Identification of Rocky Mountain Mule Deer migration routes and seasonal ranges within the St’at’imc Nation Territory and BC Hydro Footprint


The Lillooet Tribal Council began a three-year study of Rocky Mountain Mule Deer migration patterns through the northern St’at’imc Territory in March 2007. The study was undertaken to see if there are impacts on migration within the footprint of the Bridge-Seton hydroelectric power generation plant. This study was a partnership effort between the BC Ministry of Environment, Forest Investment Account, Bridge Coastal Restoration Program and the St’at’imc First Nations.


Mule Deer are experiencing declines across much of their present range, especially in the Lillooet region where numbers have fallen drastically at many traditional sites. This study was conducted near the town of Lillooet in the interior of southwestern British Columbia.

Methods and Materials / Study area

Using helicopter net-gunning procedures, fourteen GPS collars were affixed to does, or female Mule Deer, on the spring range on the west side of the Fraser River between 19 and 80 kilometres north of Lillooet. A total of 14 mule deer were collared and then monitored by helicopter and fixed wing aircraft through the summer.

Results of the Study

Twelve of the 14 collars were successfully recovered, and the results indicate a wide range of migration routes, with each doe taking a unique route to the summer fawning range. The range included 97 km one-way; less than 20 km with distinct elevational movement; and more than 20 km with significant elevational component. One doe remained in the spring range and traveled less than 3 km. Mule deer north of Watson Bar Creek migrated over five times the distance farther than those south of the creek. Spring migration began May 17 and departures continued over a period of about 10 days. Autumn departure was more synchronized with departures beginning September 22 and continuing for 7 days.

Discussion / Implications of the study

St’at’imc and non-St’at’imc residents have been noticing a significant decrease of the number of mule deer on important spring range, although there is no empirical data to support this. Some residents report there are less than a third of historic numbers present.

Mule Deer are declining in most portions of the Intermountain Province (IM) of the Columbia Basin of Washington State and adjacent regions. The cause of this decline is not known but are believed to be related to habitat changes caused by dams and irrigation agriculture.  In an interesting ecological twist, increasing White-tailed Deer populations and increasing predator populations may also be contributing to the declining population of Mule Deer.

Not much is understood of Mule Deer migration patterns despite their wide range across North America. Most research is focused on how they live as opposed to how they move through their environment. A couple of studies on Mule Deer migration distance do report that migrations appeared to vary from 60km to 120 km between winter and summer ranges.

This study indicates Mule Deer vary widely in their migratory behaviour, showing a strong tendency towards foraging on irrigated agriculture fields with escape terrain nearby as part of their spring range. Some do not stray far from these fields through the summer. However, several mule deer migrated a significant distance between their spring range and their summer fawning range. Reasons accounting for this are currently unknown, but are likely related to nutritional opportunities, predation and genetics.

Suggested action/ Future direction

This project was designed as a multi-year study to account for between-year differences in migration patterns and to increase the geographic extent of collaring. Recommendations for the future include:

  1. Continue collaring to increase sample size;
  2. Conduct ground-truthing habitat plots at important features identified in 2007
  3. Investigate productivity rates using a pregnancy-specific protein marker
  4. Relate migration routes to land use through remote-sensing imagery.

Conclusion of the Research

It is expected that information gained from this study, which is Year 1 in a 3-year study will help those charged with wildlife habitat and land management to better conserve Mule Deer populations.

  • Source Ken Wright. 2008. 2007-2010 - Mule Deer - Lillooet - BC Hydro FWCP Coastal. Report prepared by the Lillooet Tribal Council. Available at : [Accessed 03/2021].