Thursday, January 31, 2013

Owls (Strigiformes)

While we wait to see what Mom and Dad Decorah are going to do, I thought I'd write a blog to celebrate owls. I collected this information from a number of sources, but I especially want to acknowledge the Owl Pages for their help. Owl Pages also has a facebook page. See the bottom of the page for all of my sources.

Owls are a large and diverse group of mainly nocturnal birds. Over 200 species  are distributed among 27 genera worldwide, ranging in size from the tiny Elf Owl (weighing as little as 31 grams or one ounce) to the massive Eurasian Eagle Owl and Blakiston's Fish Owl (weighing as much as 4.5 kilograms or ten pounds). Despite differences in size, wingspan, color, plumage patterns, and habitat, owls share some common characteristics, including:
  • Facial disks
  • Large forward facing eyes  
  • 'Soft' feathers
  • Round heads, distinctive facial markings and/or ear tufts
  • Talons and a 'hawk-like' beak.
Owls have a number of adaptations that help them survive and thrive after dark, including highly specialized hearing, vision, and plumage.

Hearing
Although owls are renowned for their ability to see at night, their highly specialized hearing plays a crucial part in helping them catch prey in low light and under heavy snow cover.

A sound localization map. The owl's medulla maps sounds to a three
dimensional space that allows owls to locate even hidden prey with a high
degree of accuracy. See bottom of page for image credit. 
Ear tufts are not ears. An owl's ears are located on the sides of its head, under the feathers of its facial disk. The owl's facial disk, which splits into left and right sides down the middle of its face, acts as a sort of parabolic microphone, funneling sound into the ear on 'its' side of the owl's head. In addition to magnifying sound, an owl's facial disk helps provide directional hearing. An owl can move its facial disk feathers to change the disk's shape, guiding more sound into one ear than the other. Some owls can establish left/right prey directionality based on differences in sound wave arrival times just 30 millionths of a second apart.

Directional hearing doesn't end with the owl's facial disk. Many owls have asymmetrically set ear holes - that is, one ear opening is higher than the other - which helps them determine the vertical location of their prey. In this case, sound waves arrive in either the upper or lower ear first, establishing the prey's vertical location. The combination of x and y-axis locations are believed to create a three-dimensional mental image of the space where the sound source is located, enabling the owl to strike even hidden prey with a high degree of accuracy.

Picture this:

An owl perched in a bare oak tree hears a mouse rustling under snow in a wintry nighttime forest. The sound reaches her right ear slightly faster than her left ear, so she knows which direction the rustling is coming from. She turns her head until the sound reaches both of her ears at the same time, signaling that the mouse is right in front of her. Now she knows the general location of her prey, but she needs to pinpoint its location more accurately in the darkness. 

 Sound reaches the owl's lower ear hole first, which tells her that the mouse is below her line of sight. She dips her head until she hears the sound equally in both ears. Her prey is deep in the snow. She launches into the air, flying silently thanks to her highly specialized feathers. 

 Talons
Barred Owl with Prey. Photo by By NaturesPhotoAdventures (Own work)
See bottom of page for full attribution.
Owls have four sharp, curved talons specialized for sensing, catching, and killing prey. In addition to special filoplume feathers that help some species of owls sense when they've made contact - a useful adaptation for hunting in the dark - the underside of an owl's foot is covered in a rough, frictional surface that helps owls grasp and hold prey. Many owls live in cold weather, and feathered or 'booted' feet also protect them against the cold and bites or scratches from their prey.

Like many birds of prey, an owl's feet appear massive in comparison with the rest of its body. When perching, two talons are directed forward and two behind. A flexible joint allows three talons to swivel forward during flight. When striking, owls spread their talons wide in a rough oval shape, increasing their chance of success.

Once they've made contact with prey, owls knead and crush it with their large, powerful feet, using their sharp, hooked beaks to grip and tear tissue.

About two feet from her target, she brings her feet forward, spreads her talons, and strikes.  Success!  The mouse can't escape her rough feet and sharp, curving talons. She quickly dispatches it, crushing it and wolfing it down head first. 

Vision
An owl's field of vision. Image used permission of
The Owl Pages. Check them out - it's a great site!
Owls have very large eyes, accounting for one to five percent of total body weight depending on the species.  Like many predatory animals, their eyes face forward, increasing the range of binocular vision. Binocular vision, or seeing an object with both eyes at once, makes depth perception possible and aids owls in everything from capturing fleeing prey to accurately landing on a branch in the middle of the night. According to the Owl Pages, the field of view for an owl is about 110 degrees, with about 70 degrees being binocular vision.

Like many nocturnal animals, owls have tubular eyes and an abundance of rod cells, which are excellent at collecting light but don't see color well. Consequently, owls have monochromatic vision and cannot roll or move their eyes within their sockets, but must swivel their heads to visualize their surroundings. The swiveling radius of the owl’s head is around 270°, so it can see behind itself without turning around.

However, owls don't see well in the dark just because their large eyes are good at gathering light. Their fixed tubular eyes give them a long axial eye length - that is, there is an unusually long distance between the cornea and the retina, called the Posterial Nodal Distance or PND. The longer the axial length of the eye and PND, the larger the image projected onto the retina. The owl's larger retina also has room for a lot of photoreceptors, giving it heightened visual acuity since each photoreceptor processes a smaller portion of the image. In short, an owl's long, tubular eye projects a large image over a large, dense field of photoreceptors, enabling it to see detail and depth even in very low light conditions.

Finished with her mouse, the owl flies back to her favorite perch. A human might not see the branch and would be unable to judge depth and distance in the darkness, but her highly specialized eyes can see clearly even at night. As she approaches it, she raises her body into a nearly upright position and flares her wings to slow down. With feet outstretched, she has enough momentum to keep moving forward until her rough feet grasp the perch. She hears something in the distance and swivels her head to look at it. 

Feathers and Markings
Comb or fringe-like structures on the edge of an owl's
primary feather. By Kersti (Own work). See bottom
of page for full attribution.
Many birds have stiff primary or flight feathers, but owls have a special comb-like or fringe-like leading edge that helps them fly almost completely silently.

When birds fly, air rushes over their wings, creating lift and turbulence. The stiff edge of a normal bird's wing produces a larger area of turbulence, which makes a whooshing noise. However, the comb-like soft edge of an owl's wing breaks down the turbulence and muffles the sound of air rushing over the wing surface.  The lack of owl-related flight noise helps owls hear prey while keeping prey from hearing their approach.

