Why did Mom and Dad lay eggs later this year?

We've been getting questions about egg timing. Why did Mom and Dad lay eggs later this year? Overall, avian egg-timing in the temperate zone is heavily regulated by the light cycle. As the days begin to lengthen, birds' gonads swell and produce sex hormones. Around the end of January, our bald eagle pairs switch from infrequent copulation to frequent, highly enthusiastic copulation, putting us on notice for egg watch! Females chase males, males entice females, copulation takes place on a regular basis, and our eagles start laying eggs in mid-February. We have a general egg outline, but what factors correlate to the onset of egg-laying in any given year?

New mates can equal later eggs
While it doesn't always happen, a new mate (male or female) often pushes egg-laying a little later in the eagles and falcons we watch. Sometimes it happens for very obvious reasons, like mid-season mate replacement. Let's say that female falcon A and male falcon B are nesting together on a cliff in mid-March. Falcon A has begun the process of egg production: her egg follicles are swelling, she's gaining weight, and she's copulating like crazy! Unfortunately, she's killed or displaced by female falcon C, who is producing plenty of sex hormones, but no eggs. B doesn't waste any time courting C. His bowing, gifts of food, and copulation will trigger her to begin egg production, but their egg-laying schedule will be pushed back by as much as or more than ten days. Absent other factors, it should float earlier in the years to come.

Later egg-laying can also happen in new couples that don't experience mid-season mate replacement. Both Mom Decorah and Ma FSV laid the first eggs of their lives in early March (March 2, 2009 for Mom Decorah and March 3, 2007 for Ma FSV) but moved earlier as the years progressed. Mom had just achieved sexual maturity when she bonded with Dad, but we don't know if the same is true of Ma FSV. Is initial egg production - an eagle's first egg - a factor in egg timing? How about receptivity in a new pair versus an already bonded pair? We don't know, but it's something we'll be looking at.

Cold dry weather? Predict eggs on the later side!
Having said that, we didn't have a new eagle in Decorah or at Fort St. Vrain this year. So what happened? We decided to look at weather. Using the nearest weather stations we could find to each nest (especially important in Colorado with its altitude-based weather patterns), we obtained historical figures for temperature and dewpoint from January 30 to February 10. There isn't a long time period between the onset of egg-laying and egg-laying itself, so we started around the time that both sets of eagles usually ramp up copulation and ranked our results from latest to earliest laying date.

FSV: January 30 to February 10

1st Egg Date	High Temp	Mean Temp	Low Temp	Dewpoint
2/21/14	31 F	19 F	6 F	12 F
2/17/13	48 F	32 F	17 F	15 F
2/16/16	46 F	31 F	17 F	17 F
2/14/15	60 F	44 F	28 F	21 F
2/14/17	56 F	45 F	33 F	21 F
2/12/18	51 F	37 F	22 F	22 F
Decorah Eagles:  January 30 to February 10
1st Egg Date	High Temp	Mean Temp	Low Temp	Dewpoint
2/23/14	12 F	4 F	-3 F	-3 F
2/21/18	37 F	20 F	8 F	4 F
2/20/17	30 F	21 F	12 F	15 F
2/18/16	29 F	22 F	16 F	19 F
2/18/15	24 F	16 F	9 F	12 F
2/17/12	34 F	28 F	22 F	23 F

In general, both sets of eagles laid eggs slightly earlier during periods of unusual warmth and slightly later during periods of unusual cold. But much to my surprise, humidity (as measured by dewpoint) turned out to be a slightly better predictor of egg-timing than temperature! What was going on with that - and with the one interesting exception in Decorah in 2015? Time to do a little reading!

It is widely believed that breeding female raptors gain weight by building fat and storing minerals to provide the energy reserves needed for egg-laying and incubation. But a study of female barn owls found that almost all of their pre-laying weight gain was due to water accumulation! From the study's discussion: "To conclude, the gain in body mass observed in breeding barn owls is not due to an accumulation of energy reserves but of an accumulation of water." Incubating female barn owls undergo a more complete molt than incubating bald eagles, but egg production mechanisms are very similar and it seems reasonable to believe that water retention would be similar in both species. The nutrients required for egg formation can be obtained by routine food intake during egg formation, but if the weather is extremely dry, it might take longer for female bald eagles to accumulate the water reserves they need for egg production, especially give that drier weather results in higher levels of evaporative and cutaneous water loss. It wouldn't make a few weeks difference in any given year, but it might make a few days!

I couldn't find an explanation for the anomaly in Decorah in 2015, but this is a relatively small dataset. As we keep records longer, we may learn more about trends in egg-laying. It also might be worth getting weather stations down below our nests to collect local data about temperature, humidity, and wind at each nest. We still have a lot to learn about the ways in which weather and climate affect the birds we watch.

Did you know?
The barn owl study also had some interesting information about fat/lipid dispersal in a breeding female barn owl's body. Although breeding females had fewer body lipids than non-breeding females, they had more subcutaneous fat in the area of their brood patch. The accumulated fat caused their brood patches to increase in size! So Mom's more visible brood patch and slightly larger appearance aren't just our imaginations. She has gained water weight and shifted fat to her brood patch in preparation for egg-laying and incubation. I'm sure that more than a few of us can relate to that!

While we aren't sure why Midwest peregrine falcons are laying eggs earlier, they are laying significantly earlier than they did at the beginning of falcon recovery in our area. Interested in the topic? Check out Average Nesting Trends!

Why didn't you use data from the North pair?
This was a tough one to leave out, especially given that many watchers think Mr. North was a new mate in 2016 - a year of later egg production. However, we only have three years of production here, the eagles have not established a regular laying pattern (2018 was also late), and we have no weather history anywhere near the nest, so I'm not comfortable including their data. We'll see what happens in the years to come.

Things that helped me learn about this topic

• Paper: Body reserves and nutritional needs during laying preparation in barn owls
• Paper: Cutaneous water loss in small birds. I need to do a lot more reading about this, since bald eagles have more inside to outside than the birds in this study, and would presumably experience lower cutaneous water loss. 
• Weather history in Decorah (choose 'custom' to see averages for selected time periods): https://www.wunderground.com/history/airport/KDEH/2018/03/20/DailyHistory.html
• Nest records for Decorah: https://www.raptorresource.org/birdcams/decorah-eagles/. Click the 'Nest Record' tab and click 'Detailed Information' for annual records. 
• Nest records for FSV: https://www.raptorresource.org/birdcams/xcel-energy-cams/. Click  'Detailed Information' below the two eagle feeds for annual records.

How long does it take Mom to lay an egg?

We've talked about how long it takes bald eagle eggs to hatch after they are laid (an average of 38 days from first egg to first hatch in Decorah), how long hatch takes once pip starts (it can take upwards of 24 hours), and how long it takes Mom to lay each egg (she usually lays the second egg about two to three days after the first, and the third egg roughly four days after the second egg). But how long does it take Mom to make and lay an egg?

