Ardea
Official journal of the Netherlands Ornithologists' Union

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Zwarts L. & Dirksen S. (1990) Digestive bottleneck limits the increase in food intake of Whimbrels preparing for spring migration from the Banc d'Arguin Mauritania. ARDEA 78 (1-2): 257-278
Whimbrels Numenius phaeopus are able to consume 2-3 mg ash-free dry mass per second feeding over the short term, but when the intake rate is that high, they have to pause to allow for digestion. If these digestive pauses are taken into account, the maximum crude intake rate is reduced to 1 mg s-1. This maximum intake rate does not increase during the season, even though the total daily food consumption in April is 50% higher than in February and March (24 and 36 g ash-free dry mass d-1, respectively). The increased consumption is achieved by feeding for a greater part of the time at the highest intake rates. In February and March, the intake rate of Whimbrels is reduced if low water falls before 8.00 h, and it is only high when low water falls between 9.00 and Ca. 15.00 h. This diurnal pattern disappears in April, when a high intake rate is also achieved at night. The body mass increases at a rate of 1.1% per day prior to migration. A rate of gain body mass greater than the one observed hardly seems possible because of physiological constraints (the limit in crude intake rate set by the capacity of the gut) combined with physical limits, namely the duration of emersion period. A possible limiting effect due to heat or salt stress could not be demonstrated convincingly.


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