Skagit Audubon

Watching birds, protecting habitat, connecting with nature

Irruption of Snowy Owls

Snowy1        Snowy2   Snowy Owl , Photo By Ron Pera



Should we expect an irruption of Snowy Owls (SNOW) this winter?  An irruption is the movement of birds based on availability of food. Lemmings are the desired prey of SNOWs. They may eat up to 1600 lemmings per year. The four to five year cyclical pattern of the lemming population in the tundra of North America drives SNOWs south when their numbers are low. This search for food brings SNOWs to the shorelines of bays and estuaries in Skagit County. The last irruption when higher numbers of SNOWs were observed on the West Coast was 2011/2012. Therefore, this year is a non-irruptive year, but there is still a chance to see SNOWs in Skagit this winter.

In a non-irruptive year the lone male SNOW can still be seen. Ornithologists believe these are young males that venture south during the winter. Because this pattern of movement in the SNOW population is not an annual occurrence of a sizable group of birds, they are considered nomadic not migratory. Even in an irruptive year, most nomadic SNOWs are male. The females stay in the breeding area protecting their territory. The males are whiter than the females and young, who have more dark specks. The scrape nests made by females are simple depressions on bare mounds. SNOWs like open treeless areas with rolling terrain for hunting and nest protection.

Scientists have been studying the link between the lemming population and breeding habits of SNOWs for over 20 years and still cannot definitively explain the relationship. They know SNOWs will lay fewer eggs or forego breeding all together when the lemming population is low. When they do breed the clutch size can range between 3 to 11 eggs. Therefore, does fewer owls give the lemmings time to recover and increase their numbers? With fewer lemmings more owls become winter nomads. Also, does this cycle keep the SNOW population stable? Increased data collecting from both bird banding and nesting site counts will help bring answers. Their remote and widespread nesting area plus the nomadic movement of these birds makes data collecting challenging. That doesn't even account for the aggressive territorial behavior researchers face when observing open tundra nesting sites in nearly 24 hours of daylight.

Both male and female SNOWs will defend their territories. They have very few predators, but their vulnerable eggs and young can become prey for arctic foxes, gray wolves, and avian predators like corvids, jaegers and raptors. In addition to direct attacks with talons, SNOWs have been observed using distraction displays to lead predators away from their nests. They are so effective at protecting an area that other birds such as snow geese will nest nearby benefiting from the SNOWs security. The eggs of SNOWs are laid asynchronously. A single egg is laid every other day. Depending on the clutch size, a female can be laying eggs over a three week period. Eggs hatch within 30 days, so the female will be incubating and feeding young at the same time. Or better stated “screaming” at the male to provide food while she stays on the nest. The first hatched owl can be 10 times larger than the last hatched sibling. Even with this size difference there is little to no conflict or siblicide among the hatchlings.

When SNOWs are in Skagit County they hunt for small mammals, fish and other birds. Good areas to look are on the Samish Flats at the West 90 and on Fir Island at Jensen Access. They can be seen near the ground on low perches such as driftwood, logs or fence posts. Consider joining a scheduled field trip to one of these areas this winter. Also, check for Bird Sightings under the heading Birding on our website for Snowy Owls. We do not expect an irruption, but look for first year males spreading their wings over Skagit.

References available upon request


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