The integrated antioxidant system is recognised as an essential component of an organisms self maintenance. Our knowledge of this system, however, is largely restricted to species of economic importance. The health and productivity benefits these dietary based compounds provide make them increasingly relevant for study in wildlife ecology. The aim of this research was to identify numerous components of this integrated system in a free living and endangered passerine bird, the hihi. In addition experimental supplementation with carotenoids was used to investigate the modulatory interactions with other members of the antioxidant system. Our results identified lutein and zeaxanthin as the carotenoids utilised by hihi (82% and 17% of total carotenoids respectively in control samples of egg yolk, 84% and 16% of total carotenoids respectively in control samples of nestling plasma), and that vitamin E was represented by both alpha- and gamma-tocopherol. Retinol was also present, as was selenium in surprisingly high concentrations (599.64, 91.76, 377.72 ng/g fresh weight Se in control samples of yolk, albumin and plasma, respectively). Supplementation of lutein and zeaxanthin not only increased their presence in egg yolk (F-1,(10) = 14.285, P= 0.005 and F-1,F-10 = 9.606, P = 0.015, respectively) and nestling plasma (F-1,F-19=35.126, P<0.001 and F-1,F-19 = 28.597, P<0001, respectively) but also led to increased selenium concentration in egg yolk (F-1.10 = 7.213, P=0.028), increased retinol concentration in nestling plasma (F-1.19=4.272, P=0.054) and decreased alpha-tocopherol concentration in nestling plasma (F-1,F-19=5.122, P=0.037). These results provide detail of the antioxidant system in novel taxa and importantly highlight interaction between these various compounds. Given their increased application in productivity and health in agriculture and human medicine we highlight the potential application of this knowledge in wildlife ecology and conservation. (C) 2005 Elsevier Inc. All rights reserved.