Saturday, March 19, 2005

Water Consumption by Hawks

Do you have any idea how much water Savanna drinks per day?
Would that be comparable to a wild Red-tails water consumption?

And as I'm asking about what goes in one end, what
about the other? I rarely see these birds defecate so
have no idea of how many times a day this occurs.
Could you hazard a bsllpark figure?

Donna Browne


How much water does my falconry red-tail Savanna drink each day? In the cooler months, none. In summer, when it's in the high 80s she will drink several times a day. The provision of water to captive red-tails is a continuing matter of contention for falconers and raptor rehabilitators, both of whom keep red-tails in captivity. Falconers fly and hunt their birds. Raptor rehabilitators often keep disabled (wingless or flight-crippled) red-tails as so-called "program birds" that are used in educational programs on raptor conservation.

On one side of the issue are those who are certain that red-tails need to drink copiously each day. For them, water must be continuously available to the bird at all times of the day and year. These people are certain that red-tails would soon dehydrate from a lack of drinking water. They point out that Cooper's hawks and peregrine falcons are famous for taking daily baths (even in winter!) and drinking frequently. They presume that red-tails would do this, too, if given an opportunity.

On the other end of the scale (where I tend to lean), are those who note that red-tails only infrequently bathe in the wild, not every day as many accipiters and falcons do. It is also noted that red-tails successfully occupy territories in desert areas where there is no available water. In my area of northern Ohio, we have ample winter populations of red-tails that have no available drinking water often for several weeks during frozen winter periods. It is very clear that red-tails can live very successfully without available drinking water. They do this over large expanses of their continental range, both in arid regions and cold winter periods.

If you will remember back to chemical physiology classes, you will recall that all of the oxygen breathed in for aerobic respiration is used to take up de-energized hydrogens at the end of the Krebs cycle, which forms simple H-2-Os. The red-tail, like all other animals, is forming water with each breath. A good portion of the birds' metabolized lipids and proteins end up as respiratory water. So it's not just a matter of determining how often wild red-tails land on a stream-side rock and gulp down a mouthful of water. In 40 years of field observations of Ohio red-tails, I've never once seen one drinking or bathing in the wild. I'm sure they do, but it's infrequent.

The more cogent questions are how often and in what volumes do the birds defecate. Frankly, I've just never counted these events, but I'm guessing defecation occurs every hour or two. We falconers are aware that after the bird has gorged on a big kill, such as a rabbit or squirrel (a pigeon in Central Park), copious quantities of "hawk chalk," the white uric acid remnants of the prey's proteins will be propulsively excreted in eight to sixteen hours.

Hawk watchers might wish to adopt the ancient terminology of falconers on the matter. Falcons are unable to eject their feces with any great force. Falcons, then, are said to "mute," which means that they merely lift their tails and squirt the feces (properly called "mutes") not far. Hawks and eagles, however, have much stronger anal muscles and as most Central Park hawk watchers have noted, they are able to eject the feces (the mutes) some good horizontal distance. This powerful ejection is called "slicing." When defecating, a falcon mutes her mutes. A hawk slices hers.

The slicings of bald eagles can be downright dramatic. A few hours after a full crop of Lake Erie fish, I've watched a bald eagle slice a 6-ft strand of mutes across the marsh below. Quite impressive.

And while on the subject, here's something to watch for as the red-tail eyasses begin to stand on their feet in the second week. The little eyasses begin to respond to a developing genetic urge to defecate by backing their tails right to the edge of the nest where they can slice hygenically over the edge. Sadly, some eyasses are lethally too attentive in this and back themselves too close to the nest edge. Many an eyass has sliced itself literally over the edge, falling to oblivion on the forest floor below. Yes, take a deep breath and hold it firmly when you watch the eyasses start to take their first slices over the nest edge. One wrong thrust and they will fall out. Mutes happen, sometimes with disasterous ends.

This is not so likely, however, in the 927 nest, as the metal support structure extends around the nest proper on all sides. I think our elevated eyasses up there will be safe from the incidental hazards of learning to properly and safely slice over the nest edge.

Sorry for being so mute on these matters.


