Wednesday, July 09, 2014

EWOT's Electrocution

Yesterday at about 10:45, Decorah fledgling EWOT (widely believed to be D18) was electrocuted on a high voltage power line roughly ½ mile from the mulch pile that both fledglings have been spending most of their time on. It was reported to us late in the afternoon. We collected and examined him, returning to the site of the electrocution to gather more information once that was done. Here is what we know.

The line was a 96 Kilovolt transmission line owned by ITC Holdings (http://www.itc-holdings.com/). In general, electrical delivery can be divided into two types: transmission and distribution. High-voltage transmission lines carry electricity over long distances from power plants or grids to substations. The poles or towers are physically larger and taller than those that support lower-voltage distribution lines and don’t support anything except electrical lines. Distribution lines carry electricity from substations to consumers and are supported by what most of us probably think of as utility or power poles. Utility poles are often made of wood and, unlike transmission lines, may also carry telephone and cable wires or support street lights.

ITC is able to detect fluctuations and other anomalies on their lines. When they sensed an anomaly, they sent a field technician out to investigate. He found and collected EWOT, and turned him over to the Iowa Department of Natural Resources. They saw the transmitter and called Bob to let him know that an eaglet had been electrocuted.

When we first got word of another electrocuted eaglet, we assumed it had contacted a standard utility pole. According to Refining Estimates of Bird Collision and Electrocution Mortality at Power Lines in the United States, electrocutions occur primarily at distribution lines, while collisions occur at both distribution and transmission lines. That’s certainly been our experience, since every eagle we’ve picked up has been found at the base of a distribution line. I pictured a standard wooden utility pole as we glumly drove over for our field investigation. I was surprised to instead find a high-power line between a field and a hill. We hiked out and took a look at the scene. We weren’t able to find scorch or singe marks on the pole or insulators, and the eaglet’s body was not at the base of the pole, as we’ve seen elsewhere, but under the lines three to four feet from the pole.

An examination of the eaglet’s body revealed singeing and burning around his elbow and feet. Electrocution can’t happen unless a bird’s body creates a circuit between ground and voltage, or different voltage phases, allowing energy to flow from high to low. Sitting on a wire won’t harm a bird, since it doesn’t create a circuit. But he closed a circuit with his wing and one foot, creating the flow that killed him.

In addition to singeing, the eaglet’s wing had extensive tissue damage and some severing. Although it seemed unlikely, we needed to know whether the transmitter had somehow created or closed the circuit that led to his electrocution. A quick look at the transmitter showed no damage, scorching, or discoloring. We cut the straps and removed it from EWOT’s body. The straps were intact and there was no scorching, singeing, or burning under the straps or backpack pad. Finally, we made sure the receiver could detect the transmitter. The transmitter was functioning normally, so we concluded it hadn’t been part of our eaglet’s electrocution.

Bob contacted ITC this morning. The biologist he spoke with told him that they hadn’t seen an electrocution on a high kilovolt line in the three years he’d worked for ITC. Having said that, they reported the electrocution to the U.S. Fish and Wildlife Service and the Avian Power Line Interaction Committee, and they are assessing steps that can be taken to prevent another electrocution or collision.

What we think
The pole was up to code and we haven’t had any problems at a transmission line before, so we suspect the electrocution was a terrible accident. Other electrocutions and near-misses in Decorah involved distribution poles with wonderful perching spots near the hatchery, where the eagles regularly hunt, fly, and hang out.  The transmission pole provides a bad perching spot overlooking a poor hunting ground bordered by trees. Although electrocution was clearly the cause of death, we suspect that EWOT might have collided with a wire and dropped, contacting other wires or the pole before dropping to the ground. Death was very quick.

