Snowy Owl  Stomach Pellets

Snowy Owls eat their prey more or less whole, bones and all.  They then cough up the undigestible parts as a pellet later.  I made weekly surveys for pellets out to the South Jetty of the Columbia River during the irruption of 2005-06 and searched for pellets at regular owl loafing sites.  I identified four loafing sites that owls consistently used and where pellets were recovered.  Analysis of the pellet contents follows below.  The results were also published in Northwest Naturalist [Spring 2007 88(1):12-14].  Scott Carpenter has fascinating pictures of a SJCR Snowy yacking up pellets at his photo site.  And my method for handling pellets is included (along with other information) at the SNOWY OWL FAQ.


Snowy Owl pellet 20051206-2-1

Snowy Owl pellets are pretty large and as can be seen in the above 
photograph, the bird that produced this pellet has been eating rodents
and small shorebirds. 



Black Rat (Rattus rattus) skull recovered from pellet 20051206-2-1.  According 
to Verts and Carraway (1998), the average Black Rat is about 35cm long, nose 
to tail and weighs about 120g.

Number of pellets examined = 62
Average length = 8.0 ± 2.0 cm  (range = 4.0 to 12.5) 
Average width = 3.1 ± 0.4 cm  (range = 1.9 to 4.2)

Contents as of 01-31-2006:
  Rattus rattus  40%
  Red Phalarope  31%
  jay sp. (prob Steller's Jay)  1%
  Bufflehead   19%
  unknown rodent (prob Microtus)  1%
  unknown bird  8%

Pellets containing rat bones usually had one rat per
pellet (only one so far definitively contained two).
Most of the pellets containing phalarope parts had at
least two birds per pellet (three had only one; two 
definitively had three).

South Jetty owls do some prep of prey before eating.
Phalarope wings and legs are routinely removed,  heads
are often removed.  I also found one Black Rat head 
that had obviously been removed.

 


 

These are Red Phalarope bones from pellet 20051223-2-5.  Large numbers of phalaropes were blown to shore during a series of storms beginning around Dec 20.  Many observers have reported watching Snowy Owls catching phalaropes. For a close to full-sized scan of a reassembled phalarope skeleton click here.

The beak in the center was recovered from pellet 20051223-2-4.  It has tentatively been identified as jay sp., most probably a Steller's Jay.  The other two skulls are American Robin and hesperis-type American Crow (small Pacific Northwest  variety).


Small differently shaped long bones were found in a pellet 20051212-2-3.  The picture on the left shows a femur and humerus from Black Rat above and the mystery bone (presumably a humerus) below.  This unknown bone is approximately 75% the length of the rat analog.  If we assume that it is a rodent bone and that size ratios between rodent species are approximately proportional, the body length (without tail) would be about  130mm.  This is in the range for Townsend's Vole (Microtus townsendi).  Bones found in  association with Townsend's Vole skulls in Snowy Owl pellets produced by the Newport, Lincoln Co., OR bird seem to be a good match. The Newport bird also had a Pacific Jumping Mouse (Zapus trinotatus) and shrew (Sorex sp.)

I have sent photos to Randy Moore at OSU with the hope that he can make comparisons to bones in the OSU collection.

A closeup picture of the unknown bone follows (front and back).

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This page created by Mike Patterson.  Most recent revision 01-31-2006.
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