Animals' cells are constantly under siege from damaging reactive oxygen species and they need anti-oxidants to help mop them up. When this clean-up system is overwhelmed, animals suffer from oxidative stress, which reduces their fitness. Carotenoids are one important group of anti-oxidants, which animals must obtain from their diet; however recent studies have suggested that the anti-oxidant role of carotenoids might not be as important as previously thought. To find out whether this was the case in young kestrels,David Costantini from the University of Rome, Sapienza, and his colleagues investigated whether supplementing the young birds' diet with carotenoids would increase their ability to deal with reactive oxygen species(p. 1238).

The team supplemented the diet of 7–8 day old kestrels with carotenoids, and then measured the carotenoid levels in the blood, finding that levels went up after supplementation. However, when they measured the blood levels of reactive oxygen species, mainly a type called hydroperoxides,and the overall anti-oxidant activity in the blood, they found that supplements caused no change. This shows that young nestlings can mop up free radicals, and don't need a dietary boost of carotenoids to help them do this.

Costantini, D., Fanfani, A. and Dell'Omo, G.(
). Carotenoid availability does not limit the capability of nestling kestrels (Falco tinnunculus) to cope with oxidative stress.
J. Exp. Biol.