Where do we go from here?
We don’t know whether ITC will install diverters or a similar non-collision technology over one death. Companies tend to set priorities based in large part on collisions, electrocutions, and known migration/movement paths. Reporting is key and we are very glad the company didn’t choose to sweep the electrocution under the rug.  
Bob talked to ITC this morning. If there are any more deaths, the company will report them to us, the DNR, and the USFWS.  Neither D1, D14, or Four have spent any time near the high voltage line, but if Four or D1 start hanging out, we’ll make ITC and everyone else aware of it.

Why can’t you build safe perches?
Alliant Energy, the D12 Memorial Group, the Decorah High School, and Decorah Building supply were able to make the distribution poles at the hatchery safer through insulation and safe perches. However, we’re not sure this was a perching problem and we can’t encourage perching on high voltage transmission lines since they are too dangerous. If protection is installed, it will probably be in the form of diverters that make it easy for birds, including eagles, to see the power lines.

What can we do?
Our wonderful fans want to know what they can do to make power lines safe. A few suggestions:
  • ·      Does your power company have an Avian Protection Plan? Click here for more information: http://www.aplic.org/APPs.php. Birds aren’t the only issue, either – my electrical cooperative is upgrading equipment because of squirrels! Talk to your company and find out what they have in place.
  • ·       Report electrocuted animals to your power company and wildlife agency. If your power company shrugs it off, document the problem and talk to your state’s regulatory agency. It’s my experience that most utility companies are very responsive to electrocutions. They kill animals, destroy equipment, can start fires, and are expensive.
  • ·      Learn more about the issue. A few good places to start:

While we can’t protect transmission lines with safe perches, most of our electrocutions have been on distribution lines. This seems like a good time to share the story of the D12 Memorial Group’s work with making distribution poles safer. 
We are really dismayed by the electrocution of another eagle but believe we can do better in the future. We’ll continue working with power companies to improve outcomes for birds of prey and we’ll certainly let you know what happens here. In the meantime, please feel free to share your stories of improvement and recovery with us. 

Thursday, July 03, 2014

What's up with Four (or why aren't you calling the Decorah eaglets "Dx" anymore)?

For the last couple of days, the most commonly asked question on facebook has been something along the lines of "Why are you calling D19 or EWT Four now?" We've also been asked if that means this year's fledglings are going to be referred to as D2, D3, and D4, and what this means for any other birds we've transmitted. I'll start with a recap of our EEE's:
  • Four, fka EWT or Eaglet With Transmitter (widely believed to be D19) was the eaglet found in a road where traffic had stopped for it. Bob brought her to his mews for examination and observation and fitted her with a transmitter. She has been rescued twice -- once in a corn field and another time when she was wedged against some woven wire fencing on the ground. She was the one who was relocated to the mulch pile to be with her sibling. Beak depth and hallux claw measurements taken at the time we fitted the transmitter indicated that she was a female eagle. 
  • EWOT, or Eaglet Without Transmitter (widely believed to be D18), has never been picked up and moved elsewhere. It was found at the city mulch piles about 1 mile from the nest. Gender is unknown. 
  • SOAR, (widely believed to be D20) is the eaglet who had surgery at the rehab facility of the same name (Saving Our Avian Raptors). SOAR (the eaglet) is recuperating and we get almost daily updates of his progress. Kay at SOAR and veterinarian Dr. Dirks believe that SOAR is a male eagle based on his size and weight. 
So why the name change? As looks and defining features change, (especially after fledge), Bob preferred to have new nomenclature established since we cannot be 100% sure of IDs. "Four" is the last number of Four's transmitter ID and WOT (Without Transmitter) is an obvious and easily identifying feature (or lack thereof) that can be used to differentiate between the two. 

So if we put a transmitter on EWOT, will he or she be known as "Five"? Not necessarily. I don't have all of the transmitter ID numbers so I don't know whether or not we have a sequence. If that happens, I'll amend this post to reflect whatever the new number is. We don't have any plans to change the pre-fledge nomenclature of D + N, so we'll start with D21 next year. 

