Monday, April 23, 2012

They Grow Up So Fast!

The eaglets in Decorah are 27, 26, and 24 days old. Their darker second down has been in for days, and pinfeathers are beginning to show on the edges of their wings, signaling the emergence of their first juvenile contour feathers. Here is how it works. Each feather arises from a feather follicle in the skin. The pin feathers, or feather follicles, contain undeveloped contour feathers. As the contour feathers develop and emerge from their follicles, they push the down feathers off. The down will remain attached to the contour feathers until it rubs off.

Other changes: the eaglets are more proficient at walking and pooping. They are a lot bigger, although their growth curves (when expressed in weight gain per day) will begin slowing sometime in the next three to six days. The overall size of their footpads should already have started slowing down but the growth of their juvenile contour feathers is just taking off : like many animals, parts of the eaglets' bodies grow at different rates.

If human children play house, the eaglets are playing nest. We've seen the eaglets tussle with cornhusks, move debris around the nest, nibble on everything from food to mom's tailfeathers, 'attack' prey, and explore. Socially, they spend a lot of time interacting with one another and with their parents: they alternately dominate and cuddle, observe Mom and Dad (especially when food is involved), and 'help' with nest chores. This behavior is all part of their growth and development. We sometimes think of play as being unimportant or trivial, but play lets young animals 'practice' the skills they need for adulthood, cements bonds between players, and is pleasurable to those playing.
Here are some videos that show our eaglets growing, playing, and practicing:
Sherri Elliott's daily 'Whattas' on our facebook page provide a wonderful round-up of eaglet daily and developmental events: https://www.facebook.com/pages/Raptor-Resource-Project/103786266324668?sk=notes. I wasn't able to find any information on Bald eagles and play, but here are some play links worth looking at.
I think we should all get out and play after this post is done!

We've been asked how soon we can tell if the eaglets are male or female. The short answer is that we can't tell for sure unless we capture them and take measurements or a blood test. Having said that, Gary Bortolotti notes that sexual dimorphism begins to appear in some variables after 20 days of age. Initially, size depends more on hatch order than anything else, but after 20 days, gender begins to play a role. Females are bigger than males and have correspondingly wider wingspans, bigger feet, and thicker tarsi. Without proper measurements we are speculating, but speculation is part of the fun.

Bob is anticipating that fledge will happen mid-June: a little less than two months from now. Over the next few weeks, we'll see the eaglets get bigger. Dark brown juvenile feathers will replace their fuzzy grey down and we'll see even more wingercizing and play as they transition from nestlings to flighted hunters. Have fun watching!

We are also waiting for the Great Spirit Bluff Peregrine falcon nest to begin hatch on May 2nd, and the Turkey vultures to lay sometime between May 1 and May 7. There will be a lot to see, laugh at, and learn from.

Things that helped me learn about and write this post:
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