Search

Abstract: We studied the stopover ecology of Blackcaps in Eilat, Israel, at the northern edge of the Saharan desert crossing. We investigated the Blackcaps with regard to differential migration by sex or age class in spring and autumn, and the stopover site in spring and autumn were compared. Using data from 1984 to 2003, we studied stopover length and fat deposition patterns differentiated by sex. In spring, Blackcap females remained in Eilat significantly longer than males. This suggests that males maintain a migration strategy of time-minimization, while females place more importance on energy-maximization. This difference is probably due to upcoming reproductive roles at the breeding grounds. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]