Red blood cell and white blood cell counts in sandpipers (Philomachus pugnax, Calidris canutus): effects of captivity, season, nutritional status, and frequent bleedings

Captive ruffs (Philomachus pugnax) and red knots (Calidris canutus) kept in small flocks in outdoor aviaries maintained body mass and plumage cycles resembling those of free-living conspecifics. The persistence of identifiable annual cycles enabled us to study variability in two blood parameters, one a measure of red blood cell count (hematocrit) and the other an index of white blood cell (WBC) abundance (percentage). In both species hematocrit values averaged 0.43, somewhat lower than those measured in free-living red knots. Hematocrit varied little with time of year and we were unable to convincingly confirm predicted elevated hematocrit levels during periods of storage of fat for migration. In both species the percentage of WBCs (percent WBCs) initially declined from 0.6 to 0.8%; levels stabilized at 0.4% in ruffs and 0.3% in red knots after half a year in captivity. Using observations of the same individual red knots in the years before and after the experimental year as controls, biweekly extraction of about 30% of blood volume did not negatively affect seasonal changes in body mass and moult and breeding-plumage cycles. In nutritionally stressed red knots, hematocrit levels were low, and in these birds only, the small wounds inflicted by bleeding healed with difficulty.