The plumage of owls is generally cryptic - that is, the colors and patterns of their feathers camouflage them.  For example, Snowy Owls live in the tundra and are primarily white, while Great Horned Owls live in the woods and are brown, grey, and white. Changes in cryptic patterns can even be seen within species inhabiting different ranges: Great Horned Owls that live in birch forests tend to be a little lighter than those that live in darker oak or maple forests.

Although cryptic plumage aids camouflage, many owl species have facial and head markings: face masks, ear tufts, and brightly colored irises. Wikipedia states that these markings are more common in species inhabiting open habitats and are thought to be used to signal other owls under low light conditions.  Other people have suggested that, like cryptic patterns, tufts and facial markings serve to camouflage owls.

The owl lifts off her branch. Sub-nivean voles and mice flare briefly in her awareness as they scrabble beneath the snow. Her directional hearing, acute vision, muffled flight, powerful talons, sharp beak, and cryptic plumage make her a formidable  predator as she flies silently through the dark woods to her nest. 

We have four owl cams to watch:
We're getting brief glimpses of Snowflake and Dan, the female and male at Valmont, and the Great Horned Owls at EagleCrest have been observed mating:

Eggs should begin to appear in our nests in the next week or three. The earliest date they've appeared at Valmont is February 8th (in 2008) and the latest is February 25th (2007). We hope you enjoy watching them!

Things that helped me learn about this topic:

Image credits
  • Medulla map: Solis, Michele M, and Perkel, David J(Jan 2006) Neuroethology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003380]
  • Owl feather: By Kersti (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC-BY-SA-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons
  • Barred Owl: By NaturesPhotoAdventures (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
  • Owl Vision: The Owl Pages: http://www.owlpages.com/articles.php?section=owl+physiology&title=vision
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Sunday, January 27, 2013

What Cameras Do You Use?

We get this question a lot - on facebook, via email, in person, and in chat. Unfortunately, the answer is fairly complicated since we've used different cameras at different times and locations. I can't recommend any one camera model, but I can provide some general information about cameras and streaming technology to aid research. In general, we use a PTZ camera and controller, microphone, and computer to capture, process, and unicast video stream to a service provider, who broadcasts it across the internet. To do this, you need to consider...
  • Do you have all necessary permits and do you understand the animal you are camming? Permit issues regarding wildlife and cabling may differ from state to state. Make sure you understand your state's process so you aren't inadvertently breaking the law. Make sure you understand your subject so you know when it is and isn't safe to install camera equipment. What will your subject tolerate in terms of camera size and placement? When can you go to the nest, burrow, or what have you without scaring your subject away? 
  • Does your installation have electricity and internet connectivity? If you need wireless and/or solar, talk to this company: http://www.sunsurveillance.com/. We've done one wireless installation so far, but most of our installations are wired. 
  • What challenges will your camera face? Ice, rain, cold, bugs, poop, and entrails can all damage cameras and impact the view. Depending on the time of the year, you may not be able to access and fix your cameras, so they better be up to the environment and placed where your subjects can't damage them through picking at them, pooping on them, or hitting them with prey. We use weather-hardy PTZ and bullet cams certified to below-zero temperatures. We are also very careful about protecting cables and interfaces from weather, ice, insects, squirrels, and mechanical damage. 
  • You've got the camera. How are you going to get your stream to the internet? We use a standard PC, capture card, and encoder to unicast our stream to Ustream, who broadcasts the stream across the internet. Research streaming-video providers and see what they recommend - some of them, like Ustream, provide lists of certified equipment and offer their own encoders. Not all video cards work with all encoders (especially older cards) so research this carefully before buying equipment. This page (from Ustream) provides some information on their platform: http://www.ustream.tv/platform. You should also consider PC versus streaming appliance if you don't already have a PC waiting in the wings. 
  • How fast is your internet access? You need to know the speed of the internet connection you can get prior to making some of your decisions. If you have a fast line - say, a T1 - you have different (better) streaming options than you will with a slower line.  
As much as we love watching birds, the health and safety of our subjects is always our primary concern. That's why we decided not to cam the Yonder nest in Decorah - however we might feel about the new nest, the eagles are doing a very natural thing and we don't want to risk frightening them away. Bob has been a falconer for 46 years and has a great deal of experience with birds of prey. I think it is wonderful that so many people are interested in watching and sharing wildlife, but I can't stress the important of knowing and respecting your subjects enough. A few links to aid research:
  • Ustream: our streaming video provider
  • 2MCCTV: our camera provider
  • Sun Surveillance: wireless and solar cameras
  • Xsplit: our software encoder
  • Trying to migrate an analog system to IP (network) video? Check out the EVE hardware encoder. In addition to encoding it also upscales 525 very nicely.

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Monday, January 14, 2013

What happened to SNOW1?


By Kay Neumann, Executive Director SOAR – Saving Our Avian Resources

Just like the other 13 snowy owls that SOAR worked with in 2012, SNOW1 came in starving. Seven of the 14 owls died before they got to SOAR’s facility. Five more died despite our best efforts at rehydrating, warming, and trying to reverse their severe starvation. Most had lost half their body weight. Two owls made it through. One of these had a dislocated elbow and cannot fly. He is now an ambassador for his kind as a SOAR education bird. One female, SNOW1, made it to release. This is her story.
SOAR education snowy and SNOW1 share some together in rehab

SNOW1 was rescued from a farm field by Wright County Conservation Board staff in January 2012 and conservation board volunteers, the Rector family, drove her down to SOAR. She weighed 2.5 pounds. Female snowy owls should weigh between 4 and 4.5 pounds.  She was kept warm (we do not want starving birds to have to spend any of their precious energy trying to keep warm), tube fed high calorie fluids, and slowly force fed easily digestible solid food. She was able to bounce back and started eating on her own! After a month in intensive care she was moved to a medium-sized flight pen to stretch her wings. As you can imagine, she was fairly weak and it took another good six weeks for her to get her muscles back into shape. At this point the snowy migration was over and with a few feather imperfections we decided to intermew (let her molt) here at SOAR. Then several folks worked on a plan to be able to monitor her after release.

SNOW1 gets flight practice with her transmitter on.
Bob Anderson, Raptor Resource Project, and Brett Mandernack, Eagle Valley Nature Preserve, stepped up to provide a transmitter and the expertise to gather and monitor the location data. SNOW1 made a quick trip to Decorah to have the transmitter attached with a backpack type of harness. She spent more time in SOAR’s 100-foot flight area to develop muscle and make sure the transmitter was comfortable and not interfering with any of her activities. She also had live prey practice and made easy work of this, when other food wasn’t provided.

