Barred Owls

Background:

Since Barred Owls are the main competitors of the Northern Spotted Owls, much of the loss of the Northern Spotted Owl is blamed on these predators. These two owl's food sources overlap and Barred Owls are more aggressive and eats more types of prey than the Spotted Owl. The successful expansion of the Barred Owls in part can be due to the lessened sensitivity of the Barred owls to fragmentation in comparison the the sensitive spotted owls. Northern Spotted Owls prefer old growth forests while Barred Owls can tolerate old growth, younger forests, and even suburban neighborhood forests! However, to understand why these Barred owls are moving over to the Northern Spotted Owl territory the effects of climate change needs to be investigated.

Figure 6: Percentage of Spotted

Owl territories with Barred Owl detections in Washington and Oregon( Figure 4. Kelly et al. 2003)

The migration of Barred Owls should be worth investigating, as the overlap between the Northern Spotted Owl’s decline has much to do with the more aggressive and larger Barred Owl.  The rapid increases of Barred Owl’s nesting sites in spotted owl territory from the 1970s to the late 1990s will pose a major threat to the Northern Spotted Owl (Figure 6)(Kelly et al. 2003).  Occupancy of spotted owl territories declined after Barred Owls were detected within 0.80 km of the territory center. The distance between these species and interactions is negatively  associated with distance between them. We see that Barred Owls presence is reducing the abundance of Northern Spotted Owl in that particular area as suggested by this study.

But why have they been migrating?
Historically, the Barred Owls were limited to eastern North America, but in the early 1900s the range expanded westward to parts of central Canada and from there southward towards the Pacific Northwest. The expansion then went southward from Washington in 1965 to Oregon in 1974 and to California in 1981. There is some uncertainty as why they migrated; some say increased climate while others claim that an increase in habitat such as planting forests in plains will help the migration.

How does warming climates relate?

A hypothesis for this southward expansion, when considering the scope of the Pacific Northwest, is associated with the climate change. The increase in summer rainfall and average temperature may be one cause for allowing more habitats to open up to Barred Owls.( Kelly et al. 2003).  Jack Dumbacher suggests that the few degree increase in climate is allowing Barred Owls to migrate from Eastern U.S. to Canada and eventually Westward as the planted forests in prairies allow for paths towards the West or Pacific Northwest.

           Livezey’s research investigates the expansion range of Barred Owls. As one of the criteria for expansion involves global warming, could it be possible that the barrier for Barred Owls moving West is due to cold weather?  He suggests that the warming did not enable these Barred owls to migrate over the Great Plains to the West and eventually to the Pacific Northwest. However, another study suggests that an increase in mean summer temperatures in lessened the metabolic energy requirements of nesting Barred Owls to allow range expansion. (Monahan et al. 2007)

So from analyzing multiple viewpoints, there seems to be a controversy to the explanation of the migration.  The explanation to why the Barred Owls are migrating to Northern Spotted Owls territories can be even due to logging and plantation of trees which is outside of the climate change scope. But, with increased temperatures as a hypothesis that relates to Barred Owl migration, we can see that warming has impacted our Northern Spotted Owls. Also, links to increased forest fires and the destruction of old growth forests from climate change will allow the less habitat specific Barred Owl to overtake the more habitat specific Spotted Owl, giving another reason for the concern that the Barred Owl will drive the spotted owls to extinction.