Thursday, March 31, 2005


I'm posting these again up here, since John's answers have come in. They are below.

Dear Marie,

...Not only am I monitoring Pale Male and Lola's nest, I'm also "incubating" three eggs (as of this writing) with the peregrine falcons in Harrisburg PA. The various web cam views of the Harrisburg raptors include an up close view inside the nest box. Comparing peregrine nesting activity with that of PM/Lola, I noticed that the female peregrine (hen?) often leaves the eggs and nest unattended for periods of time, and the tiercel does not sit on the nest when she leaves. I noticed this behavior after the first egg was laid, and it has remained unchanged with the arrival of each additional egg. This behavior is the complete opposite of that of PM and Lola.

I have a few questions regarding eggs and incubation that I hope either you or John can answer on your web site:
1) The peregrine eggs appear to be colored a reddish hue with dark speckles; what color is a RTH egg?
2) The daily observations always include egg rotation by PM and/or Lola. I have not observed the peregrines doing the same with their eggs. How does egg rotation benefit the embryo?
3) Are RTH's the only bird where the male shares incubation duties?

Thanks again for your courtesy, and for sharing your wonderful web site with the world.

Best regards,
Marilyn Fifer



I appreciate Marilyn Fifer’s questions, as they match red-tails to peregrines, always an interesting comparison between two species that are very different but still diurnal raptors. A synoptic (broadly encompassing) view of raptors is best. One can easily concentrate on only a single species (as I tend to do with my beloved red-tails) and fail to see and understand much wider hawk phenomena.

The colors of peregrine and red-tail eggs? I've never seen a live peregrine egg, so I'd have to look that one up. Marilyn’s description is accurate, I'm sure. Red-tail eggs tend to be of a light brown background color, with darker thin blotches or spatterings of darker brown. But this can vary from almost unmarked, to very blotchy. I'm not sure of the causative variables here. I think overall egg colors can vary geographically, perhaps as a result of different foods.

Egg rotation is very important. As the embryo develops, it is supported in the egg by a number of loose, film-like membranes. If the egg is allowed to develop unturned, these membranes can grow together or fuse, distorting and eventually killing the embryo. We do something of the same thing while sleeping. Even in deep sleep we turn over every few minutes. We don't have membranes that will stick together, but you get the idea. If you're a hawk, it’s just helpful to have the force of gravity come from various angles while still in the egg. It evens things out. The peregrine should begin to rotate the eggs.

Virtually all raptor males share incubating duties. Red-tails aren't unique in this behavioral trait. The mother needs to get up and eat, and especially to defecate (to “slice,” as the falconers say about hawk defecation; falcons “mute.”), so the male often takes his minor turn and sits for a while. He'd rather be out hunting, but he does his duty. It’s sort of like a new human father. We try to change the diapers and tuck the little one into bed, but for human dads, not much of this is instinctive. For mothers, it comes naturally. Same for the hawks. I'll never forget watching the female in my red-tail breeding trials ceremoniously settle down on her eggs. Nothing arbitrary or awkward at all. But for the male, when giving the hen her moments of relief, his incubation was just a bit contrived. He did his duty, but not always with any developed parental ease. As a male myself, I understood.

Here’s one very interesting observation, alluded to by Marilyn with her mother peregrine. She noted that the peregrine female occasionally left the eggs exposed for some length of time.. This apparent neglect has been frequently noted in many raptors, and no one knows for sure what’s happening. Here’s the best explanation, albeit a bit conjectural. We've watched red-tails leave eggs exposed for up to 20 minutes or so in cool March or April air. There is no doubt that the eggs have cooled significantly in this period of time. Doesn't this, then, kill or retard the developing embryo?

Here’s what we think may be happening (and how the parent can discern this is a mystery). If you remember back to first year chemistry, you will recall that the solubility of gases in water increases as water temperature decreases. It’s possible that it may be helpful for a warm egg to cool down once every day or so, allowing increased oxygen to diffuse across the porous egg shell into the egg fluids. This cooling period may actually be a way of restoring ample dissolved oxygen levels in the egg fluids and embryonic blood system of the developing hawk. This periodic cooling may be required to bring sufficient oxygen into the egg. An egg that stays persistently at body temperature may run out of oxygen. But by allowing a brief period of cooling, oxygen crosses the porous egg shell, recharging egg fluids. That’s the best explanation I've encountered for this parental inattention to incubation duty.