We needed to decide when and where to release her. We consulted several experienced rehabilitators and thought that taking her further north and waiting for fall, when other snowys would be moving back in would be a good plan. Minnesota DNR agreed to allow transport to their state for release. As we were preparing to do this, snowy owls began arriving in Iowa. A look at habitat areas in western Iowa showed several large wetland and grassland areas that should hold good numbers of small mammal prey items.

SNOW1 was banded, thanks to the Iowa Department of Natural Resources (Iowa DNR), and ready for release. Matt Wetrich with Carroll County Conservation Board and Paul Roisen with Iowa Ornithologist Union released her at Woodbury County Conservation Board’s Owego Wetlands. She flew beautifully and was back in the wild. It was very exciting to get the first data locations to find that she had moved several miles north, then back south, in all traveling over 30 miles to finally spend a week in and around Onawa, IA.

Paul Roisen captured this photo of SNOW1 atop a utility pole on 6 December
Before she left the Woodbury County area, Paul Roisen was able to locate SNOW1 and get a wonderful photo. She was perched on a power pole and looking in command of the situation after about a week in the wild. Then a report came from the Iowa Ornithologists Union birdline of a Snowy along Interstate 29 near Onawa. Fearing she had been hit by a car, Wildlife Lodge and Clinic volunteers were dispatched from Sioux City to try to find her and bring her in. Even with a good visual report and our transmitter data, they could not find her. An Iowa Department of Transportation staff person joined in the search and reported picking up a dead, unbanded snowy owl just a few miles north of Onawa on Interstate 29 a day or two earlier. This was not good news. Snowys were choosing to use the area, but were not fairing well. Iowa DNR biologist, Doug Chafa, stationed near Onawa, joined in the search and got a visual on her spending time in the cloverleaf interchange between Interstate 29 and Iowa Highway 175! Not the spot I would have chosen for her, but she was flying, perching and preening. She was on her own.

We had several more transmitter locations for her around the Onawa area, which seemed to be good small mammal habitat; old hayfields, mowed filter strips, and stream buffers. Then after three weeks in the wild, no movement was detected from her transmitter and we feared the worst. As it would happen, Helen Harvey, a falconer from Sioux City, was en-route near Onawa. She made a thorough walking search of the area of SNOW1’s last signal with no luck. SNOW1 must be out of sight somewhere. Dean, Ray, and Warren from the Siouxland Metal Detecting and Archeology Club volunteered an afternoon with their equipment for a high-tech search with Helen. They found her thin body under the snow. She had not survived well in Iowa. Necropsy (animal autopsy) confirmed that she was not shot, did not have any broken bones, no aspergillosis, her stomach was empty and she had no body fat.

As with most good research, this has answered one question and brought many others to mind. Could we have done something differently? Somehow better prepared her to survive in the wild? Chosen a different release location or a different time of year? As with all of our wild patients we did the very best we could with SNOW1 for her to have a good second chance at being wild.

From band return data we know that many of our released birds survive well. A red-tailed hawk was recovered eight years after release, just seven miles from her release site. An arctic-phase great horned owl that was released in Carroll County in December was recovered more than six months later in Northern North Dakota. A bald eagle was picked up in Mills County with a fractured humerus that was repaired and released in Carroll County. This eagle was found three years after release, she had flown over 100 miles back to Mills County.

Is the landscape (habitat) in Iowa so different from the tundra that snowy owls cannot figure out how to catch prey that is different from the normal diet of lemmings and arctic voles? If the snowy owls were released in March, closer to the time they should be returning north, and released near the Canadian border, would they have better survival? Perhaps the snowy owls that come this far south are not good candidates to contribute to the wild population and should not be released?

The technology to track birds after release is amazing. Even though we all wanted SNOW1 to have a successful winter and migrate back to the arctic to nest, her information will be invaluable to help with future snowy owl rehabilitation. Snowy owls are a very interesting species and may be impacted by climate change. Knowledge about their movements and survival could be an important indicator of what may be happening in the arctic. Stay tuned, we may make plans for SNOW2.

I am always amazed at how many people are willing to help wildlife in distress; it warms my heart and helps me to keep going even when things don’t work out as we would have hoped. A big thank you to everyone who helped with SNOW1’s rescue, recovery, release, and monitoring! She definitely left an impact on many people.
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Monday, January 07, 2013

Which Nest Will the Decorah Eagles Use?

I'll give the short answer first: we don't know yet, and we probably won't know for another two to four weeks. Having said that, there are some things we can all watch for. They include:
  • Mom and Dad at the tree. They do seem to have been making more visits to the Y-branch and environs lately.
  • Mom and Dad visiting the original nest.
  • Mom and Dad working on the original nest. We're especially watching for soft nesting materials such as grass and cornstalks.
I visited some older videos to take a look at Mom, Dad, and the nest in 2012 and 2011. Last winter was unusually warm, and the eagles began their nest-building earlier than in 2011. While the eagles were bringing in sticks quite regularly, softer nesting materials didn't begin appearing until sometime between January 11 and January 26, as shown by these two videos:
The winter of 2011 was more comparable to this winter: colder and snowier! Again, the eagles brought in sticks fairly early on, but soft nesting materials really didn't begin to appear until January 21st, as these two videos show.
By 2/9/11, the bowl was mostly built, as shown here: http://youtu.be/ddgd6350xpc. We'd certainly like to know what the eagles plan to do, but as usual, they will tell us in their own time. If we start seeing a lot of visits to the nest, we'll train the default camera view on it. You are welcome to view old videos on our youtube channel as we wait to see what the eagles do: http://www.youtube.com/user/ries96
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Tuesday, December 11, 2012

2012 Annual Report

Our annual report is now available online. The report discusses 2012, talks about 2013, and contains plenty of information and observations from the sites we monitor and band at. Enjoy! 

http://www.raptorresource.org/pdf/annual_report_2012.pdf
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Thursday, November 29, 2012

11/27/12: D14 Announcement

We are sorry to announce that Bob Anderson found D14 dead yesterday near Rockford, Iowa. D14, a 2012 hatch year bald eagle from Decorah, Iowa, was electrocuted after landing or trying to land on a power pole. Bob immediately notified the utility company. D14's body will be sent to the National Eagle Repository, where his feathers and other parts will be distributed for use in Native American religious ceremonies. Bob and Brett Mandernack did a close exam
ination of D14's body. He was healthy and butterball fat. There were no signs of wear from the transmitter or backpack.

How common is electrocution? A federal study done in the 1990s identified impact injuries, poisoning, gunshot, and electrocution as the top four sources of bald eagle mortality. We haven't seen it in Decorah until this year, but D14's transmitter was the only reason we were able to follow him after he left the nest. New poles commonly have bird safety devices since bird electrocutions are not only tragic, but can cause fires and power supply disruptions. However, many old poles remain and safety devices don't always work. It's been known since the 1920s that power lines and poles can present a danger to birds. As Bald eagle (and presumably other large bird) populations expand, more electrocutions may happen.

