Topic: Physiology, diseases and genetics
Moose and Winter Ticks in the Northeastern US - A 50 Year Itch…
Pete Pekins1
- University of New Hampshire, USA
Abstract
Moose (Alces alces) in the northeastern United States are at their southern range boundary, yet are the largest regional population in the lower 48 states largely due to abundant foraging habitat within private commercial forests, lack of predation, and conservative harvest. This population exploded in number and range in a 20-year period beginning in the mid-1970s, but declined measurably in the last 15 years. Data from >500 radio-marked cows and calves provided unequivocal evidence that decline within the core range was related directly to winter tick (Dermacentor albipictus) infestations causing epizootics (> 50% mortality of 10-month old calves) most years, and suppressed productivity of yearling and adult cows. The physiological impact of blood loss associated with winter ticks is related to infestation level, body mass and age of moose, and timing. Body mass and infestation level were predictive of calf survival, and although adults rarely died from infestation, maturity was delayed in yearling cows and adults had low twinning and successive birthing rates. Energy balance models predict that most pregnant cows in their last trimester would be compromised physiologically from concentrated blood loss, as would small-medium sized calves with minimal body fat in late winter. Likewise, agent-based models grounded in local field and habitat use data predict calf mortality similar to that measured with radioed moose. Because use of optimal foraging habitat is similar in spring and autumn, a local moose population creates a self-sustaining, host-parasite relationship, with the impact of a warming climate overarching – infestation level largely reflects the autumnal questing period which lengthens over time. Winter tick parasitism is arguably the major constraint in the overall health and productivity of this regional moose population, yet because it is density dependent, few remedial options exist other than reducing host density – an exercise in “counterintuitive education”.