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Posts Tagged ‘Barred Owl’

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.

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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.

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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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Spotted Owls have lots of big problems.  One is that their stands of old growth forests are dwindling due to the expansion of human development.  Another is the growing threat of catastrophic wildfires destroying what habitat has not been converted to human uses.  These two issues resulted in two of the subspecies of Spotted Owl being listed as federally threatened under the Endangered Species Act and the third to be listed as a Species of Special Concern.  But the Spotted Owl actually has a problem that is even bigger than those two.  It is the Barred Owl.  I have written previously about the conflict between Spotted Owl and Barred Owls (https://abirdingnaturalist.wordpress.com/2012/08/17/spotted-owl-vs-barred-owl/).  The basic problem is that Barred Owls are expanding their range westward into the range of the Spotted Owl.  Barred Owls are bigger and more aggressive than Spotted Owls, so when they compete for territories the Spotted Owls are driven out or even eaten.  And if the Spotted Owl is not deprived of the territory or eaten, Barred Owls sometimes breed with Spotted Owls, so they are losing their genetic uniqueness as well.

This is a developing situation that wildlife managers, ornithologists and birders have been watching since the 1960s, and there has been a lot of discussion on what, if anything, to do.  Ideas ranging anywhere from doing nothing to going out and shooting Barred Owls have been put on the table.  The idea of shooting Barred Owls started in 2009 when the US Fish and Wildlife Service first proposed the idea and started asking for public comment on it.  The idea was to send hunters out into areas that were known to have good populations of Spotted Owls.  If a Barred Owl was detected, the hunters would use recordings to attract the Barred Owl and shoot it.  There was a fair bit of public commenting on this idea, some for and some against, and then the idea dropped off the radar for most people. Well, just recently, there has been a new development.  The US Fish and Wildlife Service is going ahead with the plan to shoot Barred Owls.  They are proposing a four year trial period beginning in 2013.  During this period, each fall (the non-breeding season) hunters will be sent out into four areas, two in Washington, one in Oregon, and one is California.  The goal will be to kill 3,603 Barred Owls, and then see if Spotted Owl numbers increase.  Why 3,603 specifically?  I have no idea.

I have several problems with this plan, but let me get one issue that I do not have a problem with out the way first.  I am not, categorically, against killing Barred Owls.  I eat meat, I am even a hunter, so it is not the killing of animals that I take issue with.  I am sure that others do feel that it is somehow morally wrong to kill an owl, any owl, but that is not me.  From a population biology standpoint, the Barred Owl is doing really well as a species and so there is no danger at all of the species as a whole being damaged by some birds being killed.  Far more than 3,000 die each year due to starvation, disease, exposure to the elements, or flying into cars or buildings or antennas.

No, my biggest problem with this plan is that it is not going to work.  The Barred Owl population has been increasing in number and expanding in range pretty darn fast.  To think that killing a few is going to make any kind of difference is like thinking that if you beat at the ocean with a garden rake, you will be able to hold back the tide.  Every owl that is killed will be replaced by another from the expanding population.  To top that off, this four year trial is going to cost around 3 million dollars.  A much better use of that money would be to purchase 3 million dollars of land and set it aside as protected wilderness.  This trial will also waste a lot of personnel hours that, just like the money, could be much better spent elsewhere.  And that is just the money and personnel hours for the trial.

An even if this trial run is a success and does lead to a decrease in Barred Owl numbers and an increase in Spotted Owl numbers, this plan will still not work.  The only way that lethal removal works is if you kill  large number of individuals in a given area, and then keep doing it every year.  The constant level of effort that this would require for hunting Barred Owls is simply not sustainable.  To protect the Spotted Owl it would be necessary to remove Barred Owls from all, or most, of the Spotted Owl breeding areas (not just the four limited regions in the trial) and to continue doing so forever (since the moment the hunters stop, more Barred Owls will enter the protected areas).  This would require vastly more time and money than anyone is actually going to have.

 

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The Broad-winged Hawk (Buteo platypterus) is one of North America’s smaller Buteos being about two thirds the size of a Red-tailed Hawk.  It is common and wide spread in the eastern half North America with an estimated breeding population of at least 1.7 million individuals.  It breeds throughout deciduous and mixed conifer-deciduous forests and hunts mostly small mammals and reptiles, but also includes the occasional bird, amphibian, or even more occasional insect.  Breeding densities have been estimated to range from 1 pair every 2 to 5 square kilometers.  However, breeding bird surveys appear to be inadequate at detecting Broad-winged Hawks do to how secretive they are when on their nesting territory.  Migration has proved to be a better point in their annual cycle to monitor population levels.