D12, a sibling of D14, was electrocuted earlier this year. A group calling themselves The Memorial for D12 Facebook Group (aka The Raptor Nation) responded by working with Alliant Energy, Puget Sound Energy, Decorah High School, and Decorah Building Supply to develop and fit bird-safe perches for the hatchery. I have a blog post and links about that here:http://raptorresource.blogspot.com/2012/11/bird-safe-power-poles.html.

If you'd like to initiate a perch project in your area, please talk with your local power company. The following links provide wonderful sources of information:

Avian Power Line Interaction Committee: http://www.aplic.org/
D12 Memorial Group story: http://raptorresource.blogspot.com/2012/11/bird-safe-power-poles.html
Avian Protection Devices: http://www.srpnet.com/environment/aviandiagram.aspx
D12 Perches: http://www.flickr.com/photos/68092929@N03/8203641600/

All raptors - all wild animals - face myriad dangers in their lives. It is easy to forget that watching and tracking them doesn't protect them. We'll miss following D14.
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Monday, November 26, 2012

Bird Safe Power Poles

Adult Eagles on Perch
This post is about a group inspired by the electrocution of eaglet D12 in the summer of 2012. The Memorial for D12 Facebook Group/The Raptor Nation worked with Alliant Energy, Puget Sound Energy, Decorah
 High School, and Decorah Building Supply to make and install safe perches at the hatchery. In their own words: 

"After the death of Decorah Eaglet D12 by electrocution, D12 Memorial Facebook Group/The Raptor Nation member Ruth Mitchell came up with an idea. Her vision was to build perches to make the electric poles in the hatchery area safer for the Decorah Eagles. Becky Burland agreed to explore the possibility and do the footwork in Decorah.

From the beginning, Alliant Energy's Shawna Sailor was very interested in the project. She realized the magnitude of the loss of D12 as the first known tragedy at the DE nest. Shawna and Alliant engineer Dennis Dye worked diligently to learn about perches and Alliant's ability to use them along with their existing equipment.

Mel Walters of Puget Sound Energy was instrumental in educating us about perches and how Alliant might design a perch to meet their specifications. Puget Sound Energy is a leader in the industry in making electricity safer for raptors and other wildlife. Mel explained that they have 1000 eagle nests in their area and they are always working to increase safety for the area raptors. Along with perches, they also use bird guards and perching deterrent strategies. We were lucky to have Mel share his experience and knowledge with us.

Part of Ruth Mitchell's vision was to have local students build the perches. It was hard to imagine Alliant allowing students to be a part of this specialized collaboration, but Becky talked with John Condon, the Industrial Tech teacher at Decorah High School. He was excited to participate in a project that would help teach students the basics of reading a blueprint and executing its construction. John was also confident that the students could meet Alliant's quality assurance expectations. A previous class made the eagle bike rack that was installed at the hatchery in 2012.

Representatives of Alliant Energy, Decorah High School and The Raptor Nation met recently to finalize the Perch Project. Alliant Energy is donating all the hardware and installation labor, Decorah High School students are donating the labor of building twenty perches, and Decorah Building Supply donated 50% of the lumber needed for the perches.

John Condon of Decorah High School reports the class will start building the perches sometime between Thanksgiving and Christmas. Alliant will install seven perches on the hatchery poles that Bob Anderson of the Raptor Resource Project identified as most important for protection. They will use the other thirteen perches as popular bird poles are identified."

The Raptor Resource Project thanks The Raptor Nation/D12 Memorial Facebook Group, Alliant Energy, Puget Sound Energy, Decorah High School, and Decorah Building Supply for their hard work on behalf of the Decorah Eagles. We'll keep you posted on the installation. Follow the link below for a look at the perch blueprint.

http://www.flickr.com/photos/68092929@N03/8203641600/

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Friday, October 26, 2012

The Decorah Eagles Have Surprised Us With A New Nest!

Mom and Dad are surprising us again.  We have noticed in recent weeks that they seem to be building an alternate nest in the neighborhood.  This is not unusual for bald eagles, but it is new for Decorah.


The two bald eagle nests in the photograph above are located roughly 500 feet away from one of Minnesota's busiest interstate highways. The nest at the left was the first nest built by the resident bald eagles, who raised at least eight clutches before deciding to build a new nest in the same tree. I watched them raise young in the lower nest last year, observing in fits and starts as I drove by or sat immobilized in traffic. But I wasn't able to watch them build their new alternate nest, located above and to the right of the original nest, so I'm not sure exactly when they started.  I've seen eagles sitting in and perching by the alternate nest this fall, and I'm pretty sure the female will lay eggs in it come late winter.

Bald eagles build the largest nests of any North  American bird (Stalmaster 1987). So why would they invest the time and energy to build a new nest when the old one remains perfectly serviceable as far as we can tell?  Several hypotheses have been proposed to explain it:
  • Alternate nests may serve as 'insurance'. If the occupied nest is destroyed or rendered unusable, the eagles can quickly occupy the alternate without having to build a new nest.
  • Changing nests from year to year helps the eagles avoid parasites and 'nest mates' who are attracted by the food the eagles bring in. Shifting nests from year to year may help the eagles avoid parasitism.
  • The additional nests may be a way of marking territory. They warn other breeding pairs away and demonstrate fitness on the part of resident adults.
  • Eagles like to build nests.
Although we haven't seen it in Decorah before, multiple nest building is a relatively common activity: in most but not all instances bald eagles will have more than one nest in their breeding territory. In one study of 924 territories, eagles were found to have an average of 1.5 nests in their breeding area. In another study of 318 territories, 45% of eagles had two nests or more (Stalmaster, 1987). Eagle nests can be classified as active (shows or showed evidence of breeding by bald eagles during the current or most recent nesting season), alternate (intact or partially intact and used by bald eagles at any time during the past five nesting seasons, but was not used during the current or most recent nesting season), or abandoned (inactive through six or more consecutive nesting seasons). It takes six years for a nest to go from 'alternate' to 'abandoned', since last year's alternate nest might become this year's occupied nest. Why? Only the eagles know for sure.
It is interesting to us that, like the bald eagles in Lino Lakes, the Decorah eagles occupied a single nest for several years before beginning an  alternate. The new nest in their territory is located nearer the trout hatchery, roughly 300-500 feet from their current nest near the woodshed. We don't know at this point which nest they will occupy next spring. Bob did find a dead buck beneath the foot of the 'alternate' tree, which could have played a role in their decision to choose this particular location. But we don't know that for sure.
Here's a peek at the alternate nest (photo by Jim Womeldorf):

To recap:
  • Bald eagles commonly build multiple nests on their nesting territory.
  • Mom and Dad have started construction of an alternate nest about 300-500 feet from their current location.
  • We will not do anything that might influence them to abandon construction of this nest, including camera installation or nest invasion. We cannot and will not disturb them: building multiple nests is part of eagle life. The health and welfare of the eagle family is more important than the nest they choose or our desire to watch them on camera. We'll miss following them, but it is exciting to see them building a new nest! Once again, Mom and Dad are giving us new insights into the lives of bald eagles.

