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Female and Male Galápagos Short-eared Owls Differed in Several Blood Values

Galápagos Short-eared Owl on Genovesa Island
Research · Physiology

A 2026 study established haematology and plasma-biochemistry reference intervals for Galápagos short-eared owls (Asio flammeus galapagoensis) from Floreana Island. Reference intervals describe the range of blood values expected in clinically healthy animals and provide a baseline for interpreting later samples. The analysis used results from 62 clinically healthy adults temporarily held in human care during a rodent-eradication programme designed to protect the island ecosystem.

The owls had been brought into care because eradication bait created a risk of secondary rodenticide exposure to the island’s native raptor. Health examinations and blood sampling were carried out after the birds had spent several months under managed care, with the intention of releasing them after the poisoning risk had subsided. Molecular sexing identified 29 males and 33 females, allowing the researchers to compare blood values between the sexes.

Several blood values differed between females and males

Several blood values differed between the sexes. Females had higher packed cell volume — the proportion of blood made up by red blood cells — as well as higher monocyte counts, total protein, calcium and phosphorus. Males had higher uric acid and glucose concentrations. The authors note that the monocyte difference was too small to suggest a clinically important change. They also point out that calcium and total protein can vary in female birds with reproductive hormones; the elevated values here occurred outside the period normally associated with preparation for egg laying and may therefore reflect broader physiological differences between the sexes. The study also documented leukocyte morphology.

The reference values can support future health monitoring

The authors present these baselines as a tool for assessing the health of this distinctive island population during conservation work and for comparing values after the owls return to the wild.

Sources and image credit

  1. Vaasjo, E., Nieto-Claudin, A., Castaño, P. A., Mendoza-Alcívar, G., Fessl, B., Huacuja García, V., Apakupakul, K., & Deem, S. L. (2026). Haematology and biochemistry reference intervals of Galapagos short-eared owls (Asio flammeus galapagoensis) from Floreana Island. Conservation Physiology, 14(1), coag013. https://doi.org/10.1093/conphys/coag013Primary open-access research article published 2 March 2026 under CC BY 4.0. Blood results from 62 clinically healthy adult Galápagos Short-eared Owls temporarily held in human care during a rodent-eradication mitigation programme were used to establish haematology and biochemistry reference intervals. PCR sexing identified 29 males and 33 females; females had higher packed cell volume, monocyte counts, total protein, calcium and phosphorus, while males had higher uric acid and glucose.

Image: claumoho — wild Galápagos Short-eared Owl (Asio flammeus galapagoensis) on Genovesa Island, Ecuador, photographed 26 August 2011; Wikimedia Commons / Flickr; representative photograph of the same subspecies, not an owl sampled in the Floreana study · CC BY 2.0 · Source

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