April 12, 2007
Ospreys and Eagles
I wanted to spend a little time talking about the last few days on the osprey nest, because the osprey action we’ve been seeing has been a little confusing.
Up until a few days ago, our ospreys were doing great. They were mating, nest building, eating together, and defending the nest together. Then a few days ago, we started seeing only one bird on the nest. I thought we were seeing both the female and male at different times, but now I’m not so sure. What makes it hard to tell is that our female has a very light necklace (chest coloring), and size is the only other indication we have of gender, but size is not always helpful unless the male is there for a comparison.
In the last two days, we continued to see only one bird on the nest for most of the time, and it appeared to be the male. Then on Wednesday, while the lone adult was away, a bird (likely a crow that had been visiting the nest) quickly flew in and stole the remaining sod ball (or marsh root ball), which the ospreys had collected for the nest. As soon as the clump disappeared, the adult osprey came back to scold the thief, but the event was odd because if the adults had been properly tending the nest, the theft shouldn’t have happened.
On Thursday morning, we finally saw two birds in the nest again, but we’re not sure if they are our couple. The second bird looks almost like a male in size and has had no real interaction with our other bird. Instead they spend a lot of time standing one in front of the other, as if watching to see what the other will do. Normally a male osprey would not let another male hang out at his nest, so it seems odd that this would happen if both birds are male -- but we don't know for sure that they are.
We expected egg laying to possibly start this week, but it’s hard to lay eggs when you’re rarely together or when you're both male. :-)
Our cam technician -- who has an osprey nest near his house -- says his birds have also seemingly lost interest in nesting lately, as if they’ve slowed down their preparations a bit, possibly because of the unusual snow and cold we had about a week ago. We're not sure if weather is playing a part in this odd behavior -- causing the birds to delay egg laying -- but we hope so, because the weather will improve.
We’ve asked the folks at the Visitor Center to keep an eye on the monitor to see if any mating is occuring. Also, I plan to visit the Refuge this weekend to tape some new video of the eaglets, and I’ll check out the platform and osprey monitor while I’m there. But right now, we’re just watching to see what's going on with the ospreys that are showing up at the nest.
Ospreys and Eagles
In this web log entry, I wanted to talk about the relationship that our resident eagles have with our resident ospreys, especially since Blackwater Refuge has a healthy population of both species of raptor. Eagles and ospreys have an adversarial relationship, and the eagles normally get the upper hand in any battles, due to their larger size. In this wonderful photo, you can see very clearly how much larger the bald eagle is when compared to the smaller osprey and why the eagle can often dominate mid-air confrontations.
Bald eagles are notorious for stealing fish from ospreys. In fact, this was one of the reasons why founding father Benjamin Franklin did not want the bald eagle to be America’s national symbol. Franklin thought the eagle was lazy because it would wait for the osprey to catch a fish, then harass the osprey in mid-air until the smaller raptor dropped its prize.
Biologists are not quite as critical of the eagle for this behavior because they see this as normal, since the eagle is just making the most of the fact that ospreys are excellent fishermen and the eagles have a size advantage over them. But I’m sure the ospreys would side with Ben Franklin in this debate. :-)
It should be noted that ospreys are not totally helpless. Sometimes they will work hard to keep the fish away from the eagle, forcing the eagle to fly under the osprey and then roll on its back and grab for the fish with its talons while beneath the osprey. Also, sometimes osprey couples will team up to protect their food from the eagles. Tom Miller, the ranger at Blackwater Refuge, saw an osprey fly toward an eagle to intercept it while the other osprey quickly flew to the home nest with the fish.
Ospreys can be even more aggressive if they are protecting their nests or young from eagles. At Pelican Island National Wildlife Refuge in Florida, local photographer Bob Montanaro just captured this type of event on film as he watched a group of four ospreys drive off a group of immature bald eagles that were flying too close to the osprey nests. Be sure to view these amazing photos where you can see the osprey aggressively flying at the immature eagle and making it clear that the ospreys will not tolerate the eagles in their territory.
And this brings up the second danger that eagles represent -- sometimes eagles will attempt to take osprey nestlings, and there are even reports of adult osprey remains being found in eagle nests. Biologists are not sure if the adult ospreys were dead when the eagles found them or if they were the result of a kill, but there is no doubt that ospreys do not want eagles hanging out near their nests.
When you’re watching our Osprey Cam, you will sometimes see the ospreys looking to their right (your left on the cam) and calling out. There are snags and trees in that direction where bald eagles like to perch. Just the fact that eagles are perching there can be enough to get the ospreys upset.
And just a side note in case anyone is wondering: Having eagles there would not deter the ospreys from nesting at the cam platform. Eagles are all over the Refuge, and ospreys have to learn to live with them if they are going to raise young near the Blackwater River.
During the 2005 Osprey Cam season, we had a chance to witness how the ospreys deal with pesky eagles. That season we saw the mother osprey leave her nestlings at the cam platform and fly off to those trees where she proceeded to dive-bomb a perching eagle.
Normally the father osprey would do this type of work when the mother is protecting young birds, but that was the season we had our delinquent father, and since he would often disappear for most of the day, the mother had to do a lot of this work herself.
Below are two videos of this event -- one showing the eagle flying into the trees and the other showing the mother consequently dive-bombing the eagle. In this instance, the mother did a good job of sending a strong message to the eagle, but it was somewhat risky for her to have to leave the chicks alone to do this. Left-click on the Windows Media Video file links below to play, or right-click on the links and choose "Save Target As" to download to your computer:
| Eagle Flyby (3.5MB) |
| Osprey Dive-bombing (2.5MB) |
We love our eagles at Blackwater Refuge, but it’s important to remember that they’re predators by nature, and sometimes their prey can be the other animals that we enjoy at the Refuge.
Until next time,
Lisa - webmaster
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