Along with the Swainson’s Hawk (Buteo swainsoni), the Broad-winged Hawk is one of the raptor species that migrates the longest distances between its breeding grounds and non-breeding grounds which stretch from Mexico to Brazil.  As might be expected from the combination of how common they are and this long migration distance, this species is a very common member of fall hawkwatch counts in the eastern USA and in Central America.  Numbers in the 10s of thousands are not unusual at many sites (such as Hawk Mountain PA) and several sites have counts of 100s of thousands (such as Corpus Cristi, TX) and even over 1 million (such as Vera Cruz, MX).  It is unusual for a raptor in that groups of these birds migrate in flocks frequently forming large kettles that fill the sky as they move south.  But these are all eastern sites.  Do Broad-winged Hawk occur in the western half of the continent?

Before the 1980s the answer would have generally been no, but during the 1980s something started to change.  Sightings during migration have been increasing in many western states including Idaho, Montana, Wyoming, Colorado, New Mexico, and Arizona.  This suggests that the breeding range of the Broad-winged Hawk is extending to the west into Alberta and British Columbia.  The Golden Gate Raptor Observatory (GGRO) in California have been seeing them regularly since that fall migration was first discovered in 1972.  It remains the best place to spot a Broad-winged hawk west of the Rocky Mountains.  This year was an amazing Broad-winged year at the GGRO.  Most fall seasons see between 25 and 240 Broad-winged Hawks with numbers generally concentrated in the last half of September.  But during the 2012 season (and only through the end of November, since the count season is still ongoing) hawkwatchers have counted a record-shattering  755 Broad-winged Hawks!  This total included one day which recorded a total of 295 which is higher than the previous record season total of 248!  No one is completely sure what caused this boom of Broad-wings, but one interesting facet is that of the 755 birds seen this year, about 99% of them were hatch-year birds.  This indicates that the population of Broad-winged Hawks that breed in western Canada had a very good year this past spring and summer.

The western expansion of the Broad-winged Hawk breeding range roughly matches the westward movement of the Barred Owl (Strix varia).  It also roughly matches the eastern expansion of the Evening Grosbeak (Coccothraustes vespertinus) across the same geographic area of Canada, although the Evening Grosbeaks moved east earlier than the hawk or owl moved west.  All three of these species prosper in mixed deciduous-conifer forests, and that hints at a possible explanation.  These range expansions could be the result of increasing edge habitat that results from timber harvesting in areas of what would otherwise be wide swaths of coniferous forest.  They could also be due to the increased numbers of trees that are being planted in and around cities in the great plains of Canada and the USA as wind-breaks.  Such human-induced changes to the landscape will no doubt cause changes to the distributions of other organisms, and these three species may be examples.  More investigation into these changes in range are needed before any convincing explanation is reached.

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In the western U.S., Spotted Owls (Strix occidentalis) are one of the banner species for the protection of old growth forests, and several subspecies are federally endangered.  A small owl, it has a huge impact on conservation in North America.  But now they face a threat that is harder to deal with even than human disturbance and habitat loss.  It is a fellow owl, the Barred Owl (Strix varia).  The two species are very closely related.  The Barred Owl is most commonly found in the eastern portion of the continent, but that is changing.

Due to an increase in the number of planted trees in the central parts of the continent, the breaking up of large tracts of continuous forests by timber harvesting, and probably other factors that we do not yet understand, the Barred Owl has been expanding its range westward.  There are now breeding populations of Barred Owls in Washington, Oregon, and California, and this posses a special problem for the Spotted Owl.  With their larger size and more aggressive behavior, Barred Owls can drive out Spotted Owls from nesting territories, sometimes eating the Spotted Owls!  However, even when the Spotted Owls stand their ground (and don’t end up being a meal) a problem still exists.  Since the two species are so closely related, they can interbreed.  The hybrid, or Sparred Owl, can then mate with other Sparred Owls or members of their parent species.  Since the total Spotted Owl population is small and the total Barred Owl population is large, and getting larger, the overall result is that the Spotted Owl is getting absorbed into the Barred Owl.

Now, we face a dilemma: what should we do to save the Spotted Owl?  For that matter, what can we do to save the Spotted Owl?  Ideas abound across a wide spectrum.  At one end are those that feel that the Spotted Owl must fend for itself.  This viewpoint is generally driven by the idea that a species its range is a natural process and should not be interfered with.  If one species out competes  another where they come in contact, that is just how the world works.  Many advocates of this viewpoint point out that if the two species are so closely related that they can interbreed, they probably should not have been categorized as two different species in the first place, but are rather two populations of the same species.

At the other end of the spectrum are those that feel that the Spotted Owl should be protected at almost any cost.  Proponents of this viewpoint feel that a large part of what brought these two species together were human induced changes to the land, and we are therefore responsible for the results.  Among the most drastic of the plans that have been suggested is to actually kill Barred Owls when they are found near known Spotted Owl nesting territories.

So, who is right?  The debate continues.  There may be nothing we can do to stop the Spotted Owl from disappearing.  But we can learn.  Ecosystems are incredibly complex, and we did change the landscape in such a way as to allow this situation to occur.  In the future, we need to consider carefully the possible consequences of our actions and perhaps apply the precautionary principle a bit more often.

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