We'll start with copulation. It is believed that female bald eagles begin laying eggs five to ten days after productive mating begins. Mom laid her first egg at 7:28PM CT on February 21st, or about eleven days after copulation went from casual to frequent...and very determined on Mom's part.  Between February 10th and February 18th, Mom and Dad copulated nine times that we saw and had an additional 2 failed attempts. Mom took the lead five times - beak biting Dad, footing him, loudly vocalizing her intentions, and mounting him while wagging her tail (https://youtu.be/I4xlu9IEItY). You didn't need to be a male bald eagle to know that Mom meant business!

So we know that bald eagles ensure fertile eggs by copulating regularly, storing sperm in storage tubules, and concentrating sperm at the infundibulum, or site of fertility. But how long does it take Mom to lay an egg once her first yolk has been fertilized? The short answer: approximately two days (48-50 hours). It goes through a lot of changes along the way! Note that our oviduct times were derived using the ratio between bald eagles (~48 hours) and domestic chickens (~25 hours). The actual times could be slightly different.

Step one: I'm ready!

Diagram of the egg-laying process

According to Tim Birkhead, there are no known cases of copulation-induced ovulation in birds. As we've seen in Decorah, female birds signal their fertile status by their interest in (or their insistence on) copulation. In response to an internal clock and the presence of a male - say, Dad - one of Mom's yolks swells until it ruptures the follicle that produced it, releasing a ripe yolk into her oviduct.

How long does it take for her yolk to swell? Our observations suggest about eight to ten days. For comparison, it takes four to five days in small birds like great tits and white-crowned sparrows, six to eight days in larger birds like ducks and pigeons, 10-13 days for large gulls, and up to 16 days in some penguins.

How many follicles are swelling inside Mom each season? In domestic hens, each follicular cohort (follicles that will become eggs) numbers six to twelve follicles, and follicles are selected roughly every 24 hours. We know that Mom's annual cohort measures at least three. Since it takes roughly 48 hours for her to lay an egg, follicle number two must rupture about the time egg number one is laid. Follicle number three experiences a delay of about 48 hours, giving Mom's 'egg-machine' a chance to rest and resupply!

Step two: The infundibulum! Length of stay: ~15 minutes (T - 47+ hours)
While the name infundibulum (funnel) suggests a passive process, the microscopic yolk stays in one place while the infundibulum flows around it. Since Mom and Dad have been copulating regularly and Mom has been storing sperm, hundreds or thousands of Dad's sperm are waiting inside to fertilize it! Fertilized or not, the infundibulum seals the yolk after 15 minutes, and it proceeds on its journey down her oviduct.

How does the yolk stay in the center of the egg? The infundibulum's seal, or chalaza layer, forms the egg's first layer of albumen, aka egg white. The ends of this dense chalaziferous zone twist with other proteins to create two filaments as the egg spirals through the magnum. These filaments will eventually anchor the yolk to the egg's hard calcareous shell, keeping it in place. 

Step three: The magnum! Length of stay: ~5 hours (T - 42.5 hours)
Her yolk makes its next stop in the magnum, where it receives another coating of albumen. The albumen is secreted by special cells in the magnum wall that absorb water and proteins from Mom's bloodstream. The albumen will cushion the developing embryo and provide much of the protein needed for its development. Remember Dad's food gifts? Mom needs all the protein and calcium she can get to produce viable eggs!

Step four:  The isthmus! Length of stay: ~3 hours (T - 39.5 hours)
The yolk moves into the isthmus next. It receives a little more albumen and its inner and outer soft shell membranes, which (like Mom's feathers, beak, and talons) are made of keratin - another protein! The inner shell membrane provides a point of contact for the chorioallantoic membrane that develops in the first three to four days of an embryonic eagle's life. Both membranes help protect the porous egg from bacterial contamination and keep water from escaping too quickly. The membranes sit closely together during the egg's trip through the oviduct, but separate after the egg has been laid.

An egg in cross section, modified from Romanoff and Romanoff, 1949

Step five: The shell gland! Length of stay: ~39 hours (T - 15 minutes)
Mom's yolk, wrapped snugly in its jacket of albumen and shell membranes, moves into her shell gland or uterus. Water and minerals are pumped into the developing egg and a hard calcareous shell is formed around it. 

Mom is removing a lot of calcium from her body to produce the egg shell. While I couldn't find figures for bald eagles, hen chickens remove about 25 mg of calcium from their blood every 12 minutes during active egg shell formation. Since bald eagle eggs are significantly larger than chicken eggs, it seems very likely that she is removing more calcium than that. Anything that can't be derived from dietary sources will be obtained from her skeleton - another reason that food is extremely important right now! 

Step six: The vagina and egg labor! Length of stay: roughly 15 minutes!
We finally have an egg! Mom's initially microscopic yolk has been wrapped in membranes, plumped up, and surrounded by a hard shell. While we don't know whether Mom was aware of the egg before, she is certainly aware of it now! Contraction of a powerful sphincter muscle causes the egg to rotate in her muscular vagina and enter her cloaca pointed-end first. Mom's powerful vaginal muscles and full-body contractions eject the egg through her cloaca and into the waiting egg cup. Two days after Mom's first egg was started, it emerges after her brief egg labor and she lays down for a well-deserved rest! Her second egg is just beginning its journey!

Does Mom feel pain during egg labor? 
We often get asked whether Mom experiences pain or discomfort, especially in the final phase of laying. Whether or not she knows her follicle burst, egg laying is an energetically expensive process and her behavior changed substantially since she started chasing Dad around the nest! Two or three days before she laid egg number one, we started seeing her on and around the nest more. Dad brought several meals to her, and she spent a long period of time in the nest the morning before the egg was laid. While her soft chirps were lovely to hear, she was obviously experiencing some discomfort. It was a relief to all of us when she finally laid the egg!

Mom will incubate her first egg between 35 to 37 days before it hatches. While Dad does his share of incubation, incubation gives Mom the time she needs to rest and build up her reserves. Sweet eagle dreams, Mom - you've earned them!


What happens when a bird loses its nest and mate with an egg in the pipeline? 
We also get asked what happens when a bird's season is interrupted. We haven't seen it at any of our bald eagle nests, but we have seen it in several peregrine falcons. Last year, an interloper laid an egg in the nest box at Dairyland Alma before the returning female ousted her, and Newman spent a lot of time courting and copulating with St. Louis Girl before Michelle showed up and kicked her out. While there isn't much information about it, I would guess that any eggs in the pipeline get laid somewhere. But if follicle stimulation is about more than just lengthening daylight hours - which it appears to be, at least in wild birds, which don't tend to lay eggs absent a male, copulation, and a nest - losing a mate and territory may shut follicle stimulation and yolk production down. This would prevent additional eggs from forming: a wise strategy given how energy intensive egg production is! 

