The findings of a new study are sounding alarms over the health of Vermont’s moose population. Research conducted by Vermont Fish & Wildlife and the University of Vermont shows that the mortality rate for moose under the age of one is high (over half of all yearling moose don’t survive their first winter), and that female moose appear to be having fewer calves.

The primary culprit in both cases appears to be winter tick infestation, and mirrors a similar decline in moose numbers seen in neighboring states. Due to the warming climate in northern New England, ticks are able to survive and thrive during the winter months. The tick infestations on some moose can be so severe that they cause anemia, weakness, and death. While adult moose are better able to cope with tick infestations, mature female moose are giving birth to fewer twins in response to this environmental stress.

During 2017-2019, researchers captured 36 adult cow moose and 90 calves (~8 months old) in Essex County and fitted them with GPS tracking collars to monitor their health, survival, and reproductive rates. The study results are outlined below, and the numbers are shocking.

Results

• 87% of adults survived each year, but only 57% of adult cows gave birth, a decline of around 50% compared to birth rates in the early 2000s.
• Only 66% of newborn calves survived their first 60 days.
• Only 49% of calves (8-12 months old) survived their first winter.
• With no ticks, over 90% of calves would have survived.

Conclusions

• Winter ticks were the main cause in 74% of all mortalities and 91% of winter calf mortalities.
• Winter ticks caused the health and productivity of surviving moose to be very poor, and were the primary factor limiting growth of the moose population.