Intrinsic factors influence a physiological measure across a forest bird community
Authors/Creators
- 1. Philipps University of Marburg
- 2. University of Giessen
Description
Physiological stress parameters have the potential to serve as valuable early warning indicators for the conservation of animal populations. However, measuring stress in wildlife is often challenging, due to the lack of knowledge about baseline levels, and intrinsic differences between individuals across species. This study is aimed at filling this gap by investigating the influence of intrinsic factors, including sex, age, body condition, and reproductive status on the physiological stress of a forest bird community. For measuring stress levels, we used the heterophil to lymphocyte (H/L) ratio of the bird community, which was assessed using a novel deep learning approach based on Convolutional Neural Networks applied to whole blood smear scans. Using phylogenetically controlled analyses across the bird species, we found higher H/L ratios in adult birds than in juveniles and observed higher stress levels in females than in males. While body condition had no effect on the H/L ratio, reproductive birds tended to have higher H/L ratios than non-reproductive birds, regardless of their sex. Furthermore, we found a robust phylogenetic signal of the H/L ratio in the studied bird community. Our results emphasize the importance of considering intrinsic factors when using stress physiology for assessing the condition of bird populations and communities.
Notes
Funding provided by: Hessian State Ministry for Higher Education, Research, and the Arts
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Methods
Birds were captured during the breeding seasons between mid-March and August at ten sites in the forest interior. No lures were used to attract the birds to the nets to avoid artificially influencing their natural movement or stress levels. The mist nets were checked every 15 to 20 minutes. Upon capture, each bird was marked with a ring for future identification (e.g., re-captures), with the necessary permissions obtained from the Heligoland Bird Observatory (Institute of Avian Research "Vogelwarte Helgoland" (IAR), Germany). We measured morphological characteristics of each bird and assessed sex, age, and breeding status. Further, a blood sample was taken for identifying the sex if morphological identification was not possible, and a blood smear for leukocyte counts was taken. The blood smears were fixed in methanol and treated with Giemsa stain. To determine the H/L ratio, we digitized the blood smears by scanning them with a Leica Aperio AT2 Scanner and a 40X microscope objective lens and applied a novel Convolutional Neural Network for determining and counting the cells.
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Additional details
Related works
- Is source of
- 10.5061/dryad.0cfxpnw8d (DOI)