Does it feel like the parts of a female bird's reproductive system were named by committee? Technical language is daunting enough when it fits together nicely! But people have studied birds, especially domestic chickens, for a long time. Not everything we are describing now was named at the same time by the same people, which can lead to an odd combination of words. 

• Infundibulum is derived from a16th century Latin word for "pour in" (or funnel): infundere.
• Chalaza is derived from a Greek word that means "small knot": Khalaza 
• Magnus is a Latin word that means "great". The magnus is the largest part of the oviduct. 
• Isthmus is derived from a Greek word that means narrow neck of land: isthmos.

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Things that helped me learn and write about this topic!

• The 'Guide to Bald Eagles' produced by our mod team
• Avian reproductive system, female: http://articles.extension.org/pages/65372/avian-reproductive-systemfemale
• The avian egg: http://www.poultryhub.org/physiology/the-avian-egg/
• The avian egg: http://people.eku.edu/ritchisong/avianreproduction.html
• Formation of the egg: http://www.thepoultrysite.com/publications/1/egg-quality-handbook/2/formation-of-the-egg/
• The avian ovary and follicle development: some comparative and practical insights: http://dergipark.gov.tr/download/article-file/134144
• Sperm-Egg Interaction during Fertilization in Birds:
  https://www.jstage.jst.go.jp/article/jpsa/53/3/53_0150183/_pdf
• Book: The Most Perfect Thing: Inside (and Outside) a Bird’s Egg (Tim Birkhead)
• Book: The Hen's Egg and its Formation in Atlas of Chick Development (Ruth Bellairs, Mark Osmond)
• Book: Ornithology (Frank B. Gill)

Image Credits

• Diagram from the paper Sperm storage in the female reproductive tract in birds, Sasanami T, Matsuzaki M, Mizushima S, Hiyama G - J. Reprod. Dev. (2013). Taken from Open i, US Department of Health and Human Services, https://openi.nlm.nih.gov/detailedresult.php?img=PMC3944358_jrd-59-334-g001&req=4. 
• Egg cross section derived from The Avian Egg: Alexis L. Romanoff, A.J. Romanoff, 1949. Image credit poultryhub, although it appears in other places as well: http://www.poultryhub.org/physiology/the-avian-egg/. If you own this image and do not want it posted or need the credits changed, please contact me: ries93@gmail.com.

2017 by the Numbers! #GivingTuesday #Budget

To help kick-off Giving Tuesday on Tuesday, November 28, we wanted to talk about what got done this year. Here are the things your donations helped us get done! Please donate to the Raptor Resource Project to help us continue our work in 2017 and beyond!

New Projects
In 2017, we expanded our educational partnerships with Luther College and the Fish and Wildlife Service, kicked off the Robert Anderson Memorial Scholarship Fund, and began working on short  videos to expand our online educational program. We:

• Began a banding station in collaboration with Luther College. We were awarded a grant by the Iowa Department of Natural Resources’ Conservation Education Program to develop a collaborative educational partnership with the Luther College Center for Sustainable Communities and Environmental Studies. The proposal included the construction of a raptor banding station at Hawk Hill on the NW corner of the Luther campus. The station was masterminded by Dave Noble, who built it with the help of Dave Kester, John Howe, and amy Ries. It is managed by RRP’s board member and master bander permit holder Dave Kester, who is working closely with Emily Neal of the Luther College Center for Sustainable Communities and Environmental Studies.  The partnership strengthens the connection between academia and non-profit conservation to provide students with unprecedented direct access to conservation research.  Our first year is almost done and we are excited to continue this valuable program in 2018 and beyond! You can read more about it here! http://www.kwwl.com/story/36319000/2017/09/Friday/new-partnership-allows-luther-students-to-get-out-of-the-classroom-into-the-field
• Kicked off an educational endowment in Bob Anderson's name.  The Robert Anderson Memorial Scholarship Fund is managed through the NE Iowa Community Foundation and we have a running start at funding it to the goal of reaching a sustaining level of $25K.  When we reach that goal, we will offer our first scholarship at Luther College in his honor.  We have witnessed the type of students we envisioned during the first year of our raptor banding station at Hawk Hill.  With good momentum and visibility of the fund, we may reach that goal by the end of 2018! If you are interested in donating to the endowment, please visit https://cfneia.org/giving/contribute/712-as. 
• Filmed with Sustainable Driftless Inc and Untamed Science to collect footage of falcon banding and create some educational short videos, including a video about Bob's falcon recovery. We also collected data about how peregrine falcons react to the presence of drones, which was shared with other banders and members of the North American Flyway Council. you can read our report and observations here:
  https://www.raptorresource.org/pdf/falconsanddrones2017.pdf
• Embarked on a collaborative project to create a live cam with the US Fish & Wildlife Service that will help educate people about the importance of the Mississippi River Flyway to raptors and other birds.  Imagine a live display where field trip classrooms and home viewers can observe bald eagles, pelicans, tundra swans, passerines, and countless varieties of ducks and waterfowl!  

Online Interaction and Education
We also kept busy with our online interaction and education program! Since January 1, 2017, we have:

• Provided 1,785 hours of chat on the Decorah eagles channel, including 449 hours of dedicated educational chat. Our Decorah North group provided 576 hours of moderated chat. 
• Posted 368 times on Facebook. Topics and photos included the Decorah Eagles, the Decorah North Eagles, the GSB Peregrine falcons, the Fort St. Vrain eagles, tracking D27, Robin Brumm's trips to Decorah, peregrine falcon banding, nest box work, and many other topics related to our nests and birds. Posts were shared from Neil Rettig Productions, SOAR, the Cornell Laboratory of Ornithology, and Jim Brandenberg's 365 Nature project. 
• Wrote 31 blogs. We addressed questions about the eagles, the nests, nest intruders, eaglet growth and development, eagle vision, eagle dreams, hunting and fishing lead free, prey remains in the nest and much more!
• Started an ad-free stream in partnership with Explore.org. We now offer ad-free streams of the Decorah Eagles, the Decorah North Eagles, and the Great Spirit Bluff falcons! Those can be watched at Explore or on our website at www.raptorresource.org.

I need to give a shoutout to our amazing volunteer moderators. I have said it before and I will say it again - our volunteers make our pages the best on the web and we could not provide our online educational program without their help!

Monitoring, Banding, and Recovery
Our peregrine falcon program is key part of who we are and what we do! In 2017, we:

• Monitored over 50 peregrine falcon and bald eagle nest sites and potential territories in Minnesota, Wisconsin, Iowa, Illinois, and Colorado.
• Banded 58 falcons at 22 sites in Minnesota, Wisconsin, Iowa, and Illinois between May 25 and July 5th! Our northernmost territory was in Cohasset, Minnesota and our southernmost territory was in Peoria, Illinois. As always, we reported all banding and follow up data to the Bird Banding Lab and the Midwest Peregrine Society.
• Installed a tracking platform on D27, who is still going strong near Strawberry Point in Iowa! 
• Retrieved the bodies of two falcons from the Great Spirit Bluff nest for autopsy. The Raptor Center concluded that they died from black fly bites. 

