Sex differences in testosterone and hematocrit levels reflect mating system differences of two Arctic-breeding shorebird species.

In females, this pattern was reversed, although not quite significant, with red phalaropes having twice as high average plasma testosterone concentrations compared to pectoral sandpipers (red phalarope: 0.4 ± 1.2 ng/ml, pectoral sandpiper: 0.2 ± 1.3 ng/ml, P = 0.06, Fig. 2b ; ESM Table S2 and S3 ).

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