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 r esembling those of free-living conspecifics. The persistence of identifiabl e annual cycles enabled us to study variability in two blood parameters, on e a measure of red blood cell count (hematocrit) and the other an index of white blood cell (WBC) abundance (percentage). In both species hematocrit v alues 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 con vincingly confirm predicted elevated hematocrit levels during periods of st orage 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 ru ffs and 0.3% in red knots after half a year in captivity. Using observation s of the same individual red knots in the years before and after the experi mental year as controls, biweekly extraction of about 30% of blood volume d id not negatively affect seasonal changes in body mass and moult and breedi ng-plumage cycles. In nutritionally stressed red knots, hematocrit levels w ere low, and in these birds only, the small wounds inflicted by bleeding he aled with difficulty.