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burrowing owl

6

Banding Burrowing Owls

A chick is banded with its new identifier, 48X.

A chick is banded with its new identifier, 48X.

This summer, I had the opportunity to assist with the San Diego Zoo Institute for Conservation Research’s western burrowing owl banding effort in San Diego County. A team of researchers worked this spring and summer to trap, band, and observe burrowing owls in South County to monitor the population in the area (see My Summer Staycation: Burrowing into Owl City. The bands serve as unique identifiers and allow us to track individual birds over the course of their lives, monitoring such things as survivorship, breeding success, and home range. For the previous two years, I have been researching California ground squirrel and burrowing owl habitat requirements in San Diego County grasslands, so it was very exciting to finally participate in some work with the actual owls.

On a summer afternoon in late June, we arrived at our site. We pulled off the main road to a place where we could observe the owls’ behavior without disturbing them. We set up our scope and saw them: two adults hanging out by a California ground squirrel burrow they had chosen as their nesting site earlier in the year. The chicks were hidden inside the burrow.

We take morphological measurements of a burrowing owl chick.

We take morphological measurements of a burrowing owl chick.

It was especially meaningful for me to help out with trapping and banding the chicks at this site, as I had visited this location earlier in the year to conduct ground squirrel surveys and gather habitat data and soil samples. On our last day of ground squirrel surveys here in April, we had seen a male burrowing owl using one of the squirrel burrows. I wondered at this moment if this was that same bird I had seen months before, now paired with a female and with chicks of his own.

As we approached the nesting burrow, both adults flew away, in an attempt to distract us from their chicks, and continued to keep a close watch on what we were doing. We used burlap sacks to block all but the main burrow entrance at the nest, and then placed a one-way door trap at that entrance. While the chicks could exit the burrow and enter the trap, they would be unable to leave the trap once inside.

We returned a short time later to find three burrowing owl chicks inside the trap—success! Carefully removing the chicks from the trap, we placed them in a pet carrier so they would be more comfortable as they waited to be banded. During the banding process, we took morphological measurements such as weight, wing length, bill length, and tarsus height and length. A small blood sample was also taken from the birds for genetic analysis. We moved quickly so the chicks could be returned to their burrow as soon as possible.

Upon their release, the chicks scurried back into their burrow with their new bands on. I hope they will survive the rest of the non-breeding season, and we’ll see them again in the spring—maybe with chicks of their very own!

Susanne Marczak is a research technician with the San Diego Zoo Institute for Conservation Research. Read her previous post, Citizen Science: Engaging People in Conservation Research.

1

Burrowing into Owl City

Nan holds a burrowing owl chick.

Nan holds a burrowing owl chick.

Being a native San Diegan, the world-famous San Diego Zoo and Safari Park had an immense impact on my interest in the natural world during my early adolescent years. One thinks of the word excellence when it comes to the Zoo and Safari Park being able to showcase rare and endangered plants and animals from all over the globe. Yearly visits to the Zoo and Park instilled many valuable lessons. The most valuable lesson of all: to be able to personally experience biodiversity at such an intimate level was, and still is, an extreme privilege.

Naturally, these types of experiences eventually led me to pursue bachelors of science degrees in biology/ecology and environmental sciences at San Diego State University. Realizing that the activities of humans had a direct impact on vulnerable species and ecosystems around the world, and having an innate desire to make a positive difference in the field of conservation, I made a commitment to myself to become a conservation scientist. I was then extremely excited to find out that I had been selected to conduct research as the Sefton Summer Research Fellow within the Applied Animal Ecology (AAE) Division of the San Diego Zoo Institute for Conservation Research.

A burrowing owl family peers at the researcher studying them.

A wild burrowing owl family peers at the researcher studying them.

This summer, my research project focused on a very charismatic species of concern in our very own backyard: the western burrowing owl. Once thought to be thriving in San Diego County, burrowing owls are now a rare sight, due to habitat loss, fragmentation, and degradation due to human activity. With the help from my super team of AAE mentors—Dr. Lisa Nordstrom, Colleen Wisinski, and Susanne Marczak—we are currently seeking how to answer such questions as: how do burrowing owls select their nesting habitat from different spatial scales? Do burrowing owls reproduce more successfully when nesting in artificial burrows or when nesting in natural burrows excavated and engineered by California ground squirrels?

To help gain valuable information about burrowing owls and their habitat, I had to learn how to conduct habitat assessment surveys, extract soil cores for soil texture analysis, identify many different types of exotic and native grassland and coastal sage scrub vegetation, and use state-of-the-art computer software such as geographic information systems to tease apart the environmental factors that may potentially affect owl site selection at different spatial scales. To obtain these types of data, many long, grueling, yet very fun and fulfilling hours were spent outside in the field and inside the Ellen Browning Scripps Spatial Ecology Lab.

