Meeting Abstract
Hummingbirds might be limited in their ability to increase nectar consumption because most water consumed is absorbed and processed through their kidneys. If water processing imposes a cap on feeding rate, then increasing energy intake during periods of extreme energy demand could be difficult. We measured maximum feeding rate in four hummingbird species by sequentially feeding them nectars that decreased in sucrose concentration (10-2%). Feeding rate in broad-billed (3.2g) and magnificent (7.5g) hummingbirds peaked at 4% (0.55 and 0.53 gs g-1h-1, respectively) whereas black-chinned (3.0g) and blue-throated hummingbirds (8.0g) peaked at 6% (0.77 and 0.55 gs g-1h-1, respectively). Maximum water consumption occurred at 4% for broad-bills and magnificents (0.53 and 0.51 mL g-1h-1, respectively), and at 6% for black-chins and blue-throats (0.72 and 0.51 mL g-1h-1, respectively). Maximum energy consumption occurred at 8% for all species (0.50-0.79 kJ g-1h-1). Further nectar dilution past the point of peak feeding rate appeared to result in reduced activity, presumably to compensate for reduced energy intake. Species differences in consumption was not related to body mass. All species except black-chins maintained mass for the duration of the experiment. Mass loss in black-chins might suggest higher energy demand or lower assimilation efficiency than the other species. The unusually high water consumption of black-chins could indicate lower intestinal water absorption. Since hummingbirds appear to be able to meet daily energy demands by consuming 2-3 times their body weight in nectar per day, our data predict that in periods of extreme energy demand compensatory feeding can be substantially increased if nectars contain typical amounts of sugar.
