Abstract
Breath-hold diving presents air-breathing vertebrates with the challenge of maintaining aerobic respiration while exercising underwater. Adaptive increases in the oxygen (O-2) storage capacity in the lungs, blood, or muscle tissues can enhance these reserves and greatly extend aerobic foraging time underwater. Here, we report blood- and muscle-O-2 storage parameters (blood hemoglobin concentration ([Hb]), hematocrit, and myoglobin concentration ([Mb]) in the pectoralis and gastrocnemius) for 16 species of diving and dabbling ducks found in North America, and investigate which parameters are correlated with the diving behaviors reported in both the sea ducks (Mergini) and the pochards (Aythini). Both [Hb] in the blood and [Mb] in the gastrocnemius, a major leg muscle used in propulsion for these predominantly leg-propelled divers, were significantly higher in the sea ducks compared to the dabblers (Anatini). The pochards also showed a significant increase in [Hb] and were intermediate between the sea ducks and the dabblers in hematocrit and [Mb] in the gastrocnemius. Among these four variables and total body mass, [Mb] in the gastrocnemius was the most significant predictor of mean species dive time, and these two variables were correlated across the phylogeny. Our results indicate that the observed changes in O(2 )storage capacity in the blood and muscles are positively correlated with diving behavior in two clades of ducks, such that larger increases are correlated with longer dive times.