Thanks to our utility, industrial, and landowner partners for all of their help and support! A huge thanks to Brett Mandernack for including 'our' eagles in his studies and for sharing all of the data about their whereabouts and fates. Thanks also to David and Ann Lynch and Brian Malaise for their help with the transmitter project. We couldn't do it without all of you!

Camera Research and Installation
John Howe, Kike Arnal, David Kester, Amy Ries, Richard Meredith, Bill Heston, Tina Lopez, John Kaczmarek, and Liam Grainger installed a total of fifteen new cameras and  microphones at N1, N2B, Decorah North, Fort St. Vrain, GSB, and Xcel Energy's Sherco and Allen S. King plants this year. We did our three eagle cam sites between August 22 and September 29th, when the eagles are at their loosest point of attachment to their nests! It was a busy season but the upgrades in video and sound were well worth it! The installations took roughly 950 hours total.

We also replaced the Great Spirit Bluff nestbox! Our caring, dedicated livecam viewers helped greatly by raising funds to replace the original box installed by Bob Anderson and Dave Kester in 2003. It served fourteen productive years and produced 41 falcons, making it one of our most productive cliff sites. Rather than completely re-designing the box, we transitioned to a design built by John Howe that resembles a cliff eyrie. The lack of a back exposes the falcons to the bare rock of the cliff, and the added insulation allows it to better retain the temperatures of the massive rock face.

John Howe put in hundreds of hours researching, ordering, and testing cameras this year. While the majority of our installs are done in September and October, camera and streaming research take place year-round.

Other Stuff

• We threw our annual After The Fledge party between July 13th and July 16th. Almost 100 eagle fans and volunteers had a blast celebrating the Decorah eagles and Decorah itself! Pagent Decorah added a very cool boat ride on Sunday this year, and we're looking forward to doing it again next year!
• We upgraded our website and our live streams to give users a safer, easier, and faster way to watch our eagles and falcons on a variety of platforms, including mobile devices and tablets!
• We added new remote volunteer camera operators to increase our coverage. This has given us new insights into the lives and habitat of the birds we watch!  

Our Budget
In 2017, our annual expenses are hovering around $254,000 per year. They break down like this:

• Staff and contractor compensation will cost an estimated $142,000 this year. We hired John on January 1st of 2017, paid two busy contractors (Amy and Dave), and incurred additional expenses hiring climbers and helpers for four camera projects and the new nest box installation at Great Spirit Bluff. These were extensive projects, with roughly 500 hours spent on the Decorah and Decorah North installs in September alone. Although Iowa’s Conservation Education Program helped pay for our banding station with Luther College, we still need to compensate master banders and our master builder! We are committed to paying a fair wage for work, which means that everyone we contract with is compensated at a living wage or better. 
• Camera equipment and IT expenses – cameras, microphones, cables, encoders, software, licensing fees, website costs, and so on – will come in at around $42,000. HD and 4K cameras are amazing, brilliant, and breathtaking…but they don’t come cheap.
• Office and field supplies – paper, printer expenses, new ropes, slings, rappelling tools, hardware, zip ties, screws, silicon gel, rope bags, harnesses, lumber, paint, tape, bands, banding equipment, and trapping equipment – will cost about $7,500. Given all the trips we made to the hardware store this year, I think it’s a pretty good deal! Several of us also pay for our own climbing equipment instead of having RRP do it, which helps keep expenses lower and gives Amy a great excuse to go shopping! 
• Office and land rental fees cost $7,500.
• We can’t work or drive the company vehicle without insurance! Although it isn’t nearly as exciting a topic as eagles or falcons, John did an excellent job negotiating insurance, which will cost us $1,300 this year. This was a decrease from last year, and we have better coverage, too! Other things I would put in the necessary-but-ho-hum category include vehicle expenses ($4,500), fundraising fees and gifts ($6,000), accounting ($4,000), postage and delivery ($5000 – and that’s with the non-profit rate!), and our endowment funding ($2,000 and please consider donating to the Bob Anderson Memorial Scholarship fund). 
• Travel and meetings cost us $8,000. While this might sound expensive, Amy alone put over 30,000 RRP-related miles on last year. This number would be much higher if Amy and John didn’t donate a significant amount of their travel. Although we don’t usually go too far from home, we put a lot of miles on during banding and camera season! Despite our mileage donations, I suspect that this number will be a little higher than projected.
• Printing and copying isn’t cheap! We’re projecting a total of $12,000 for this year. That includes two large newsletter printings, all of our thank you letters and envelopes, and any printing related to talks, events, and presentations.
• Speaking of events, After the Fledge will cost about $1,500 this year. You should come next year – it is a great celebration of our eagles!
• And finally, grants to partner organizations will total $10,000.

Our income is generated by a combination of donations from viewers, grants from corporate partners, and (new this year!) a grant from the Iowa DNR’s Conservation Education program. But donations from viewers like you remain our biggest single source of income. We sincerely appreciate your generosity and support of the Raptor Resource Project mission. Would you please help us make a difference with your donation? Thank you so much for your support and we hope you enjoy watching in 2018!

A Reflection and a Thanksgiving

November 23rd would have been Bob Anderson's birthday. I assume that our friend and founder would finally have achieved his dream of retirement - or at least semi-retirement - and be busy with his book by now. Given the thankful nature of the season, it seems like a good time to take stock of where the Raptor Resource Project has been, where it plans on going, and what I have to be thankful for.

For those of you who don't know, Bob founded the Raptor Resource Project to propagate and release peregrine falcons. He was the first person to successfully breed peregrine falcons in Minnesota. MF-1, one of the first falcons he produced and released, became the first returned falcon to breed in the mid-continent following the species' extirpation in the mid-1960's. It took an incredible amount of work to keep the peregrine falcon from joining the long list of species that will be mourned on the remembrance day for lost species. I am thankful that the peregrine falcon is still with us. Where we have a will, we have a way.

Falcon MF-1. Produced by Bob, she was the first falcon to return and breed in the wild mid-continent. 

I am thankful to have met Bob. He responded to an ad my little writing business was running back in 1994. I began by writing grants, but very quickly moved into field work. Did I want to attend a banding and take pictures? Yes! Did I want to hold falcons? Yes! Did I want to rappel? Yes yes yes! The writer William Least Heat Moon said in the Wonsevu chapter of the book PrairyErth that "I'm not sure what to make of it, but I think a dream can set you on another path." Bob's dream of restoring the peregrine falcon set many people's lives on another path.

Most of the power plant people originally involved in our utility-peregrine program have retired, but a new generation of men and women have replaced them in this unique marriage of industry and conservation. The peregrine would not be where it is today without their help and whole-hearted involvement in the program. Together we've put up nest boxes and internet cameras, cared for falcons, eagles, and kestrels, and looked at ways to make generation and distribution safer for our birds. I am thankful to have worked with the fine men and women employed at America's power plants. The utility-peregrine program is an example of the ways in which humans can support wildlife even in the unlikeliest of areas. You guys are awesome...and great fun, too!