I'm going to close with a quote by William Shakespeare, which seems appropriate both for its subject matter and the Bard's great fondness for falconry metaphors: "What's in a name? That which we call a rose by any other name would smell as sweet." Fly on, fledglings! You are such stuff as dreams are made on!




Citations

BA1, personal communication and information about Shakespeare's falconry metaphors.
http://www.raptorresource.org/

SE1, personal communication and facebook responses.
https://www.facebook.com/pages/Raptor-Resource-Project/103786266324668?ref_type=bookmark


TW1, personal communication and Ustream responses.
http://www.ustream.tv/decoraheagles


Wednesday, July 02, 2014

Your Top Thirteen Questions For SOAR and Dr. Dirks

Last week we asked Decorah watchers for their questions about the Decorah fledging that went to SOAR. Thanks to Kay and Dr. Dirks for answering them. Next week we'll ask for questions from Bob and Brett about development and fledge, so stay tuned!

Where will the eaglet be released?
This is a big leap to the end – IF he is able to be released… I think it would be an excellent idea to release him in the NE Iowa area. The exact location will depend a lot on the time of year. We will definitely be too late/too much time will have passed to expect that the Parents would take over any care or guidance. When the time comes we will do some consulting with our eagle experts (Bob and Brett) and find a spot where there is not a current eagle territory – just to avoid any conflicts there – usually the juvies are pretty safe. The big thing will be HABITAT – a good spot for scavenging and fishing. As we know from eagles with transmitters, eagles can travel long distances in short amounts of time. If he is able to be released, he will go wherever he wants to go. 

How do you determine where to release the birds you find, especially if they have been held for a while?
Again – good habitat is what we look for so the birds will not have to work too hard for food. We also look at time of year and weather. Winter is hard for everyone so we hold most birds late November through to early spring for release. Along with the quality appropriate habitat type, we look for travel corridors such as a river. If we release in a resident bird’s territory, which we try very hard not to do, the released bird can easily move to a new spot through the corridor habitat. 

What do you feed your eagles?
We need to mimic the things that they would be eating in the wild the best we can. This helps them to recognize what we are offering as food and is also completely nutritious. We try to give variety. Our eagles really seem to like carp – rough fish that most human anglers do not like to eat – so this helps us with donations of this type of fish. We salvage road killed deer – this meat is rich and dark – lots of vitamins and iron. We have a friend that provides some grown chickens and rabbits.

We start with hand-feeding our extremely ill patients. As they recover, they will eventually take food on their own.

The eaglet looks comfortable with humans. Does it try to bite or how does it react to handling?
A good question. Biting is involved when we need to handle him, so we have big gloves and we handle him carefully yet firmly. Overall comfort is an important part of our care. 
Most of the time our intensive care or ICU patients are in carry crates so we can limit movement. Like humans in ICU units, these birds have severe, often life-threatening injuries or conditions. We provide climate control and make sure that food and water bowls can be seen and are accessible. We also need to be able to easily administer medication and capture our patients to change bandages and perform other necessary tasks.  Of course as they feel better, they want out! When they are ready we have larger flight areas they move into for exercise pre-release. 

This little eaglet would not sit still in a crate. So he is in our small ICU room, which gives him a bit more room to move around. He is quite comfy there right now. 

What is the ICU and what does it look like?
Intensive Care is basically two large rooms and one smaller one that we heat and cool. Check SOAR’s web page for photos of SOAR facilities, including flight areas: www.soarraptors.org

How does the eaglet learn to fly and hunt absent parents?
If they are physically able to fly, they will fly. While skill is learned on the wing, flying and hunting are instinctual. SOAR has a 100 X 20 foot flight area for our eagles. After bone healing is complete, which could take approximately eight weeks or more, our patient will spend time in this large flight area with our other eagles. We have Spirit and Liberty, a bonded pair of non-releaseable education bald eagles that have fostered two different eagle chicks so far in their own large enclosure. He will not need to be fed, but they can model socialization, vocalizations, and eagle behavior. He is well past the age when he would imprint on humans, so we have no worries there. He is not going to like us no matter what!

