In case you missed it, we hosted a live chat with Dr. Rob Bierregaard, Osprey Expert, this past week. Below, you can find both the video and transcribed live chat. We want to thank Dr. Rob Bierregaard for his time and expertise and look forward to having him back again! Watch the Osprey Live cam every day here!
Dr. Rob Bierregaard – Audubon Osprey Nest – Live Chat 25 July 2017
Transcribed by Robinette
Okay everybody thanks for your patience, sorry about the delay, technical problems always seem to pop up when we do this.
So I’m Rob Bierregaard, a lot of you know me from the chat and my osprey website, my work with migration work. But a few of you have been up and spent the week with me at Hog Island, the Raptor Rapture camp.
I’ve been studying ospreys since 1971, and I started banding nestlings on Martha’s Vineyard, I’ve been tracking ospreys with satellite telemetry since about the year 2000—hang on a sec, I’ve got to turn my volume down here—okay, I was getting some feedback there, that was confusing.
So, I’ve got a whole bunch of questions here; they are excellent questions. I’m not going to be able to get to all of them, but I’ll answer the ones I don’t get to—after our hour here, I’ll answer them in text and they’ll be posted somewhere on the website.
So not surprisingly, the first set of questions are all focused on the great horned owl attacks that have been happening for a week or so. As a little bit of a forward, this is all really unprecedented stuff. We osprey researchers have never seen this happen because we’ve never had, until the last ten years or so, we’ve never had cameras with infrared lights on them, so we were never able to tell what was going on at osprey nests during the middle of the night. So this is all new stuff, and some of you have seen more osprey behavior with great horned owls than some of the so-called experts have.
What might explain the ongoing attack in spite of Rachel’s defense of the nest, wouldn’t small mammalian prey be easier for the great horned owl?
Certainly they would; but great horned owls don’t seem to care about easier or not; they are probably the most ferocious bird of prey in North America. Over in Europe, there is the European–Eurasian eagle owl, which is even bigger and scarier. So great horned owls don’t really seem to care, and this bird has already taken two of the young out of the nest, so it knows that there’s a rich resource there. One osprey chick taken out of that nest is worth—in terms of meals the owl can get out of it—a lot of small mammalian prey, so this particular great horned owl (we presume it’s the same one) has been rewarded, if you will, and there’s certainly great rewards in term of the bang for the attack in terms of how much food the owl would get, so the owl seems to be willing to take on Rachel in order to get another meal.
Is there anything unique or unusual about the way in which Rachel has been trying to thwart the great horned owl attacks?
We have no way to answer that question because we’ve never seen this before, so this is all news to us and so we don’t know. This may be what most other ospreys do when they’re faced with this. I have seen other attacks at other nests in the past, only a few, and I’ve never seen a female attack or defend the nest the way Rachel has been.
The incident on the, I think, the second attack when Rachel seemed to be attacking Bailey—why was she so aggressive, why did she attack Bailey?
Again, I think that’s hard to say. I think she was just so riled up that she was attacking anything in the nest, and remember that ospreys aren’t as rational as we are, so I think she was just at a complete sensory overload and was attacking anything that was moving in the nest and unfortunately it looked like she came close to actually pushing Bailey out of the nest which would have been really the ultimate irony. Fortunately, that didn’t happen.
Has Rachel adapted since the owl attacks?
She seems to have. She seems to be perching closer to the nest, not as far out on her perch at night.
Is this learned behavior we’re likely to see again next season?
It certainly could be.
Could Rachel’s adaptations to the owl attacks have been accelerated by her experience with losing chicks to eagle predation over the last two years?
I don’t think so, I think that’s really sort of two very different events: the daytime attacks with the eagles, the nighttime attacks with the owls.
Will Bailey be a more alert and defensive predator as a result of observing Rachel’s defensive behavior? Will she be more likely to avoid Great Horned Owl territories when she migrates?
The first question I don’t think so. I don’t think she’ll be any more alert and defensive after watching what her mother has done. I don’t think ospreys learn that way. And there’s no way that she can avoid great horned owl territories when she migrates. She doesn’t know as she’s migrating south. As a bit of back-story to that, the ospreys that I’ve followed in migration, we’ve probably lost five or six to great horned owl and we’re assuming that’s because we have migrating ospreys that fly into a wood lot at night, at the end of the day to roost, and that they don’t come out in the morning.
<Technical issues interrupt feed>
So, talking about great horned owls, again continuing that conversation, I was saying that we’ve lost some adults, probably to great horned owls while they’re migrating, but there’s no way that Bailey could tell whether a wood lot that she lands in has a great horned owl in it or not. And even if it does, it’s really a crapshoot as to whether or not a great horned owl would find her and would decide to take on an adult.
There have been some questions about why Steve isn’t defending the nest at night, never responding to Rachel’s alarm calls, especially given that other male ospreys do stay near their nests. Is there a nighttime behavior for male ospreys that is considered “standard”?