Banding at Xcel's Allen S. King plant in 2010

Bob was also working on his cliff release project. Back in 1994, he began to believe that nest-site imprinting was preventing the crossover of peregrines from power plants to cliffs. The Iowa DNR was very interested in working with Bob, so he picked up lock, stock, and barrel to move down to Bluffton, Iowa in 1996. He did a successful pilot release on the Upper Iowa river in 1997 and released a total of 19 falcons from Hanging Rock at Effigy Mounds National Monument in 1998 and 1999. The Upper Iowa hackbox can still be seen from the river, although the Effigy Mounds hackboxes are long gone. In 2000, our cliff-released falcons became the first falcons to return to the cliffs of the Mississippi. I remember going to see them quite well, since I was very pregnant with my last son. I did a lot of crazy things for and with Bob, but the only time I remember him being really worried about me was just after I huffed and puffed my way up the back of Queen's Bluff. Pat Schlarbaum's story about peregrine recovery includes information about our cliff releases. It can be read here: http://www.gladysblackeagle.org/project-ideas/longwings-return. I am thankful to have played a small piece in this story, and very grateful to the men and women of the Iowa DNR who supported Bob's work.

Falcons raised for cliff release, 1997

In 2006 and 2007, Bob was working with Neil Rettig on the movie American Bald Eagle. After the two wrapped up, Bob said "Wouldn't it be fun to put this nest on the internet?" We made Bob's dream a reality in 2009, when the Decorah Eagle Cam uploaded an image to Xcel Energy's website every two minutes. In 2010, Luther College hosted a live feed. In 2011, we moved to Ustream and the Decorah eagles became a worldwide sensation. While we celebrated the eagles, Bob also mourned the loss of his dear friend and fellow falconer Rob MacIntyre, the 'mad scientist' who was featured so prominently in the movie RaptorForce. Rob did a lot of the work on our earlier cam systems, and his death was a real blow both personally and professionally. I am thankful to have known him and his wonderful wife Jan. They brightened every room they entered.

Rob and Bob

While Bob never lost his drive to recover birds of prey, he suddenly had a new focus. He was deeply engaged in using our bird cams to reach learners and provide a palliative window to the outside for ill, injured, and bedridden people. Online education became a major focus, but cameras still needed to be researched and purchased, and HD was increasingly looking like the next step. Enter John Howe! John began working with Bob to research cameras and camera technologies, including solar/wireless technologies (Rob installed our first solar/wireless system back in 2003) and HD. The longer Bob worked with John, the more he was impressed. Shortly before Bob's death, he let us all know that John was to follow him as Director of the Raptor Resource Project.

John and Bob

This brings us up to the present. In the two years since Bob's death, John has worked diligently to keep up with camera and streaming technology, deploy cameras, expand our online educational offerings, honor Bob's legacy, and secure funding (an organization doesn't run very long without money). He has more than proven himself as a director and a leader. I am thankful for John Howe and only wish that Bob was here to see the positive change that John has brought to the Raptor Resource Project.

So where do we go from here? We are sustained by our mission: to preserve and strengthen raptor populations, expand participation in raptor preservation, and help foster the next generation of preservationists. We follow our vision: to deepen the connection between people and the natural world, bringing benefits to both.

• Education: We served 1,270 educators through our educational video stream and chat in 2018. We also added a kestrel live stream in partnership with Neil Rettig Productions and Cornell University and completed the second fall of our research and educational banding station in partnership with Luther College. Teachers Deb Ripple and Lori Carnes have started to produce curriculum for our educational program and teachers are also sharing ideas on a platform started by Lori. 
• Preserving and Strengthening Raptor Populations: Despite the rain and lower hatching success this year, we banded 72 falcons in 2018. We will continue to monitor our nests, band falcons, consult on nestboxes and habitat for a variety of species, provide input on conservation issues, and work with federal and state wildlife agencies to benefit of birds of prey. We are also looking at ways to strengthen existing partnerships and build new ones. How can we connect our passionate followers with organizations looking for volunteers? How can we work closer with our utility and industry partners on providing or improving habitat for the many birds that nest on or use utility land and water in other ways? How can we advocate for birds of prey? We have done a lot, but we can do more. We stand on the shoulders of giants!
• Fostering the Next Generation of Preservationists: We've begun an educational endowment in Bob's honor. Please follow this link to learn more and to donate! We hope to fund our first students next fall.
• Connecting People with the Natural World: John upped the ante on our cameras! We are currently providing top-notch, HD, ads-free streams through Explore, and streams plus live chat at our website. John's current camera installations are also letting us take a look at life outside our nests - an important part of understanding and caring for the eagles and falcons we watch. A challenge for me: how do we develop quantifiable data from the thousands of hours of footage and anecdotes we've collected? Our knowledge has already changed since we first began watching the eagles (remember eagles are always monogamous?), but there is so much more to learn! 

So what else am I thankful for?

• I am thankful for our amazing volunteers. In addition to your incredible work, my life is better for having known you. I've said it before and I'll say it again...your work makes us the best site on the web!
• I am thankful for fans of the Decorah eagles and our other birds. Please, keep emailing and mailing your stories and art. You have deepened our lives an immeasurable amount.
• I am thankful to our Board for providing direction and guidance. 
• I am thankful for an unexpected and unlooked for gift: the honor to be part of the Raptor Resource Project's work. My 1994 self - I was 28 years old! - had no way of knowing what saying 'Yes' to Bob's first request would lead to. Bob, we will remember and celebrate you until we join you.

Thank you, everyone. I'm going to close with a link to a favorite blog I did on Bob back in 2012: Watching Bald Eagles. In re-reading it, I affirmed my own goal to help our eagles' futures stretch as long as their past. May Mom and Dad's progeny survive into a beautiful future, and may falcon MF-1 have thousands more descendants! Long may they all fly!

The Raptor Resource Project wishes you and yours a very Happy Thanksgiving!

When will our eagles lay eggs? Bald eagle breeding in Iowa and Florida

We're getting some questions about why the Decorah Eagles aren't laying eggs yet. Are they going to lay eggs? Will the nest be productive? The short answer is 'Yes' - the Decorah eagles historically lay eggs in February, while the Decorah North Eagles laid eggs in March in 2015, and in February in 2016. The longer answer is more complicated. If you don't want to read it, skip down to the bottom of the blog for breeding season information.

Bald eagle breeding season: not the same everywhere
We know that Bald Eagle breeding season varies by latitude. While breeding chronologies differ from nest to nest and state to state, in general:

• In the SE United States, bald eagles may begin laying eggs in November. 
• In the SW United States, bald eagles may begin laying eggs in December.
• In the northern United States, bald eagles may begin laying eggs in mid-January.
• In Alaska, bald eagles may begin laying eggs in late March or early April.

