Blakeman on Brown-tails and Sex Hormones

The stick killing Brown-tail flies perpendicularly.

After reading yesterday's post about the stick killing yearling Red-tail, John Blakeman sent in his thoughts.--

Donna,

Actually, I think the immature's attacking of a stick is a combination of -- a season's confusion of -- normal hunting behaviors and the effects of lengthening days on breeding behaviors. As with Pale Male in his first breeding attempt, first year birds are affected by spring sex hormones. So, with this bird, it's impelled to do something with a stick. Hormone-induced instinct prompts this, but there is no mate, no nest territory, or other more mature factors to shape this behavior into real nest building.

This bird is an immature, acting immaturely, much like a child playing house or building a shack out behind the barn. It's preparation for the more serious and adult breeding behaviors in years to come.

--John Blakeman

I'd wondered if the young Red-tails behavior might have been a response to a surge of Springtime hormones. He was having a strong urge that was compelling the adolescent to do something but he just couldn't figure out just yet what it might be. John came up with an excellent deduction which makes perfect sense. The use of large sticks to practice hunting behavior in the youngest Red-tails just might be becoming confused with the use of smaller sticks to build nests by mature. Both activities start with sticks after all. And as John suggests, without all the other cues, the poor guy just didn't have the whole thing nailed down yet and reverted to "baby" behavior.

I've also always thought that as all Red-tails don't do things exactly alike that their "wiring" isn't as specific as some birds. Therefore more trial and error behavior must be undertaken to solve what feels right to satisfy the urge of the moment. That way, appropriate solutions can be found for a variety of situations and environments.

One of the things that made me think about hormone surges was the top photograph. The Brown-tail took off at break neck speed and then flipped to the perpendicular and flew quite a long way, sideways. Was he having an urge towards courtship flight? Or was he just so fired up with Spring that he was doing the Red-tail equivalent of a teenaged human with a sports car?

Donegal Browne

A Brown-tail Kill and John Blakeman on Finding Replacement Mates

A yearling Red-tail in Caumett Park has a bite of newly caught prey.

Even though we later learn these two raptors are in one of the Osprey's favorite trees at Caumett Park, the Ospreys obviously aren't back for the season as yet, or this pair of relaxed Red-tails, (note the lower bird has fanned out her red tail), just might have been a dispute waiting to happen. Microbiologist Linda Schiess and I decided to go check out Caumett Park, Sunday, without any optical help in the way of magnification if you can believe it, and the place was crawling with Red-tailed Hawks, flocks of Canada Geese, Red-winged Blackbirds, Robins, lesser groups of assorted other migratory birds plus, my favorite, an escape artist Kestrel in the Gift Shop.

3:13:41PM A Red-tail, whose tail is brown therefore a yearling, is perched near the paved path. All is well for photography as long as I stay on the path. The moment I step off she's gone. But as it turns out, not gone for long, as she's got a kill in mind.

3:15:55PM We've perhaps gone a half dozen yards past the tree the brown-tail was perched in, when towards our side of the mowed grass area coming from the other side, a Red-tail swoops by and pounces on prey in the leafy verge of the tree line.

3:16PM She stands gripping for a few moments.

3:17:00PM Then, BAM, BAM, she lifts up off the ground, prey in talons, and smashes something gray onto the ground repeatedly. BAM! She then flips whatever it is up in the air and grabs it again. BAM! BAM!

3:17:21PM She hops over and looks down.

3:17:31PM The prey flips into the air again, Brown-tail turns and takes a heroic stance, looking left. Has anyone noticed?

3:17:36PM Now she looks front.

3:17:49PM Brown-tail straddles the prey, then leaps into the air and comes down, talons extended. By this time, a small group of watchers has gathered.
3:17:54PM Leaning down, see today's top blog photo, she takes a bite of her prey. Gray prey takes to the air once again albeit stiffly and someone behind me says, "It's a squirrel. I have to leave. I have to leave!" Everyone leaves but Linda and I.

3:17:59PM Brown-tail mantles and watches them go.

3:18:11PM Oops, not dead yet. Get it! Get it!

3:18:16PM Wings up, talons raking.

3:18:20PM MINE!

3:18:26PM Is anyone looking?

3:18:31PM Bang! Smack! Dead yet? One talon is extended. Stab! Stab!

3:18:43PM Get it!

3:18:55PM She pounces. Leaves swirl up.

3:19:11PM She's up on her toes, she grabs, prey flies through air again.

3:19:17PM Finally!

3:19:44PM But a little more bamming can't hurt.