We have no idea what nighttime behavior is for male ospreys because they’re almost always away from the nest. They could be a long way from the nest. So we don’t know what is standard. Steve could be all the way across—is probably across the bay and he can’t see what’s going on and so it’s not his fault that he’s not there standing up to the owls with Rachel.
Someone wants to know if I think that Rachel and Steve created a decoy osprey following the attacks, or is that wishful thinking on our parts?
I would definitely say that’s wishful thinking.
It appears that she brought moss to shield or cover Bailey, is that typical behavior?
First of all I’m not sure if that was actually trying to cover Bailey, and again, we don’t know what typical behavior is, so I can’t answer that question.
Is this year’s great horned owl a young bird?
No way to tell. It certainly could be a young bird that’s dispersing from its nest. Great horned owls nest quite early. I’m not sure about up in Maine, but down in a lot of their range they’re nesting in January when the snow is still on the ground, so it’s very possible, absolutely, this could be a young great horned owl that’s dispersing from its territory somewhere. We certainly hope that’s the case. The neighborhood would definitely be going downhill if a pair of great horned owls was breeding nearby.
Would a great horned owl ever try to attack Rachel directly or take her instead?
Yes, that could happen. There have been adult ospreys killed on the nest while they were incubating, by great horned owls, so that could happen.
Is it possible that Bailey’s trauma is causing her to regress in the way that human children or dogs do?
I’m not really an “osprey whisperer,” so I can’t tell what’s going on. It certainly doesn’t look like it to me just looking at Bailey. She looks like a normal young osprey now at age six and a half weeks or so, I think that’s about what she is.
Okay, the next set of questions is about Bailey’s wing and the status? Do we know what caused it and what’s the nature of the injury? I’ve been watching this afternoon, and the right wing looks a little droopy.
<Technical issues interrupt feed>
We seem to have lost me for a bit, so I’ll back up. Talking about Bailey’s wing. It looked a little droopy to me, it’s certainly not broken. What caused it is almost certainly something happening with the great horned owl attack—at least one owl actually had its feet and talons on or into Bailey. There might be a puncture wound in there somewhere; but ospreys recover from all sorts of injuries. I think Bailey will be okay, but it’s impossible, really impossible to tell.
Will the injury affect Bailey when she fledges?
We’ll be able to tell that in a week or so when Bailey begins to do her little helicoptering and begins to exercise the wing, we’ll be able to see what’s going on.
Question is, is there a chance that Rachel might leave before Bailey fledges?
Almost certainly not. Rachel may leave not long after Bailey fledges; but the female almost always stick around until the young have fledged and have been out on their own for a week or so, maybe a couple of weeks. Typically females head south on their migration in the middle of August, and so I would guess Rachel would leave sometime in the third or fourth week in August; but certainly not before Bailey fledges.
If Bailey is still injured when she fledges will she be more vulnerable because she is alone, or less vulnerable because she can fly?
She will certainly be less vulnerable to the owl because she won’t be in the nest and sort of a sitting target the way she is now. If she can’t fly very well, then there are other issues about her hunting and that is really impossible to predict right now.
Is there a point at which you will intervene?
I guess “you” means the Hog Island gang. =This is under discussion, I think we’re … well it’s not really under discussion. The standard procedure is no intervention unless there’s something that’s clearly human induced. If Rachel or Steve brought in some plastic bags or fishing line and the young got tangled in that, certainly that would be a reason for intervention. If Bailey can’t fly and tries to fledge and ends up somewhere on the ground where she can be captured I’m sure that they would – that we would take her to a rehab center somewhere. But as long as she’s capable of flying we’re going to let nature run its course here and not intervene under these circumstances.
Why did Bailey not receive a Darvik band?
That’s a color band. That was simply a question of logistics. The team that came to band Bailey from the Biodiversity Research Institute didn’t have enough snap rivets for two bands, so they only were able to color band one of the two young and unfortunately the bird that was color banded was the one that the owl caught. So that was simply just a logistical issue.
Is there any similar damage to Bailey’s wing as to Ollie’s wing injury?
I’m not sure who Ollie is so I can’t answer that one.
Bailey did a full wing extension earlier today. If she were badly injured would this not be possible?
Yes, the wing… <looks at monitor>… oh, she’s just doing a good wing extension there.
<Technical issues interrupt feed>
So we’re talking about Bailey’s wing, and just as I was dropped offline I was watching Bailey on the feed and it looks like she was putting out that right wing pretty well, so I think it’s going to be okay, but again it’s something that we really can’t predict.
So, now some general questions on ospreys and the cam….
When ospreys are migrating that fly during the night occasionally…
and that happens at night when they’re going out over the water. Very rarely do ospreys migrate at night when they’re over land; but when they go out over the Caribbean from Hispaniola to South America they take more than 12 hours and they’re always flying at night. A lot of ospreys go down the east coast will get to the Outer Banks of North Carolina and from there they will go over about 500 miles of open water from North Carolina to Florida and that’s about 20 hours of flight, they fly about 25 miles an hour when they’re migrating. So out of necessity they fly at night when they’re over open water. They can’t land on the water and rest like a duck or a gull does. So they do fly at night…
And this question is about, the person has seen at least four cases when ospreys caught fish during the night, even during the new moon. Can you tell us more about their night vision?
