August 08, 2006
The Need to Migrate
Nest Update: We had planned to schedule the bucket truck to come out and clean off the lens at the end of this week, but a big thunderstorm Monday night did the cleaning for us, and now the cam looks great. A dirty lens shouldn't be a problem again this year as there is not much slicing going on at the nest now.
I wanted to thank everyone who sent in photos for our recent Gallery update. The Gallery now has shots that show us when our youngest chick -- Cloud Dancer -- took his first couple flights. We also saw one shot of a chick mantling his food -- mantling is when a raptor spreads its wings over a meal as if to indicate "Back off! It's mine!" Another group of photos showed a chick engaging in some nest maintenance -- good to see the youngsters learning those domestic chores. And finally, we saw several photos of fish crows on the nest scavenging for leftovers while the ospreys were away.
One cam watcher asked about Cloud Dancer's meals. The youngest might be fishing for himself by now, but if not, the parents will make sure the littlest has food. I saw a parent on the nest Tuesday morning with a fish. The one chick on the nest didn't seem interested, so the parent flew away with it. It was hard to tell if the adult was the father or mother, but once the end of August comes, the mother will likely be gone, and any adult we see will be the father.
Since Cloud Dancer fully fledged, we've seen fewer shots of the other fledglings -- Hunter, Wind Runner, and Skye Diver -- on the platform. I think when Cloud Dancer was nest-bound, it made the older chicks come back more often since the odds of getting a meal at the nest were better. But now that the youngest is actively flying, the older chicks don't have as much of a reason to hang around the platform.
I can't tell for sure, but the one chick we see spending the most time at the nest is likely the youngest. Cloud Dancer will get more independent as time goes on and he realizes that if he wants to eat more, he needs to go fishing.
And for those cam watchers who tell me that they have a hard time telling the difference between parents and chicks -- here is a photo that shows how you can tell: The parents' body feathers are solid brown, while the chicks' body feathers have a light-colored edge.
Why Do Ospreys Migrate
In our next web log, I'm going to post several images from Google Earth to show you where our ospreys will likely go when they begin their migration south. But in this web log, I wanted to talk about why the ospreys have to leave in the first place. At Blackwater Refuge, our adult bald eagles do not normally migrate from the area, but the adult and juvenile ospreys do. So why the difference?
Blackwater Refuge is located in the mid-Atlantic region of the U.S., and although we sometimes experience cold winters, the ospreys could actually survive the cold temperatures if they stayed here during the winter months -- just as the bald eagles do. But what makes the two raptor species different is that the ospreys' main prey -- fresh fish -- is very hard to find in the winter. Cold temperatures drive the fish into deeper water and out of reach of ospreys, and during some of our more harsh winters, the Blackwater River can actually freeze over (see photo). Since an osprey's diet is normally about 99% fresh fish, the ospreys would likely starve if they stayed.
Bald eagles are more flexible in their diet, which means that while they prefer fish, they can switch to other forms of prey during the winter. Those who watch our Eagle Cam remember that in December and January, we often saw the eagles bring ducks and rabbits to the nest. The ospreys do not have this option of switching to another meal choice, so they must migrate to an area where the fishing is good throughout the winter months. For mid-Atlantic ospreys, their wintering grounds are most likely South America, although some ospreys might stay in Central America.
But what about the ospreys that already live in warm areas? The ospreys that live in southern Florida, Mexico, and the Caribbean will not leave their region once nesting season is done -- these are called "non-migrant" ospreys. These non-migrants might roam around their region during their non-breeding season, but they won't leave it completely. Also they will frequently nest earlier than our birds, with the ospreys in the Florida Keys nesting as early as November and December (ours begin nesting in March).
At this stage, it's natural to wonder why the Blackwater ospreys don't just stay down south where the weather is warm. Unfortunately for the ospreys, they do not have that option because the southern wintering grounds do not have the space and resources required to support all breeding ospreys. Many raptors need space when raising a family, and it would not work to have all the continent's ospreys in one area where they would have to compete with large numbers of fellow ospreys looking for the same food sources and limited nesting sites during the crucial breeding season. So instead, the ospreys migrate north and spread out around the continent when it comes time to breed.