It's my understanding that bald eagles can present unique challenges in housing and handling. If so, can you elaborate a little?
They are big and powerful. So housing requires large spaces. Handling requires experience and protective gear, including gloves, goggles, and a heavy coat. 

What particular challenges do you anticipate during the Decorah eaglet's rehab, both short term and long term?
We have crossed several hurdles. He survived his initial injuries. His fracture was not compound (bones sticking out of the skin) and was not too severe to surgically stabilize. He went through a successful major surgery. He’ll be on antibiotics to prevent infection and the next step is eating on his own. 

After about three weeks of healing, we will head back to Dr. Dirks for another x-ray to determine the amount of healing and whether or not we can remove the pin. If we can, he’ll have another three to four weeks of limited movement, but no flight attempts yet, since we need to make sure everything is solidly healed. After that, he’ll need physical therapy to get muscles into shape, and of course he’ll need to grow a tail back and we don’t know how long that will take. We will have to see how it goes/grows! 

What percentage of eagles make a full recovery and can be released back into the wild after an injury like this?
We don’t have an answer for that off the top of our heads.  We’ll have a better prognosis at the three week check up.

What is the gender of this eagle?
Judging by size, Dr. Dirks and I both think it is a male. 

Will P's recognize it and care for it or will it just be another eagle to them now?
He is in for a quite long recovery period. He will be with us too long for the parents to be in the mode of caregiving and he will be too old to need them. I don’t know if they will be able to recognize him or not.

How much of the hunting skills are learned vs instinct?
Instinct gets them started hunting and experience hones skill, since there are rewards for doing certain things and disappointment for doing others. 

Do you feel that the break in his/her humerus was due to the owl attack? 
This break is way up in the shoulder area – there is a lot of muscle around the bones there. Owls look big – but they are big puff balls – mostly fluffy feathers. These eaglets out-weigh owls by a lot.  There were no puncture wounds near the break area. I don’t think owls could have done this. Dr. Dirks and I discussed this a bit. This break would take quite a bit of trauma – like being hit by a car. But we just have no way to know for sure what happened. His feathers were grown in well enough to glide/fly from the nest, so it is doubtful leaving the nest would have resulted in this type of break either. [Amy's note: Bob made a similar observation after handling "Four", the fledgling formerly known as EWT. He also confirmed that the eaglets were developed enough to fly].


Wednesday, June 25, 2014

3rd Decorah Eaglet Found?

We've confirmed a fledgling eagle without a transmitter a little over one mile from the nest. While we can't know for sure, we are quite hopeful that this is our missing eaglet, especially when we compare the data with D14, who was tracked in almost the same location on 6/27/12. We'll be watching to see if the eaglet comes back to N2, appears in N1, or is seen over at the fish hatchery. In the meantime, please stay back and give the eaglet plenty of room if you see it on the ground. Bob reported that the eagle was flying very proficiently this morning.

The NWZ just got a little larger! Thanks to Frank Ermel for the tip and photo. We aren't trying to ID this eaglet at all right now - we've got our hands full just keeping track of everything that's going on. We hope to have an ID post for everyone later today or sometime tomorrow.

A link to D14's late June/early July map for comparison: http://www.raptorresource.org/maps/pdf_maps/761-Map-07-05-12.pdf


Friday, May 16, 2014

Eagle Valley: How did the owl get by Mom and Dad?

We're getting a lot of questions about how the owl could have gotten past Mom and Dad in Eagle Valley. Are Mom and Dad bad parents? Unobservant? Poor protectors? No. However, they are primarily diurnal birds. Although we've seen bald eagles awake and active after dark, they tend to sleep at night: http://www.ustream.tv/recorded/47617300. In contrast, owls are outstanding nocturnal hunters. They fly silently, have very large, tubular eyes with an abundance of light gathering rods, and possess exceptional hearing thanks in part to their facial disks and in part to ear hole placement. The owl could have landed on the nest before either parent was aware of it. When Mom reacted, she may have uncovered her young and unintentionally made them available to the hunting owl.

