Olive ridley sea turtles, Lepidochelys olivacea, exhibit polymorphic nesting behaviors including a mass nesting behavior called arribada, where thousands of turtles nest at once, and solitary nesting. Arribada nesting may provide benefits including mate finding during nearshore aggregations and predator satiation at the time of hatching, but the potential costs of nesting in arribada have not been explored. We collected blood from olive ridley sea turtles after nesting in arribada and solitary. We measured circulating concentrations of hormones (progesterone, estradiol, corticosterone, thyroxine, and triiodothyronine), markers of oxidative damage (4-hydroxynonenal: 4-HNE, malondialdehyde: MDA, protein oxidation: protein carbonyls, and protein nitration: 3-nitrotyrosine), and glucose and lactate. Nesting in arribada was associated with increased levels of progesterone, thyroid hormones, corticosterone, and glucose suggesting increased metabolic activity. Moreover, nesting in arribada was also associated with increased circulating levels of oxidative damage (4-HNE, MDA, and protein carbonyls). These results suggest that nesting in arribada is metabolically more expensive than nesting solitarily and that oxidative damage is a potential cost of such behavior.