Levels of antioxidants in breeding female Audouin's gulls and their deposition in eggs across different environments

• Albumen antioxidant capacity is more variable between populations than yolk.
• The yolk and the total antioxidant capacity of the egg decrease along the clutch.
• Rice field diets are related to lower antioxidant capacity in the eggs.
• Female plasma antioxidant capacity decreases during the incubation period.

Diet quality and dietary antioxidants are interrelated factors that influence many animal traits. However, little is known about this relationship in wild birds, especially how it may affect the deposition of antioxidants from the female to the eggs over the laying sequence. In this context, albumen has been far less studied than yolk due to its lack of carotenoids, which are a common focus of dietary antioxidant research. Our study was conducted in the Audouin's Gull (Larus audouinii), a seabird that shows a great dependence on trawl discards, although in the Ebro Delta also exploits resources from neighbouring rice fields, especially the American crayfish (Procambarus clarkii). We examined the relationship between diet (traced through stable isotope analysis) and the antioxidant capacity (not only carotenoids, but also other non-enzymatic antioxidants, like tocopherols and retinol) of plasma in females from two breeding groups and their clutches. In the eggs we analysed antioxidants in both albumen (hydrophilic antioxidants) and yolk (hydrophilic and lipophilic antioxidants) fractions, taking into account the laying sequence. A decrease in the antioxidant capacity of female plasma was found over the incubation period. We found little difference between groups in the antioxidant deposition pattern in the yolk and whole egg over the laying sequence, but a greater variation was observed in the intra-clutch patterns of albumen antioxidant capacity, probably related to quality differences. When taking into account total antioxidant deposition in the clutch, a declining tendency over the laying sequence was found. Both yolk lipophilic and whole egg antioxidant capacity were negatively related to δ15N, indicating that marine fish diets (with depleted δ15N values) contain a higher amount of antioxidants than rice field prey.