Effects of urbanisation and pollution on the heterophil/lymphocyte ratio in birds from Brazilian Cerrado.

Stressing agents can cause morphophysiological and behavioural changes in several animals, including birds, which are good study models for environmental biomonitoring. The heterophil/lymphocyte ratio (H/L) is an efficient indicator of chronic stresses in birds. In this study, we aimed to compare the H/L ratio of birds between the areas with different levels of urbanisation, anthropogenic noise and carbon monoxide (CO) emission rates. A total of 1288 birds were captured in six Cerrado forest fragments between 2013 and 2019, from which we took blood samples to produce blood smears. In each of these fragments, the noise level was measured with a sound pressure level metre. The CO rates were obtained from the National Institute for Space Research database (INPE-Brazil). There was a higher H/L ratio in individuals captured in urban areas or close to urbanisation with high anthropogenic noise levels and high CO rates, and a lower H/L ratio in individuals from preserved areas, far from urban environments with low noise levels and low CO rates. Six species (Antilophia galeata, Leoptopogon amaurocephalus, Cnemotriccus fuscatus, Lathrotriccus euleri, Turdus leucomelas and Eucometis penicillata) showed a significant difference between the areas and followed the pattern shown by the individuals. The present study showed that birds living in the urban and peri-urban sites have higher values of H/L ratio than birds from rural sites. These results suggest that the H/L ratio can be used as an environmental biomonitoring tool and an efficient parameter to assess chronic stress in birds in degraded environments.