John A. Blakeman


BLAKEMAN ON NOMENCLATURE, HENS, ETC. [With a question for John from MW at the end]


The questions about the origin of “eyass” (or “eyas”) are useful.

I've used the modern spelling, eyass, one that I believe is most often used in modern falconry literature. Both spellings are acceptable.

A question was raised about why the little hawks shouldn't just be called hawk babies. They could be, and they are. But equestrians seldom refer to horse babies (colts), and dairy farmers don't call calves cow babies. These antiquated but useful distinctions of animal age and sex are utilitarian, not just complicating contrivances of arcane nomenclature.

Here are some more, as they refer to hawks. “Hawk” refers to a broad variety of diurnal (day active) raptors in the order Falconiformes, including both specific hawks and falcons. A peregrine falcon is a specific kind of hawk. All falcons are hawks, not all hawks are falcons.

The use of hawks, falcons, and eagles for the pursuit of prey is “falconry,” stemming surely from the original use of falcons in the sport. The techniques of training falcons to hunt in the presence of humans were subsequently used for a variety of hawks, goshawks in particular. Falconry involves all diurnal raptors used in the sport, not just falcons in particular.

Falconers divide themselves by the hawks they use. Those flying real falcons, such as the peregrine, are said to be “longwingers.” Falcons are said to be longwinged hawks. Falconers flying goshawks are properly called “austringers.” Austringers are falconers who fly goshawks in particular, and other accipiters such as the Cooper’s or sharp-shinned hawks in general. Those of us who fly red-tails are known as “broadwingers,” flying the broadwinged hawks generally in the genus Buteo. Also generally included are the social Harris’ hawks of the desert Southwest.

A female falcon is properly called the “falcon.” Falcon means the female of a member of the genus Falco. The male is called the “tiercel” (sometimes, “tercel”). All male hawks and falcons may be called tiercels. Only female falcons can be called, in reference to her sex, the “falcon.”

Therefore, Pale Male is a very fine tiercel, the term that runs in my mind when I think of him. Sadly, modern falconry has no elevating term for the females of non-falcon hawks. Lola is merely the “hen.” Personally, I find this a pejorative diminutive referring to a female chicken. For a chicken, “hen” is most appropriate. For a noble hawk, I find the term somewhat deprecating. But I fear we are stuck with it. Lola, sadly, is a “hen.” (Falconers need to convene a convention of literary types and come up with a much more romantic term for female hawks. English is a great language, but it has some holes. This one, in my mind, is a gaping one. Lola, a mere “hen?” I think not!)

I don't mean this to be any treatise on the terminology of falconry. But it would be well for Central Park hawk watchers to be at least familiar with some of these terms, as they succinctly connote important characteristics, the exact purpose of arcane terminology.

For example, my present red-tailed hawk Savanna, is a twice-intermewed passager. Falconers instantly know all of what that means. And since passagers are frequently seen in Central Park, hawk watchers there should know at least the term “passager.” There may be as many of five passagers in the park right now. A passage hawk is one that has fledged and is now out on its own, primarily in migration, in “passage” as the ancient falconers would say. I trapped Savanna in September, during the early migration season. Consequently, she shall remain a “passager” for the rest of her life, a reference to when she came into human care and protection. A hawk or falcon taken from the nest (just before fledging) remains an “eyass” for it’s entire life, again referring to its age when taken from the wild.

A hawk is “intermewed” when it completes a molt in captivity. My bird has done this twice, so she is twice-intermewed. I've had hawks that intermewed as many as 16 times -- fine old ladies these were.

Pale Male and Lola are “haggards,” adult birds in the wild. Falconers are not permitted to capture haggards for use in the sport, and this is most appropriate. No falconer would ever want to attempt to train these stubborn birds. As a part of my raptor research, I trapped two haggards and kept them in captivity for several years. These animals never, ever lost their sneering resentment of my removing them from the wild. Had I ever flown them free, in the manner of my trained falconry birds, these haggards would have instantly flown off and never returned. Once a falcon or hawk reaches its second year, after molting a new set of feathers, her mental processes become hardened to life in the wild. Life in the care of even the most caring falconer would be forever a severe imposition upon her developed sense of what’s right. Sitting on a falconer’s fist is not among what’s right for these hard-wired birds. No falconer wants a haggard. They are best left in the wild where they do their wild things so well,

John: I felt a pang when you told of the two "haggards" you captured and kept for several years as part of your raptor research. Would you be able to tell us what you gained for science, or were trying to gain, by keeping these wild birds captive for this period of time? Marie


At the end of John Blakeman's interesting essay about hawk and falconry terminology , he noted that he had had two captive redtails that he kept for purposes of raptor research. I asked him to explain what might be learned from such research. He promptly sent me a letter answering my question. [You might want to read his essay first, before reading his explanation, to understand some of the terminology].