On February 25, an owl jumped on Mom in Decorah. While she wasn't injured and there were no young in the nest, the video below provides an example of just how silent they can be in flight. Thanks to David Lynch for finding it. If you'd like to read more about owls, click here: http://goo.gl/W0pL0K

We've also been asked why an owl would target an eagle's nest. Owls eat a wide variety of prey and the nest was a potential source of food, adult eagle or not. The eagle nest invaders we've seen include owls, raccoon, red-tailed hawks, squirrels, starlings, sparrows, and mice. Some of them were drawn by eggs and young birds, others wanted nestovers, and one hungry red-tailed hawk attempted to steal prey from Dad in 2011 (clearly visible at 2:15 in the video): http://youtu.be/VbrBUMS_ZPc. Many animals are willing to risk approaching the nest for a meal. Sometimes they are successful and sometimes, like the hawk at Duke Farms last year, they die in the attempt (warning: some readers may find this video disturbing): https://www.youtube.com/watch?v=QqooTTD8sn4

In short, the parents at Eagle Valley are not deficient or lax. I've watched the footage a number of times and I can't hear an owl coming (or see anything). The nest was targeted by a specialist nocturnal hunter who was able to get into the nest before either of the adult eagles were aware of it. We hope the remaining eaglet survives until fledge.

Tuesday, May 13, 2014

Birds in Flight, or Why Did Dad Fly That Way?


This video shows Dad bringing a freshly killed rabbit to the nest. After pausing in a tree, he circles over a field before landing in the nest with his catch. What is going on? Why did Dad pause in a tree, and why didn’t he fly directly to the nest after taking a break? I’m going to write a little bit about the basics of flight and why Dad might have flown the way he did.

There are four basic forces that govern flight: lift, thrust, weight, and drag.
  • Lift pushes birds upwards. Lift is produced primarily by wing curvature, which induces low air pressure on the top of the wing and high air pressure on the bottom. Primary and secondary feathers both help create lift. 
  • Thrust propels birds forward. When a bird flaps, its primary feathers twist at an angle relative to the rest of its wing and the bird’s line of flight. This twisting or spinning motion induces low pressure ahead of the bird’s wing and high pressure behind it, aiding forward motion. Depending on the strength of the flap, a bird’s entire outer wing might twist in response. 
  • Weight equals mass times the acceleration of gravity, so weight can be defined as the force of gravity on an object. Weight pulls birds down and puts an upper limit on flighted bird size.
  • Drag counteracts forward motion. Air passing over the bird’s wing produces friction and creates wingtip vortices that direct the air behind the wing downward, inducing downwash and causing drag. We think birds have a number of ways to counteract drag. Wing slots increase the span factor of bird wings and spread vortices horizontally and vertically, dissipating their kinetic energy and reducing their sucking power. As the bird’s wing is tilted upwards, its angle eventually becomes so steep that air cannot flow smoothly over the surface of the wing and lift decreases. The alula, a small projection on the front wing of birds, can be manipulated to create a temporary slot that allows birds to steeply angle their wings without stalling out. 
Catching prey in flight requires less force, since acceleration, lift, and thrust are already part of the equation. Unfortunately, Dad is on the ground. The rabbit could be adding two or more pounds of weight and has no aerodynamic qualities whatsoever. Dad needs powerful wing flaps and a lot of force to counteract gravity, gain lift, thrust forward, and hoist his rabbit into the air.

Dad takes a breather on a tree limb before bringing his prey to the nest. But if carrying prey is so hard, why doesn’t he fly directly to the nest? Although the angle makes it hard to tell, the tree limb is below the nest and the approach may not have been good. Dad puts gravity to work by dropping from the branch, gaining a little no-cost acceleration. He spreads his wings wide and pitches them slightly back as he launches, catching the air for a little free lift. This reduces the amount of work required to lift and carry prey, since force = mass x acceleration and Dad is using gravity to assist lift - something he can't do from the ground. His spread alula can be seen at 1:11, allowing Dad to steeply angle his wings for a bigger downstroke without loosing his hard earned lift. Note that we don't see the alula in regular flight later in the video.