Nan feds a rhino during a Caravan Safari at the Safari Park.

Not all work and no play! Nan feds a rhino during a Caravan Safari at the Safari Park.

I’ve also had a number of various experiences this summer that complemented my internship, which included releasing translocated California ground squirrels to new study sites, releasing critically endangered mountain yellow-legged frogs into their native creek habitat in the San Gabriel Mountains, and getting up close and personal with the giraffes and rhinos on a spectacular Caravan Safari at the Safari Park.

My goal for this summer was to have a better understanding of what it took to become a scientist in applied animal conservation, and I feel that I have definitely met those expectations from working closely with a wonderful and intelligent team who truly cares about effectively protecting the planet’s threatened wildlife with well-thought-out science. Though I am only in the infant stages of my scientific conservation career, the experiences this summer at the Institute for Conservation Research have definitely provided me with unique insights, valuable learning experiences, and a solid foundation on what it takes to become a conservation ecologist.

Nan Nourn is the 2013 Sefton Summer Research Fellow for the San Diego Zoo Institute for Conservation Research.

4

A Closer Look at Burrowing Owls

Note the difference in coloration (female on left, male on right) with this burrowing owl pair.

Note the difference in coloration (female on left, male on right) with this burrowing owl pair.

For the past two years, our burrowing owl project has been focused on how to effectively relocate California ground squirrels to help re-engineer nonnative grasslands and make them more amenable to burrowing owls (see Burrowing Owls: Closer than You Think and Digging into Burrowing Owl Recovery). But this year, we get to take a closer look at the owls themselves. Don’t get me wrong, I love the squirrels (more than I ever thought I would), but I’m a bird biologist, so I’m really excited to start working directly with the burrowing owls!

Burrowing owls range widely across the western US and make use of a variety of “grassland” habitats, from open prairie to empty suburban lots to airports. But their populations are declining, mostly due to loss of habitat and eradication of the fossorial (digging) mammals that they depend on to build burrows. One solution is the installation of artificial burrows. However, artificial burrows are not self-sustaining like natural squirrel burrows and, although we know the owls use them, we don’t know how they compare to natural burrows.

A male burrowing owl guards his burrow entrance.

A male burrowing owl guards his burrow entrance.

This year, one of our main objectives is to compare reproductive output, food provisioning, and predation at natural versus artificial burrows, using camera traps and banding the birds to accomplish this. The camera traps allow us to see what is going on at the burrow while we aren’t there, and the banding allows us to identify each individual (see Bling with a Purpose).

At this point, the breeding season is in full swing. We are monitoring almost 30 nest burrows (both natural and artificial); this includes placing camera traps at about 20 of the burrows. We check on each burrow about once a week (we don’t want to visit too often and risk disturbing the birds) and do any camera trap maintenance needed, such as changing batteries and switching out the memory cards that contain our priceless data in the form of photographs. We also watch the birds from a distance to figure out what stage of the breeding season they are in—for me, this is the best part!

A camera trap photo shows a burrowing owl pair allopreening at their burrow entrance.

A camera trap photo shows a burrowing owl pair allopreening at their burrow entrance.

Over the last two months, we have been inventorying burrows and following their progression through the breeding season. On any given day, we head out to the field in the morning and work our way through our route for the day checking on each burrow as we go. When we arrive at a burrow, we observe from the truck (which acts as our blind) from a safe distance to see what is going on at the burrow. Early in the breeding season, we might see both parent birds or just the male standing guard at a burrow. In general, the males are lighter in color than the females, because they spend more time outside so the sun bleaches their feathers. As the breeding season progresses, the difference in plumage becomes more marked, as the males get more and more bleached. By the end of the summer, though, it can be hard to tell the males and females apart as both get bleached by the sun.

Two burrowing owl chicks rest at the burrow entrance while Mom stands guard. Camera trap photo.

Two burrowing owl chicks rest at the burrow entrance while Mom stands guard. Camera trap photo.

Once the pair has chosen their nest burrow, we usually only see the male of the pair; he is often standing watch over the burrow from nearby (often at the entrance of a satellite burrow where he spends much of his time—we call it the “man cave”). At this point, the female is spending most of her time in the burrow incubating the eggs. After about a month, the eggs hatch, and two weeks after that, the young start to come out to the burrow entrance. We usually do a quick examination of the photos in the field to help us determine if there are chicks present, but we also get good clues from the female’s behavior. If she is very protective of the burrow or stays very close to the burrow when we approach, it’s a safe bet that there are babies in the burrow.

