# Peregrine Falcons **URL:** \ **Category:** Factual Questions\ **Created:** [June 22, 2004, 4:06pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652 "2004-06-22T16:06:42Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Consumer\_Sovereignty](https://avatars.discourse-cdn.com/v4/letter/c/e99b99/32.png) [@Consumer\_Sovereignty](https://boards.straightdope.com/u/Consumer_Sovereignty)\ **Post date:** [June 22, 2004, 4:06pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/1 "2004-06-22T16:06:42Z")
I’ve always loved the Peregrine Falcon; whenever somebody asks ‘what is your favourite animal’, I would reply ‘the peregrine falcon’. I’ve heard numerous different reports as to what its top speed is, claims from 200 km/h to 200 mph are not uncommon. I know that the speed recorded depends on various factors such as dive height, wind speed, angle, etc etc, but there would need to be a maximum that the PF could endure physically, I would assume. So, does anybody have the straight dope on what the maximum speed a Peregrine Falcon could realistically attain without appreciable injury? ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [June 22, 2004, 4:19pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/2 "2004-06-22T16:19:32Z")
[http://www.google.com/search?hl=en&ie=UTF-8&q="peregrine+falcon"+"maximum+speed"](http://www.google.com/search?hl=en&ie=UTF-8&q=%22peregrine+falcon%22+%22maximum+speed%22) ---
**Author:** ![pravnik](https://avatars.discourse-cdn.com/v4/letter/p/8edcca/32.png) [@pravnik](https://boards.straightdope.com/u/pravnik)\ **Post date:** [June 22, 2004, 4:31pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/3 "2004-06-22T16:31:07Z")
Frome the New Grolier Multimedia Encyclopedia: “Falcons are strong, fast fliers with great aerial agility. They seldom soar in the manner of hawks. The peregrine has been clocked at 290 km/h (180 mph) in a stoop, or dive. This speed and agility make falcons successful hunters of birds, reptiles, and small mammals.” ---
**Author:** ![Tuco](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tuco](https://boards.straightdope.com/u/Tuco)\ **Post date:** [June 22, 2004, 4:47pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/4 "2004-06-22T16:47:56Z")
> [@Consumer\_Sovereignty](#): > > So, does anybody have the straight dope on what the maximum speed a Peregrine Falcon could realistically attain without appreciable injury? Is there a reason why it’s top speed wouldn’t be its terminal velocity? I can’t think of anything organic that would break because it went too fast, especially on something as streamlined as a hawk. You’ll have to wait until someone who knows how to calculate drag coefficients and terminal velocities to come along to answer your question entirely. I saw on a TV show a test to find the top speed of a PF; they hooded it, took it up in a hot air balloon quite high, tempted it with a piece of meat, then jumped out. They measured the time it took for the falcon to catch up and calculated it’s velocity from that, it was 180mph ish. Then it just hung around the skydivers, toying with them until they opened their parachutes. The program makers say speeds of 200mph seemed plausable seeing as it took so little time to catch up. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 22, 2004, 10:13pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/5 "2004-06-22T22:13:15Z")
> [@Tuco](#): > > Is there a reason why it’s top speed wouldn’t be its terminal velocity? The falcon is attaining speeds far in excess of its terminal velocity, which is achieved when a falling body reaches equilibrium with air resistance and ceases to accelerate further. Terminal velocity for a falling human is about 200 km/h, or 124 mph. A peregrine’s own terminal velocity is much much smaller than that, since its weight is much smaller in relation to its surface area. Peregrines reach these speeds through a power dive; their powerful musculature coupled with a high degree streamlining enable them to overcome air resistance. ---
**Author:** ![mischievous](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@mischievous](https://boards.straightdope.com/u/mischievous)\ **Post date:** [June 23, 2004, 2:31am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/6 "2004-06-23T02:31:28Z")
> [@Colibri](#): > > The falcon is attaining speeds far in excess of its terminal velocity, which is achieved when a falling body reaches equilibrium with air resistance and ceases to accelerate further. > > Terminal velocity for a falling human is about 200 km/h, or 124 mph. A peregrine’s own terminal velocity is much much smaller than that, since its weight is much smaller in relation to its surface area. > > Peregrines reach these speeds through a power dive; their powerful musculature coupled with a high degree streamlining enable them to overcome air resistance. Um, WHAT?!?! Falcons can’t “power dive”, there is nothing for their “powerful musculature” to push against in midair. (Except their wings, which would slow them down, not speed them up.) They are not equipped with rockets. They just fold their wings against their bodies and fall. They are sufficiently streamlined that they encounter very little air resistance. Low air resistance leads to higher terminal velocity, so they do get moving pretty fast. By the end of the fall, they can hit pretty hard. How, exactly would a falcon “attain speeds far in excess of its terminal velocity”? mischievous ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 23, 2004, 2:51am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/7 "2004-06-23T02:51:37Z")