Well apparently they have some. No one has tested ospreys’ night vision, so what we know really is based on what we learn from birds that are migrating at night. It’s not too surprising out over the ocean… it’s never pitch-black dark out over the ocean. Birds catching fish even during a new moon is pretty remarkable. Again this is a lot of information that we’re getting is from osprey nest cams that we had no idea about before this technology came on the scene. So you all know about as much about ospreys’ night vision as I do now based on the observation that they actually do catch the fish at night.
This season at four different nests in different locations there were 12 eggs laid between the four nests; 11 were viable and now only two chicks remain. Is this typical, or is the survival rate lower than normal? If it’s lower, what might explain that?
So that’s lower than we would expect. Typically, in a colony of ospreys, if the average number of young raised… is a little bit over one, that’s pretty good. If we get up to one-and-a-half per young—per active nest that had eggs in them—that’s quite good. In super years, you might get an average of close to two young per nest; but that’s really unusual. So if we had four nests typically we would expect to have say five young to be fledged from those four nests, so now we’re down to two chicks instead of four or five so that’s a little bit smaller than we’d expect, but then four is a very small sample size and these are scattered across widely distant areas there’s nothing, that’s just a random luck of the draw.
Are there researchers, graduate students in ornithology or ecology who use the footage from live cams as a source of primary data to study osprey behavior?
I think somebody is doing that and this is something that I’ve been preaching for quite a while. As long-time followers of the cam and my sessions know, the osprey nest cams are providing all sorts of cool data that we’re using. I recently revised the osprey account in Cornell’s Birds of North America project and there were three or four little tidbits of information that are included in that report that are based on observations that the osprey cam community has made. So when I needed to know, for instance, ‘when do osprey eggs hatch,’ I polled the community at this nest and one of the nests down in Long Island and I got a list of exactly when each of the eggs—I think 12 eggs that pipped, so that information is now part of the scientific knowledge base for ospreys. And I think there are students who are using some of the behavioral stuff; and if there aren’t there will be soon. This is a really rich source of information that is available now and being tapped into by more and more scientists.
We’ve seen osprey nests fail this year due to weather as storms can prevent ospreys from being able to fish. Does their all-fish diet put them at an evolutionary disadvantage? Do they prey on other animals if they are unable to catch fish?
So every evolutionary advantage or adaptation entails giving up something. In evolution, as in life, there’s really no such thing as a free lunch. So for instance, when birds evolved the ability to fly, they gave up using their forelimbs to manipulate food for the most part. So when ospreys specialized in fish they became very good at it; there are very few other raptors in the world that are as good at catching fish as ospreys, and none are as reliant on fish as ospreys are. So becoming that specialized does, indeed, have its costs; but on the other hand it provides a remarkably rich resource for the ospreys to raise their young. To some extent, it is an evolutionary disadvantage, but the advantage of opening up that resource of all those fish that are swimming around, huge schools of menhaden and alewives and herring, has opened up just a really rich resource for ospreys. Very rarely they’ll take other kinds of animals; sometimes those other animals are things that are in the water and they’re sort of acting like fish. I’ve heard about a nest up in Cayuga Lake in New York where there’s a pair of ospreys that almost specialize in water snakes and the neighboring pair rarely brings in any at all. One male just happens to really have a thing for water snakes. Sometimes they’ll catch a muskrat, or baby alligators have been reported; very rarely they’ll bring in mammalian prey, but probably 99.99 percent of their prey are fish or things like fish.
Okay, here’s a real general question: When do osprey chicks fledge?
About eight weeks. I think this nest is… 55 to 60 days is the range for which the ospreys at Hog Island have made their first flight.
How well can ospreys see at night?
We’ve pretty much covered that. We know they can and in some cases they can even see well enough to catch fish at night.
What’s the bald spot on Bailey’s breast?
I haven’t seen it very closely, but that sometimes involves some kind of a scar so Bailey may have somehow been cut on her breast. The feathers grow from follicles under the skin, so if Bailey got cut somehow—and it might have been in the owl attack, I don’t know whether that bald spot appeared before that— but she basically has some kind of scar on her skin and that’s messing up some of the feather follicles where those body feathers are coming out.
There was a famous Peregrine in Montreal that lived for about 19 years in an insurance company building and she had a similar sort of spot on her breast. You could tell it was her every year, because this was before color banding; but it was easy to tell that it was the same bird coming back because she had that same spot on her chest.
How do we tell the sex of the juvenile?
This bird was, it’s practically impossible to tell by plumage. We had these birds in our hands and by the time they’re this big their bodies are full-grown. All of their skeletons are full grown and right now all Bailey is doing is growing the feathers in, growing her wing and tail feathers in. So she’s as big as she’s ever going to be in terms of her skeletal system, and so one of the ways we can tell is when we band the birds we can see how thick their leg is. Females are bigger than males in ospreys, significantly so. There might be some overlap with a real big male and a real small female, there’s a little overlap, so we’re basing it on weight and the size of the bird’s leg when we had them in our hands.