Currently, we have nests in all different stages of breeding—some have pretty large chicks, some still have eggs, and some still seem to be deciding if they are even going to breed. In the coming weeks, we will band all of the owls from burrows that have camera traps, and over the next several months, we will pour over the hundreds of thousands of camera trap photos to catalogue how often prey was delivered to the burrow, what type of prey was brought, what types of predators come to the burrow, and other pertinent information. This is a huge undertaking, since we have almost 40 camera traps set up that can take over 30,000 pictures in one week alone! Any volunteers? Seriously, if you’re interested in helping, visit our volunteer page and sign up! Who wouldn’t want to spend their time looking at pictures of these adorable and comical little birds?!

Colleen Wisinski is a senior research technician for the San Diego Zoo Institute for Conservation Research.

4

Bling with a Purpose

Bands used on cactus wrens and burrowing owls, far left is aluminum wren band, middle are wren color bands, far right is alphanumeric band for owls.

Bands used on cactus wrens and burrowing owls, far left is aluminum wren band, middle are wren color bands, far right is alphanumeric band for owls.

Bird banding is an important tool for researching wild birds, allowing them to be individually identifiable in the hand or by sight. This can be especially important for birds that are too small to carry tracking devices such as radio collars or GPS tags. Both conservation research projects that I work on involve understanding some aspect of the population dynamics of birds that are too small to put transmitters on: coastal cactus wrens and western burrowing owls. An alternative method of distinguishing individual birds is to mark them with color or alphanumeric bands, in addition to standard aluminum bands from the US government, which are required for all banded birds and have a unique ID number.

This cactus wren sports a unique color band combination.

This cactus wren sports a unique color band combination.

To mark cactus wrens, we use plastic bands that come in several different colors and also have our US government aluminum bands dyed green so as to distinguish them from bands used by other organizations also conducting research on cactus wrens in southern California. Each wren gets two bands on each leg (two plastic on one leg, one plastic and one aluminum on the other), giving us lots of combinations to work with so that each wren has a unique color combination. In the field, we use binoculars, spotting scopes, and photographs to identify individual birds. Because we know where and when each bird was banded, we can get a sense of how long the birds live, how far they move, and how they interact with each other.

Federal and state governments both require researchers to have a permit to band birds, and obtaining one can be a lengthy process because it involves gaining a lot of experience with bird handling and capture techniques. Throughout my academic and professional career, I have been involved with capturing and banding many different species of birds, but only at a trainee/apprentice level. Recently, I took a class in bird banding through University of California, Riverside, Extension to gain additional experience with mist netting and banding of small passerines (songbirds).

A Gambel’s white-crowned sparrow is caught in a mist net.

A Gambel’s white-crowned sparrow is caught in a mist net.

Mist netting is a commonly used technique for capturing songbirds; mist nets are made of very fine material that is difficult to see when set up properly. They are usually set up in high flight traffic areas (e.g. between trees or shrubs), and when the birds fly into them, they are caught in a pocket and become slightly tangled. The nets must be checked often or watched from an inconspicuous location so birds can be removed in a timely manner. Although we already use mist nests to capture cactus wrens, taking the class allowed me to gain a lot of additional practice in extracting birds from the nets. We also had the opportunity to work with many different bird species that we don’t usually catch.

After a bird was captured, we identified its species, banded it, determined its age and sex, and took standard morphometric measurements. Determining the age of birds can be very difficult, and in many cases you can only say that a bird is a juvenile of that year (a hatch-year bird) or an adult (an after-hatch-year bird). We learned how different feather wear and molt patterns can be used to determine the ages of the birds we caught. We also assessed body condition by looking at fat deposits on the breast and hips (birds have very thin skin, so it is easy to see the fat layer just below the skin). Over the course of the weekend, we captured and banded almost 300 birds! We also recaptured birds that were banded in the past and recorded their band numbers. All of the data collected will be given to the Federal Bird Banding Lab (part of the US Geological Survey) and used to look at trends in bird populations across the country.

Steve Myers (instructor) bands and takes body metrics of lesser goldfinches.

Steve Myers (instructor) bands and takes body metrics of lesser goldfinches.

This experience will help me in the permitting process and proved to be an invaluable opportunity to learn new skills and get lots of practice with banding and mist netting. I can’t wait to get out and put my new skills to use. Watch out, cactus wrens, here I come!

Colleen Wisinski is a senior research technician in the Applied Animal Ecology Division at the San Diego Zoo Institute for Conservation Research. Read her previous post, A Sense of Wonder for Wildlife.