> [@Consumer\_Sovereignty](#): > > So, does anybody have the straight dope on what the maximum speed a Peregrine Falcon could realistically attain without appreciable injury? From [Gliding flight: speed and acceleration of ideal falcons during diving and pull out](http://jeb.biologists.org/cgi/content/abstract/201/3/403): > [@](#): > > Some falcons, such as peregrines (Falco peregrinus), attack their prey in the air at the end of high-speed dives and are thought to be the fastest of animals. Estimates of their top speed in a dive range up to 157 m s-1, although speeds this high have never been accurately measured. This study investigates the aerodynamic and gravitational forces on ‘ideal falcons’ and uses a mathematical model to calculate speed and acceleration during diving. Ideal falcons have body masses of 0.5-2.0 kg and morphological and aerodynamic properties based on those measured for real falcons. The top speeds reached during a dive depend on the mass of the bird and the angle and duration of the dive. Given enough time, ideal falcons can reach top speeds of 89-112 m s-1 in a vertical dive, the higher speed for the heaviest bird, when the parasite drag coefficient has a value of 0.18. This value was measured for low-speed flight, and it could plausibly decline to 0.07 at high speeds. Top speeds then would be 138-174 m s-1. Assuming the 157ms[sup]-1[/sup] figure is accurate, that comes out to ~351mph. A mathematically-ideal falcon could achieve even higher speeds. This is all based on modelling and estimates, of course, since no-one has ever actually recorded a falcon diving in excess of 300mph. But it does seem plausible, and more importantly, survivable. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 23, 2004, 3:21am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/8 "2004-06-23T03:21:06Z")
> [@mischievous](#): > > Um, WHAT?!?! > > Falcons can’t “power dive”, there is nothing for their “powerful musculature” to push against in midair. (Except their wings, which would slow them down, not speed them up.) They are not equipped with rockets. You don’t seem to understand basic aerodynamics. What they are pushing against, of course, is the air. > [@](#): > > They just fold their wings against their bodies and fall. They are sufficiently streamlined that they encounter very little air resistance. Low air resistance leads to higher terminal velocity, so they do get moving pretty fast. By the end of the fall, they can hit pretty hard. Nonsense. Have you ever seen a falcon execute a power dive? To attain their fastest speeds, they first pump the wings vigorously to accelerate. _Then_ they fold their wings to take advantage of their streamlining. A falcon’s fastest stoop is not a “gravity only” drop. From [here](http://listserv.arizona.edu/cgi-bin/wa?A2=ind9907e&L=birdchat&F=&S=&P=4678) > [@](#): > > Curiously, the peregrines reached the highest speeds not in high, steep dives, but by pumping their wings to accelerate into relatively shallow dives at angles near 30 degrees to horizontal. > [@](#): > > [The falcon’s] average stoop consisted of approximately one mile. The first half mile, he pumped vigorously, then folded and dove the remaining half mile, catching his quarry approximately 100-200 feet in the air. Tucker found that this bird consistently dove at between 150-180 mph. Most of his dives were “power assisted” before he tucked up and his highest speeds were reached in shallow dives. Note that in my post, I was using “terminal velocity” in the sense of the final speed acquired in free fall, without a previous powered acceleration. Falcons achieve speeds greater than what they would by simply dropping out of the air in free fall. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [June 23, 2004, 3:50am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/9 "2004-06-23T03:50:48Z")
> [@Colibri](#): > > Note that in my post, I was using “terminal velocity” in the sense of the final speed acquired in free fall, without a previous powered acceleration. Falcons achieve speeds greater than what they would by simply dropping out of the air in free fall. Not according to Darwin’s Finch’s quote. There are a pair called Frodo and Frieda who nest on a building about a hundred yards from my office. I see them (very briefly) outside my office window all the time. They move, even in level flight, like you are seeing speeded up film. I have seen them stoop (on pigeons) only a couple of times, and then their pace is like no other bird you have ever seen. For pictures see [here](http://thecouriermail.com.au/extras/frodocam/default.htm). Pictures 3 and 4 from the Photo Gallery are pretty much the view out my office window. ---
**Author:** ![mischievous](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@mischievous](https://boards.straightdope.com/u/mischievous)\ **Post date:** [June 23, 2004, 3:55am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/10 "2004-06-23T03:55:12Z")
> [@Colibri](#): > > You don’t seem to understand basic aerodynamics. What they are pushing against, of course, is the air. > > Have you ever seen a falcon execute a power dive? To attain their fastest speeds, they first pump the wings vigorously to accelerate. _Then_ they fold their wings to take advantage of their streamlining. A falcon’s fastest stoop is not a “gravity only” drop. I will admit that I didn’t know that they pre-accelerated their dives. Thanks for the info. This still does not, in my mind, meet the definition of “powered dive”. The first phase is accelerated by wing power, yes, but then the bird folds its wings and allows gravity to take over. Which (to me) means it is dropping, not power diving. > [@](#): > > Note that in my post, I was using “terminal velocity” in the sense of the final speed acquired in free fall, without a previous powered acceleration. Falcons achieve speeds greater than what they would by simply dropping out of the air in