Pathogens, Nutritional Deficiency, and Climate Influences on a Declining Moose Population

• Published in: Wildlife monographs 2006-12, Vol.166 (1), p.1-30
• Main Authors: MURRAY, DENNIS L, COX, ERIC W, BALLARD, WARREN B, WHITLAW, HEATHER A, LENARZ, MARK S, CUSTER, THOMAS W, BARNETT, TERRI, FULLER, TODD K
• Format: Article
• Language: English
• Subjects: Alces alces; Animal and plant ecology; Animal populations; Animal, plant and microbial ecology; Animals; Anthropogenic factors; Applied ecology; Bears; Biological and medical sciences; Blood; Bone marrow; climate; Climate change; Climate effects; Competition; Conservation, protection and management of environment and wildlife; Death; Deer; Demecology; Depopulation; disease; Energy balance; Fascioloides magna; Females; Food; Food quality; Fundamental and applied biological sciences. Psychology; Infectious diseases; Liver; liver fluke; Malnutrition; Mammalia; Minnesota; moose; Mortality; nutrition; Parasites; parasitism; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Pathogens; Pathology; Population decline; Population dynamics; Population growth; population viability; Pregnancy; Summer; Time series; Trace elements; Vertebrata; Wildlife ecology; Wildlife management; Winter
• ISSN: 0084-0173; 1938-5455
• DOI: 10.2193/0084-0173(2006)166[1:PNDACI]2.0.CO;2

Several potential proximate causes may be implicated in a recent (post-1984) decline in moose (Alces alces andersoni) numbers at their southern range periphery in northwest Minnesota, USA. These causes include deleterious effects of infectious pathogens, some of which are associated with white-tailed deer (Odocoileus virginianus), negative effects of climate change, increased food competition with deer or moose, legal or illegal hunting, and increased predation by gray wolves (Canis lupus) and black bears (Ursus americanus). Long-standing factors that may have contributed to the moose decline include those typically associated with marginal habitat such as nutritional deficiencies. We examined survival and productivity among radiocollared (n = 152) adult female and juvenile moose in northwest Minnesota during 1995–2000, and assessed cause of death and pathology through carcass necropsy of radiocollared and non-radiocollared animals. Aerial moose surveys suggested that hunting was an unlikely source of the numerical decline because the level of harvest was relatively low (i.e., approx. 15% / 2 yr) and the population usually grew in years following a hunt. The majority of moose mortalities (up to 87% of radiocollared moose [n = 76] and up to 65% of non-radiocollared moose [n = 84]) were proximally related to pathology associated with parasites and infectious disease. Liver fluke (Fascioloides magna) infections apparently constituted the greatest single source of mortality and caused significant pathology in the liver, thoracic and peritoneal cavities, pericardial sac, and lungs. Mortality due to meningeal worm (Parelaphostrongylus tenuis) was less prevalent and was manifested through characteristic neurological disease. Several mortalities apparently were associated with unidentified infectious disease, probably acting in close association with malnutrition. Bone-marrow fat was lower for moose dying of natural causes than those dying of anthropogenic factors or accidents, implying that acute malnutrition contributed to moose mortality. Blood profiles from live-captured animals indicated that those dying in the subsequent 18 months were chronically malnourished. Relative to other populations, average annual survival rates for adult females (0.79 [0.74–0.84; 95% CI]) and yearlings (0.64 [0.48–0.86]) were low, whereas those for calves (0.66 [0.53–081]) were high. Pregnancy (48%) and twinning (19%) rates were among the lowest reported for moose, with reproductiv