2

Squirrels: There’s No Place Like Home

Data is collected on vegetation type and height in ground squirrel habitat.

We are moving California ground squirrels from one location to another (tranlocating) to test if their presence can help restore grassland habitat and provide natural burrow homes for western burrowing owls. Currently, management of burrowing owl populations requires a lot of human intervention; artificial burrows are built in hope that owls will come and use them. However, there hasn’t really been enough focus on this issue from a grassland ecosystem restoration standpoint.

In areas where ground squirrels are relatively common, lots of native plants and other animal inhabitants benefit. Ground squirrels serve as “ecosystem engineers,” building intricate burrow systems, clearing large amounts of vegetation, and serving as anti-predator sentinels for some species. They also play the role of dinner, too!

A transect begins to search for California ground squirrel burrows.

But what determines where a ground squirrel likes to live? Sometimes it seems like they are everywhere: in parks, at the beach, alongside roads, and around our properties. But when it comes to grassland habitats in San Diego County, they’re not always present where you might initially expect them to be. Figuring out where ground squirrels can and prefer to live is especially important when you want to move them to places where they are going to be successful. After all, we want them to establish a new population in a place that will allow them to help the habitat as a whole.

One exciting thing I’ve been working on over the last few months is collecting data for the California ground squirrel habitat suitability model in order to determine what habitat variables predict the presence or absence of ground squirrels in a particular area. The idea is that the more we know about what makes excellent ground squirrel grassland habitat, the higher our chances of success will be when translocating them to a new environment that is in need of some “natural” restoration.

An old California ground squirrel burrow we found was actively being used by a pair of burrowing owls. Note the “white wash” (bird droppings) at the entrance.

At study sites around the county, we’ve been surveying for ground squirrel burrows and collecting data on the surrounding habitat characteristics, vegetation type, and height in the area and any potential burrow protection observed. We have also noted if we’ve seen squirrel predators in the area, like coyotes or red-tailed hawks. In addition, we’ve also been taking soil cores to determine soil density and other attributes, which we’ll assess later in the lab. Because ground squirrels are fossorial, we think soil type has a huge influence on their habitat preferences. I’m eager to process the samples and see the results after all the dirty work of collecting them. Working with soil has turned me into the filthiest-looking researcher in the building. I’ll be happy to know that all of those extra loads of laundry I’ve had to do have paid off!

Susanne Marczak is a research technician with the San Diego Zoo Institute for Conservation Research. Read her previous post, A New Nature.

5

Burrowing Owl Returns

Is this the same burrowing owl as before?

At the beginning of this year I wrote about a burrowing owl that lives across from the manure dump at the San Diego Zoo Safari Park (see Burrowing Owl Buddy). For several years now animal keepers have been watching this little owl watch us. On one occasion we even saw two owls. The owl is usually found standing tall just outside of its burrow. When we drive up next to it with our vehicles, it usually crouches down as if to hide. If we wait quietly, the owl gradually relaxes and stands tall again, making for some great bird-viewing for us.

We mammal keepers were asked by our burrowing owl researcher (see post Burrowing Owls: Closer than You Think) if we could start keeping a log of sightings, so I made up a binder in which we would note dates of sightings, weather, location, etc. A few weeks after my last blog we discovered that some domestic sheep living in the vicinity had chewed down the thick, natural vegetation on the owls’ hillside. The owl was not seen for many months. With its habitat greatly degraded by the sheep, we wondered if it would ever return. It saddened us to think that loss of habitat was happening right before our eyes!

Well, I’m happy to report that as of October 25, 2011, just in time for Halloween, a burrowing owl returned to this site. It is almost the same color as the dirt on the hillside. If it wasn’t for its piercing yellow eyes, we may not have noticed it. We wonder if it is the same individual that was here earlier this year, but we have no way of knowing. For the time being we are working on getting signs put up to prevent any future disturbance to the burrowing owl’s habitat on this hillside.

If you want to get a good look at some burrowing owls, visit the San Diego Zoo Safari Park. Our burrowing owl exhibit is in the area known as Condor Ridge. The pair we have living here has produced many owlets over the years. Their clutch size is usually two to three eggs, but one time there were seven owlets in a clutch from this pair! We do not yet know the gender of the owl across the way. We will watch eagerly to see if owlets make an appearance!

Gloria Kendall is a lead mammal keeper at the San Diego Zoo Safari Park.

3

Burrowing Owls: Closer than You Think

You may not know this, but there is an owl that lives underground right in our own backyard—San Diego County. Yes, the burrowing owl lives in a ground squirrel burrow near you where it is busily catching mice, insects, and small birds to feed up to a dozen young owlets.