If the eagles do adopt the new nest:
  • We will provide photographs and updates from the ground.
  • We will consider putting a camera in it next year, in early fall.
A few things to ponder: 
  • Is the length of time a mature pair stays on territory correlated with the construction of alternate nests? Five or six years would be plenty of time for parasites and 'nest mates' to become problematic, or at least annoying.
  • Is the length of the bond between the pair a factor? More experienced (older) Bald eagles seem to be better at parenting in many ways. Would a more experienced pair be more likely to build an alternate nest for insurance?
  • Does the actual or perceived encroachment of other adult eagles play a role? If other eagles are present, resident eagles might feel a little more compelled to mark territory.
We would really like Mom and Dad to use the nest they have occupied for so long, but we cannot and will not interfere if they decide to use the new nest. As we said in an earlier post on intervention, their lives are a gift we have been privileged to share. We can only hope we'll get another chance in 2013.
Stay tuned and we'll keep everyone updated as the situation develops!

Things that helped me write and learn about this:
  • Book: The Bald Eagle. Mark Stalmaster, 1987. This is a wonderful book, and the eagle illustrations are charming.
  • Book: The Bald Eagle: Gerrard and Bortolotti. Another great book.
  • Green Value Nursery, Hugo, MN. Thanks for letting me park and walk across your land to get photos of the Lino nest. I'll buy flowers from you next spring!
    http://www.greenvaluenursery.com/
Note: I got an email from Nancie Klebba in Lino Lakes. She says:

I spoke with a few people on the board that live on the lake and the City's environmental coordinator and they believe the nest has been on Peltier since about 1993 or 1994.

Marty the environmental coordinator said he would check back to see if he could find the exact date.  He  also said the old nest has not been used the last few years.

Thanks, Nancy!

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Tuesday, October 16, 2012

Migration!

At whatever moment you read these words, day or night, there are birds aloft in the skies of the Western Hemisphere, migrating. If it is spring or fall, the great pivot points of the year, then the continents are swarming with billions of traveling birds...
- Living on the Wind: Across the Hemisphere with Migratory Birds

We get a lot of questions about migration. Do the Decorah eagles migrate? Do our Peregrine falcons migrate? Where do they go when they leave? We fitted two young eagles with tracking devices in part to help answer some of these questions.

I used to think migration was very simple. Like a lot of people, I thought that all birds except chickadees, pigeons, crows, and woodpeckers migrated once it got cold. They went south to escape snow and ice, returning to nest when the weather warmed up. 'South' was anywhere it didn't snow, or at least didn't snow much: Georgia, the Gulf Coast, South America. I had no idea that many birds don't migrate, or that 'south' could be Minnesota or Wisconsin. Peregrines and Bald eagles taught me otherwise.

Bald eagles and Peregrine falcons are partial migrators - that is, some members of the species migrate and others do not. Mom and Dad Decorah both stay put on their territory year round. They have abundant food and water, so there is no reason to leave. Belinda, the falcon at the Xcel Allen S. King plant in Stillwater, Minnesota, also has a history of staying put. There is abundant food on territory and an open water supply slightly south of the plant. In both cases, the resident bird or birds' presence may make it easier for them to preserve their territory without having to chase off interlopers that set up house in their absence.

However, other birds, even those with defined nesting territories, leave. Immature and adult Bald eagles congregate in large numbers by open water along the Mississippi river, a very important flyway for many kinds of birds here in the midwest. Belinda may stay put but it is not uncommon to see interloping falcons at empty nestboxes: just two weeks ago, Brenda Geisler spotted a Peregrine falcon from North Dakota at the Great River Energy nestbox in Elk River, Minnesota. What is migration and why do some birds stay put while others leave?

Among birds, migration is the regular, endogenously controlled, seasonal movement of birds between breeding and non-breeding areas (Salewski and Bruderer 2007). Bald eagles and Peregrine falcons are partial migrators - that is, some members of the species migrate and others don't. This is the most common type of migration, which makes sense since migration is driven by a number of factors, including daylight length, food availability, weather, the time it takes to raise young, and the distance between wintering and breeding grounds. Migration allows exploitation of different habitats as environments change seasonally or successionally (Dingle, 1996). Food availability seems to play a very important role in the migration of Bald eagles: inland northern Bald eagles tend to move southward after ice and snow start putting a lid over their favorite food source - fish, while southern Bald eagles are thought to move northward once warm weather drives fish into deeper water (there is some debate about this). Weather can also impact migration timing in other ways: for example, a favorable wind pattern might help compel a bird to leave for its wintering or summering grounds if other factors are in place.

In general, young Bald eagles are much more nomadic than adult Bald eagles, something we've seen with both D1 and D14. In spring and summer, hatch-year and young sub-adult eagles may fly north to over-summering areas in the northern United States and southern Canada, returning to their birthplace in late summer or early autumn. Or they may not, as we've seen with D14. We don't know why D1 dispersed so much farther than D14 in her first year. Among Peregrine falcons, females tend to disperse farther than males* , but I haven't been able to find documentation of gender-related dispersal in Bald eagles. I'll keep looking, and you are welcome to post links and resources in the comments. Perhaps further study will shed some light on the issue. Eagle migration and dispersal is very complex.

So how do birds navigate? Migration studies have found four major methods:
  • Magnetic sensing: Some birds, including pigeons, are able to use the direction and strength of Earth's magnetic fields to orient themselves. http://www.nytimes.com/2012/04/27/science/study-sheds-light-on-how-pigeons-navigate-by-magnetic-field.html?_r=0
  • Geographic mapping: When I'm in Minneapolis, I use a number of tall buildings to help me orient the city. It turns out that birds do the same thing, using landforms and geographic features such as rivers, coastlines, and mountain ranges to guide them.
  • Celestial navigation: migratory birds use the position of the sun (during the day) or the rotation of stars (at night) to orient themselves. Experiments done by Dr. Emlen in 1967 indicate that celestial navigation is learned. http://www.birds.cornell.edu/AllAboutBirds/studying/migration/navigation
  • Learned Routes: Some bird species, such as sandhill cranes and snow geese, learn migration routes from their parents and other adult birds in the flock. Once learned, younger birds can travel the route successfully themselves.
What do Bald eagles and Peregrines do? It seems they most likely use multiple sources of information, including celestial and magnetic clues, light polarization, wind patterns and direction, and geographic cues (which would likely be highly correlated with geography). Although parents and young don't migrate together, D1 and D14 were in the company of other eagles every time we saw them, so I suspect that some degree of learning, or at least following, also plays a role. Again, we really have no idea why D1 and D14 behaved so differently.

