By Dr. J.F. Therrien
A genuine Arctic species, snowy owls have been part of the cultural identity of Inuit and northern communities for centuries, and are featured in many tales and legends. From both traditional knowledge and a few punctual studies from various regions of the Arctic, we know that the snowy owl is a highly irruptive species, showing up in large numbers in a given region in a given year while being seldom seen in following years at the same site.
The main reason for such extraordinary and erratic behaviour lies in its food base. Indeed, the owl’s main prey during summer time, the lemming, also shows remarkable variations in abundance from one year to the next. The changes in lemming numbers are still under debate, but seem to be caused by a combination of snow cover and depth, as well as primary production and predators, such as the owls themselves. The snowy owl thus mirrors lemming peaks and lows by invading and deserting sites according to the abundance of its small mammal feast.
While those extraordinary peregrinations capture the imagination of many, the nomadic nature of the species poses a challenge to biologists trying to study its basic ecology and population trends. Because breeding numbers are highly variable from one year to another, conventional research methods such as banding birds with aluminum leg tags have provided very little information. Indeed, since the birds show almost no fidelity to breeding sites (they don’t return to the same nest site in consecutive years) individuals cannot be re-sighted or followed through time.
To remedy the lack of knowledge regarding this species’ basic ecology, a research group I feel lucky to be part of has been monitoring reproductive activity of snowy owls for over 20 years on one of its breeding grounds in Canada’s Arctic. Over the years, the Ecological Studies and Environmental Monitoring at Bylot Island project, led by Gilles Gauthier from Université Laval, has provided invaluable data through long-term monitoring of the sensitive Arctic ecosystem. This unique long-term Arctic-monitoring hub has scrutinized almost all species inhabiting the fragile tundra ecosystem as well as the interactions between them.
Among its most significant discoveries, the team has uncovered how tundra ecosystem organisms are tightly connected. Snowy owls are no exception and strongly react to variations in numbers of other species. Indeed, more than 95 percent of their diet during the breeding season is made of lemmings, and when those small mammals reach high densities, snowy owls show up in big numbers.
Every spring since the early 1990s, following a schedule similar to migratory birds, our research team heads North to settle on the south plain of Bylot Island in Sirmilik National Park. Facing Pond Inlet, Bylot Island is a truly special place, with spectacular mountain views and valley landscapes. The luxurious summer vegetation and typical tundra habitat serves up a perfect breeding ground for several iconic terrestrial Arctic species such as Arctic foxes and, of course, snowy owls.
Since the beginnings of this project, we have been monitoring nesting density and nesting success of snowy owls. This information is crucial in order to assess population trends, conservation status, and ecological relations between ecosystem members. For snowy owls, the breeding season starts as early as late-March. Because they rely almost exclusively on lemmings for food during the breeding season, and because lemming numbers fluctuate enormously from one year to another at a given site, going back where they bred the year before is not a good option. Instead, owls engage in continental-wide prospecting as they search for a place to settle and breed — a place with lots of lemmings.
Contrasting with most other organisms exhibiting some degree of breeding site fidelity, mobility allows snowy owls to move from one place to another annually in one of the most spectacular breeding dispersal movements on the planet. However, studying detailed patterns of zigzagging owls over huge distances and far from most northern communities is an almost impossible challenge. Luckily, recent technology has now evolved to allow us to track individual birds remotely, using satellite telemetry trans – mitters. The small backpack harnessed to the owl sends signals to orbiting satellites, which then locate the origin of the signals and send its location to researchers. This exciting technology allows us to track birds wherever they are around the globe in almost real-time.
So far, our team has tracked more than 30 breeding adults over several consecutive years from various regions of Canada’s Arctic and the results have been phenomenal. After successfully breeding on Bylot Island, individual birds have covered up to 4,000 km over more than 50 days in spring annually, scattering across Baffin Island but also as far as Prince Patrick and Borden Islands, and even Greenland and northern Quebec to breed in following years. Annual breeding dispersal distance averages 725 km, one of the largest distances ever reported, at least in terrestrial vertebrates. This predator fears few species in the Arctic and moving from one site to another doesn’t seem to discourage them. Even more, it seems to be paying off since they can lay large clutches of eggs when settling in a spot where lemmings are plentiful.
Indeed, once a pair settles for breeding, usually in May, the female will lay an average clutch of seven eggs, but we’ve seen as many as 11. The female will then exclusively insure that the precious eggs stay warm throughout the 32-day period, getting up to stretch only a few minutes a day. The male will usually be around, providing food both for himself and his incubating partner.
