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1 June 2013 Decreased Hematocrits in Common Terns (Sterna hirundo) Exposed to Oil: Distinguishing Oil Effects from Natural Variation
Ian C. T. Nisbet, Florina S. Tseng, Victor Apanius
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Hematocrits were measured in Common Terns (Sterna hirundo) (n = 75) that were exposed to oil from a spill in Buzzards Bay, Massachusetts, USA, in 2003, and that laid eggs 17–39 days following the spill. Comparative data were obtained in three pre- and two post-spill years and from three unoiled reference sites. In non-spill years, annual means of hematocrit varied in parallel with breeding performance. Hematocrits were lower (mean 45.3, n = 75) and more variable in the oil spill year than in non-spill years, and 20% of birds sampled were anemic (hematocrit < 41.7). However, hematocrits were almost as low (mean 46.4, n = 44) in 2002, a year with naturally adverse conditions. In 2002, hematocrits and body-masses were depressed following two storms and recovered in parallel following the storms; hematocrits were positively correlated with body-mass and ambient temperature and negatively correlated with wind speed. In contrast, in 2003 hematocrits were negatively correlated with body-mass and temperature and positively correlated with wind speed. Hematocrits were very low (mean 39.8, n = 15) when birds were first sampled 20–23 days after the spill and recovered toward normal levels by day 39 (mean 49.4, n = 14). Reduced hematocrits can be a useful indicator of sublethal oil intoxication, especially in females, provided that they are not associated with low body-masses or adverse weather. Measuring hematocrits could be useful for rapid screening of populations sublethally exposed to oil.

Ian C. T. Nisbet, Florina S. Tseng, and Victor Apanius "Decreased Hematocrits in Common Terns (Sterna hirundo) Exposed to Oil: Distinguishing Oil Effects from Natural Variation," Waterbirds 36(2), 121-252, (1 June 2013).
Received: 4 April 2011; Accepted: 1 January 2013; Published: 1 June 2013

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