Measuring physiological stress in Australian flying-fox populations

Abstract

Flying-foxes (pteropid bats) are the natural host of Hendra virus, a recently emerged zoonotic virus responsible for mortality or morbidity in horses and humans in Australia since 1994. Previous studies have suggested physiological and ecological risk factors for infection in flying-foxes, including physiological stress. However, little work has been done measuring and interpreting stress hormones in flying-foxes. Over a 12-month period, we collected pooled urine samples from underneath roosting flying-foxes, and urine and blood samples from captured individuals. Urine and plasma samples were assayed for cortisol using a commercially available enzyme immunoassay. We demonstrated a typical post-capture stress response in flying-foxes, established urine specific gravity as an attractive alternative to creatinine to correct urine concentration, and established population-level urinary cortisol ranges (and geometric means) for the four Australian species: Pteropus alecto 0.5-305.1 ng/mL (20.1 ng/mL); Pteropus conspicillatus 0.3-370.9 ng/mL (18.9 ng/mL); Pteropus poliocephalus 0.3-311.3 ng/mL (10.1 ng/mL); Pteropus scapulatus 5.2-205.4 ng/mL (40.7 ng/mL). Geometric means differed significantly except for P. alecto and P. conspicillatus. Our approach is methodologically robust, and has application both as a research or clinical tool for flying-foxes, and for other free-living colonial wildlife species.

Figure 1

Flying-fox roost study sites for pooled urine collection and individual animal capture in Queensland and New South Wales, Australia.

Figure 2

Individual plasma cortisol concentration of P. alecto (n = 6) at 3 min and 60–90 min bleed post-capture.

Figure 3

Mean plasma cortisol concentration ± standard error of mean (SEM) of P. alecto (n = 11) at 3 min and 60–90 min bleed post-capture.

Figure 4

Mean urinary cortisol concentration (USG corrected) ± SEM of P. alecto (n = 8) at 3 min and 60–90 min collection post-capture.

Figure 5

Mean blood glucose concentration ± SEM of P. alecto (n = 11) at 3 min and 60–90 min bleed post-capture.

Figure 6

Distribution of pooled population urinary cortisol concentrations (USG corrected) of Australian Pteropus species.