Bald eagles lay eggs earlier than many other diurnal raptors, or daytime birds of prey, and eagles in the southeastern US lay eggs earlier on average than their counterparts in other places. This is more unusual than it looks. Roughly speaking, a non-tropical bird's year can divided into two big parts: the photosensitive period and the photorefractory period. In the northern hemisphere, the photosensitive period starts when daylight length begins increasing after the winter solstice in late December. Birds' gonads swell and produce sex hormones, leading to productive mating and egg-laying. During the photo-refractory period, which starts after eggs are laid, birds' gonads shrink and mating becomes less frequent or stops altogether. Bald eagles in Florida are an interesting exception to this rule, since they begin laying eggs as early as November, when daylight length is still decreasing and their gonads should be (but obviously aren't) senescent. 

So why do Florida bald eagles lay eggs so early? One possibility: daylight length, especially in south Florida, is a poorer predictor of the season than it is in Decorah, Iowa. This might free the gonads of Florida eagles from the circannual light-based cycle of swelling and shrinking that regulates northern bird breeding. In Fort Myers and elsewhere in south Florida, the difference between the longest day and the shortest day is just 3 hours and 21 minutes, compared to 7 hours and 26 minutes in Decorah.

Birds that live in habitats where environmental cues such as photoperiod are poor predictors of seasons must rely on cues other than daylight length to regulate their circannual clocks. So if daylight length isn't especially important in SW Florida, what is? Check out the chart below.

Annual Averages, Fort Myers, FL

Daylight length isn't a great predictor of seasons in Fort Myers, but rain sure is! And what comes with rain? Clouds! The Max Planck Institute for Ornithology suggests that equatorial (and possibly near-equatorial) birds use daytime light intensity instead of length to regulate their internal clocks and breeding cycles. Under this scenario, the rapid increase in daylight intensity that begins in early September swells SW Florida eagle gonads and begins their annual breeding season. How tightly coupled is the increase in light intensity with the onset of the breeding season? Check out this cloud cover chart from Fort Myers...

Cloud Cover Chart, Fort Myers, FL

Two things. Firstly, the cloud cover chart for Fort Myers, Florida, somewhat resembles the daylight length chart for Decorah, Iowa. Like the daylight chart, it has a steep-sided trough that shows rapidly changing light availability, even though we are measuring intensity instead of length. Secondly, the breeding cycle of eagles in SW Florida appears to be tightly coupled with light intensity. Their overall cycle is quite similar to that of northern eagles, but the external cue that fires breeding behavior appears to begin in September or October instead late December. Of course, laying eggs in November and December also allows nesting eagles along the Gulf coast to avoid the hurricane/rainy season, which runs from June 1st through November 30th, and takes advantage of seasonally available flushes of food when eaglets are at their most vulnerable. Fledglings will have two to three months to gain their wings and hone their hunting skills before light intensity drops and the rainy/hurricane season starts up again.

This results in a chicken/egg quandary for me. Gulf coast eagles appear to be responding to a change in light intensity instead of length. Given the timing of the hurricane/rainy season, it also seems very likely that laying eggs in November and December results in higher offspring survival rates among eagles along the Gulf coast. Is the difference in southwest Florida/Gulf coast breeding cycles the result of an evolutionary process over generations, or does the ability to change breeding cycles and circannular clocks quickly lie dormant in bald eagles and other organisms? This might be important to know given the weather and climate changes facing us today. We wish the best of luck to the southwest Florida eagles this year!

Important events in Decorah, Decorah North, and Fort St. Vrain
Interested in key events at the Decorah, Decorah North, and Fort St. Vrain nests? Mark your calendars as follows!

• In the nests we watch in Iowa and Colorado, bonding and copulating behaviors become more pronounced and frequent after the winter solstice. Female eagles begin laying eggs 5-10 days after productive copulation begins. This usually happens in mid-February at all of our nests, but can change if an eagle takes a new mate. New mates often seem to push nesting chronology a little later, especially in the first year. 
• Each egg is laid about 3-5 days apart, and incubation starts with the laying of the first egg. However, eagles may spend more time off their eggs in warmer weather. 
• Eagle eggs begin hatching roughly 35 to 39 days after they are laid. This usually begins in late March at all of our nests. Hatch can take more than 24 hours for any given egg.
• Eaglets spend 75-80 days in the nest before fledging. This usually happens in mid to late June at all of our nests.

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Did you know?
Fledglings appear to leave the SW Florida nest in May, just as cloud cover begins increasing and light density drops. Fledglings in Decorah leave the nest area between August and mid-October, just as daylight length goes into a steep decrease. It is interesting to speculate that these behaviors are driven by the same circannual clock that drives eagle breeding biology.

Circannual clocks drive circannual rhythms, or biological rhythms that occur on an annual basis - in northern birds, think nesting and migration. But we are also driven by circadian clocks, which keep us in sync with Earth's day/night cycle. Clock genes are extremely influential, affecting the activity of most other genes in the body in one way or another. To read more about our internal clocks, try starting here: http://www.sciencemag.org/news/2017/10/timing-everything-us-trio-earns-nobel-work-body-s-biological-clock and here: https://www.scientificamerican.com/article/molecular-clocks-scattered-throughout-your-body-not-just-in-the-brain-keep-your-tissues-humming/.

Things that helped me learn and write about this topic:

• Bald Eagle Management Guidelines:
  https://www.fws.gov/northeast/ecologicalservices/pdf/NationalBaldEagleManagementGuidelines.pdf
• Gwinner E. Circannual rhythms in birds. Current Opinion in Neurobiology. 2003;13(6):770–778. https://www.ncbi.nlm.nih.gov/pubmed/14662381
• Seasonal changes in day-light intensity as a potential zeitgeber of circannual rhythms in equatorial Stonechats: https://link.springer.com/article/10.1007/BF01653467
• timeanddate.com, weatherspark.com, usclimatedata.com
• SW Florida Eagle Cam
• USNO daylight tables: http://aa.usno.navy.mil/data/docs/Dur_OneYear.php
• The book "Sync: How Order Emerges From Chaos In the Universe, Nature, and Daily Life", which I bought a couple of years ago on the recommendation of my Dad: https://www.amazon.com/Sync-Order-Emerges-Universe-Nature/dp/0786887214.

What's on the menu at Fort St. Vrain? An exploration of nest remains, part II

The last time we blogged about prey remains from Xcel Energy's Fort St. Vrain bald eagle nest, we talked about mammals. This time, we're going to explore fish and turtles! In all, we found 35 fish remains, seven prairie dog skulls and one foot, one desert cottontail skull, one common muskrat skull, three western painted turtle shells, and some unknown vertebrae. Even in a relatively dry environment, the eagles show a clear preference for fish. Our aquatic remains included:

• seventeen opercular bones (eleven left and six right, from at least twelve different fish)
• eight preopercular bones 
• one otolith 
• four skull tops 
• five skull fragments, and; 
• three turtle shells. 