Are ospreys that nest along rivers more prone to starvation events for nestlings than those that nest lakes, ponds, inlets, coastlines, etc.? As it happened with the Hellgate nest in Montana and others along the Clark Fork River, prolonged rainy weather made for difficult fishing conditions for several days and resulted in nest failure.
Hard to say, that seems like a logical conclusion. Most ospreys, even those nesting along rivers, will have some alternate fishing spots. The birds that are hunting along the coast are often hunting inland and not feeding as much offshore as we expect they might have been. So that’s hard to say but it’s likely to happen.
What does Steve do all day?
Mostly fish. When he’s not fishing, he’s probably just sitting on a perch preening and resting up for the next fishing bout. He’s got a lot of… well he doesn’t have so many fish to bring in now, but when he’s feeding three or four young that’s a lot of work, and we know males do most of the fishing. This is an unusual nest in the amount of fish that Rachel catches. This is partly why they’re more successful and these birds, when they’ve lost young, it’s been due to circumstances beyond their control. [For] most young ospreys that don’t make it, it’s because the parents aren’t bringing in enough food, and there are some nests where females do almost no hunting at all and there are others where the females do a lot of hunting. One of my graduate students studied nestling mortality and she was looking at sibling aggression and how that related to the success of nests, and one of the things she observed in her study was that the nests where females hunted were more successful than the nests where the males did all of the hunting.
Why doesn’t Bailey practice flapping and hopping like juvenile eagles do?
She’s just not at that stage yet. That’ll happen pretty soon.
Here’s a question from one of the volunteers for our Martha’s Vineyard osprey surveys who was assigned to watch a pole with a nest and for the past two years they have made their nest bigger and bigger but they have no offspring. “I’ve seen the male bring fish to the nest for the female. Is it possible the nest is too deep for the offspring to thrive, I can’t see into it?”
No, that wouldn’t happen. As the nest keeps getting built up, they can get taller and taller especially for birds that have, where the male is really, I call them “Home Depot Birds” and some males really seem to like to bring nest material in. And there are some nests where the males are sort of like me, they’ll bring about three sticks in and say, “okay, honey, the nest is ready!” So the nest in question here is clearly one where we’ve got a male and probably a female too who are bringing a lot of nest material. But just the way you can see the nest here at Hog Island, they keep bringing in nest material, and right now they’re at the stage where we say they’re putting the baby gate up and if the young are beginning to wander around the nest it seems the adults will build up a rim of sticks around the nest. We’ve even seen the young ospreys in the nest will actually trim their own nest and that’s something that we never knew happened until the advent of nest cams. So what will happen next here in this nest is that once Bailey gets big enough, and really she’s at that stage now, the adults will stop bringing so many sticks and they’ll keep bringing in seaweed and moss and so the bowl of the nest will fill up and by the time Bailey’s about to fledge the nest will be pretty much flat straight across so the next year when they build the rim of sticks up the whole nest keeps building, it doesn’t get deeper and deeper.
When the young birds learn to fly, will they return to the nest for a period of time until they find a place of their own and will they stay in touch with their parents for a time?
What will happen when Bailey starts flying is that she will go out and wander around her home range and to explore the world, begin to try to catch fish. Typically they’re starting to try to catch fish after about a week to ten days, and typically they’re not very good at it at first. So the parents will keep feeding them. The young will keep coming back to the nest—I like to say it’s sort of like the fridge for teenage ospreys, they keep coming back to the nest. In areas where there are a lot of osprey young, young from different nests will often just hang out, stop in and visit other nests.
So the young keep coming back to the nest, the male keeps bringing food, the female will feed them for a while. Then she’ll take off for South America and the male will sort of be on duty. Typically the males leave in the first two weeks of September, and that’s about when the young leave as well, although sometimes the young will linger on well into the fall before they start migrating.
We had a young bird last year that we tagged in Newfoundland who got to Maine and stayed in Maine until November 7th or 8th I think before he finally started migrating. And I had a bird from Martha’s Vineyard who wandered all the way from Martha’s Vineyard to Lake Superior and stayed there until November 15th when she finally decided it was time to migrate. By the time she started to migrate, her parents had probably been at their home territories or winter territories for about two or three months. So they’ll only stay in touch with their parents in terms of hanging out at the nest to get fed. It’s really like the young…
<Technical issues interrupt feed>
Okay, so we were talking about young staying in touch with their parents at the nest. They hang around the nest until they’re really ready to hunt on their own. Dad will leave early September.
Can ospreys see in color?
Most birds do. We can tell that because birds have colorful feathers and if they couldn’t see in color they wouldn’t bother with colorful feathers. So almost certainly ospreys can see in color.
Why do the eyes of ospreys change color from orange to yellow? Is there an advantage to having yellow eyes as an adult?