We suspect that D1 will come back to NE Iowa this winter, following Lake Superior's western shore. We don't know whether she will come down along the Mississippi river or go back into western Wisconsin, where she spent so much time in the fall of 2011. But we are looking forward to finding out!

Some things that helped me write this post:
* Regarding male Peregrine dispersal: of course, there are exceptions. We released Zeus, the male at Woodman Tower in Nebraska, in Rochester New York. We were very surprised when he showed up in Nebraska. Did he fly west intentionally or was he some how blown off course or lost?




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Thursday, September 27, 2012

Return to the Nest 2013: Q&A Session

Social Stream moved very quickly during the interview with Bob on Tuesday, September 25th! I wanted to publish his answers to a couple of the very commonly asked questions I saw floating around in the stream, and hopefully answer a couple that he didn't get to.

Before I start with the questions, videos are here:

What did you guys do when you installed the cam?

Bob Anderson directed the installation. He designed and tested the equipment, planned and oversaw the deployment, worked with Dave and Neil via the webcam to make sure everything was installed correctly, and staged on the ladder to help pass equipment.

Neil Rettig and Dave Kester climbed the tree. They cleaned the old camera dome, replaced the broken IR cam, removed an unnecessary screw, and added two new cameras: a new PTZ and a very high resolution fixed bullet cam. As Bob pointed out, we'll have new views. You will sometimes be able to see one of the cams appearing on screen.

Jim and Charlie worked on the computer and power protection systems and helped haul equipment.
Amy Ries briefly staged midway up the tree to help get the camera bag up, set anchors, and helped haul equipment.

What is new this year?

We have a new PTZ cam, a new high resolution fixed cam, new views of and from the nest, better surge suppression and electrical protection, new video cards, and a new system to switch back and forth between the cams on site or remotely.
Kudos are due John Howe for designing the switching system, and Kenny from Simms Electronics for his technical assistance and computer systems.

When is the cam turning on?

We don't have an exact date yet. We need to get a T1 line pulled in for faster service and make some changes to our computer system. It will be sometime between mid-October and mid-November.

When will chat re-open?

Chat will re-open in February. We will announce an exact date as it gets closer.

How did Mom and Dad react to the camera installation?

Mom and Dad weren't at the nest when we got there.  They did fly by in the early afternoon and vocalize two or three times before leaving. We saw them briefly soaring over the bluff later in the day, which was warm, windy, and perfect for flying.

Are Mom and Dad already working on the nest?

Yes, they are! They have begun adding crib rails to the side in preparation for next year's brood.

Were you able to get permission to lighten the nest? Who would you get permission from?  

The US Fish and Wildlife Service oversees permits and other issues related to the Migratory Bird Treaty Act, including falconry, raptor propagation, scientific collecting, special purposes (rehabilitation, educational, migratory game bird propagation, and salvage), take of depredating birds, taxidermy, and waterfowl sale and disposal.  We have permits to go into the nest and install cameras, and we have permits to band and attach transmitters to eagles, but we did not get permission to lighten the nest this year.

Bob pointed out that Neil, Dave, and all the gear weighed more than the eagles were likely to bring in this year, so we think the nest will be fine. We'll probably ask again next year.

Did you leave a treat for the eagles?

We usually do, but we did not this year. Fortunately, they didn't seem to hold it against us.

Is the crossbow dangerous to the eagles?

We use a dull bolt, but we also don't shoot the crossbow when the eagles are in or near the nest. We don't want to take any risks with them.

Will Mom and Dad migrate?

Probably not - they have a history of staying through the winter. Eagles are partial migrators - that is, some eagles migrate and others don't. For eagles to be non-migratory, there must be sufficient food during the winter.  The Decorah eagles have a nest in a relatively sheltered location, with ample access to food year round. The adults are not migratory.

Are D13 and D14 still around?

Yes, for D14, although we haven't seen D14 at the nest. D14 spends a lot of time NW of Decorah, near the Upper Iowa river. He has been seen in the company of other adult and hatch year eagles, but we don't know whether those eagles are family members. It is certainly possible, although there are other eagle families in the area. You can follow his adventures at: http://www.raptorresource.org/maps/D14_latest.php

Probably for D13 - D13 was believed to be spotted recently, but we don't know for sure.

Why do these eagles always lay three eggs?

They don't - in 2008, her first year at this nest, Mom laid a two-egg clutch. She has, however, laid three egg clutches every year since. Three egg clutches are not common in Bald eagles.  According to Gary Stahlmaster:
  • 79% of clutches have two eggs
  • 17% of clutches have one egg
  • 4% of clutches have three eggs
  • Less than 1% have four eggs.
Food availability impacts Bald eagles in a number of ways, although there is a lot of debate about whether or not it impacts clutch size.  Some studies say 'No', while others hint at a link. Our nests don't make it any clearer either way: one nest (the Decorah nest) has a reliable high-quality food supply in a relatively sheltered area, while the other nest (the Fort St. Vrain nest)  is at the foot of the Rockies in an area with harsh weather and a more limited food supply.  Yet the eagles at both nests have a tendancy to lay three egg clutches. We don't know why.

Are you going to turn the nightlight off this year?

No: the nightlight is infrared light, which the eagles can't see. Click here for more information on the IR cam.

Are you going to have cameras in the kestrel nests?

We don't have any plans to do so right now. The kestrel project is a pilot that explores using county right-of-ways along gravel roads to expand the kestrel population. We don't easily have a way to get power or connectivity out to the boxes, which are located in remote areas. If you would like to learn more about that project, click here.

What was that about Philippine Eagles?

The Raptor Resource Project will be working with the Philippine Eagle Foundation to raise awareness of the highly endangered Philippine Eagle. From the foundation:  The Philippine Eagle Foundation firmly believes that the fate of our vanishing Philippine Eagle, the health of our environment, and the quality of Philippine life are inextricably linked. We are therefore committed to promote the survival of the Philippine Eagle, the biodiversity it represents, and the sustainable use of our forest resources for future generations to enjoy.