In short, it’s a lot easier to drop off a high place than fly up from the ground, especially when prey is involved. With a little assist from the tree branch, Dad was able to spiral around at the far end of the field and gain enough lift to drop easily into the nest. Eagles fly so wonderfully that it’s easy to forget how much work and experience goes into it.

Thanks to Rick Black for the video! Check out the Canadian Museum of Nature to see a brief animation of birds in take off, flapping, and gliding flight: http://nature.ca/discover/exb/hwdbrdsfly/index_e.cfm



Sources


Wednesday, April 30, 2014

Decorah: Why is Mom Being So Mean to Dad?

We’ve had several questions and comments about Mom’s behavior lately. Why is Mom mad at Dad? Why is Mom so demanding? Why is Mom so mean? While I can find snippets of behavior that would seem loving to human observers – shared incubation duty, mutual nest control, and Dad feeding Mom, to name a few – both adults are going through hormonal changes and their behavior reflects that.

Daylight length, or photoperiod, strongly influences hormone production in birds. In the northern hemisphere, our story begins shortly after the winter solstice in December. As daylight length increases, a cascade of hormones causes birds’ gonads to swell, increasing the production of testosterone in males and progesterone (plus a small amount of testosterone) in females. Testosterone is associated with aggression, territoriality, courtship, nest-building and, in males, testicular development and spermatogenesis, while progesterone, the “pregnancy hormone”, induces egg production in females.

Mom and Dad share incubation duties, so both of them experience another hormonal change once incubation begins. Production of prolactin, a hormone that induces incubation and stimulates brood patch development, rises sharply, while testosterone and progesterone production rapidly decrease. Opioid peptides help stimulate prolactin production, which may be another reason that normally active birds suddenly want to spend the entire day sitting on eggs.

So in the first part of their reproductive cycle, Mom and Dad’s interactions with one another and their young are mediated by hormones that stimulate courtship, mating, territoriality, egg-laying, and lethargy. We humans are moved by their relationship with one another and their tender devotion to their offspring. It’s hard not to see hearts everywhere – I know I did! – as Mom pursues Dad around the nest, Dad brings food gifts to Mom, and both eagles work together to keep their eggs safe from all the extremes Iowa’s winter and early spring can bring.

And then they start shaking the prolactin off.

If the eagles’ earlier behavior added up to love, it’s hard not to see this as its opposite. Mom suddenly seems mean, snappy, or demanding to some watchers. Dad still loves his offspring but seems more distant. In this narrative, our eagle couple is drifting apart – or maybe Mom’s behavior will cause Dad to reject her for a less snappy, more appreciative mate. While compelling to human watchers, this scenario isn’t true.

So what is happening to our eagles? It isn't eagle divorce, but it isn't entirely our imagination, either. As their gonads begin shrinking, they decrease courtship and pair bonding behaviors. As prolactin ebbs, their metabolisms speed up, they become more physically active, their body fat drops slightly, and they probably become hungrier. Mom’s whistling ‘tea-kettle’ makes its first appearance as vocalizations change, although it still stimulates food delivery and/or an appearance by Dad. What we interpret as a falling out is simply a pair of mature, active bald eagles beginning to resume the non-reproductive phase of their lives. To paraphrase Scott Weidensaul, sex hormones pull many strings in a bird’s body. We are seeing that in Decorah right now.



Things that helped me write this post:



Did you know? 

In humans, females are xx (homogametic) and males are xy (heterogametic). But in birds, females are zw (heterogametic) and males are zz (homogametic). Unlike humans, female birds determine the gender of their offspring. http://en.wikipedia.org/wiki/ZW_sex-determination_system