Feeds:
Posts
Comments

Posts Tagged ‘Population Status’

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.

Spotted Owl - USFWS

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.

barred_owl_ashley_hackenberry

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.

Read Full Post »

The Tricolored Blackbird (Agelaius tricolor) is a bird both fascinating and beautiful. One of its unique characters is that it is found nowhere in the world except California and a small portion of Baja California. This alone makes it pretty special to anyone from California! The glossy, black male Tricolors can be identified by the thin slice of white just below the red on their shoulders. This distinguishes them from the similarly plumaged Red-winged Blackbird because the later has a slice of yellow below the red, or sometimes just red.

Tricolored Blackbirds form huge flocks of many tens of thousands of individuals. These are larger than any other bird species in North America today. They can get so big and so dense, that they blacken the sky. However, while these flocks are big, they only rank as the second largest flocks of North American birds ever. The Passenger Pigeon was another sky darkening bird which once formed even larger flocks. However, the Passenger Pigeon when extinct in 1914. There are actually several parallels to be drawn between the Passenger Pigeon and the Tricolored Blackbird. Some of these parallels may give rise to concerns about the long term survival of the Tricolored, but these parallels may also give us a chance to save the blackbird where we were unable to save the pigeon.

One of these parallels between the Tricolored Blackbird and the Passenger Pigeon is that they are both highly social and nest in huge colonies. Tricolored Blackbird nesting colonies sometimes get as large as 50,000 birds! This colonial breeding lifestyle is one the factors that is thought to have been the downfall of the Passenger Pigeon. Social cues can play very important roles in controlling when birds come into breeding condition. It may have been that Passenger Pigeons could only breed if they were surrounded by other Passenger Pigeons that were also breeding. As populations of Passenger Pigeon were decimated by market hunting, the colonies may have fallen below some critical threshold where even though there were many individuals left alive, there were not enough to trigger each other into breeding. This would have resulted in practically no young birds being hatched and the total collapse of what was the most numerous bird species in the western hemisphere. The fact that Tricolored Blackbirds also only breed in very large colonies suggests that they may also need the social cues of having many breeding neighbors in order to reproduce. This makes the Tricolored Blackbird at risk of the same fate as the Passenger Pigeon.

Another parallel between the two species, that goes hand in hand with large numbers required to breed, is that the breeding colonies occupy a fairly small area. All those birds pile in to relatively small patches of suitable freshwater marsh habitat in the central valley. These patches of habitat are more and more often agricultural lands such as rice fields and the feed fields for dairy cows. This high density in a small area is one of the reasons that Passenger Pigeons were so profitable to hunt. Market hunters could go to a colony and bring down tremendous numbers of birds in a very short time. While not hunted, small and concentrated breeding colonies is a problem for the Tricolored Blackbird because nestlings are usually not ready to fly when harvest time comes around. As many as 20,000 nests were destroyed when a single 10 acre rice field was harvested.

These characteristics have contributed to a dramatic decline in Tricolored Blackbird numbers over the last two decades including a particularly sharp drop in the last six years from an estimated population of 395,000 in 2008 to a population of 145,000 in the 2014 breeding season. This severe drop has led the U.S. Fish & Wildlife Service to grant this species temporary status as Endangered under the Endangered Species Act. This temporary listing, the first of its kind, means that the Tricolored Blackbird will be treated as a fully listed species but only for six months with the potential for a six month extension after that. This is to help protect the breeding colonies into and through the 2015 breeding season. If numbers respond well in 2015, it seems likely that this will provide impetus to list the species permanently.

Only time will tell if we have been able to learn the lessons taught by the Passenger Pigeon at so high a cost. The Tricolored Blackbirds surely hope that we have.

Read Full Post »

Beginning now, and continuing until early January, something amazing is happening.  Thousands of  people are going out into the world around us and participating in the annual Christmas Bird Count (CBC)!  Christmas Bird Counts are systematic counts that cover particular geographic areas and are repeated each year.  They have been conducted every year since 1900 making the CBC the longest running citizen science project ever.

Before 1900, famous ornithologist Frank Chapman wanted to create an alternative option to the Christmas hunting competitions that were common at the time.  It used to be that people would go out into the field and see how many birds they could kill.  Chapman wanted to harness this energy and enthusiasm for the outdoors and direct it towards something that could benefit the birds in the long term.  He decided that if people went out and counted the birds in an area each year, a valuable data set could be created and we could learn a lot about the birds around us.   To this end he organized the first CBC in 1900.  In that first CBC, a total of 27 people participated, and they counted birds in 25 different locations.  The CBC has grown tremendously since then.  In the 113th CBC which was last year, 71,531 people participated and counted birds in 2,360 different locations, and it is continuing to grow with more participants and locations expected this year.

And Chapman was right, we are learning valuable things about the birds around us.  Over 200 peer-reviewed papers have been published using CBC data!  One of the most significant findings that CBC data has revealed is the response that many bird species are having to climate change.  Of the 305 species that winter in the North America, 60% of them have shifted their ranges north by an average of 35 miles over the course of the last century.  This is generally interpreted as the birds needing to move farther north to find the appropriate foods and temperatures as global temperatures have risen.  Another prominent finding has been the tracking of the Bald Eagle and Peregrine Falcon recoveries since the banning of the insecticide DDT.  Populations of both species were drastically reduced in the 1950s and 1960s, but with the help of ornithologists and falconers have made dramatic comebacks!

