Altitudinal variation in oxidative status between breeding and non-breeding seasons in a Neotropical bird

The mountains pose oxidative challenges for organisms due to their lower temperatures, increased ultraviolet radiation, and reduced oxygen levels. To understand how local populations deal with oxidative damage during reproduction or wintering under these conditions, a comparison of the oxidative status of breeding and non-breeding birds at different elevations is needed. In a study conducted at low and high elevations in central Chile (33°S), we compared levels of thiobarbituric acid-reactive substances (TBARS) as an indicator of reactive oxygen species, total antioxidant capacity (TAC) as an indicator of non-enzymatic molecular antioxidants and TBARS/TAC ratio as an indicator of oxidative status in 71 adult individuals of Rufous-collared Sparrows (Zonotrichia capensis). Our findings revealed that TBARS levels were significantly lower at high than low elevations, suggesting that birds at high elevations might have specific mechanisms to reduce oxidative damage. Regarding TAC levels, the results indicate that TAC levels were significantly lower at high than low elevations, suggesting that better weather conditions at low elevations may support a higher availability of dietary antioxidants regarding high elevation inhabits. Finally, the TBARS/TAC ratio indicates that during the breeding season at low elevations, the birds exhibit a significantly higher TBARS/TAC ratio, suggesting that these birds have a limited capacity to counteract oxidative damage during reproduction regarding bred birds at high elevations. In contrast, at higher elevations, they would better manage reproductive effort by minimizing oxidative damage by limiting their TBARS production and TAC needs. These findings highlight the presence of phenotypic adaptations associated with the oxidative state in this species in response to local environmental conditions in the Andes.