ENVIRONMENT YUKON






 

Mammals

Density of snowshoe hares

 

Significance

Snowshoe hare is a key component of the boreal ecosystem. In Yukon, hares make up almost 50 per cent of available food for predators (Figure 1). Their abundance regulates the predator populations that rely on them for food. They also have a significant impact on the plant communities that they eat, and other small mammals that predators eat when snowshoe hare numbers are low.

 

Figure 1: Predators of snowshoe hare

 

The number of snowshoe hares fluctuates in 9–10 year cycles throughout the boreal ecosystem. The dominant driver of this process is predation. The cycles appear to be in sync across Yukon.

Because snowshoe hare are one of the most important components of boreal food webs, monitoring their numbers is valuable. Long-term data on their abundance can provide information on the population fluctuations of their key predators, such as lynx, which is a valued furbearer to trappers.

The timing and size of the snowshoe hare population peaks help biologists see where trends are headed when assessing potential changes in the boreal ecosystem, such as predator abundance, alternative prey abundance (e.g., arctic ground squirrels or grouse) or browse intensity (impact on shrubs). This information is valuable to research programs, park and forest management, and as baseline information for environmental assessments.

Monitoring of snowshoe hare numbers provides a continuous record of the response of this key ecosystem component to changes over time. The consequences of climate change on boreal ecosystem dynamics are difficult to predict, and biologists rely on long-term monitoring programs to detect and understand these responses.

 

Young snowshoe hare.

 

 

What is happening?

The Kaystone Boreal Species Trend (KBST) project monitors snowshoe hare density at undisturbed forested sites in different regions of Yukon.

 

Figure 2: Population density estimates for snowshoe hares in KBST areas, 2005–2015. Mark-recapture data from Kluane are given as histogram bars, and estimates from fecal pellet counts at other areas are given as points (95 per cent confidence limits). Note that the data from fecal pellet counts integrate hare density over the previous year.

 

  • 2006 was the last peak in the snowshoe hare cycle; data from the 2015 and 2016 period is being assessed to understand when the peak may (or has) occcurred, and what the amplitude was (or how high the peak was).
  • The amplitude of the snowshoe hare cycle has been diminishing over the last 30 years in Yukon, demonstrated by research in the Kluane area going back to 1973 (Krebs et al. 2015).
  • The reason for this change is currently unknown. Because the snowshoe hare cycle is mostly driven by predation pressure, the answer may be related to changes in predation success. Snow conditions are likely to change with climate change and this may affect the hunting success of both avian and terrestrial predators of snowshoe hare.
  • KBST also monitors lynx abundance via winter track counts. Their abundance fluctuates with snowshoe hare abundance. Lynx numbers appear to be increasing in all areas as the hare numbers have increased in recent years. However, lynx abundance was higher than expected for the last low of the hare cycle in Kluane, indicating potential predation pressure on alternative prey populations.

 

Taking action

 

  • The Keystone Boreal Species Trends project (KBST) has five stations for ongoing monitoring in Yukon’s boreal forests. There are stations near Faro, Kluane, Mayo, Watson Lake and Whitehorse.
  • An annual report on these trends is produced, and various researchers utilize these data to assist in understanding the dynamic food web of the boreal forest ecosystem. Access to this information is provided by the Department of Environment’s Biodiversity Programs.

 

Snowshoe hare in winter.

 

 

Data quality

KBST estimates the number of snowshoe hares by live trapping, marking and releasing individuals at the Kluane monitoring station. They also count fecal pellets yearly at all monitoring stations to come up with an estimate of how many hares are in each area.

Hare density is calculated by dividing the number of hares by the number of hectares in the monitoring area.

Data from most KBST areas are available from 2005 onwards. Monitoring has occurred in the Kluane area since 1973, but the protocols and additional areas were developed in 2004, so comparisons can only occur from 2005 onwards.

 

References

Krebs, C.J., R. Boonstra, S. Boutin, A.R.E. Sinclair, J.N.M. Smith, B.S. Gilbert, K. Martin, M. O'Donoghue, and R. Turkington. 2014. Trophic dynamics of the boreal forests of the Kluane Region. Arctic 67, Supplement 1:71-81.

Krebs, C., T. Powell, M. O’Donoghue, T. Jung, V. Loewen, S. Gilbert, S. Taylor, A. Fontaine, R. Boonstra, S. Boutin, A. Kenney. 2015. The Community Ecological Monitoring Program Annual Data Report 2015. Yukon Department of Environment, Whitehorse, Yukon, Canada.