That’s hard to say. It may be a kind of a signal, there may be some physiological change that takes place. That’s a question that I’m really going to wave the white flag on. I don’t have an answer for that and don’t know anybody who does, if anybody does. In some birds it may be a way for adults to identify young. We think that the reason young raptors have a different plumage from adults, is that it’s basically a free pass, like a hall pass as they’re moving through a territory. Adult raptors in the territory will see a juvenile and not see it as a real threat so they can let the young bird go through the territory. If they saw a bird going through their territory with full adult plumage then they’d know that that was a threat, someone they’d want to chase out of their territory. That doesn’t make sense as an excuse for a change in eye color because an osprey isn’t going to get close enough to a juvenile to have to use the orange eye color as a clue as to where that is a juvenile or an adult.
Why do osprey eggs have patterns?
It’s almost certainly camouflage, it’s the same reason that the young have the speckling on their body feathers as they grow in, it turns into real camouflage. When they’re lying down in the nest and the adult ospreys hear danger near the nest they’ll give an alarm call and the young will lie down. They really “play possum.” I think the term that seems to have been picked up on the chat group here is that the young “pancake” in the nest. I think that’s a term that’s been invented here, it’s a good one and it works, so when the young pancake in the nest, that speckling really does help camouflage them.
After catching a fish, why do ospreys orient the fish head first as they carry it back to the nest?
They do that because they’re taking advantage of the fish’s hydrodynamic design. The hydrodynamic design of the fish makes it easier for the fish to swim through water and that hydrodynamic advantage is similarly an aerodynamic advantage when the osprey is carrying a fish. So that is almost certainly instinctive behavior and not learned, although it could be learned; but it almost certainly is instinctive and it’s easy to watch when you see an osprey carrying a big fish out of the water, they’ll often when they pull it out of the water have it cross-wise and as they’re flying they will manipulate one foot to go in back of the other and get the fish so that it’s going head first. And you can almost watch the osprey sort of shoot forward as soon as they get the fish lined up right because the wind resistance is so much less.
Do adult osprey feathers age? Do they change in color as they get older?
Definitely, they bleach out. So ospreys need to molt every year, almost all of their body feathers every year; their wing and tail feathers need to be molted as well. It will take several years for an osprey to molt all of its wing and tail feathers; but it is, that process of changing and molting all of their wing and tail feathers is necessary, and it’s obvious when you look at an osprey that’s been… an adult osprey that is several years old you can see, it’s easy to recognize new feathers/newly grown in feathers because they’ll be dark chocolate, almost black, and the feathers that are sometimes two or three years old will be bleached out, very light brown. When you look at those old feathers you can really see why the osprey needs to molt. They just wear out in the sun, and every time the osprey moves it’s rubbing feathers against feathers so the feathers just wear out, they abrade. The tips of the feathers that the young birds have, the speckling…
<Technical issues interrupt feed>
Alright, we seem to be back again and we were talking about feathers molting. One of the reasons that ospreys and all birds preen their feathers is they have an oil gland at the base of their tail which they squeeze with their beaks and get oil on their beaks and then preen their feathers. That helps with waterproofing but it also helps lubricate the feathers, which are rubbing against each other, and that gives the feathers a bit of an extended lifetime.
Oh, and I was also talking about the young birds, when they have the scalloping or speckling on their back and shoulders—that wears out. The tips of those feathers just wear off due to abrasion, so that by November or December, you couldn’t tell that it was a juvenile based on the speckling that we see in the young birds.
Are there variations in size and coloration among ospreys of North America and Europe?
Yes. There are four subspecies of ospreys—one in Australia… some people believe that’s a separate species, it hasn’t been completely confirmed yet, so we’ll just call it a separate subspecies, there’s the European, there’s the North American and then there’s a subspecies down in the Caribbean which is a non-migratory one. So the two largest subspecies are the North American migratory subspecies and the European. The European and the North American birds are about the same size. The European birds tend to be quite a bit darker, the chest band on females if you’ve watched any of the nest cams for over in Europe, you’ll see that they are typically have darker heads and the females are really dark across the chest band, much more than our North American birds.
Why didn’t I add a strip of white birch bark to the nest this year? I’m thinking that might sort of serve as a landing beacon in pale moonlight. Obviously this is my effort to reason why Rachel has such a difficult time landing in the nest in the darkness. Any thoughts?
The white birch bark was just a… that goes back a few years where the adults brought in a white birch bark as a nest trimming and one year I put a piece of white birch bark in but it was just as a joke because people had fun watching the birds with the white birch bark the year before. There is nothing to that, there’s no advantage to that and so I didn’t do it just because it wasn’t appropriate.
When will Rachel quit feeding Bailey in order to force her to fledge?
That’s not how it works. Rachel and Steve will continue to feed Bailey. They don’t do anything that forces Bailey to fledge. Bailey will fledge because Bailey develops the ability to fly and Bailey’s instincts will drive Bailey to start to fly and explore the world around her and she’ll start to go down and drag her feet in the water, she’ll… sometimes young birds do belly-flops in the water. It’s a bit funny to watch them as they’re first exploring. But there’s no teaching involved as far as anyone can tell, and we always… in science, we always look for the simplest, the most parsimonious explanation for any behavior. And ospreys, young ospreys that go off—they typically do not stay with their parents. When they go off to hunt and practice, they’re doing so on their own, they don’t maintain contact with the young, they’re not following their parents they’re not watching what the parents do when the parents hunt. There have been some studies looking at how osprey… how fast ospreys learn to fish and for some reason it seems that ospreys, young ospreys will sometimes stick in contact with each other and it seems that those ospreys tend to get better at fishing a little faster than the young ospreys that are fishing on their own. That observation has been thrown out there without a real explanation for why it’s happening. So Rachel will keep feeding Bailey as long as she’s around.
