Exploratory behavior is associated with plasma carotenoid accumulation in two congeneric species of waterfowl

• Waterfowl with higher plasma carotenoid levels were more exploratory.
• In contrast, circulating carotenoid levels did not affect activity level.
• There was no species- or sex-specific variation in exploration or activity level.

Recently, carotenoid pigments have received considerable attention as modulators of animal health and performance. While studies show that elevated carotenoid intake and accumulation can influence activities like parental care and escape-flight performance, little is known of how carotenoid status influences the expression of animal personality traits, which can be energy-demanding and entail survival costs but also rewarding in the context of foraging and mating. We experimentally investigated the effects of carotenoid availability on exploratory behavior and activity level, using adult males and females of two species of waterfowl: mallard (Anas platyrhynchos) and northern pintail (Anas acuta). We assessed behavior using a novel-environment test designed to measure an individual’s response to novel objects and a potential predator threat (fox urine scent). We found that carotenoid availability was positively associated with some aspects of exploratory behavior: birds with higher concentrations of circulating carotenoids entered the test arena sooner and approached and entered predator-scented bedding material more frequently than birds with low carotenoid concentrations. These results suggest that the availability of carotenoid resources can influence personality traits in waterfowl, and we discuss putative physiological mechanisms underlying this effect.