February 10, 2007

Preening

eagle eggsI know we've had some recent publicity for our web cams and for the eagle watching at Blackwater Refuge, so I want to welcome those who are just joining us. If you're new to our site and wonder what we're watching, we have two eggs that we hope are fertile, and if so they will hatch in less than three weeks. Here is our egg scorecard for 2007:

1st egg laid: 01/24/07
Possible hatch date: 02/28/07

2nd egg laid: 01/26/07
Possible hatch date: 03/02/07

In future web logs we'll talk more about what to expect when hatching is near, but if you'd like an early preview, be sure to read our Eagle Watchers' Guide (2.5MB PDF file), which offers a recap of our first Eagle Cam season when we were privileged to see three eaglets hatch and fledge successfully.

I also wanted to address a couple recent questions. First, folks were wondering about the corn cob in the nest. There are cornfields near the Eagle Cam nest, and sometimes when the eagle parents bring in stalk pieces for nesting material, a corn cob comes along for the ride. We think the eagles are pecking at the corn, but we don't think they're eating it.

Also, several cam watchers have asked about which parent is on the nest at night. Normally the mother eagle spends the majority of the time on the nest at night, but we've seen shots on a couple evenings where it looks like the parents might be arguing a bit over who gets to sit on the eggs. This might be due to the bitter nighttime temperatures we've been having lately. Maybe the warmest place is on the nest.

Eagles can withstand very cold temperatures -- they have a warm coat of down underneath their feathers -- but I'm sure that they like to be comfortable. We hear we might get more cold temperatures and a snowstorm around Monday and Tuesday. But I guess if this harsh weather had to arrive, it's better that it comes before the eaglets are here.


Preening

I wanted to talk about preening since we've been seeing a lot of images showing the parents working on their feathers while they've been on the eggs. The importance of feathers cannot be overstated as they literally mean life and death to a bird. And so consequently, eagles spend a lot of time maintaining their feathers, which includes cleaning them, waterproofing them, smoothing them, etc.

An eagle will molt (shed its feathers and grow new ones) every year, although biologists report that not all feathers get replaced in each molt. Molting is a gradual process that occurs mostly in summer but might extend into spring and fall. The flight feathers are not lost all at once, so the eagle is never flightless.

In order to maintain the feathers they have, an eagle will straighten and smooth them, often by using its bill to "zip up" the feathers, so the feathers maintain their smooth and aerodynamic appearance.

In addition, an eagle will apply oil from its preen gland (also called the uropygial gland), which is located at the base of the tail. The bird will squeeze the gland to extract the oil and then work the oil into its feathers. This oil cleans and waterproofs the feathers, and also deters feather parasites. Although our eagle parents are spending a lot of time on the eggs -- and not fishing as much -- they still need to have waterproof feathers so they don't get chilled when it rains or snows on them.

At the falconry site called The Modern Apprentice, they have several photos posted where you can clearly see the preen gland.

When eagles are preening, they will often use their nictitating membrane to prevent their eyes from getting damaged while rubbing their head into their feathers. A nictitating membrane is also called the "third eyelid," and it's a transparent, whitish membrane that moves horizontally across the eagles' eyes and protects their eyes while maintaining some vision.

Eagles also use their third eyelid to clean and moisturize their eyes, to protect their eyes while tearing into a fish or duck, and to protect their eyes while feeding their eaglets, since eaglets can accidentally damage the parents' eyes when lunging for a piece of food.

Woody Dawson, one of our talented photographer friends, sent me an animated GIF that he prepared showing an eagle using its third eyelid. Right-click on the image below and choose "Save Target As" or "Save Link As" to download it. The file is 400KB, so it might play better if you download it first. Thanks to Woody for this excellent example of the third eyelid.

Eagle third eyelid


Final Thoughts

A few miscellaneous items that I wanted to mention: First, our 7th Annual Eagle Festival is coming up on March 10. We'll talk more about the Festival in our next web log, but I wanted to say that we've now posted a schedule of activities for the Festival. We might add a few things to this schedule over the next week or so, but this gives you an idea of what to expect.

If you've thought about coming to Blackwater Refuge for a visit, the Eagle Festival would be an excellent time to come as it's our most popular event and it's a wonderful time to look for bald eagles. We will have one of our resident eagle experts on hand to take you around on an Eagle Prowl and point out our local eagles and maybe even some of their nests. Also, we'll be celebrating the Grand Opening of our newly renovated Visitor Center, which features a new second-floor observatory that has spotting scopes which you can use to observe birds on the Osprey Cam platform.

And last but not least, there are a couple other eagle cams online that are seeing some action, so I thought I'd post their links. Our good friends at the National Conservation Training Center in Shepherdstown, West Virginia, have an eagle cam online, and we hear rumors that the nest has two eggs. They recently had some equipment trouble, but it looks like they're back online now.

Also, there are eagle cams posted by First Light Power in Massachusetts, by the Channel Islands in Santa Cruz, California, and by the BioDiversity Research Institute in Maine.

These cams all offer slightly different technology, so we can't say for sure that they will work on every computer and browser, but they're worth visiting as eagle nesting season begins to pick up steam.

Until next time,
Lisa - webmaster
(contact)

Posted by Webmaster at February 10, 2007 01:45 PM