Nicholas Larter and Danny Allaire

Government of the Northwest Territories

Department of Environment and Natural Resources (ENR), Fort Simpson

Northwest Territories, Canada

Authored by Thomas Gray, CLS America

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The Dehcho boreal caribou study was initiated in 2004 at the request of local First Nations. Boreal caribou have cultural and spiritual significance to First Nations people, and are designated as a Threatened species. 

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The Department of Environment and Natural Resources, Dehcho Region, initially deployed 10 Argos satellite collars on adult female caribou that year and have deployed collars each year since (exception 2011) with a total of 145 deployed including both Argos and Iridium transmitting collars. Note: CLS America offers Argos and Iridium data management solutions.

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This study is the longest running study of boreal caribou in the Northwest Territories, Canada.

 

Location data showed that female caribou spread out during the calving period, likely to avoid predation. The team discovered that daily movement rates of pregnant females dropped dramatically from 6km per day, to 0.2km per day when calving, and remained at less than 1km per day post calving for about a week (Nagy 2011).

 

This distinct movement pattern allows the team to determine when and where a female boreal caribou calved, or not. The team analysed these data to determine if females exhibit site fidelity to calving locations. In some cases they do and in others they do not thus it is a bit inconclusive although still debatable.

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Historically, the peak of calving season is 15 May ± 7 days.  In May 2015, 58% of all calves were born before the 15th of May, 2015. Individual females have remarkable consistency in birthing dates. For those females collared over 4-6 calving periods, many had calves on almost the same date each year.

 

The high numbers of births (94% based upon movement data of collared females) and pregnancies (92% based upon blood samples of captured females) implies that capture and wearing a collar has not prevented females from becoming pregnant nor bearing calves. Because calf births can be determined from movement data, aerial surveys to monitor calving are unnecessary which reduces disturbance.

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Despite high pregnancies and births, annual weather variability plays a large role in calf survival. Calves born in May 2015 suffered the lowest survival rates in the last five years with only 24% making it through March 2016.

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This low survival rate can be attributed to a relatively mild winter (2015/2016) with little snow cover through February and warmer temperatures (rarely dropped to -35o C). Due to the weather conditions, caribou movement increased; therefore, predators such as wolves had a greater chance of crossing paths with caribou.

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Since the project began in March 2004, 67 collared caribou have died, and of those 53 death sites were visited. The greatest mortality factor of the visited sites was suspected wolf predation (77%) followed by harvest (11%), natural causes associated with malnutrition (9%), and one from black bear predation.

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The team was able to gather age at death on 25 of the 53 visited sites. Age at death is determined by counting stained cementum annuli on the cross sections of teeth (preferably the incisor), similar to counting the rings of a tree. Until this year, age of death included six teenagers (the oldest 17).

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This year caribou #206 became the oldest recorded death, 22 years old. She had given birth at 20 and 21 years old, but the team was unable to determine if she calved at 22 years.

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How does this compare to caribou elsewhere? 

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As of August 2016, Matson’s Laboratory had aged 45,014 caribou teeth from all over North America, only one other tooth (from an Alaskan caribou) was aged at 22 years (Larter and Allaire 2016).

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Nic Larter, ENR, noted, "Without the Argos satellite data we would not have been able to document the distinctive movement pattern indicative of calving, or document the amazing longevity of boreal caribou in the region.”

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This program has been funded by the NWT Western Biophysical Program, Environment Canada, and the Cumulative Impacts Monitoring Program (NWT).

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Read the latest full report by clicking the PDF button below, and for all progress reports, visit the ENR website.