SALIVARY CORTISOL RESPONSE TO FLIES BY MOOSE CALVES

Abstract

Young animals are particularly vulnerable to environmental stressors that can impair growth and compromise survival. We used salivary cortisol, a glucocorticosteroid hormone, to measure possible stress response of moose calves in Alaska to the abundance of biting and non-biting flies relative to calf age, time of day, and ambient air temperature. We measured salivary cortisol in 5 captive calves up to 4 times daily on 25 days in June-August with corresponding on-host fly collections. We simultaneously collected 2,618 flies, of which 68% were moose flies (Haematobosca alcis), 13% coprophagous flies, 9% mosquitoes (Culicidae), 5% horse and deer flies (Tabanidae), and 2% black flies (Simuliidae). The proportion of moose flies increased steadily, representing nearly all flies by study end. Salivary cortisol levels were minimal and similar (<0.2 μg·dL^-1) from 25 to 89 days of age at ambient temperatures ranging from 13 to 34ºC, and did not increase with relative fly abundance. The lack of cortisol response is consistent with observations of minimal reaction to most flies by moose. The dense and fuzzy characteristics of calf pelage may provide a unique, protective barrier to minimize fly bites and exposure to pathogens sometimes associated with wounds or bites. Although a cortisol response to flies was not detected, vector borne pathogens are predicted to increase in a warming climate and warrant surveillance as part of proactive moose management.