<Technical issues interrupt feed>
Alright, we seem to be back again, so where we were talking about fledging, the adults will just stop feeding; well Rachel will leave, and so in that sense she stops feeding but by that point Bailey should have fledged.
Will the vocalizations… do the vocalizations osprey make when the great horned owl is present do anything to actually deter the owl or any other predator for that matter?
The answer to that would be “no.” The great horned owl that’s intent on taking an osprey out of a nest is not going to pay any attention to the osprey vocalizing.
So I’ll talk a little more about vocalization. Regular nest watchers know they can often tell what is going on at the nest simply by listening. How is that different or similar to what an osprey’s mate hears? Well it’s not different at all, just the way we can tell by watching. You can hear Rachel will give a certain call when she sees another osprey invading her territory—she gives one sort of a vocalization, and she’ll give a very different vocalization when she sees Steve coming in with a fish. So with a little bit of experience watching the nest cam, you’ll be able to tell what’s going on. And Steve, he knows as well when he hears her give the alarm call—if he’s nearby and he can’t have seen the danger that’s coming, that will alert him that it’s time to pay attention and look for an intruding osprey or even an eagle. When I was up at the raptor camp this summer, we had a spectacular sight of Rachel chasing a young bald eagle out of the territory. Steve, rather, did it. At one point he actually hit the eagle on its back and when the eagle was hit by Steve it just took off and flew across to the mainland (or “America” as I call it when I’m up there) in a big hurry. So the males know the same things we know; but they know it instinctively, we know it because we learn it by watching the nest cams so much.
Is there a correlation between excessive preening and fledging in an osprey chick?
The amount of preening seems to intensify when they get close to fledging. Probably they’ve got more feathers, the feathers are longer and as they’re growing in there is a lot of… the sheathes at the base of the growing feathers are flaking off, so it’s just the way that the birds are taking care of their feathers, so it’s not surprising to see a lot more preening as the birds are getting close to fledging.
Sibling rivalry leading to death has been observed this year on more than one nest. I find it one of the most difficult things to watch and avoid doing so when warned. Can you shed any more insight or logic to this subject, anything that might make it seem more acceptable, for lack of a better word, to lead to more understanding?
This is indeed a difficult subject and can be really hard to watch. There was a… there have been some gruesome examples, not so much at this nest but at some of the other nests. So what’s going on there is very typical osprey behavior. Ospreys almost always lay three eggs, and as we’ve said before they really only average a little over one young per nest, so what’s happening… and add to that they lay three eggs and typically they start incubating on the second egg, so there’s a bit of an age gap between the second young… the first two that hatch and the third. And this difference can be quite a bit if they take a while before they lay the third egg. So that sets up a hierarchy in the nest, with the smaller young being at a disadvantage when it comes time to eating food/getting food from the parents. The parents will feed the young that’s most aggressive and most in their face, so those are the strongest, and the first hatched young are almost always first in line to get fed.
So what’s going on, if there’s enough food to go around for all three young, the third young will eventually get enough food and will catch up eventually to its older and bigger nestmates, and all three young will fledge. But if there is not enough… for all three young to fledge, let’s say there’s—let’s use the numbers. Let’s say there’s only enough food to raise two young, just because the fishing’s bad for some reason, the weather’s bad, the herring didn’t show up, for whatever reason the fishing isn’t very good this season. There’s only enough food coming in for two young. So if the three young were all hatched at the same age and they didn’t set up the hierarchy… behaviorally, the older young will often peck at the smaller young and set up a behavioral dominance hierarchy, which adds to their physical ability to get food because they’re bigger. So one, this hierarchy is set up if there’s enough food for two young coming into the nest… and only enough for two, then that third young will starve and two young will fledge. So if the three young were equally good at getting food from their parents, they’re all the same size and there was no dominance hierarchy set up, enough food for two young would be divided between three young and none of them would make it.