We plan to add a Philippine Eagle cam and help sow the seeds for a recovery effort for and by the Philippine Eagle. We will post more about that as it gets underway.

Thank you for watching!
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Tuesday, September 18, 2012

09/17/12: D14 and D1

D1 is on the move! She's roughly 77 miles of her northernmost point right now, although she's a little north of the southernmost point we've tracked her at this month.http://www.raptorresource.org/maps/latest.php

Back in Decorah, Bob took some time to track D14 this afternoon. He writes: "I had a bit of free time this AM so I tracked down D14. He was perched in a white pine tree on the top of a bluff overlooking the Upper Iowa River. There were two adult eagles perched nearby. I returned to this area a few hours later and got a beep pointing down stream. I got a booming signal when I pointed the yaggi at three immature eagles soaring high over the river. They were so high up I could not tell which one was wearing the transmitter."

D14 along the Upper Iowa River
D14 with other eagles

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Wednesday, September 12, 2012

7 nestboxes in 2 days!

I've blogged a little about our pilot kestrel project [click here for kestrel nestbox plans]. We kicked it off last week when we installed the first six boxes along a rural gravel road in Bluffton, Iowa. The kestrel (Falco sparverius) is a small falcon that is in decline throughout parts of its range. There are a number of theories about the kestrel's decline: HawkWatch International's list of factors includes development and reforestation of preferred habitats, poisoning, and the West Nile virus. We've focused on the loss of grassland in Iowa, where farms have grown larger, woodlots, fencerows, and fallow land have shrunk, and small grains and hayland have been replaced with row-cropped soybeans and corn. The Iowa DNR states:

"Between 1990 and 2010, Iowa lost 2,615 square miles of potential pheasant habitat. This habitat was a mix of small grains, hay land, and Conservation Reserve Program (CRP) acres. To put this loss in perspective, 2,615 square miles is a strip of habitat 9 miles wide that would stretch from Omaha to Davenport!" [2012 Iowa Roadside Survey]

So why use rural ditches? Bob started talking about ditches as a sort of habitat of last resort in heavily developed areas. I don't tend to think of farmland as heavily developed, myself - it's all green, right? - but mile after mile of row-cropped corn and soybeans is not a natural environment. As grassland and pothole prairie are converted into farmland, animals and birds are forced into ditches. Water, rodents, insects, and plant life attract a wide variety of larger animals, including deer, rabbits, woodchucks, gophers, mink, muskrats, badgers, fox, raccoon, skunks, snakes, frogs, red-tailed hawks, harriers, kestrels, sparrows, mourning doves, gold finches, bobolinks, and pheasants.

A little back-of-the-envelope calculation. Iowa contains a total of 36,016,640 acres. Over 90%, or 32,414,976 acres, is under till. So how much of what's left is ditch? That's a hard question. The DOT manages about 175,000 acres along interstate and state highways, but that figure doesn't cover county, city, and town roads. When those are added in, the total jumps up to about 1.6 million acres, or 44% of the remaining 3.6 million acres left. Although broken and fragmented, that is a lot of potential habitat. Winnesheik County gave us permission to install nestboxes along 5 miles of dirt road in rural Bluffton, Iowa, and the fun began!

In the wild, kestrels nest in cavities in trees, cliffs, and buildings. They like to be up high, they want perches, and they need a fairly long box with a hole toward the top, preventing direct sunlight from reaching the box's bottom. We didn't want to use cement in the holes we dug to support the pole, since that would mean hauling water out to each site. The pole needed to be strong but also breakaway, given that it was in the county right-of-way. Bob wanted the nestboxes to have a slightly slanting roof to shed rain, sun and weather resistant siding, and a perch for the kestrels to, well, perch on. Here is what the finished boxes look like, absent a coat of paint. Bob and board member John Dingley built the boxes out of T11 siding, which we also use to construct falcon nestboxes:

Board member John Dingley with the kestrel nest boxes







Now for the posts! We weren't able to get 18’ 4x4 posts, so Bob ordered 15 green-treated 2x4 boards. He decided it would be easier to haul materials than posts, so we constructed the posts on site by gluing and screwing them to create a laminated 4x4x18' pole. Voila! Strong enough to stand against the wind, yet still break away against cars, trucks, tractors, and other vehicular interlopers. 

Bob assembles a kestrel nestbox in his mobile workshop

Last Tuesday dawned hot and humid! Bob and John borrowed a truck from camera operator Charlie and set off. The procedure went something like this: they reached a spot, stopped the truck, put up orange cones, and went to work. While John dug a fout-foot deep hole (among many other things, John is a mason), Bob built the pole, attached the pre-made nestbox, and added about two inches of sand in each box.

John digging a nestbox hole

Once the hole was dug and the box was ready, we levered the box up and into the hole. We added dirt, tamping roughly every two inches. When the hole was about half-way full, we added roughly a five gallon bucket of gravel, tmaped that, and finished with dirt. The gravel compacts extremely well - almost like cement - and provides drainage to help keep the wood from rotting.

John with an installed nestbox
The next day we installed a peregrine nestbox on a cliff just south of Bellevue, Iowa, at Bellevue State Park. We were were very pleased to find Indian mounds at the top of the cliff, just above the spot we intended to hang the nestbox. Although these were conical mounds, the Mississippian people revered the falcon and built falcon mounds. It seemed like an appropriate place to put a falcon nestbox. We were joined by Pat Schlarbaum from the Iowa DNR and Park Manager Shannon Petersen, who helped carry gear and were in general very enthusiastic about the project.

Dave, gear and mound 


Bob went down the wall to find a good spot for the nestbox. It has to be unavailable to raccoons (as usual, we found raccoon poop all over the ledges), fairly flat, high up, and visible - it can't be hidden behind foliage. Once he tagged a spot, he came up, cutting brush out of the way to make it easier to handle the nestbox. The nestbox is roughly two feet by three feet, weighs 30-40 pounds, and is constructed of T11 siding in a steel frame, which will not warp or pull off the anchors. It can be a bear to handle, especially in thick brush. The time we took to cut away branches and vines saved us a lot of work!

Bob lowered the nestbox to me, on a ledge, and I caught it and carried over to the edge, belaying it down to Dave. As usual, hazards included rocks and the box itself. Bob put a long rope on the bottom side of the box, which made it much easier for those of us below him to guide it over cliff edges and keep the box away from rocks. I got the box down to Dave and then joined him on rope, where we levered the box into place and anchored it to the wall with our awesome new hammer drill (donated by Pat Schlarbaum, thank you very much!).  Once it was firmly in place, Bob lowered down 80 pounds of pea gravel and a perch. We filled the box with the pea gravel (roughly 3 inches deep, to add drainage and prevent egg breakage), attached the perch, and got off the wall. 7 nestboxes in 2 days - done!

