Physiological and Behavioral Costs and Consequences of Fly (Diptera) Exposure for Moose (Alces alces)

Abstract

I studied the responses of wild ungulates to harassment by flies (Diptera) by reviewing the literature on North American ungulates and studying the behavior and physiology of female moose (Alces alces) in a boreal forest in Alaska. Hair and skin provide morphological resistance to flies at low exposures, but behavioral and physiological responses are used to reduce and tolerate flies as exposure increases. Caribou (Rangifer tarandus) avoid flies, which displaces foraging and reduces body mass gain in summer. Moose tolerate flies through the summer. I found that flies do not trigger a release of glucocorticoid hormones in either moose calves or adult moose as a stress response. The dense hair of the neonatal coat resists flies, but calves still suffer morbidity and mortality from parasitic diseases carried by flies. Adult moose molt and lose their barrier of protection in June and July when flies are the most abundant, and sores appear on their hind legs. Leg sores of adult moose were infected with a parasitic nematode within the genus Onchocera, which is likely transmitted by black flies (Diptera: Simuliidae). The number of sores on the hind legs of an individual was positively correlated with total body fat, which suggests that tolerance of flies increases gain of energy from foraging over the summer. Conversely, the number of sores was negatively correlated with serum albumin, which indicates the use of body protein to repair injuries from flies and parasites. Moose altered daily movements in response to flies; on cool days (8°C), movement rates increased with the abundance of flies. However, on warm days (20°C), movement rates were not affected by flies probably because cooling takes priority. Time spent in black spruce forests increased with both air temperature and with counts of flies. Warm summer temperatures create an ecological trap for moose when heat gained while foraging is dissipated at rest in shady, wet habitats preferred by flies that adversely affect the fitness of moose.