Migration Hot Spot
Once migration starts (around mid August), birds all around the country will begin to move toward their winter homes, and our osprey family will be in that group. When discussing bird migration, you often hear biologists talk about the major "flyways" -- these are popular aerial highways that birds use to move between their summer and winter homes. Blackwater Refuge is a major hub on the Atlantic Flyway, and many birds either stop here to fuel up or spend their entire winter in our marshlands. When our ospreys leave, they will be on the Atlantic Flyway.
There are several areas around the country that are considered natural bottlenecks for migrating birds -- meaning these areas have a land topography that forces ospreys and other birds into a smaller area, making it easier for humans to locate and watch the migration spectacle. One of the best places to observe migrating ospreys on the East Coast is at the famous Hawk Mountain Sanctuary in Pennsylvania. Between August 15 and December 15, an average of 20,000 hawks, eagles and falcons pass the Sanctuary's North Lookout, where the birds are observed and tallied.
The reason Hawk Mountain is such a popular bottleneck is that the mountain is part of the Kittatinny Ridge -- the eastern-most ridge of the central Appalachian Mountains. The Kittatinny Ridge is one of the tallest and most continuous ridges in the mountain chain and attracts many raptors looking to take advantage of the updrafts of air, which help the birds cover more ground with less effort as they head down the East Coast during migration. Here is a photo from Google Earth where you can see the ridge and the Sanctuary.
Starting on August 15, you can keep tabs on the autumn migration at Hawk Mountain by visiting the sanctuary's home page where they will post the daily count every evening after 5pm. On the website's Migration page, you can read more about migration and the dates when the different raptor species are seen (scroll to the bottom for the dates). You can also subscribe to their email updates to receive news about the migration season as it develops. While Hawk Mountain does see quite a few birds during spring migration, the fall migration season is the one that attracts the largest numbers of raptors. In 2005, Hawk Mountain tallied 480 migrating ospreys.
If you're lucky enough to live on the East Coast, I highly recommend taking a trip up to Hawk Mountain during migration season. Besides getting a chance to see many species of raptors, you can also enjoy some people-watching, as well as some leaf-peeping as the mountain hillsides explode with color during the cooler weeks.
And if you don't live on the East Coast, you can still enjoy a quick aerial video of Hawk Mountain on the Audubon Pennsylvania website.
General Osprey News
Our friend Russ Yeaton reports that the three chicks at his local osprey nest at Spring Point Light in South Portland, Maine have all fledged. Here we have three photos from Russ: The first photo shows a pre-fledgling hovering over the nest; the second photo shows a fledged juvenile on a rock (notice the light-colored edges on its feathers); and the third photo shows a beautiful sunrise shot from Spring Point Light. Congrats to the new fledglings, and much thanks to Russ for his photos.
Speaking of Maine, I wanted to share an interesting cam link. The National Audubon Society's Project Puffin has put a Puffin Cam on Seal Island National Wildlife Refuge in Maine, which is the only U.S. state with a population of Atlantic puffins. If you've never seen a puffin, be sure to check out the website's movie page where you can see footage of puffin chicks inside their rock burrows.
The Puffin Cam's live video stream alternates between two regular ground-level cameras and a new infrared "burrow cam." They move the cam view around, so you have to be a bit patient to see action, but it's an unusual project and worth checking out.
Vermont Eagle News
And on a final note, here is an interesting article about the Vermont Bald Eagle Restoration Initiative. They report that the last eaglet has fledged from their program. As our Eagle Cam watchers remember, birds from Blackwater Refuge were used in this hacking program to reestablish nesting bald eagles in Vermont. We're thrilled that the program has been such a wonderful success. Best of luck to all the fledgling eaglets!
Until next time,
Lisa - webmaster
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