Joining a CBC is easy.  Just contact local Audubon chapters and they will have a list of CBCs in your area.  More counters are always welcome.  So go out and participate in the 114th Christmas Bird Count, and help to continue this incredible legacy!

Read Full Post »

I just received the latest Time Magazine and was interested to read the cover article by David Von Drehle entitled “America’s Pest Problem: Why the rules of hunting are about to change.”  The article discusses how the populations of several species of North American wildlife have expanded in recent history to the point where they are now doing ecological damage and entering human dominated landscapes leading to damage and difficulties there.  Overall, the message of the article was that humans have caused these population increases, and so now need to play a more involved role in wildlife management to correct them, and that hunting should be a prominent part of that role.

I agree with this overall message, and it is one of the  major reasons I started hunting a few years ago.   The other possibilities for controlling wildlife populations generally fall into one of two categories: contraceptives or aversion training.  The idea behind treating animals with contraceptives is to reduce the birth rates of these species and so slowly reduce the population level.  However, this involves the sometimes quite difficult task of injecting the animals with the hormones by either capturing them and injecting them directly, or shooting them with drug loaded darts.  Either method of delivery is time consuming, usually results in a relatively small number of animals being treated, and is expensive.  Furthermore, the drugs usually do not work well, if at all.  Aversion training is when animals are disturbed by flashing lights, sirens, fireworks, lasers, rubber bullets, or other non-lethal devices frequently enough that the animals decide that they need to leave a particular area and go elsewhere.  This does not work for several reasons.  One is that in many cases the animals quickly learn that the lasers and loud noises don’t actually do anything, and so the animals simply ignore them.  Another reason is that human environments are so attractive to some species that they are worth suffering through some pretty serious annoyances to get to.  A third reason why aversion training does not work is that it assumes that there is empty habitat for these animals to move into.  In many cases, this is a very bad assumption, and the animals have no choice but to come back to the human dominated landscapes.  So, removing animals, permanently, from the population is one of few effective methods: a.k.a. hunting.

But, while I agree with the article overall, I was troubled by some points, and also the way in which some of those points were made.  First off, the subtitle “Why the rules of hunting are about to change” implies…well, that the rules of hunting are about to change.  Now, it is true that some cities scattered across the nation have changed ordinances that relate to hunting, but that does not mean that we are on the precipice of some major change in hunting laws at the state level or above.  Another, major, issue I take with the article is how the author mixes what should be viewed as good wildlife interactions in with troublesome wildlife interactions.  For example, in one paragraph, the author sympathizes for the plight of retail employees in Florida having to deal with alligators at their doorsteps (which could be quite dangerous) and office workers in New York who have a hawk nesting on the side of a skyscraper (which is a wonderful thing that has no detrimental effects on humans).  These are not the same category of wildlife encounter, and it seems misguided to lump them together.  Another worrying aspect of the article is that it plays into the commonly held fears about top predators.  Part of the article discusses how the increasing populations of prey species is allowing the populations of predators such as Grey Wolves, Grizzly Bears and Mountain Lions to increase as well.  The author states that hunting to reduce the prey populations will help to reduce the amount of human-predator interactions and so avoid “an invasion of fangs and claws.”  This kind of fear mongering is simply not appropriate.  The numbers of humans injured or killed by wild predators is ridiculously low.  Here are some rough estimates of deaths from large predators in all of North America since 1900: Black Bears = about 70, Grizzly Bears = about 70, Mountain Lions = about 20 people (which is fewer than the number of people killed by lightening strikes), Gray Wolves =  just 3.  A final issue that I take with the article is that is lumps native species and invasive species, and basically treats them the same.  One of the figures depicts the increases in population size of 10 species since the mid-1900s.  The caption for the figure says that these are 10 species that have come back from the brink of extinction; however, two species are Wild Pigs and Wild Turkey.  Wild Pigs are a non-native and highly invasive species that really should not be on this continent at all and have never been close to extinction, and Wild Turkeys are increasing in number partly because they were introduced to the western U.S. and are flourishing in this new habitat.  The management goals for these species are very different from, say, Beaver or White-tailed Deer or any of the other native species in the figure.

So, while I liked the message that hunting is a responsible and useful tool in wildlife management, I felt that the article was subtly misleading and definitely oversimplified, and such a portrayal is not in the best interest of hunting or wildlife management.

Read Full Post »

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.

 

Read Full Post »

This month marks the end of my first year serving on the board of directors of The Hawk Migration Association of North America (HMANA).  HMANA is an organization that is serving as a central clearing house of raptor migration data across the continent.  Member sites upload the count data they have collected, and HMANA sorts it and makes it open and searchable to anyone who is interested.  HMANA also analyses and presents much of the data it collects in their journal, Raptor Migration Studies.  Other than migration counts, HMANA has also been working on a project called the Raptor Population Index which is attempting to track the population status of all of North America’s raptor species.  Yet another HMANA project, and one that I have been helping with a fair bit, is the Winter Raptor Survey.  What we want to set up is a network of survey routes that are run each year and that will allow us to monitor the wintering population of birds of prey in North America.