Dave is above the box and Amy is below it
Note: We forgot to add sand to one of the kestrel nestboxes, so Bob and John went out to fill it late last week. They saw 8 kestrels between the first box and the last box, and one box already appeared to have been claimed by a male. We anticipate banding babies here in the spring!

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Resources that helped me write this article:





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Monday, September 10, 2012

9/10/12: Weekly Roundup

John Carton got photographs of both recently fledged Turkey vultures! He writes: 

"The turkey vultures are now able to fly very capably with strong wingbeats, but still are staying close to their "home territory".
Presumably their parents still return to the area to feed them. One would guess that the young birds get some valuable flying practice following each feeding and emulating the departing parent; however, I have not yet had the opportunity to observe it. Today, first one and then the other adolescent left its perch, in strong flight low above the surrounding treetops, easily gaining altitude. Their flights were observably strong and accomplished."

I've been asked about whether or not the adult vultures are still feeding and/or teaching their young to fly and find food. While we don't know the later for sure (yet), John's observations indicate that the parents are still providing at least some food for their young. More of his photographs from 9/8/12 can be seen here:http://www.flickr.com/photos/johncarton/sets/72157631472408848/

D14 remains near Clermont, Iowa, while D1 is still up in Polar Bear Park, albeit on the southern end. Both Mom and Dad eagle have been seen near their nest, and we anticipate that they will stay through the winter once again. We don't have a date for cam turn on yet, but I'll post here once we do.

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Monday, August 27, 2012

08/27/2: Weekly Roundup

D14bybridge I'll start with a D14 report from Bob, who writes:

"Mary and I set out to locate D14 on the Upper Iowa River down stream from Bluffton, Iowa. We were getting a strong signal with the PTT receiver as we came down into the valley near what is called the Hutchinson Bridge. As we drove over the old bridge, D14 flushed from its upper beams. He flew to a nearby tree and we were able to get some pictures. Mary and I then met with Dixie Hutchinson to show her where D14 has been on their river property. The land owner from across the river joined us just as a team of horses pulling a large wagon and making lots of noise with their hoofs caused D14 to take flight once again. We were surprised to see him join another immature eagle (D13?) in the air. He broke off and returned to land on the upper beams of the old bridge. All of us could easily see his transmitter."

We believe that D1 remains in Polar Bear Park, but have not had an update for five days. Her transmitter is solar-powered, so it is possible that grey, rainy weather has prevented the battery from charging. I'll post new coordinates as soon as we get some.

The first Turkey vulture (BB) fledged yesterday at about 10:27am. We have a Ustream video highlight here: http://ustre.am/_1GOFB:1cZn. As of this post, LB is still in the barn. I've had some questions about whether or not the TV will return to the barn after they have fledged. I don't know, but have asked for a ground update. I'll post when I get it.

For the next two weeks, we will be testing equipment, building kestrel nest boxes, and installing a Peregrine nest box at a cliff in Bellevue, Iowa. Once we have plans drawn up for the kestrel boxes, I'll post them as well.

Happy birding, online and off!
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Tuesday, August 14, 2012

Turkey Vulture Musings

Some people enjoy watching the little Turkey vultures and others do not. The TVs behave quite differently from the eaglets: they spend hours a day beating each other up, don't play in a similar fashion, appear to frighten their parents (the hooligans!), and have a very unappealing diet.  They are fun to watch (if you don't mind intestinal tug-of-war) but there are not nearly as many 'awwwwwwhhh' moments. Both Bald eagles and Turkey vultures are raptors [note - I had a few of emails that pointed out this is debatable. Some experts argue that New World vultures should be placed into storks, others argue they should have their own order, Cathartiformes, and still others argue that they should be placed into raptors]. So why are their young so different? I think - and this is speculation - that the way the young birds play and interact with one another reflects their very different lifestyles as adults.

Since eagles eat live prey, they need to hunt. Since recently-killed prey has firm flesh still connected by tissue, muscle, and bone, they need to tear food. When Mom and Dad bring food in, the eaglets sometimes stalk it. Once the eaglets can stand and walk well, they also tear food with their feet, steal it from their parents and one another, and mantle to guard and protect it. Food play includes stalking, pouncing, and grabbing. A few examples:      
Turkey vultures, on the other hand, eat primarily dead food (they have been observed eating pumpkins), detectable by the smell of ethyl mercaptan.  They don't need to stalk or hunt wary prey, although they do need to eat quickly to compete with other vultures and carrion eaters, including larger Black and King vultures. I don't know that carrion or hunks of carrion could be carried to the nest without falling apart: at any rate, Turkey vultures rely entirely on regurgitation. The young don't play with food much at all that we've seen: their parents regurgitate it, they eat it, and that settles it. As John Carton noted, the chicks learn to "gulp their food properly" in response to their parents' quick in and out feedings. Eating quickly is a necessary survival skill for turkey vultures, and they don't play with their food.
Eagles build huge nests, and the young eaglets mimic Mom and Dad's nest-building activity from a very early age. They move and place sticks and other nesting material, and play tug-of-war as well (perhaps preparing for the inevitable adult differences over where, exactly, that stick should go).
Turkey vultures don't build nests the way that eagles do. In this case, the adults spent some time preparing the straw prior to egg-laying: they pecked at objects, snapped straw into smaller pieces, and formed a depression for their eggs.  However, they invested very little time in maintaining, building, or caring for it once the eggs were laid. While the young turkey vultures roam around and explore objects, they don't engage in the same kind of stick and nesting material play that the eaglets do. In this case, no nest seems to equal no nesting play.

Turkey vultures and Bald eagles are both social, and both sets of young spend a lot of time interacting with one another. When it comes to play, the eaglets tussle, cuddle, preen, steal food, and play tug of war. The young vultures (vulturelets?) beat each other relentessly, with occasional breaks for preening. While the eaglets appear to play at the complex skills of hunting, nest building, and competing for food, the young vultures appear to play primarily at competition, period. Although Turkey vultures are social, this behavior leads me to wonder about the intensity of TV to TV food competition. Is this all about other carrion eaters, or do adult Turkey vultures beat each other up over food as well?
Although the behavior of the little Turkey vultures may not be as appealing as the eaglets to human watchers, their play and interaction is equally effective at helping to prepare them for the challenges of adult life. John predicts that they will most likely begin flying between August 28 and September 3rd. I've enjoyed watching them in the nest and look forward to his observations once they have left.

If you haven't watched the Turkey vultures, you can see them at: http://www.ustream.tv/missouriturkeyvultures
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