TRACY, C.R.; WOJCIECHOWSKI, M.S.; MCWHORTER, T.J.; YOSEF, R.; KARASOV, W.H.; PINSHOW, B.*; Ben-Gurion University of the Negev, Israel; University of Wisconsin-Madison; International Birding and Research Centre Eliat, Israel: Carbohydrate absorption in migrating blackcaps, upon arrival and after refeeding, at a stopover in southern Israel

Small birds in migratory flight catabolize fat and apparently some protein as well, including gastrointestinal tract (GIT) tissue. The smaller guts, along with mucosal structural changes, probably reduce the capacity for mediated nutrient uptake and increase intestinal permeability. When refueling at a stopover, a bird’s body mass (mb) increases in 2 phases: 2-3 days of slow lean mass increase including GIT, followed by rapid fat gain. We hypothesized that in phase 1 of mb increase, blackcaps (Sylvia atricapilla) that have crossed the Sahara and Sinai deserts would have lower active uptake and higher paracellular, passive uptake of water soluble nutrients. To test this we measured absorption of sugars in newly arrived and refed blackcaps in Eilat, Israel. Refed birds were kept in an aviary at the capture site, fed ad libitum, and tested after 5 d. Fractional absorption of actively transported 3-O-methyl D-glucose was lower in newly arrived than in refed birds, indicating reduced active absorption in the former. An index of paracellular permeability, the ratio of the fractional passive absorption of a large paracellular probe (cellobiose, 342 Da) to smaller ones (rhamose or arabinose, 164 and 150 Da, respectively), attests to higher permeability in new arrivals. Further, fractional absorption averaged across all passive, paracellular probes, in refed birds was 74% of that in new arrivals. Higher paracellular uptake during refueling at stopover can compensate for the reduced active nutrient uptake capacity of the GIT, but it could also expose birds to higher levels of toxins in their food. Supported by NSF IBN-0216709 to WHK.