Written by: Audrey Robillard (Ph.D student), Jean-François Therrien (Senior Research Biologist, Hawk Mountain sanctuary and former PhD student in our team), Gilles Gauthier (Research director)

Université Laval (Laval University)

Gilles Gauthier Lab.

Québec, Canada

​

Prince of street lights and king of snow-covered fields, the snowy owl is the official bird of the province of Quebec, Canada, as it embodies the white winters and northern climate of this region. However, much remains to be known on these tundra-nesting predators with a circumpolar distribution. 

​

During the breeding season, snowy owls are considered lemming specialists as they feed almost exclusively on these small mammals. Lemmings are well-known for their 3-4 year cyclic population fluctuations, and snowy owls only settle to breed in areas with high lemming densities. In winter, on the other hand, a surprising diversity of strategies has been documented for this predator. Snowy owls are regular winter migrants in the Canadian Prairies and the American Midwest, where the open landscape resembles their tundra homeland, although their abundance fluctuates annually. In the eastern and western portions of the continent, this species also makes irruptions every 3-4 years, a not-so-surprisingly similar period to that of the cyclic fluctuations of its favorite prey. Factor influencing their southern irruptions has only been recently elucidated by our team (Robillard et al. 2016). 

​

Because of the difficulty of accessing the remote arctic areas where the species breed, we still know very little of the ecology and especially the annual movements of this nomadic and elusive predator. However, thanks to the ARGOS system, this technology now enables us to tackle this logistical challenge. In 2007, we started a project to assess the breeding and wintering ecology of snowy owls and their movement patterns during the non-breeding season. We equipped a total of 31 adult snowy owls with ARGOS satellite transmitters (Microwave telemetry, USA, PTT-100 (n=15); North Star Science and Technology, LLC, USA, PTT-30G (n=16)) in the Canadian Arctic over 4 breeding seasons. Bylot Island, NU is our main research site but as snowy owls are not nesting there every year, other sites were also visited. Thus, we have equipped 12 females on Bylot Island in 2007 and 10 in 2014, 1 male at Mary River, Baffin Island, NU in 2011 and 8 females at Deception Bay, Nunavik, QC in 2013. 

​

Transmitters were installed on the owls using a backpack harness with Teflon straps. For the owls captured in 2007 and 2011, we chose to receive greater snowy owl locations in spring and summer (i.e. ~2-3d intervals) and less in winter (i.e. ~5d intervals) as these initial studies focused on pre-breeding movement patterns. Inversely, for birds captured in 2013 and 2014, we have set transmission parameters to obtain a greater number of locations in fall and winter and rather than in spring and summer as the main focus had switched to the wintering ecology. Although transmitter batteries were originally set to transmit up to 2 years, we have been happily surprised that some of them reached 3 years. The devices weighted 30g, which corresponds to 1.4% (range 1.2% to 1.6%) of the birds’ body weight and did not affect owls’ survival or reproductive performances (Therrien et al. 2012).

 

Using these tracking devices, Therrien et al. (2011, 2012) have documented surprising migratory movements in snowy owls. Indeed, although some owls did travel far inland in the Canadian Prairies and American Midwest, the majority actually stayed in the Arctic during the winter. Moreover, most of them also made an extensive use of the sea ice, up to 186 days in one case, which was completely unknown apart for some anecdotal observations. These exciting results brought new interrogations on the relative contribution of marine prey to the diet of wintering snowy owls and the potential carry-over effects it may have on their subsequent reproduction performances, a topic that we are currently investigating. The shift to the marine environment is especially surprising for a species that specialised so much on small mammals during the breeding season. 

​

Satellite tracking has also revealed one of the longest individual breeding dispersal distance between consecutive years ever recorded in adult birds, a distance that averaged 725 km (range 18 to 2224 km; Therrien et al. 2014). This confirmed their total absence of faithfulness to a particular breeding site, a result that contrasts with the vast majority of migratory birds.

​

Tracking of snowy owls using the ARGOS system has allowed our team to document an important and puzzling part of the snowy owl annual cycle but also generated many new questions for future research!