Burrowing owls are super cute, no doubt about it. Check out their great, big forward-facing yellow eyes with broad, white expressive eyebrows. They draw your attention and keep you mesmerized as they dance, swaying and bouncing on long featherless legs at the entrance to their burrow home. Once you know where to look for them, they are easy to spot.

Burrowing owls live in open, generally flat grassy landscapes including airports, weedy suburban fields, office parks, and golf courses—all easily accessible places for urban wildlife watching. In late spring, a large brood of owlets tumbles out of the burrow to explore above ground, and anyone lucky enough to spy an occupied nest burrow can spend the next couple of months entertained by these engaging raptors. (Our team will spend the winter analyzing photo data from camera traps that we installed at nest burrows, such as the one featured here). Unfortunately, these endearing owls are in decline both locally and throughout their range, due primarily to habitat loss and eradication of burrowing mammals.

Our culture holds owls in high regard and seems smitten with the owl persona. Likenesses of owls are ubiquitous, from books and movies to clothing and greeting cards. I’ve noticed lately that cute photos of burrowing owls are increasingly used to raise funds for various organizations. Personally, I think the species needs to set up a photo royalty fund!

Another species, the California ground squirrel, is not so well-liked and is considered an agricultural pest for many of the same reasons that prompt ecologists to call them “ecosystem engineers”: they are common, abundant, and they have a penchant for digging and foraging on everything from weedy forbs to your garden produce. Yet grasslands with an abundance of ground squirrels harbor an incredible diversity of animals. Much more so than grasslands devoid of ground squirrels. Digging creates critical underground refuge sites for a variety of wildlife, including nesting sites for burrowing owls. Foraging by squirrels keeps the vegetation low and more open, which is preferred by burrowing owls and many other species.

This year, San Diego Zoo Global and our partners started digging in the dirt to restore the relationship between burrowing owls and California ground squirrels. We relocated close to 350 California ground squirrels to secure sites that will be managed as burrowing owl habitat. The idea is simple: hire squirrels as restoration engineers to create the conditions required for nesting burrowing owls. We spent our first field season reintroducing the key ingredient, California ground squirrels. Now we watch and wait for the arrival of owls as we measure and monitor the progress of our collaborative human/squirrel efforts to restore a more intact, functional ecosystem. And we didn’t have to wait long, as burrowing owls are already checking out the newly renovated neighborhood!

Colleen Lenihan is a postdoctoral associate for the San Diego Zoo Institute for Conservation Research.

Read another blog post about burrowing owls, Burrowing Owl Buddy.
To learn more about owls…

16

Burrowing Owl Buddy

Click images to view in larger format.

As an animal keeper for the past 30 years at the San Diego Zoo Safari Park, I’ve felt privileged to have worked with some of the world’s most fascinating and endangered species. Most of the species I work with come from Africa or Asia, but I am also acutely aware that we have species in our own back yard here in San Diego County that are also in peril.

I have recently learned that burrowing owls are becoming increasingly rare in the grasslands of our county and that our San Diego Zoo Institute for Conservation Research is involved with a grasslands restoration project. This is good news, as I just had my first encounter with a burrowing owl in its natural habitat here at the Safari Park a few weeks ago.

As a keeper, I have made numerous trips to the Park’s manure dump over the years to empty my dump truck. With over 3,000 animal residents, you can imagine that we produce copious amounts of endangered species feces. Fortunately for us, a farmer in the San Pasqual Valley is happy to take all we can give him; he plows this rich material into his fields, where it nourishes his crops. I had heard other keepers mentioning seeing a little owl visible on the hillside next to our dump pile. I began to look for the owl every time I went to our dump pile but could not figure out which of the 30 or so squirrel burrows might be occupied by this owl.

Finally, with the help of another keeper, I was able to spot him (or her, I’m not sure of the gender!). Now that I know where to look, I see the burrowing owl on a regular basis. Often this little bird is hunkered down inside its burrow when I first drive by to dump my truck’s load. It comes out to check out the noise after I pass, so that when I return, it’s right in plain sight. I can pull up and stop right below it. You might think it would quickly back down into the hole, but it usually doesn’t. Sometimes it just stands there, and sometimes it crouches down and freezes. This is most likely a defense mechanism against predators. This eight-inch-high owl is mottled brown and tan and easily blends in with the dry vegetation surrounding its burrow. It stands out a bit more right now, because all of the rains have turned the usually brown vegetation bright green.

I’ll admit, visiting the manure dump is perhaps not the most glamorous (or appealing) part of my day, but knowing I may get another peek at this special little burrowing owl always gives me something to look forward to.

Gloria Kendall is a lead keeper at the San Diego Zoo Safari Park.