So what are opercular bones and otoliths? The operculum, which includes the preopercular and opercular bones, is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding.

The opercular series. Nine/yellow is the opercular bone. Six/red is the pre-opercular bone

Otoliths are a calcium carbonate structure in the inner ear of vertebrates. They act as gravity, balance, movement, and directional indicators in all vertebrates, and have a secondary function in sound detection in higher aquatic and terrestrial vertebrates, including fish. Vertebrates have three pairs: the astericus (Ast), lapillus (Lap), and sagitta (Sag). Many fish can be identified to genus and species by their sagittal otoliths but alas, we found only one!

At least we had several opercular bones. While we couldn't use them to determine genus and species, they could determine the size of the fish the eagles were bringing in. Several papers document a close relationship between the size of the opercular bone and the total length (from nose to tail) of the fish. I chose Hostetter and Munroe's 1993 paper Age, growth, and reproduction of Tautoga omtis, which used the formula log10 TL = 1.2916+0.860 log10 OR for males. The paper meticulously documented Hostetter and Munroe's methodology and results, which were used in subsequent studies of several fish species. It was also well-cited and required nothing more than a dial calipers, intact opercular bones, and a good calculator - three things I had on hand!

I used the dial calipers to determine Opercular radius (OR). which Hostetter and Monroe define as the distance from the articular apex center to the midpoint of the posterior margin of the opercle. It looked something like this...

Opercular and preopercular bones of our largest fish. 

I ran my measurements through the formula log10 TL = 1.2916+0.860 log10 OR to obtain the lengths below (more on that at the end of the blog). While we collected 17 bones, only 14 were intact enough to use.

OR	Total length	Number/side
61mm	26.3" / 668.02 mm	1 / left
47mm	20.9" / 530.86 mm	1 / left
46mm	20.6" / 523.24 mm	1 / right
43mm	19.4" / 492.76 mm	2 / both left
42mm	19.0" / 482.60 mm	2 / both right
41mm	18.6" / 472.44 mm	2 / left, right
40mm	18.3" / 464.82 mm	3 / left, right, left
34mm	15.9" / 403.86 mm	2 / both left

While I was impressed by the largest fish, it was a real outlier. The average fish size was 19.0" - a nice size at just a little over 1-1/2 feet long. So what kind of fish would they be likely to be and how heavy might they have been? I checked out a fishing report for the St. Vrain state park and emailed the Laughing Grizzly fly shop to find out! Given the size of the fish and the stretch of the river, Mike suggested either sucker or bass, with the outlier possibly belonging to a carp. Their length/weight profiles look something like this:

• Common Carp: 16 to 26.5 inches at 2 pounds to 10 pounds
• Largemouth Bass: 16 to 25 inches at 2.4 pounds to 9.10 pounds
• White Sucker: 16 to 20 inches at roughly 4 to 6 pounds 
• Longnose Sucker: 15-25 inches at 1 to 2 pounds (although Montana's field guide states that the largest can be around 5 pounds and fish of up to 7.3 pounds have been reported)

In addition to sizing fish, opercular bones can also be used to age fish. Like trees, they produce annular rings that can be counted once the bones have been cleaned and held up to a strong light. However, I was confused by the age of my fish. Almost every opercular I counted yielded an age of four or older, with several between six and nine years of age and the oldest (the outlier) about fourteen. I hadn't expected my fish to be as old or as big as they were. Was I counting wrong? What was going on?

Operculars. Mr. Big is at left. It was the oldest and the largest opercular bone.

As eagle cam watchers might recall, sucker fish rise in the spring and early summer to spawn on gravel beds and sand bars. Every year, Dad Decorah and Mr. North haul in suckers by the dozens once the run starts, sometimes bringing in more than one at a time! However, Longnose Sucker don't become sexually mature until they are between five and nine years of age, while White Sucker don't reach sexual maturity until they are three to eight years old. This means that spawning suckers are a minimum of three years old at spawning, and could easily be older. Finally, my large old bones make sense! Do we know that these fish are suckers? No - but age and size as determined by the opercular bones fit the species, especially given the presence of suckers as identified by local fishing guides, their age at sexual maturity, the amount of sand and gravel bars in the area, and the seeming preference of eagles for suckers when given the choice between suckers and, say, trout. Bob would love this, since he theorized back in 2012 that sucker fish spawning could be the Midwest's equivalent of a salmon run when it comes to protein sources for eagles and other animals that eat them. We'll be watching closely during the spawning season in 2018 to see if we can identify the fish that Ma and Pa FSV bring in! (Amy's note: There were two very distinct shapes of opercular bone, which makes me think that at least two different species were brought into the nest. One was rounded [Mr. Big and several of the others], while the other was more angular).  

Of course, fish weren't the only aquatic animal the eagles brought into the nest. We also found three turtle shells. Alan Resetar, the McCarter Collections Manager for the Chicago Field Museum's Amphibian and Reptile Collection, identified them as spiny softshells (Apalone spinifera). This was very helpful, since I originally thought they might be western painted turtles or small snapping turtles. He also provided a link to this guide for identifying turtle shells and remains: http://fieldmuseumlibrary.worldcat.org/title/turtle-atlas-to-facilitate-archaeological-identifications/oclc/35793760. Take a look at the picture below, which clearly illustrates how the spine and ribs are fused to the shell, giving turtles their distinctive walk.

The underside of a turtle's shell 

So what did we learn? Collecting prey remains from the Fort St. Vrain nest gave us a couple of unexpected insights. As dry as the area is, aquatic animals (especially fish) are still an important part of Ma and Pa FSV's diet - something we didn't expect. The spiny softshells were a surprise, since they are at the extreme western end of their range. And like the Decorah and Decorah North eagles, the Fort St. Vrain eagles appear to take advantage of the spring sucker run, which comes at a very timely point in the lives of their young! While some specific prey details are different (prairie dogs!), the remains we found fit within the larger framework of bald eagle behavior - getting the most food for the least amount of effort and risk expanded. Benjamin Franklin famously called bald eagle behavior lazy, but it takes experience and intelligence to know where and how to find food, especially in a beautiful but unforgiving place like Colorado's Front Range.

Xcel Energy, thanks for all of your hard work and support. You are wonderful eagle and falcon friends, and I look forward to collecting prey remains from Fort St. Vrain next year! I was quite fascinated by this nest, which is much drier and 'stickier' than our Iowa nests. The lack of humidity means that materials don't tend to compost in the nest, although the eagles still prepare the area under the nest cup and strip bark from the sticks they bring in. We have three eagle nests to watch in Iowa and Colorado. What can we learn from their differences and similarities? We look forward to finding out!

Did you know?

I wish we found more otoliths, since researchers are using them to model climate impacts: https://blog.csiro.au/fish-ear-bones-point-to-climate-impacts/. I am hoping to send our fish and mammal collection to the Field Museum in Chicago!

