Blood oxygen binding properties for the burrowing owl,Athene cunicularia

Isocapnic O2 equilibrium curves (O2ECs) were generated for whole blood of 4 adult burrowing owls (Athene cunicularia) using thin film techniques. Atin vivo pHa (7.49 ± 0.02;mean± 1SEM) and 41 °C, the PO2 at half saturation (P50) was42.3 ± 0.8 Torr. CO2 and fixed acid (H+) Bohr slopes (Δlog P50/ΔpH) were−0.46 ± 0.01 and−0.42 ± 0.02, respectively, demonstrating a small specific CO2 effect. CO2 and H+ Bohr slopes were saturation-independent between 0.1 and 0.9 S. Hill plots forAthene blood were non-linear; the Hill coefficient (n) increased from 2.6 below 0.4 S to 3.4 above 0.6 S. Owl equilibrium data were accurately described by the equation:S= [(7.77 × 106)/(P4 + 44P3 − 108P2 + 3.5 × 104P) + 1]−1. This complex O2EC shape may result from Hb heterogeneity; isoelectric focusing showed 4 isoHbs with a molar ratio of9:1:1:1. This study revealed no apparent adaptations ofAthene blood for hypoxic and hypercapnic conditions. We conclude that the observed blood O2 binding properties promote tissue O2 delivery during periods of surface activity. While occupying its burrow, the owl compensates for moderate alterations in inspired gas composition partly through increased ventilation.