Since the female lays one egg every other day and incubation starts as soon as the first egg is laid, a large hatching asynchrony results, creating a large difference in size among siblings with the first being 14 days old or more when the last hatches. This, of course, translates into a disproportioned advantage of size when competing for limited food supplies. Indeed, growing owlets fight for food and an average clutch of seven eggs will usually produce around three or four fledglings.
Snowy owl chicks are vulnerable when they hatch and will stay in the nest under the comforting surveillance of their parents for about three weeks before they slowly start to walk around, usually in late June through July. In early August, when the chicks are about 30 to 40 days old, they are oThen seen hiding beside rocks in a 100-metre radius from the nest. At that time, both adults will hunt and provide food for the fast growing chicks.
When the chicks finally reach flying capacity in mid- to late August, they begin hunting on their own, though they still rely upon their parents for food for up to two to three months. As summer wanes and cold temperatures return, young owls become more independent and start to disperse. After a good reproductive year, many young owls, dispersing in various directions, will reach lower latitudes, creating winter irruptions — a phenomenon that attracts lots of attention from birders and the general public in southern regions of Canada and the northern U.S.
From a researcher’s point of view, a “snowy owl year” is always an exciting one. The last such event on Bylot Island happened in the summer of 2014. After three years without owls on our study site, we had high hopes for the magic to happen and the first sightings were reported by colleagues reaching Bylot Island in mid-May. This was a good sign.
Even though the actual mechanism used by snowy owls to assess lemming abundance under the snow in spring remains to be studied, we have learned over the years that owls are efficient in finding where lemmings are plentiful enough to sustain a hungry nest of young owlets. This means that when one nest has been found, other pairs should be seen as well, and right we were. After a few days of exploration, the number of nests quickly reached double digits.
What we didn’t know was that 2014 was to be a year for the record books. Indeed, in a core study plot of 100 km2 that has been systematically searched every year since the early 1990s, the highest number of nests ever found in a single year was 13, which occurred in 2004. During the summer of 2014, we sent that record to the archives when we found 20 active nesting pairs in the same study plot. Such density had never been recorded on Bylot Island before! Overall, including a larger portion of the Island, the total number of nests we found and monitored was 116, surpassing the previous total of 33 nests found in 2010.
Such results confirm that snowy owls react quickly and in large numbers to take advantage of a lemming outbreak. The findings also suggest that an apparently viable population of snowy owl inhabits Canada’s Arctic. However, given the fast happening changes facing the Arctic ecosystem, the importance of such long-term monitoring has never been so true and we are thankful for the support we have received over the years to conduct the project. Our long-term study site of Bylot Island has seen several lemming and owl outbreaks over the last decades, but because lemming and owl numbers fluctuate enormously annually, predicting the coming year’s numbers is a tricky task. After the peak year of 2014, odds are low for snowy owls to breed on Bylot Island in 2015, but the Arctic is wide and lemmings and owls are likely to breed elsewhere in this vast region. Will you get lucky?
Dr. J.F. Therrien is Senior Research Biologist at Hawk Mountain Sanctuary, a centre devoted to the study and conservation of birds of prey, located in Pennsylvania (USA). For almost a decade, he has been studying snowy owls in the Arctic with colleagues from Université Laval and Université du Québec a Rimouski as well as the Centre d’Études Nordiques among others. Dr. Therrien would like to thank the many colleagues and field assistants who have participated in field work over the years.
This project could not have been done without the support of the community of Pond Inlet, the Hunters and Trappers Organization of Pond Inlet, the Joint Park Management Committee of Sirmilik National Park, Parks Canada’s staff in Pond Inlet and the Union Québécoise de Réhabilitation des Oiseaux de Proie. Financial partners include the International Polar Year program from the Department of Indian and Northern Affairs Canada, the Natural Sciences and Engineering Research Council of Canada, the Nunavut Wildlife Management Board, Fond Québécois de Recherche sur la Nature et les Technologies, the Garfield-Weston award of the Association of Canadian Universities for Northern Studies, Baffinland Iron Mines Corporation, Glencore Xstrata, Centre d’Études Nordiques, Université Laval, Université du Québec à Rimouski, University of Saskatchewan and the network of Centre of Excellence ArcticNet. Finally, this study could not have been conducted without the financial assistance and support of the Polar Continental Shelf Program.