Most of the fish we found were within the carrying capacity of Ma and Pa FSV. Under standard conditions, Bald Eagles can lift and carry around 60% of their body weight, and in some circumstances they can carry more! A link: https://raptorresource.blogspot.com/2015/11/how-much-can-bald-eagle-carry.html

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Things that helped me learn and write about this topic:

• Alan Resetar, McCarter Collections Manager, Amphibian and Reptile Collection, Field Museum
• Age, growth, and reproduction of tautog Tautoga onitis: http://fishbull.noaa.gov/911/hostetter.pdf
• A Guide to aging Yellow Pike and Walleye (if you are a fishing family, this provides a guide for kids): http://www.rebeccaeberts.ca/wp-
• content/uploads/2015/01/EbertsAgingArticle_pg39_outdooredge22.pdf
• Vestibular system. Your ears might be stranger than you think! https://en.wikipedia.org/wiki/Vestibular_system
• Laughing Grizzly Fly Shop. Hit them up for fishing if you are in Longmont, Colorado - these guys know their business!
• Luke Ries. Thanks for the help on the math formula!
• Turtles of Colorado:
  http://cpw.state.co.us/Documents/Education/StudentActivities/COHerpQuickKey.pdf

What's on the menu at Fort St. Vrain? An exploration of nest remains, part I

So what's on the menu at Fort St. Vrain? While we were up in the nest, I decided to collect prey remains. We don't have the necessary permits to take feathers (of which I found only two, both belonging to prey), but there were plenty of skulls and a few turtle shells. I got them home, laid them out on a table, and started ID'ing them. Some Moms bring home t-shirts and postcards. I bring home skulls and photos of prey.

The photo below shows all of the remains I recovered from the nest, along with the book that Elizabeth Ries and I used to identify them. In all, we found 35 fish remains (skulls, skull fragments, opercular bones, jawbones, and an otolith), seven prairie dog skulls and one foot, one desert cottontail skull, one common muskrat skull, three western painted turtle shells, and some unknown vertebrae. Even in a relatively dry environment, the eagles show a clear preference for fish. As you can see from the opercular bones and skulls, some of the fish were pretty large!

From bottom to top: six right opercular bones, six fish skulls and skull fragments, 11 left opercular bones and one otolith, seven fish jawbones, three spiny softshells, vertebrae, four unknown skulls, seven prairie dog skulls, one muskrat skull, one desert cottontail skull

This blog will deal with mammal remains! To make the job easier, I started by assuming that most of the mammalian skulls were probably prairie dogs given the close proximity of a prairie dog colony to the nest. We divided them into groups of skulls that looked alike (which of these things is not like the other?) and got the skull book out!

Top to bottom: desert cottontail, muskrat, black-footed prairie dog

Take a look at the skulls above. The top skull is quite a bit different than the other two, with a high, rounded top and a slightly different eye socket and muzzle (although much of the muzzle was gone). The bottom two skulls are flatter, 'boxier', and have different suture patterns. I decided to start with the bottom skull, since we had seven of them and just one each of the other two. Sure enough, Animal Skulls, A Guide to North American Species verified that we had a black footed prairie dog! Our skull had well developed post-orbital processes (the bone spurs jutting out almost perpendicular from the skull over the eye sockets), v-shaped temporal ridges (the 'V' on the skull), well-developed occipital crests (the ridge at the back of the skull), and (not real visible in this photo) broad nasals with squared posterior edges. It was a prairie dog! But what were the other two?

I started by thinking about the animals I had seen around the nest. How about a rabbit? Elizabeth and I began with looking at what kind of rabbits lived in the area. After a lot of comparison, we settled on a desert cottontail. The skull has a relatively round, large braincase, the eye sockets are similar, with a posterior extension that is "long, broad, and often fused to the braincase" (this helped us rule out brush rabbit), and a broad and high intraorbital region, or top of the skull.

Elizabeth suggested we take a look at the ventral, or underside, of the skull. Good idea!

Desert cottontail, ventral view

This turned out to be very helpful! She observed that the teeth lined up exactly with the desert cottontail's teeth, the heart-shaped structure at the top of its mouth formed by the palatal bridge begins near the anterior of the second cheek tooth and terminates just into the fourth tooth, the incisive foramina are large, and the skull has a medium forum magnum that resembles the one pictured in Skulls. Unfortunately, we didn't have a mandible to compare, but I feel pretty comfortable calling this a desert cottontail.

Since the ventral view was so helpful in identifying mystery skull #2, we decided to start with the underside in skull #3. Wow - look at those distinctive teeth! This should be easy!

Ventral view

The teeth were distinctive, but not as much as we hoped. We eventually ruled out northern pocket gophers. Like this skull, they have smooth incisors, but the skull shape was all wrong. We went on to rule out other types of pocket gophers and eventually just ended up looking for teeth that matched the skull as I racked my brain to think about what else could be out there. And then we found the muskrat skull. Voilà!

It was a muskrat, not a pocket gopher!

Muskrats are semi-aquatic rodents found all over the United States, including Colorado. The skull has orange, smooth mandibles, the anterior edge of the squamosal has a strong angular projection (look at the squared off ridges protruding over the eyesockets), giving the braincase a 'squared' appearance, and its temporal ridges are developed (look at the back of the skull). The teeth descend in size to the posterior, the first lower molar has five closed triangles or loops, and the incisive foramina (aka the long slits visible in the roof of its mouth in the ventral view) are long and thin, with the posterior edges aligned with the anterior edges of the toothrows.

Elizabeth and I found the skulls quite fascinating. We discussed the distinctive teeth of the muskrat, which is the only mammal of the three to eat underwater. Its short tooth 'plate' allows it to grind tough fibers behind closed lips, which keeps water from running down its throat. We noted the high, rounded skull and facial tilt of the rabbit skull, which may help it to leap and bound - something neither prairie dogs nor muskrats do - by keeping its nose down and out from its line of sight. And we talked about the high post-orbital processes of the prairie dog, which also occur in some squirrels and marmots. These bony barbs help anchor ligaments, pulleys, and other connective tissue, but why do prairie dogs have them when muskrats don't? Were they inherited from a distant ancestor, or do they reflect a more recent evolutionary development. Even though the animals were long gone, their skulls told us a lot about the way they had lived.

We'll look at fish and turtles in the next blog!

Why so many prairie dogs versus other mammals? There is an active colony very close to the nest, just below some large power poles with great cross braces. The eagles can perch right above the colony and wait for an unwary prairie dog to get a little too far from its hole. Prairie dogs are also relatively large and meaty - a nice size dinner for the amount of energy expended catching it!

Interested in ID'ing the skulls of North American animals? Check out Animal Skulls, a Guide to North American Species, by Mark Elbroch. We would not have been able to make ID's without it! 

Did you know that prairie dogs are believed to have a rudimentary language? Given Ma and Pa's presence, I assume they have a call for 'eagle': http://www.npr.org/2011/01/20/132650631/new-language-discovered-prairiedogese