First published online January 19, 2010
Journal of Experimental Biology 213, 380-385 (2010)
Published by The Company of Biologists 2010
doi: 10.1242/jeb.040071
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Carbohydrate absorption by blackcap warblers (Sylvia atricapilla) changes during migratory refuelling stopovers

C. R. Tracy1,2,*, T. J. McWhorter3,4, M. S. Wojciechowski1,5, B. Pinshow1 and W. H. Karasov4

1 Mitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, 84990 Midreshet Ben-Gurion, Israel
2 School of Environmental and Life Sciences, Charles Darwin University, Darwin, NT 0909, Australia
3 School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy Campus, SA 5371, Australia
4 Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, WI 53706, USA
5 Department of Animal Physiology, Institute of General and Molecular Biology, Nicolaus Copernicus University, PL 87-100 Torun, Poland

* Author for correspondence (chris.tracy{at}cdu.edu.au)

Accepted 27 October 2009

Passerine birds migrating long distances arrive at stopover sites to refuel having lost as much as 50% of their initial body mass (mb), including significant losses to digestive organs that may serve as a reservoir of protein catabolised for fuel during flight. Birds newly arrived at a stopover show slow or no mb gain during the initial 2–3 days of a stopover, which suggests that energy assimilation may be limited by reduced digestive organs. Measurements of migrants and captive birds subjected to simulated migratory fasts have shown reductions in intestine mass, morphological changes to the mucosal epithelium, and reductions in food intake and assimilation rate upon initial refeeding. We found that blackcaps (Sylvia atricapilla, Linnaeus) newly arrived at a migratory stopover after crossing the Sahara and Sinai deserts had significantly increased paracellular nutrient absorption (non-carrier mediated uptake occurring across tight junctions between enterocytes) that may provide partial compensation for reduced digestive capacity resulting from changes to intestinal tissues. Indeed, newly arrived birds also had a slightly reduced capacity for absorption of a glucose analogue (3-O-methyl-D-glucose) transported simultaneously by both carrier-mediated and non-mediated mechanisms. Increased paracellular absorption coupled with extended digesta retention time may thus allow migratory blackcaps to maintain high digestive efficiency during initial stages of refuelling while digestive organs are rebuilt.

Key words: migration, refuelling, carbohydrate absorption, paracellular absorption, blackcap, Sylvia atricapilla


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