3:19:49PM Take that!

I make the mistake of stepping off the path, desperate for a better look.

3:20:17PM I take another step and off she goes. She hasn't anything in her talons. Her prey has been left behind. She'll be back.

What is the prey by the way? Is it a squirrel? We scurry over to check. Where is it? Linda says dryly, "I think it's that stick."

As you've no doubt seen from the zoomed photos all along, "the prey" is a heavy stout stick. Zoom being an advantage we didn't have at the time with our very long range view, sans binoculars. More fools we, the jokes on us.

It really was quite the display which went on for a good five minutes. I wonder how much longer it would have gone had I not stepped off the path? It did get me to thinking. Killing rocks and sticks is something we've seen very young Red-tails do. I'd no idea that a yearling would participate in imaginary killing at this late age. Strength training? It is a far heavier object than those chosen by just fledged eyasses. Or perhaps the bird I've been calling a she, is really a he, and he's hoping to impress a possible future mate with his strength, speed, prowess, and last but not least--creativity?

Never underestimate a Red-tail.

Speaking of unusual behavior, as I've previously posted, James O'Brian, http://yojimbot.blogspot.com/, saw Isolde of the Cathedral nest, do something he'd not seen her do before. She flew up very very high and then made a beeline into other Red-tail territory. James felt she might well be off to choose a new mate at the time. I felt that might well be the case as she had been being harrassed by other raptors, and mobbed by Crows Isolde needed some help to hold the territory and Red-tails do come up with new mates very quickly. So I emailed John Blakeman with some questions about how Red-tails might acquire new mates so quickly and forwarded along James O'Brian's sighting and theory. I also asked for his thoughts concerning Rob Jett's sighting of the interaction between the resident formel in the territory he watches and the confined female. Here's what Ohio Red-tail expert, Mr. Blakeman had to say---

Donna,

Yes, perchance, I did see the photos and story on the free-flying RT harassing the enclosed bird. The crucial, revelatory behavior here was the bowing of the wild bird. Red-tails have an interesting intraspecific (same species) threat display, contrasted to threat displays against other species.

To threaten a non-Red-tail, some other bird or animal, a resident bird will flare its hackles (head feathers), open its wings, and stand very erect. This warns any nearby species that the hawk means business and is about to attack if threatened. Eyasses do this when a human approaches them on a nest.

But these flared-wing displays are never used to warn nearby or intruding Red-tails. Instead, the offended resident hawk takes a perch and leans over and assumes a very horizontal posture, with the wings sometimes slightly flared a bit out to the side, and the head just a bit lower than the horizontal back of the bird.

I once had a Red-tail that was illegally taken from a nest as an eyass. It imprinted to the teenager who tried to raise it, before wildlife officers confiscated it. Because it was so severely imprinted to humans, it was given to me to use as a hawk in my education raptor education programs.

I could never figure out if the bird thought it was a human, or if I was a hawk. At any rate, especially in winter and early spring, when breeding hormones were flowing, Goldie (she was one of the local birds at the west end of Lake Erie with a peculiarly golden plumage) would bow right to the ground when I approached her enclosure. If I walked up to her, she would grab my foot or gloved hand. She never figured out why I didn't appropriately retreat when she so clearly displayed her displeasure of my encroaching upon her territory.

My falconry Red-tails, all taken in the fall migration, never display the low, bowing intraspecific threat displays. They know they are hawks and I'm something else.

Goldie, by the way, was the female in my captive breeding program, from whom I learned first-hand how Red-tails behave on the nest and with eggs and eyasses.

Now, just how do hawk widows or widowers attract, gain, or accept new mates, and how does this happen so quickly? The details of all of this will probably be an entire chapter in my Red-tail book -- a chapter I'll have to spend a great deal of time working out. In short, no one really knows exactly how new mate selection and acceptance really works. It's almost always very quick, often within days, or even hours, of the loss of a mate. Was the new mate, a "floater," hanging around at the periphery of the territory, awaiting a mating opportunity? Do floaters, unmated young adults, spend their winters and early springs flying a circuit between the edges of multiple occupied Red-tail territories, on the continual search for new "openings?"

The observation of the new widow skying up and off into the distance, perhaps thereby announcing her availability, is very intriguing. I've never seen this, but I don't get to see nesting Red-tails as continuously has they could be studied -- of all places -- in Manhattan. This is a very reasonable possibility.

There is so much we now know about this remarkable species. But for each new behavior we discern, there are a dozen other antecedents that remain unexplained

--John A. Blakeman


Indeed.

