Birds

Owl Vs. Owl: Species Overlap

Barred owls (Strix varia) are one of the most commonly found owls in Eastern part of North America — at least they used to only be found in the East — now they can be found on the West Coast of U.S. The invasion of barred owls on the West Coast has become problematic for their smaller cousin the Northern spotted owl (Strix occidentalis caurina). Now that the two species’ ranges overlap, the spotted owls are losing the competition with barred owls for resources.

Spotted owls and barred owls look a lot alike. They both have round, stocky heads that lack ear tufts and are both a rich chocolate brown-colored spotted with dots of white. Differences in appearance include streaking on the breast of the barred owl and size — the spotted owl is smaller. The northern spotted owl is listed as “threatened” under the Endangered Species Act and has been since 1990. The International Union for Conservation of Nature (IUCN) has determined that the species is nearing the margins of extinction.

The negative impact of the species’ overlap has been so severe that the U.S. Fish and Wildlife Service (USFWS) has supported an experiment that includes harvesting barred owls. The idea behind the experiment is to thin barred owl populations in the Pacific Northwest in order to halt their encroachment on spotted owl territories and to allow spotted owl populations to increase.

Image Credit: PIXABAY

Image Credit: PIXABAY

Barred owls reached the West Coast due to the planting of trees in mid-Western areas. These trees were planted with the intention of suppressing fires. Not only do the two congeneric owl species battle for resources, barred owls evict spotted owls from their native forests.

Image credit: Orietta Estrada

Image Credit: Orietta Estrada

The barred owls shot in the experiment were classified as “territorial”, meaning that an owl displayed aggressive behaviors when lured with audio-calls. No brooding or nesting barred owls were killed. The results of that experiment showed that when barred owls were removed from areas where spotted owls originally flourished, the spotted owl populations increased.

In another study published by The Condor Ornithological Applications, researchers (including the lead researcher from the aforementioned studies) evaluated 11 different study areas to assess populations of Northern spotted owls. They found that barred owls contributed to spotted owl declines in all 11 study areas.

Other factors which impact the declines of Northern spotted owls are climate change and habitat loss.

Other factors which impact the declines of Northern spotted owls are climate change and habitat loss. Climate change impacts populations because it causes changes in forest tree species composition which impacts specialist species like the spotted owl.

Furthermore, climate change impacts habitat loss associated with forest fire because it increases the risk for their occurrence. It’s important to point out that spotted owl habitat loss has not mainly come from forest fires though, it has come from development and logging.

Image Credit: Orietta Estrada

Image Credit: Orietta Estrada

In each of the 11 study areas, declines in spotted owl populations were significant. In some areas 95 percent. Harvesting barred owls to save the declining populations of spotted owls is just one method of conservation. Another option would require a joint effort at the state and federal level (and funding) to support habitat restoration across multiple states. For now, to save the Northern spotted owl, killing barred owls is the immediate alternative.

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Categories: Birds

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