Hematocrit Does Not Indicate Condition in Nestling or Adult European Starlings

Hematocrit, the percentage of packed red blood cells in blood, has been used as a measure of avian condition. We investigated the relationship between hematocrit and condition in a wild, breeding population of adult European Starlings (Sturnus vulgaris), and their nestlings (at 5- and 11-days post hatch). Hematocrit was not correlated with condition in adults or nestlings at either 5- or 11-days post-hatch. Adult males and females had similar hematocrit values. Hematocrit increased with age; adults had significantly higher hematocrit than both 5- and I l-day old nestlings, and 11-day old nestlings had significantly higher hematocrit than when they were 5 clays of age. Hematocrit was not correlated with sampling date, ambient temperature, or relative humidity level, but was positively correlated with sampling time in the day for nestlings (but not adults). Our findings caution against using hematocrit as a measure of condition in birds. Received 30 November 2011. Accepted 23 June 2012.