I understand your concerns regarding the removal of breeding adults from the wild, a concern of mine, too. Falconers never, ever do this to use haggards in the sport, so that is not a concern here. Scientific researchers do this only for good purposes, and I think mine were such.

One bird borrowed from the wild, for a season, was a gigantic old female. I trapped her to determine food requirements at various temperatures. She was kept in a large temperature-controlled environmental chamber where we could change light and temperature exactly as those changed in the wild in both summer and winter. The amount of food the hawk consumed in cold winter was compared to the reduced amount of food consumed in warm summer weather. At the time, 37 years ago, there was very little published data on the actual caloric requirements of raptors in general, and specifically the red-tail. There was a question of whether mature, experienced adults required more or fewer calories each day than inexperienced, inefficient immature hawks do. My data showed that they were very similar, and the bird was then released back to the wild, where it was seen nesting the following year in the same territory. The bird was trapped in the autumn and released in the following May. Not much was known then about the daily food requirements of wild raptors, and my data confirmed the data of some others regarding the common red-tail.

Today, this information would be taken (and has been) from the hundreds of adult hawks held in raptor rehabilitation centers. In the 1960s, these didn't exist. At the time, there was even a question if wild raptors could be successfully kept in captivity, especially for breeding. And how much food would captive raptors require? Would this vary by age and sex?

Bald eagles, Cooper’s hawks, peregrines, and several other species were rapidly declining and their extinction was on the horizon. A number of raptor researchers scrambled to collect data on how these birds might be rescued. The place to start was with common species such as the red-tail. We could have just sat there and bemoaned the rapid declines of our beloved wild raptors. Conversely, we could have devised scientific trials and procedures that would yield real data that could be used to restore declining populations. Had raptor researchers (most of whom were also falconers) not taken decided actions with captive hawks, the peregrine falcon most likely would have become extinct or extirpated here. Virtually all of the breeding peregrines in the East and Midwest descend from peregrines breed in captivity and released for re-introduction. With the peregrine, it was a hands-on approach, one that yielded great successes.

I, and others, were initiating the same things with red-tails, on the outside chance that this great species might someday become endangered like the peregrine. Fortunately, that day never arrived. The red-tail is safe. But in the 60s, our knowledge of the physiology and reproductive biology of even the common red-tail was abysmal. We can't save something that we don't understand, and in the 60s we didn't understand either red-tails or peregrines. Simple, baseline data such I collected on this single wild adult bird were required. The rest is history, thankfully now with red-tails and peregrines gracing our skies across the continent. We weren't so sure that would be the case in 1969.

My breeding trials of red-tailed hawks proceeded from this, but I never used a wild-caught adult for these, as it was very clear early on that wild-caught adults would not breed in captivity. I'll give an account of my red-tail breeding experiences sometime later, as they are rather detailed and lengthy. It was from them that I saw red-tail nesting activities first hand, activities that all will be seeing once again as Pale Male and Lola do their thing up there at 927 Fifth Ave.

The second adult red-tail that I trapped from the wild was the part of another, somewhat lengthy story. But in summary, she was a remarkable white, albinistic female that I discovered in mid-winter 1970. I watched her build a nest and breed with a normal male. The pair raised a normally colored tiercel eyass, which we banded. But because the mother was so blazingly prominent in her glistening white, she was seen everywhere that she went within her two square miles of territory. After asking residents of the area about the bird, I learned that many people were familiar with her, and I was warned that several locals had taken gunshots at her. I had state scientific collecting permits that allowed me to trap the bird, and for her own safety I did, in August, long after the breeding season. We kept her for two molts, as her plumage coloration changed during the first molt, something that had never been seen in “albino” red-tails before. After the second molt the bird was released in Nevada, away from all humans.