But there is one other form of inattentive incubation. Often, the female will fail to sit closely on the eggs until the very last one is laid. We know that newly laid eggs can be taken from the nest and held safely at refrigerator temperatures for some time. By leaving the first eggs cold in the nest, incubation can begin at essentially the same time for all eggs. If there is a three or four day difference between the first and last eggs laid, and if the first egg got solid incubation from the start, the unfortunate last egg would hatch to find it’s older siblings much larger and more competitive for food. This occurs in many species, but seems to be minimized in red-tails. This is why the red-tail female sits rather high over the eggs until she has laid her last egg. She then sinks low into the nest and begins a fair, equal-start incubation for all of her future eyasses.


John A. Blakeman


John Blakeman writes that he and his wife finally had a chance to see a video of Frederic Lilien's PALE MALE. Here are some comments about what he saw in the film:

... I have to comment on two specific scenes. First was the somewhat disconcerting footage of the newly-fledged eyass hanging forlornly upside down in the tree. Just as the camera panned toward this spectacle, I told my wife that the bird is going to be hanging precariously upside down. And it was. Classic first flight complications. Few people ever get to see this. Those in Central Park did, and just as it usually does in wild rural areas, the birds quickly learn how to land and take off in trees. For a day or so, these simple actions are not so simple.

The other scene was the quick plunge of Pale Male into the foliage of a tree to snag a perched pigeon. This is what I really wanted to see. You know that I've always had questions about the hunting techniques of the CP red-tails. What I saw in this one or two seconds of a red-tail hunt was revelatory. Falconers who fly red-tails would recognize this hunt instantly. It was a classic wing-over brush crash. The hawk flies not high over an area with prey. When prey is spotted, the hawk instantly folds its wings over and inverts itself. All of its forward momentum is instantly directed downward. In the plunge it folds its wings and crashes through the vegetation at an exceptional speed. I've watched my falconry birds do this many times, and each time it is breathtaking. The red-tail can drop 50 to 100 ft. straight down with folded wings right to the ground, hitting the earth at what must be 50-70 mph. When this is first observed, the hawk's instant death seems inevitable. A striking low thud is heard as the bird's plunge is instantly stopped by the earth. The bird is presumed dead.

But in fact, red-tails are adapted to this earth-crashing mode of hunting. In a fraction of a second before striking the ground, the bird extends its very long legs out in front of its head, and its leg musculature is perfectly adapted to cushion the collision with the ground. It is a remarkable event to watch, and only falconers have seen it frequently up close. I am still awed every time I see it, after 30 years or so.

This was Pale Male's method of plucking the pigeon, who thought it was safe within the confines of the tree's vegetation. The pigeon was betrayed by its inadequate instincts. A peregrine will never plunge into tree branches, as this smaller raptor can be hurt thereby. The big, muscular red-tail, however, has a propensity to brush-crash, when food conveniently presents itself. The pigeon had no genetic prompt regarding its perched vulnerability to our marauding red-tail. Any pigeon that elects to perch in a tree, thinking it's thereby safe from raptors (as it would be in its ancestral native homeland of the rocky Middle East and Central Asia), is likely to lethally contribute its proteins to our hawks. That single one or two seconds of the Pale Male DVD explained, to me anyway, how pigeons can be captured by the red-tail, a raptor that nowhere else is noted for pigeon hunting.

A great program. So good to see and hear the actual people and live hawks of your wonderful book.


John A. Blakeman

Tuesday, March 29, 2005



Wondering if you could ask your friend John Blakeman if he knows of any way to identify individual kestrels. We have a pair that has moved into the nestbox we installed, and we're watching anxiously via the nestbox cam (and hundreds of people are watching on the Internet) to see how many eggs she lays (3 so far) and how many chicks hatch, etc. But we've begun will we know if they come back next year, if this is the same pair, or a different one? I'm *terrible* at individual bird identification, even for large raptors (I'm much better at large mammalian predators, like wolves) do these small falcons have any unique *individual* markings that we could observe?

