EPOW - Ecology Picture of the Week

Snowies on the Driftwood

Snowy Owl (Bubo scandiacus), Family Strigidae
Washington State, USA

Explanation:   This winter is providing a rare treat for birders, photographers, and anyone with an interest in wildlife and nature.  An impressive "invasion" of Snowy Owls has occurred in southern Canada and all over northern U.S., and is generating considerable public interest and media attention. 

In some locations, the density of these wintering Snowy Owls is truly impressive, with as many as 20 owls visible from a single location!

Snowy Owls breed on the Arctic tundra and seek out similar, open habitats during winter. 

There has been considerable discussion and speculation about the causes for the Snowy Owl irruption, but one aspect of their winter habitat ecology, when they appear along the coastline of western North America, has received little attention.  That is the role of driftwood logs. 
  

Driftwood logs long recognized as important habitat features in estuaries and other coastal habitats (Maser and Sedell 1994).

But they also serve as important microhabitat features for the wintering Snowy Owls that favor these coastal habitats.

Coastal dune and grassland areas are favored winter habitats which owe their persistence at least in part to driftwood logs which block windblown sand and help stabilize these sites.

Snowy Owls often perch on coastal driftwood logs for a number of possible reasons, including:

• spotting small mammal prey such as rats and voles,

• keeping an eye out for predators such as hawks and falcons, and

• display prominence for mate attraction,

They also often perch beside driftwood logs as shelter from coastal storms and high winds.

These driftwood logs may also provide cover and habitat for small mammal prey.  And possibly, Snowy Owls may be perching up high as an interspecific signal to other Snowy Owls to announce or even defend their feeding territory.  

Snowy Owls also perch on higher ridges on the ground, at least some of which, along the coast, are created by buried driftwood logs.  

In other environments, such as the high Arctic where trees do not grow and logs are not available, Snowy Owls use other raised sites including vegetated hummocks and fence posts.
  

Snowy Owl hunting for tundra voles and lemmings 
from a tussock of tundra grass on the 
North Slope of Alaska along the Arctic Ocean. 
No trees grow here!

Along the Dalton Highway in the wind-swept open tundra
of far northern Alaska, Snowy Owls sometimes use whatever
vantage points they can gain, from which to spot prey.
  

We are unaware of research that has studied the relationship between the availability of driftwood logs along the coast and the health of Snowy Owl visitors.  But it is clear that the logs play a key role in the owls' behavior and perhaps in their very survival.  

  

Information:
     Sedell, J., and C. Maser.  1994.  From the forest to the sea: the ecology of wood in streams, rivers, estuaries, and oceans.  St. Lucia Press, Delray Beach, FL.  200 pp.