So you can think of the third egg really as an insurance policy. In case times are really good, we’ve got that third egg and we can raise that young, but if the fishing isn’t so good then one of the young is going to die. Or maybe there’s only enough food for one young in a really bad year. So think of it as an insurance policy, it’s natural behavior in young. I had a graduate student that studied sibling aggression in ospreys to see how it affected their survivorship rates. So, it’s gruesome to watch, but it’s nature’s way, if you will, and it’s how ospreys have evolved and have been raising their young for millions of years. I often hear people say that nature is cruel, and especially in circumstances like where you see one young pecking another to death that certainly does seem cruel, but this is a point that I make as often as I can in these circumstances, that nature isn’t cruel. Nature is harsh. Being cruel implies that you’re doing something to harm an individual just for the fun of it, just for harm’s sake or doing evil for evil’s sake. That’s not what’s going on here. Nature is harsh, it’s very unforgiving, it’s very often random, as we’ve seen when owls come in and snatch… when owls or eagles came in and snatched the young out of the nest. Natural selection has nothing to do with that, that was just the pure bad luck of the draw which young gets taken out of the nest. So nature is harsh, it’s unforgiving, it’s random; but it’s not cruel. So that’s the message that I preach as often as I can and it comes up when this issue of the pecking order and watching young birds starve to death is seen in the nest. So that’s just nature’s way and that’s the way it works and that’s sort of why we still have osprey.
Is there an optimum range of wind speeds for osprey chicks to begin their helicoptering and eventual fledging?
Probably. I don’t know, I couldn’t put a number on it. They certainly like to helicopter when there’s a little bit of a breeze, but they don’t like to helicopter when there’s a lot of a breeze. And I think probably some young ospreys’ first flights are accidental, when they’re up helicoptering and there’s a gust of wind hits them and may blow them off the nest so when they come down they’re not over the nest any more, so all of a sudden they’re flying. I’ve watched a lot of ospreys make their first flight and they look really good when they’re flying—on their first flight, looks like they’ve been doing it forever—but then you see them make their first landing and you realize, “Oh, that’s the hard part!” So no real optimum speed… oh, there is some optimum speed, but only the ospreys know exactly what that is.
Are there any stats that show an osprey nest success rate when the female is ten years and younger as opposed to more experienced females 11 years and older?
Yes. Alan Poole has good data on this. He’s been studying ospreys forever, even longer than I, and so he’s done a lot of work looking at success rates and probably around 10-12, 9, 10, 11, 12 – is the sort of peak productivity. When adult females are getting up into their mid-teens, productivity tends to drop a little bit. Ospreys can breed into their 20s. The record for an osprey breeding is a female in Scotland that bred until she was 27 years old and fledged 50 young over the course of her life span. And I think she went through six or seven males during the course of that time span. So yes, there is a peak time for productivity and it’s about 10-12, 13 years. And ospreys, as we’ve seen—the boathouse pair is probably an example of a young pair that probably doesn’t have their act together, and it may take a new pair of ospreys two or three years to get it all straightened out and start cranking out young.
Are the bees and wasps in the nest a threat to the nest?
I’ve never seen this before. There is certainly no shortage of drama at the Hog Island osprey nest over the past three or four years. The bees and wasps are a new twist to the story. In theory they could be; but things seem to be progressing okay now. Again, this is something that we’ll just watch, and I think it’ll sort itself out. But again, I don’t think this is something that anyone’s witnessed before so we’re going to just have to see what happens.
How is Rachel able to stay rested during her nightly vigilance? How much sleep does she need?
Birds don’t need a lot of sleep, and they can actually sleep one side of their brain while the other is attentive/awake, which is a pretty cool thing. This has actually been documented… swallows or swifts over in Europe will stay on the wing for months and through the night, and it’s been shown that… the part of the brain that’s attached to the side of the eye that’s on the outside of the circle is the part that stays awake and they can sleep the half of the brain that’s on the inside. You’ll often see Rachel will be sitting on the perch—I know you’ve all seen her shut her eyes—and so she will sleep, she catches cat-naps, she doesn’t need to sleep a long time… When they fly at night, some of our birds migrating at night… we’ve had one young osprey from Newfoundland last year that migrated for 83 hours nonstop. So they can stay awake for a long time and it’s probably [that] they’re sleeping one side of the brain and resting the other.
Considering the steady increase of raptors following the ban of DDT, how do you think the ospreys will manage when there are more and more avian predators? In Southern areas ospreys have banded together to help protect their young. With the ospreys in the Northern part of the country spread considerably thinner, do you think the ospreys will be able to continue to maintain a healthy population?
This is a good observation. In southern New England in some areas, especially around the mouth of the Connecticut River where… and the Westport River in southeastern Massachusetts… where you can stand in one place and see 30 or 40 osprey nests. And those ospreys sort of form an Air Force, and a bald eagle doesn’t have a chance of getting close to those nests. So there is some safety in numbers, and that may be one of the reasons that ospreys tend to form these colonies. There’s an area down in Florida called Blue Cypress Lake where there are 300 pairs of ospreys around one lake. If you get a chance to go visit that you definitely should, it’s a natural phenomenon in the world of ospreys. So they do get some defense from being in close proximity. It’s reasonable to hope that if the boathouse pair gets going and we have four adult ospreys around, that that will make it a tougher place for bald eagles to come in and invade the air space. But in general, bald eagles have not come back as quickly as ospreys, so now they’re coming back in big numbers, so the only areas where we see osprey numbers not going up, or even going down a bit, are in the areas where bald eagle numbers are going way up. So it may be that post-DDT, because ospreys have a shorter generation span—they can start breeding when they’re three or four years old and bald eagles will not get going until they’re four, five or six years old, so the ospreys recovered sooner… they could move into all this territory that was vacated by both bald eagles and ospreys due to DDT, so they were sort of first on the scene and their numbers have grown substantially. There are more ospreys now than there were pre-DDT. So what’s happening now is the bald eagles are beginning to catch up, so there are areas where the osprey numbers are going to go down from the highs that we’re seeing now. But they’ll sort it out. Ospreys and bald eagles have co-existed for millions of years, they’ll sort it out. There will be more ospreys in some areas and fewer in others as the bald eagle numbers increase; but certainly there’s going to be a healthy equilibrium and ospreys in general are not at risk because of the changes in other predator population sizes.
