Wounded but unstressed: Moose tolerate injurious flies in the boreal forest

Abstract

Moose (Alces alces) in boreal habitats feed and rest where they are exposed to Dipteran flies and the parasites they carry. We collected 31,905 flies during the summer from 12 habituated moose on the Kenai Peninsula, Alaska. Moose flies, Haematobosca alcis (Snow), Diptera: Muscidae-a species that completes its entire life cycle on or around moose-accounted for 91% of flies collected; the reminder of the flies collected included mosquitoes (Culicidae), black flies (Simuliidae), and deer flies (Tabanidae). Flies impose physiological costs for moose, e.g., vectors for parasites such as Legworm (Onchocerca spp.) which causes sores on the hind legs of moose. We found that the number of sores present on the hind legs of moose is positively correlated with body fat, which suggests a correlation between gains of energy and damage from flies. We also found that the number of sores is negatively correlated with serum albumin, which is indicative of an inflammatory response and body protein being used to repair injuries from flies and parasites. The number or type of flies present on a Moose were not correlated with the concentration of corticosteroids in saliva or feces. Flies do not elicit a stress response in moose even though the costs of repairing wounds and resisting infections of those wounds likely reduce gains of protein from summer foraging. Moose can tolerate the injuries from biting flies with regular gains from summer foraging but exposure to insect-borne parasites poses a risk to reproduction and survival.

Keywords: Alces alces; Diptera; cortisol; flies; immune response; molt; moose; serum; sores.

Fig. 1.

Box plots with median, 25th percentile, 75th percentile, and range (bar) of the start of loss of hair on the area above the hock (n = 32; left box plot), emergence of sores in this area (n = 33; middle box plot), and completion of molt (n = 28; right box plot) in female adult Moose at the Kenai Moose Research Center, Kenai Peninsula, Alaska, United States.

Fig. 2.

Marginal predictions of ingesta-free body fat (%; A) and serum albumin (g·dL⁻¹; B) on the average number of sores per hind leg of female adult Moose (n = 10 series of colors, individuals) in July at the Kenai Moose Research Center, Kenai Peninsula, Alaska, United States, based on robust linear regression (R² = 0.599, P = 0.014).

Fig. 3.

Marginal predictions and observations (dots), of Julian day on flies (flies·s⁻¹) netted from female adult Moose (n = 12) at the Kenai Moose Research Center, Kenai Peninsula, Alaska, United States, based on linear regression (R² = 0.216, P = 0.007). Pie chart shows the percent of total flies collected in each group (colors).

Fig. 4.

Flies (flies·s⁻¹) predicted to occur at time of collection and the stress response of female adult Moose (n = 12) at the Kenai Moose Research Center, Kenai Peninsula, Alaska, United States, measured as cortisol in saliva (A; µg·dL⁻¹) or corticosteroids in feces (B; µg·g⁻¹).