Editor´s Choice - Movements and breeding dispersal of Snowy owls

Submitted by avianbiology on 13 November 2014.

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This is a highly fascinating study of how spring migration and breeding dispersal are combined in a unique way by snowy owl females based on satellite tracking results from nine females during three years. The study focuses on the birds’ movements from March to June, from their departure from winter sites to settling at a breeding site. State-space modelling has been used to estimate the most probable routes and to distinguish between directed and search movements. The initial phase of spring movements has been designated as directed movement, followed by prospecting movement from the first occasion of search movements up to settling at breeding site. Thus prospecting movement consists of an alternation between search periods and directed movements. The variation in durations and distances of the owls’ spring movements and locations of breeding sites in relation to spatial and temporal variation in lemming abundance are highly fascinating, providing much novel insights about movements and breeding of snowy owls and their potential importance in the arctic predator-prey systems. Breeding dispersal distances between consecutive years were impressive (up to more than 2000 km) and similar to the geographical scale of lemming cycle synchrony.

Thomas Alerstam, Editor in Chief


Below you can read the author´s own words about the study.

Tracking snowy owls has been (and still is) a great challenge. The fact that those birds are highly mobile, that they show almost no breeding site fidelity and disperse over huge distances from one year to another yet increases the challenge. The use of satellite telemetry has obviously helped tremendously in recent years, but still, working conditions in the high Arctic breeding grounds, with the inherent technical and climatic difficulties remain daunting.

So, to be able to track snowy owls over 4 years consecutive breeding seasons (2007 to 2010), was very exciting. Every year, we were thrilled to see "our" tracked birds moving so much between different breeding locations. But we were even more surprised when we noticed one of those owls coming back to our 400 km2 study site in 2010, after breeding on Baffin Island in 2008 and then on Greenland in 2009. Exactly 3 years after being caught on its nest, that bird settled and bred roughly 1 km away from its 2007 nest site. As part of our global project, we wanted to take that rare opportunity to know if the bird was doing all right after wearing a transmitter for 3 complete years and to remove the unit as the battery was dying out.

So, with a lot of efforts (and some luck), we were able to recapture the bird, 3 years later, and remove the unit. We assessed the bird’s mass as an indicator of body condition and confirmed breeding (that female was raising a clutch of 7 chicks). Those few pictures clearly show a happy biologist (!) with a perfectly fine and healthy breeding female snowy owl.

When we think of our 400 km2 study area and compare it to the actual circumpolar breeding range of the species, and taking into account the dispersal capabilities of the species, we feel pretty lucky to have been able to meet that owl on 2 different non-consecutive breeding seasons.

Jean-François Therrien (Author)

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Editor´s Choice