Thursday, April 30, 2015

Red-tailed hawk growth and development in the nest

Eaglets aren't the only thing growing right now! The two eyas red-tailed hawks at Eaglecrest are morphing into adults right before our eyes. Like bald eagles, different parts of their bodies grow at different times and different rates, reflecting developmental priorities and impacting behavior. How will hawks EC2 and EC3 (also known as Speckle and Snickers on the Eaglecrest Wildlife facebook page) grow?

  • 0-7 days: the culmen achieves maximum growth. Red-tailed hawks hatch with a culmen (the dorsal ridge of the upper mandible) that is about 30% of the maximum size it is likely to achieve in the nest. During a red-tailed hawk's first week of life, its already large culmen nearly doubles in length, going from an average of 6.9 mm in length to an average of 12.3 mm in length. Since the consumption of food is the root of all else besides, the hawk's food-consuming apparatus is given developmental priority. While the culmen continues to grow after week one, its rate of growth slows dramatically, becoming almost flat by week five. Bald eagles follow a similar pattern, although they have almost twice the growing time in the nest that red-tailed hawks do and their developmental milestones reflect that.  
  • 7-14 days: third toe and tarsus achieve maximum growth. Eating has priority, but movement isn't too far behind. A young hawk needs to move to build muscle and feed once it is past the point where Mom and Dad simply stuff food into its waiting mouth. In the second week of life, a red-tailed hawk's third toe and tarsus are given developmental priority. The third toe is the real stand out here, nearly doubling in length from 16.9 to 27.9 millimeters. With longer toes and thicker, longer tarsi, the hawks are better able to sit up, move around the nest on their feet and knees, and interact with one another. We see a similar pattern with bald eagles, who reach asymptotic mid-toe and tarsus size about half-way through their nestling period - 40 days, in their case. 
  • 14 to 21 days: body weight achieves maximum growth. With food intake well in hand, young hawks gain weight rapidly. While they've been growing all along, weight gain is the biggest actor in week three. The young hawks spend a great deal of time eating and sleeping as their weight increases. 
  • 21 to 24 days: weight gains decline, independence increases. During the fourth week, weight gain declines, the nestling hawks begin feeding independently, and feather growth takes over. The hawks have the strength and physical structures they need to stand upright on their feet, manipulate food, and feed on their own. At about day 24, the length of primary seven overtakes weight as the best indicator of age.  At this point, fledge is just two or three weeks away. 
  • 24 to 35 days: Feathers take front and center. As fledge comes closer, developmental energy is channeled into growing feathers. The primaries enter their maximum growth phase during weeks four and five, the two weeks prior to fledging. The young hawks will also be growing sub-adult feathers elsewhere, including their backs, their tails (which won't become red until molt two, in their second year of life), and their chests. 
  • 36 to 44 days: Time to fly! Feather growth will slow, but the growth of flight-related muscles is happening in leaps and bounds. Wingercizing will take front and center stage as they young hawks practice for the big event by flapping, wing-hopping, hovering, and eventually taking flight! 
Both red-tailed hawks and bald eagles allocate developmental energy into producing weight and structure first (day 0 to day 24), and feathers second (day 24 onward). While feathers often seem light and simple, these two distinct periods of growth point to the incredible amount of energy needed to produce a proper 'coat' of feathers. Enjoy the hawks now, since they will be leaving the nest soon. It takes just 44-46 days to grow a red-tailed hawk from hatchling to fledgling! 

Did you know?
Red-tailed hawks are excellent falconry birds. While their are many excellent falconry organizations, I'm most familiar with NAFA. Interested in falconry? Follow this link:

Wednesday, April 08, 2015

A Four Recap

Earlier this week, a follower asked us for a recap of eagle Four’s life. Four was one of three eaglets that hatched in 2014. While early life in the nest was fairly ordinary, gnats and record-breaking rain interfered with fledging. For the first time that we know of, only one of the 2014 Decorah alumni successfully transitioned to life in the wild. One of Four’s siblings was injured and went to SOAR, where he  remains. The other sibling died of electrocution from a high voltage transmission line not far from the hatchery.

Four’s transition from fledge to flight was a bumpy one. During her first month on the wing, Bob rescued her from a location at the side of a highway, a fence, some deep woods, and a corn field. She roosted on the ground, traveled only short distances, and remained in the vicinity of the nest longer than any other eaglet we are aware of. We were starting to ask ourselves if Four would ever go when, on October 19, she abruptly left. Between June 22, 2014 and March 1, 2015, we received 302 valid fixes on Four. She traveled a total of 686 miles, averaging 2.2 miles a day. She achieved her furthest distance from home on January 8, 2015, when she was tracked 159 miles south of her natal nest. Her longest contiguous flight took place on December 1st, when she traveled 34.8 miles between the Maquoketa River and a roost near Lake McBride. She was electrocuted on March 2nd, roughly 130 miles south of N2.

After Four was electrocuted, we documented her death and reported it to the US Fish and Wildlife Service. We also contacted Alliant Power with photos of the pole under which Bob found her. When we were told it was up to code, Bob decided to get a second opinion. Contact number two told us that several things needed to be fixed to make the pole safe for birds. We passed the information back to Alliant Energy and decided to survey the area for more eagles. Two Ustream mods volunteered to conduct the survey for us. They didn’t find any eagles, but they did learn about another electrocution. They provided photos of that pole and several others. Alliant stated that they would fix the fatal poles and others like them. Thank you very much to IzzySam and Faith for taking this on for us.

We plan to take a trip back into the area where Four died to see whether Alliant fixed the poles as promised. The code we used to follow the travels of our eagles will be repurposed to map electrocutions and identify problem spots. While not every pole can be immediately protected, we can make dangerous poles a priority. Four touched a lot of hearts during her brief life. It is our hope that her death will bring about a safer environment for eagles and other birds.

Four's data is retained here:

What can you do?

  • Find out whether your utility has an avian protection plan. If they don't, they should consider adopting one. An APP helps keep animals, equipment, and people safe.
  • Report electrocuted birds and other animals to your power company. Electrocutions are deadly to animals, harmful to equipment, and potentially dangerous to human beings. 
  • Report collisions to your power company. While our eagles have been electrocuted perching on poles, collisions are also deadly. Swan diverters and other deterrents can be installed.
  • If you are a member of an electric cooperative, make your concerns known to the board. I know of at least one electric cooperative in the process of retrofitting all their poles are safe. Electrocutions destroy equipment, require unscheduled repair time, and are expensive.