Shooting Bars Does Save Spots (sort of)

I have written about the conflict between Spotted Owls (Strix occidentalis) and Barred Owls (Strix varia) a couple of times before (here and here). The basic situation is that Barred Owls (generally native to eastern North America) have been expanding their range into the range of the Spotted Owl (western North America) for the past 40 years or so. The Spotted Owl has been declining for a long time and two of the three subspecies are federally listed as Threatened under the U.S. Endangered Species Act. The intrusion of Barred Owls is now a big problem for the Spotted Owls for several reasons.

A subadult Spotted Owl (photo by USF&WS)

One reason is that the total Spotted Owl population is smaller than the total Barred Owl Population, and small populations are more at risk of declines and extinction. Another reasons is that the Barred Owls are bigger and more aggressive than Spotted Owls and push the Spotted Owls out of nesting territories. Sometimes the Barred Owls are big enough and aggressive enough that they eat the Spotted Owl. Yet another issue is that the two species of owl are so closely related that they can hybridize and produce so called Sparred Owls. This genetic mixing has much more profound implications for the long term persistence of the Spotted Owl than the Barred Owl due the much smaller population size of the the former.

The primary solution that has been proposed to save the Spotted Owl from extinction has been to alter logging practices and set aside the old-growth forests that the Spotted Owls depend on. However, this has not been enough to halt the Spotted Owl decline. An additional plan that the U.S. Fish & Wildlife Service has been pursuing is the lethal removal of Barred Owls from areas where Spotted Owls are nesting or have nested in the recent past. From 2009 to 2013, USF&WS scientists killed approximately 90 Barred Owls. This had a marked effect on the Spotted Owl population. In areas where Barred Owls were removed, Spotted Owl population levels did not change any more than in areas where Barred Owls had never been observed. Also, territories that were held by the removed Barred Owls were fairly quickly re-occupied by Spotted Owls.

This result is a surprise to me. In my past posts, I was quite critical of the plan, and was skeptical that the removal of Barred Owls would actually benefit Spotted Owls. The results of the removal study suggest that this strategy might work to preserve Spotted Owls. But there are still problems.

An adult Barred Owl (photo by Ashley Hockenberry)

Spotted Owls respond well to the removal of their Barred Owl competitors. But how will these removals be maintained? Shooting Barred Owls takes a fairly considerable effort, so there is no way that this process can be enacted over the whole range of the Spotted Owl. It will not be possible to even do it over large areas. Instead, the only way that this plan will be able to be put into practice will be on very small areas of core Spotted Owl habitat. The other problem is one of time. To be effective, these core areas will have to be patrolled regularly, forever. New Barred Owls are perfectly capable of re-invading areas where the earlier Barred Owl inhabitants had been shot, and they will do so in short order.

So, much of my skepticism and critiques from my earlier posts still stand. I do not think that killing Barred Owls is a long-term solution for Spotted Owls on really any scale that will be useful for the survival of the species. It will simply require more time, effort, and money than anyone has to devote to the issue. That having been said, the fact that killing Barred Owls made any impact on Spotted Owls at all is more than I thought would happen.

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A Moment of Silence for a Fallen Flycatcher

A sad landmark has been reached.

A fellow species has fallen.

Let us each take a quiet moment to consider what we have lost.

A male San Cristobal Flycatcher

The landmark that has been reached is the first extinction of an endemic Galapagos bird species. For a long time, many species of animals found on the Galapagos Islands, and no where else on earth, have been declining. Biologists have warned for years that if dramatic steps are not taken, many of these species will go extinct and the ecosystems of the Galapagos Islands will be impoverished forever. Exactly this has now happened. The San Cristobal Flychatcher (Pyrocephalus dubius) is the first species to fall. Found only on a couple of the Galapagos Islands, this stunning flycatcher used to be thought of as a subspecies of the more widely distributed Vermillion Flycatcher (Pyrocephalus rubinus). Recent studies, however, have shown that it and the Galapagos Flycatcher (Pyrocephalus nanus), also a former subspecies of the Vermillion, both warranted elevation to full species status. And now, surveys of the islands have found that there are no San Cristobal Flycatchers to be seen.

A female San Cristobal Flycatcher

The reason for this tragic loss is not completely known, but it is likely due in part to invasive Brown and Black Rats and in part to the parasitic fly Philornis downsi. The rats have been transported to the islands unintentionally by humans. They climb up trees and eat the eggs out of the nests of many songbird species. The flies were another accidental introduction to the islands by humans when their eggs were brought to the islands on imported fruit. The fly larva infect nestling songbirds feeding on blood and tissue. Infestations frequently become severe enough to kill the nestlings.

How many more species will go extinct before sufficient actions are taken? How many more species can go extinct before the ecosystems of these fragile islands collapse into a ghost of their former selves?

I leave that to your consideration.

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