I’ve noticed that ospreys choose to nest out in the open when they choose their own nesting sites, not platforms, whereas eagles choose trees. Is the ospreys choice of a nesting site due to the way ospreys learn to fly with their helicoptering and taking the final leap of faith versus the eagles who do their helicoptering, branching and then fledge?
Not really. I think the big difference, and the reason that ospreys really like to have that nest out in the open, is more because they have really long wings and they’re not very maneuverable. So they want to have—and it really doesn’t have anything to do with the young doing their wing flapping and the way they fledge—it’s really about the adult ospreys being able to come into the nest and land into the wind from any direction. As we all know, no pilot wants to land… wants a downwind landing. That’s why airports have several runways, so that pilots can always have a somewhat upwind landing. Well ospreys are the same way, and when they come in to the nest they want to be able to fly into the wind so they can sort of parachute in with their heavy fish and not try to come in too fast with a downwind landing. So a nest that’s out in the open with nothing around it provides that opportunity to land from any direction, and that’s really why ospreys nest out in the open. It also gives them some protection. The more out in the open they are the more they like it—there’s no place that ospreys like to nest more than a tree or a nest platform that’s out over open water. That gives them the added benefit of no ground predators like raccoons being able to get to the nest.
After the birds have been banded and then fledged, under what circumstances will you hear where they are? Have you heard anything about any of them?
Well in the case of these birds, we will know only if somebody—in the case of Bailey, since Bailey doesn’t have a color band, we’ll only know about Bailey if Bailey happens to be discovered someplace and the band reported. If that happens it almost always means that Bailey is dead for some reason. Very rarely do band returns come in from birds that are caught and released, although it happens every once in a while. A few times when I’ve been trapping an osprey nest to put satellite-tracking devices on birds, I will catch a female or a male who’s already been banded; I’ve caught some birds who were 19 and 20 years old. So for those I just write down the number and we report that number to the Fish & Wildlife Service and we find out where those birds came from. So it could happen. Much more likely with the color banding—I have a whole folder in my email inbox of emails I’ve gotten from people who have taken pictures of ospreys with color bands. So there’s a good chance that the birds we color banded last year, we may hear from them. And of course the way that we definitely hear about birds are the ones that I’ve put satellite radios on. And those we hear about, we hear from every day. Basically we’ll only hear from Bailey if it’s bad news. The color banded birds from last year and next year we’ll sort out the logistics and we’ll be sure to have enough equipment to color band the birds next year—for those birds we’re likely to get reports from people who’ve seen the birds and taken pictures of them. So that’s that.
Do ospreys ever lay a second egg batch if all chicks die before a certain age?
Probably not at the stage when chicks are… after hatching, I would be really surprised. We do have some nests on Martha’s Vineyard where they are really late, and I think those are almost certainly replacement clutches; but it’s probably from clutches and eggs that were lost early in the season. I think if the ospreys get to the stage where the eggs hatch, I think that’s just going to be too late for them to recycle and lay again. But it does happen when eggs are lost early in the season.
And, amazingly enough, our last question! Are all the male raptors smaller than their female partners?
For most species the answer is yes, but there are some species where you can have a big male that’s larger than a very small female. Ospreys, I think, might see some overlap. Most of the raptors that eat other birds, like peregrine falcons, Cooper’s hawks and sharp shinned hawks there’s no overlap at all. There’s a really big difference. The male falcons tend to be a third smaller than the females. So most birds of prey the males are smaller, in some cases are a lot smaller; in some species there is very little difference and in some you could have some overlap.
So that’s all the questions! It’s the first time I’ve made it through all of them. It went a little long. Everybody seems to have hung with us there. That was a great set of questions. We’ll keep watching this nest and keep our talons crossed that Bailey survives to fledging and that wing heals up. I’ve tagged another at a nest down in Washington, DC, on the Anacostia River… just about three days ago I tagged a young osprey, so if you go to the ospreytrax.com website and if you follow the links you can follow that osprey, named Layla. We’ve got some young… we’ve got an adult osprey up in Newfoundland, a female with a radio, she has two young that are probably four weeks behind the nest here. I’m going to be satellite tagging some birds up there. So if you go to my website you can get onto those other nest cams and see what’s happening. The bird down in Anacostia has already fledged. They come and go, and we were watching her eat all day today.
So it’s been a great set of questions as usual. I’m sure we’ll chat some more on the website and we’ll see you sometime soon for another live Q&A session. Thanks a lot!