Winter marks a poorly studied part of the annual cycle in the lives of birds of prey.  Where raptors spend the winter, how many there are, and what they are doing are all questions that have, at best, only general answers.  The studies that have been done have given some very interesting and important results.  In Argentina in the mid-1990s, there were reports large numbers of  Swainson’s Hawks being found dead at their communal roost sties.  In 1995 and 1996 some 6,000 Swainson’s Hawks were found dead at such roosts.  The cause was determined to acute pesticide toxicity.  Since Swainson’s Hawks feed largely on insects during the winter, they were being poisoned when they eat insects that had been sprayed with highly toxic chemicals, or were being sprayed directly when they were perched on the ground in crop fields being sprayed.  Specifically, an organophosphate called monocrotophos proved to be especially deadly to raptors.  This chemical had already been banned in the USA, and the deaths of the an estimated 20,000 Swainson’s Hawks led to the banning of this chemical in Argentina in 1999.  A different study on the winter ecology of raptors that was conducted here in central California found that male and female American Kestrels use different habitats to hunt.  Females generally use the more productive open grassy territories, while males are generally relegated (probably due to their smaller size) to less productive mixed shrub habitats.  Such habitat partitioning is vital to know if conservation is gong to be effective.  If a declining species displayed a similar habitat partitioning, and only one habitat type were known and conserved, the population would still decline.

So, how is the HMANA Winter Raptor Survey hoping to monitor the winter populations of birds of prey in North American?  The goal is to establish survey routes that are run once a month for the four months (November, December, January, and February).  This span of time covers the ‘winter’ months of most raptor species.  Along the routes, which are between 30 and 100 miles long, the habitat is described according to one of the categories we have established and the position and identification of all raptor species seen along the route are recorded.  This survey data is then uploaded to the WRS website.  This data can then be used to track habitat use, landscape and habitat change, raptor numbers and densities, and the interactions between any and all of the above.  So, to all the raptor-philes out there, we need your help!  Now that the fall migration is over, please lend a hand in monitoring raptors in the winter.  Set up a route!

HMANA is largely volunteer run.  Check out the HMANA webpage at http://www.hmana.org/ for general HMANA information and news, and the HMANA WRS webpage at http://wrs.hmana.org for specific details on how to set up and run routes.  While you are at these websites become a member of HMANA!  It is a great organization that is showing what citizen scientists can do on continent-wide scale.

Read Full Post »

As my wife and I were driving out of Berkeley a few days ago, we saw a group of five Wild Turkeys walking down the side walk of one of the  major streets.  When we turned a corner at the next intersection we saw another group of five crossing the street in front of us.   Many people were stopping their cars or coming out onto their front porches to watch and photograph the birds as they sauntered by.  The turkeys were completely unfazed by the attention as they calmly walked through the neighborhood.  With the Thanksgiving holiday just past, and this encounter fresh in my mind, I thought it would be appropriate to post on the Wild Turkey population of California.

Wild Turkeys (Meleagris gallopavo) are native to North America, and there are six recognized subspecies.  In the late 1800s they were nearly driven to extinction by a combination of heavy hunting and habitat loss which reduced the continent wide population to around 30,000 individuals restricted to remote locations.  In the 1970s reintroduction programs began to successfully bring the Wild Turkey back to large portions of its historical range.  But, Wild Turkeys are not native to the west coast.  The first recorded introduction of Wild Turkeys to California was in 1877 on a ranch on Santa Cruz Island where they were released for the express purpose of hunting.  More introductions followed, especially from the 1950s to the 1970s, and now there is an estimated population of 240,000 birds in California alone and they are found across 54 of 58 counties.  The birds we have here are largely of the Rio Grande subspecies (M. g. intermedia).  This subspecies is particularly long legged, generally weighs between 20 and 25 pounds, have body feathers that have a coppery-green sheen, and tail feathers and upper tail coverts that are tipped with tan.

As the population of Wild Turkeys in California has grown, they have increasingly moved into suburban areas.  Like deer, turkeys can adapt to human dominated landscapes and learn to thrive there.  This has led to an increase in human-turkey interactions.  Some of these interactions come in the form of turkeys doing damage to gardens and landscaped areas.  Agriculturally, turkeys eat wine grapes and have become a nuisance in many vineyards. And while males can become aggressive during the breeding season, the vast majority of the interactions between Wild Turkeys and humans are completely benign; just don’t feed them.

As an interesting aside, the reason they are called Turkeys has always puzzled me since these birds are not found in the country of Turkey at all.  I recently learned that the when these birds were first being imported to Europe from the new world they all came through trade routes that stopped in Turkey before being distributed to the rest of the continent.  The name of the bird became entwined with the shipping location, and the name has stuck ever since.

Read Full Post »