Here's a quick pic of our two...quite the couple, don't you think? I'm sitting her watching her sleeping soundly right now :) It's actually more entertaining than any "entertainment" on television!

Stephen H. Watson

Here's Blakeman's helpful response:


As it happens, I worked with probably a dozen or so American kestrels along with my red-tails in my undergraduate research on raptor caloric requirements at varying temps. I know the species well.

Each bird will be different, with unique feather patterns on the head and chest. Detailed close-up pictures of these can reveal individual IDs. But even as an experienced expert, this gets too far beyond tedious . Occasionally a bird will have a feather or two that is quickly diagnostic, but in most cases it's going to be lengthy periods of time comparing jpeg after jpeg. I don't recommend it. It's frustrating and ultimately confusing.

The far better approach --one that can really work -- is to get the eyasses banded. Check with the California wildlife authority, or a local US Fish and Wildlife Service office and ask for a raptor bander. Tell them the unique situation you have. Banding of eyass kestrels causes no problems. The adults are back feeding the young just about as soon as the bander closes the door on the nestbox. An ornithologist at any of the local universities should know of a bander.

You might ask the bander to apply colored bands, for easier ID. This may not be authorized by USFWS, as they prefer to do this only with important research birds but give it a try).

As always, I'm very interested in what the adults are feeding the eyasses. I have no idea what Pasadena kestrels feed their young. I presume insects are a notable fraction of the prey, but what mammals are being fed? I don't think you have the common vole (Microtus spp.) there. I may be wrong.

Keep me posted.


John A. Blakeman

PS: In the next communication, Watson informed Blakeman that the kestrels seemed to be eating mainly lizards.




Like others, I appreciate your posting of the kestrel notes. The species was the first raptor to invade and abide in urban areas, in the 19th century with the construction of taller buildings.

I don't think we want this website to stray too far from Central Park's red-tails, a central story theme of your wonderful webpage. But because American kestrels (formerly called "sparrow hawks") can be so commonly encountered in every city of any size, their appearance here only adds to the urban hawk story. These delightful little falcons are full of spunk and inhabit cities without inhibition.
Urban hawk watchers should be aware (as many certainly are) of this engaging species. It was the first raptor I worked with, and I shall never forget its wonderful personality. These little falcons always act like they are the size of gyrfalcons, uninhibited by hardly anything they encounter in the city.

In rural areas, they share one trait with the red-tail that keeps them from being held in universal high regard -- they are merely common. Personally, I don't let commonality restrict my respect and esteem for either species. Some folks think they have to go to the Arctic to see a wild gyrfalcon, or to Africa to see a hawk-eagle of some sort to be "significant." For me, the kestrel and red-tail are quite sufficient. As visitors here can see, there is still much to be learned about these common species, and always much to be thrilled by. I'll leave the gyrs and African raptors to others. My spirits rise when I see a rural kestrel or red-tail -- and even more so at the sight of one in the city.

[And may I help everyone get the pronunciation of "gyrfalcon" right? I know, it looks like it should be "GIRE-falcon." But like so much else dealing with raptors used in early falconry, the bird's name derives from some antiquated terms from a former time in the development of English. The proper modern pronunciation is "JERR-falcon," spelling notwithstanding. And technically, a male gyrfalcon is called the jerkin, pronounced as spelled.

I hope this helps someone new to all of this. I embarrassed myself royally before some professors as a freshmen when I made some revelatory comment in class about a "gire-falcon." Oh, well.]


John A. Blakeman

Sunday, March 27, 2005

Kestrels and the Bigger Mom

Sunday, March 27, 2005



Steve Watson, the Pasadena GHO guy, is also involved with a pair of kestrels that have settled into a box near his house. He comments below on the raptor sexual dimorphism conundrum, based on the fact that kestrels are much, much smaller than redtails.:

"As an aside to the size discrepancy, I read up on kestrels...they are sexually dimorphic in size, but by a much smaller amount...female is only 10% larger than the male. I wonder if there is a relationship between absolute body size and dimorphic difference (smaller raptors are less sexually dimorphic than larger ones)? Hmmmm...if so, I'd have to think about why that might be the case...."