For a decade after that, I trapped many adult red-tails, but only to attach ID bands. Each was immediately released back to the wild.

I'm a certain that many readers disagree with the necessary interventions wildlife researchers often take to learn about, restore, and protect wild animals. But these are necessary. Wildlife management must be evidence-based, moving on the sound findings of dedicated and knowledgeable individuals. An example of this has occurred here. The restoration of the 927 nest support structure was based on design suggestions derived from understandings of red-tailed hawk nest requirements, both in the wild and in captivity. Pale Male, Lola, and their progeny will benefit from past experiments with captive red-tails. I'm glad that my experiences can be put to good purposes here, along with those of other professionals.


John A. Blakeman

Friday, March 18, 2005

Male or Female Hawks for Falconry?

Hi Marie,

I have a question raised by John’s wonderful letter today -- we all know that his ‘Savanna’ is a female red-tail, or ‘hen,’ but he made other references to the fact that he has worked with several red-tailed hawks -- and they all were referred to by him as female. Are female hawks merely his preference (and why)? Or in training hawks for falconry, is the use of ‘hens’ preferred in general? And why, (of course)?

I’m sure other people have noticed this and raised this question!!

Thanks Marie and have a wonderful day!


Here's Blakeman's answer to the question:


Yes, I tend to work with red-tailed hawk females, "hens" for lack of a better term. This is for several reasons. The first is that more females are fledged than tiercels, for reasons no one knows. At least 60% of all fledged red-tails are females. Tiercels aren't equal in any way with the big females.

Hen red-tails, as in virtually all other raptors, are markedly larger than the males. In fact, that's the origin of the term 'tiercel," an English corruption of a 16th-century French term meaning "one third." Peregrine tiercels are about one-third smaller than the falcons (the females).

No one has come up with a good reason for the greater size of raptor females. In fact, it makes no sense whatsoever. While big Lola is up there whiling away her many hours of motherly incubation, our patriarch Pale Male must be out on the hunt, not just to feed himself, but also his larger sedentary mate. His hunting prowess must more than double, although he is the smaller and less muscular of the pair. The smaller mate should get the incubation task, but universally across all raptor species, the diminutive male is genetically assigned the daunting food provision task.

And it gets even more difficult after eyasses hatch. The tiercel then must feed not just himself and his sitting mate, but also bring to the nest sufficient food for the rapidly developing eyasses. The tiercel has to spend virtually all daylight hours in late April trying to find, capture, kill, and transport food for everyone in the family -- a daunting task. (See why it's important to know the daily caloric requirements of adult hawks?) Why the tiercels aren't the larger bird, more capable of attending to the demands of family food supplies during incubation and eyass brooding, is a complete mystery. I've utterly given up all thoughts on the matter. There are some ecological questions that may never have answers. This is one of them.

But why do I refer to every hawk except Pale Male with the feminine gender? It's an ancient convention of falconry, deriving from the abundance of hawk females in the wild, and their preference in the sport. Because hawk females are larger, falconers for centuries have preferred them over tiercels. Now don't misinterpret this. Tiercels can make exceptionally fine hunting birds, as with a remarkable red-tail tiercel captured and used by my current falconry apprentice here in Ohio. He has done notable things with this bird, and it holds its own against any prey it chooses to pursue, primarily cottontail rabbits. It just completed a very fine hunting year, and just "went up for the molt." It is being retired to the mews where it will sit contentedly and grow new feathers until autumn. (Incidentally the place falconers keep their hawks is called a mews. The Royal Mews of Buckingham Palace today houses the royal carriages. In former centuries, it housed the King's falcons.)

From all of this, falconers simply refer to any hawk of unknown sex as a female. It is a matter of respect and honor. Tiercels have their place in falconry, but the big females are most highly regarded. (And the greater presence of females is one reason that falconry has persisted for several millennia without reducing wild raptor populations. At the height of Renaissance falconry, in Shakespeare's time and the century following, there were 600 or so known peregrine eyries (cliff side nests) in Great Britain. One or two falcon eyasses (females) were removed from each of these every year for royal falconers for several centuries without diminishing the wild population. That's because an abundance of females is always produced, and just like the red-tails that have colonized Central Park, these excess falcons would have died without progeny in the wild, for lack of un-occupied nest sites after reaching adulthood. For red-tails today, the same thing happens with the very few falconers in the U.S. We much prefer the giant females, and often refrain from taking a rarer male. European and American falconry has never had any impact on wild raptor populations except for the positive, as in raptor education and captive breeding of peregrines, etc.

