Astaxanthin is the major carotenoid in tissues of white storks (Ciconia ciconia) feeding on introduced crayfish (Procambarus clarkii).

We studied the carotenoid pigments in plasma, skin and body fat of white storks (Ciconia ciconia) from a colony in Spain feeding mainly on the recently introduced red swamp crayfish (Procambarus clarkii). In control colonies, where crayfish was absent, plasma was collected for comparison. Our objective was to determine whether the astaxanthin contained in the crayfish reached the blood, accumulated in fat, and finally was deposited in the red-colored bill and legs. If that was true, the visual cues provided by those tegumentary areas would be altered, with potential behavioral consequences. Plasma carotenoids were directly extracted with acetone, whereas skin and fat samples needed harsher conditions, i.e. grinding, sonication and extraction with diethyl ether. The extracts were analyzed by thin-layer chromatography (TLC) and UV/Vis spectroscopy. In crayfish-eating storks, astaxanthin was confirmed to be the dominant pigment in all analyzed tissues. This red pigment was absorbed unchanged in the gut, and was responsible for the red color of plasma and the abnormal orange pigmentation of the feather-covered skin. It was also present in large quantities in the exposed bill and tarsi, which are typically red-colored in the stork. Control storks with no crayfish in the diet only presented lutein in their plasma.