The frontal shield of the moorhen: sex differences and relationship with body condition

Moorhens Gallinula chloropus have a conspicuous frontal shield, which is used in competitor assessment, and whose size and colour is testosteronedependent in both sexes. During 2 months in winter we examined sex-related differences in size and colour of the red or red-orange shield and the yellow-tipped bill of free-living adult moorhens, as well as their relationship with indices of body condition (body size, tarsi fluctuating asymmetry, fat index, serum lutein carotenoid concentration, and a number of blood parameters). Shield area was greater in males and more red in females. In females, area and colouration intensity of the shield were positively correlated, respectively, to body size and concentration of circulating lutein. In males, area and intensity of red colouration of the shield were positively correlated, respectively, to albumin/globulin ratio and body size, while shield colour saturation was negatively related to the leukocyte index. Our results suggest that shield area and colour of male and female moorhens may provide cues to their opponents for assessment of body size and health status, and therefore of their competitive ability.