo et al. 2011). Other metrics of fat use in flight, such as high plasma free fatty acid concentrations, respira
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