Donegal Browne

John Blakeman on Red-tail Hawk Nest-Site Selection

Pale Male and Lola Switch on the Nest

Yesterday I published an excerpt from a news article in which the opinion was expressed that urban Red-tails preferred nests on buildings. John Blakeman took exception to this and here is what he has to say.

Donna,

Someone in one of your postings stated that Red-tails prefer to construct their nests on buildings and ledges, compared to trees, which move around too much.

Not so. Even in the West, where there are many cliffs, Red-tails generally prefer to place their nests in trees (if any are large enough there). This is particularly true with the Red-tails in the East and Midwest, where cliff-nesting Red-tails are virtually unknown in the wild.

Our birds instinctively prefer to put their nests in trees. Their genetic behaviors have this strong preference. But when tree nests don't seem to be preferable to a Red-tail, as when they are harassed by crows in the trees in Central Park, they will, as Pale Male and the others did, head up above the trees and nest on building ledges, free from the avian and human racket down below.

Yes, I designed a Red-tail "Nest Nook" device that could be bolted to a building wall or placed on a building ledge. But I'm not certain that this would actually attract a new Red-tail. Great-horned Owls, Ospreys, and Peregrines can be rather easily enticed to nest on created new nest platforms. But Red-tails seem to want to put their nests where they so arbitrarily decide. Nest site selection for this species is another of its great mysteries.

For example, the photo by www.palemale.com of the new (still meager) nest at a New York school window ledge is interesting. Just why there? Certainly there weren't any appropriate trees in the neighborhood, free from human and avian disturbances. But why this particular ledge, compared to the many others that also could have been chosen?

There does seem to be some unknown magic about some nest sites. I've watched in passing (at 65 mph) a single tree in the middle of a small woodlot here that has had a Red-tail nest on and off for over 25 years. Different birds, at different times. But repeatedly, new birds have chosen this tree over the several hundred other similar trees in the woodlot. Why? I don't know. It's hard trying to think like a Red-tail.

--John Blakeman

I don't know if we can generalize about Red-tailed Hawks, particularly those rather creative adaptable urban ones. Watching the sites urban Red-tails choose has given me the feeling that there is a set of criteria, perhaps some wired in and some learned from experience, known to the birds for nest site selection. We'll all most likely agree that there are few if any perfect nest sites and it seems to me that a bonded pair uses their judgement as to which are the most important criteria for them and choose a site accordingly. After a year some pairs build elsewhere, as Momma and Papa seem to be doing, whereas others hang in for years as Pale Male has done.

How much does successful hatching have to do with the change? Hard to tell, as Pale Male and Lola have now stuck into the fourth season of a three season failure run. Momma and Papa were successful last season and moved sites anyway.

What is the criteria? They know and we don't. Is the tree nest overhanging the road of the Riverside pair the best tree to hold a nest in the area? Quite possibly in their opinion and they may be quite right, but it can't possibly be the best place from which to fledge eyasses. Is safe flight of eyasses, one of the nest site criteria? If so it seems lower on the list for the Riverside Park pair than other criteria.

Another problem with urban tree nests at least in Central Park, and at up at Morningside Park as well, is the vulnerability of these nests to Crows. Crows may well have been a good part of the reason that Pale Male and his mate decided to make the revolutionary adaptation to nest on a NYC building. Attempting to protect a tree nest from Crows is what sent Pale Male and First Love to rehabbers in the first place. Pale Male's next serious nesting attempt was from 927 Fifth Avenue.

As forests become more and more truncated in the U.S. many species of breeding birds have become far more vulnerable to Crow predation. Our woods now have too many edges, as does Central Park with it's mostly widely spaced trees. More edges allow the sharp eyed Crows the visibility to spy out nest locations. A pair of Red-tails can stave off a murder of Crows from a nest with a wall to their backs. I've seen Pale Male and Lola do, and I've also seen Lola and Tristan do it. It is much harder for them to do with a 360 degree field of battle over a tree nest. Therefore in my opinion does an urban Red-tail pair prefer tree nests or building nests given their druthers?

It all depends, I think, on the blended hierarchy of the nest site criteria for any given pair of Red-tailed Hawks. The variables are legion, and John's right, it's hard to think like a Red-tail. Only they know their particular criteria. Sometimes that criteria puts them on buildings and sometimes in trees and that's where their criteria choices has led them to be.

Donegal Browne

P.S. We must also take into account that at least anecdotally form Peregrines to Red-tails where they hatched themselves, on a building, a bridge, a tree, or a cliff colors their own choices for a nesting site.