So, if you see a red-tail sitting in a Central Park tree, it's a she, unless you can surely tell otherwise. It's a matter both of convention and respect.


John A. Blakeman

Tuesday, March 15, 2005



On 3/15/05 I wrote to Peter Post, a highly accomplished birder who has been birdwatching in Central Park for more than fifty years:

Peter, I've been contending that as recently as 1991 [when Pale Male arrived in CP] red-tailed hawks were unusual visitors to Central Park . I'm not talking about flyovers, but birds staying in the park for some period of time. Am I right about this? Marie

Peter responded:
I agree with everything you say, except I cannot specify a year when Red-tails started to come down and actually perch in the park.


I sent this exchange to John Blakeman, with a note stating that I CAN specify 1990 or 1991 as a year when redtails were still rare. That is because Pale Male's arrival created such a great stir.. The appearance of a redtail in Central Park or anywhere else in NYC is pretty everyday now. Here is Blakeman's answer:


Authoritative comments or data on the beginning of red-tail residencies in CP will be very, very useful. If this began in the late 80s, or early 90s, it fits very well with my anecdotal recollections of red-tail saturation of my countryside populations. Illegal shooting and trapping of red-tails declined dramatically in the 80s, as the arrest and citation records of state game authorities would reveal. By the 90s (and continuing today), there were simply no holes, no unoccupied habitats for large populations of maturing young red-tailed hawks. There was, and is, a severe "housing" (open habitat) shortage for red-tails. Tens of thousands of young red-tails are fledged in our respective areas each summer, but these birds simply have a hard time finding unoccupied territories with adequate prey populations. Those are owned and defended by old resident adults. In rural areas with markedly reduced prey populations (compared to the abundance of food animals in Central Park), red-tail territories are large, up to several square miles, and are strongly defended against invasion by young hawks.

If this scenario is an accurate characterization, and I think it is, then the incursion of red-tails into Central Park in the 80s and 90s begins to make a great deal of sense. The species is demonstrably able to adapt its hunting to the unique prey animals of Central Park. Pale Male began this urban colonization, and others have likewise learned to exploit the formerly untouched hawk resources of the Park. A wonderful story. I hope some accounts can be posted of early occurrences of red-tails in NYC.


John A. Blakeman

Now that we're entering a peaceful month of incubation, there's time to return to some of the basic questions about the red-tailed hawk presence in Central Park. It has been suggested that the enormous amount of pigeon-feeding that occurs in the park, and thus the presence of great numbers of pigeons there is what served to attract redtails in the first place. John Blakeman responds:


I'm not so certain that the pigeons by themselves were the only Pale Male prompt to get him to take up residence in Central Park. There have been a lot of human-fed pigeons in CP for decades, and not many red-tails. I still think our patriarch entered the Park because he could find no unoccupied territories in traditional rural habitats. But the plethora of pigeon surely didn't reduce his impulses to stay. A few hundred pigeons competing for a few pounds of scattered grain can quickly lose wariness in a crowd of other food-crazed birds.

And this raises a background question I've pondered. Is the real source of CP red-tail food actually from humans, from scattered bird food and horse-feeding grain? Could it be that the real, basal food resource for our hawks are humans themselves? Looks like it is.The Central Park food web or pyramid is quite different from anything out here in wilder, more rural areas.

How many pigeons would spend much time foraging in Central Park in the absence of human-provided grain? Without human-scattered food, I think the pigeons would be forced to fly across the river over into industrial areas and rail yards and work out a more mundane pigeon life eating natural weed seeds over there. Instead, the birds just fly around a corner or two, up a block or two, and drop down to quite artificial provisions of ample grain. But of course, the rock dove is artificial itself, not being a native species of the Western Hemisphere. Nature continues to evolve here.


John A. Blakeman