Impacts of selective logging on the oxidative status of tropical understory birds

1. Selective logging is the dominant form of human disturbance in tropical
forests, driving changes in the abundance of vertebrate and invertebrate
populations relative to undisturbed old-growth forests. 2. A key
unresolved question is understanding which physiological mechanisms
underlie different responses of species and functional groups to selective
logging. Regulation of oxidative status is thought to be one major
physiological mechanism underlying the capability of species to cope with
environmental changes. 3. Using a correlational cross-sectional approach,
we compared a number of oxidative status markers among 15 understory bird
species in unlogged and selectively logged forest in Borneo in relation to
their feeding guild. We then tested how variation of markers between
forest types was associated with that in population abundance. 4. Birds
living in logged forests had a higher activity of the antioxidant enzyme
superoxide dismutase and a different regulation of the glutathione cycle
compared to conspecific birds in unlogged forest. However, neither
oxidative damage nor oxidized glutathione differed between forest types.
We also found that omnivores and insectivores differed significantly in
all markers related to the key cellular antioxidant glutathione
irrespective of forest type. Species with higher levels of certain
antioxidant markers in a given type of forest were less abundant in that
forest type compared to the other. 5. Our results suggest that there was
no long-term effect of logging (last logging rotation occurred ~15 years
prior to the study) on the oxidative status of understory bird species.
However, it is unclear if this was owing to plasticity or evolutionary
change. Our correlative results also point to a potential negative
association between some antioxidants and population abundance
irrespective of forest type.