free fall. So, did you use “terminal velocity” to mean “final velocity” (i.e. the velocity at the end of the dive)? Maybe I’m missing something here but I understood that terminal velocity was: > [@Colibri](#): > > terminal velocity, which is achieved when a falling body reaches equilibrium with air resistance and ceases to accelerate further. This velocity is not dependent on previous acceleration. The fact that falcons may accelerate first only means that they will hit their terminal velocity sooner in the dive. My understanding of the situation is this (and if I’m wrong, I’m willing to be educated): In the start of a dive, a falcon is moving relatively slowly. It starts flying actively (powered dive) downward to push its initial acceleration up. At some speed, the added air resistance of having its wings open cancels out the acceleration it can provide with wingpower. So, it folds its wings into the most streamlined form it can, and allows gravity to continue to accelerate it (passive drop). Gravity will continue to accelerate it until the acceration of gravity is canceled out by the increased air resistance, which would be when the bird hits terminal velocity. The bird cannot go faster than this. If this is correct, than the point of the initial wing-powered boost is so that the bird can hit terminal velocity (or at least a high velocity) in the space between it and the ground - which is not infinite. So, feel free to educate me on basic aerodynamics. mischievous ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [June 23, 2004, 4:38am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/11 "2004-06-23T04:38:15Z")
> [@Colibri](#): > > Terminal velocity for a falling human is about 200 km/h, or 124 mph. A peregrine’s own terminal velocity is much much smaller than that, since its weight is much smaller in relation to its surface area. Altitude can determine terminal velocity, and one human [has broken the sound barrier on his way down.](http://astronaut.mybookcenter.com/n_1557507325.htm) > [@](#): > > Joseph Kittinger, for example, rode a balloon up to 103,000 feet in an open gondola and then stepped out and freefell to Earth, becoming the only person to break the sound barrier without a vehicle. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [June 23, 2004, 6:19am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/12 "2004-06-23T06:19:00Z")
**Consumer Sovereignty,** here’s a link to a web cam on a tall building in downtown Indianapolis, Indiana, USA. A pair of peregrine falcons has raised four chicks this year. [www.indystar.com/special/falcon](http://www.indystar.com/special/falcon) The site is jointly run by the Indianapolis Star newspaper and the Indiana Dept. of Natural Resources. ---
**Author:** ![Morgyn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/morgyn/32/3041_2.png) [@Morgyn](https://boards.straightdope.com/u/Morgyn)\ **Post date:** [June 23, 2004, 6:38am UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/13 "2004-06-23T06:38:08Z")
You can also try [the Kodak Birdcam](http://birdcam.kodak.com) site, which is run by volunteers at Kodak who work closely with several different peregrine falcon organizations (such as [the Canadian Peregrine Foundation](http://www.peregrine-foundation.ca/)). According to the Kodak site, a peregrine in a stoop can reach speeds over 200 mph, and at least one was reported as [having passed a plane that was diving at 175 mph](http://hypertextbook.com/facts/1999/ChrisSantoro.shtml). ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 26, 2004, 6:44pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/14 "2004-06-26T18:44:51Z")
I stand corrected on a falcon’s terminal velocity. **Darwin’s Finch’s** information indicates that it is higher than I expected relative to that of a human. Given a falcon’s higher surface-area to mass ratio (because of its much smaller size) I would have expected its terminal velocity to be lower. [This site](http://hypertextbook.com/facts/JianHuang.shtml) indicates that the typical terminal velocity of a human skydiver spreadeagled (maximum air resistance) is about 120 mph. The record achieved at normal elevations without special equipment by minimizing air resistance is listed at 321 mph. It surprises me that a falcon’s terminal velocity could exceed this, since it is only about 1/35 the weight of a human. Clearly, its streamlining relative to a human clearly has a very large effect. > [@mischievous](#): > > This still does not, in my mind, meet the definition of “powered dive”. The first phase is accelerated by wing power, yes, but then the bird folds its wings and allows gravity to take over. Which (to me) means it is dropping, not power diving. Well, it’s _called_ a power dive because it is, in part, powered. Its not the quite the same as a dive-bomber, which may be applying power throughout the dive, but the falcon is certainly doing more than simply dropping like a stone. > [@mischievous](#): > > > [@Colibri](#): > > > > Note that in my post, I was using “terminal velocity” in the sense of the final speed acquired in free fall, without a previous powered acceleration. Falcons achieve speeds greater than what they would by simply dropping out of the air in free fall. > > So, did you use “terminal velocity” to mean “final velocity” (i.e. the velocity at the end of the dive)? Maybe I’m missing something here but I understood that terminal velocity was: > > > [@Colibri](#): > > > > terminal velocity, which is achieved when a falling body reaches equilibrium with air resistance and ceases to accelerate further. There are various definitions of [terminal velocity](http://www.google.com/search?hl=en&lr=&ie=UTF-8&oi=defmore&q=define:Terminal+velocity), but the most common one is the velocity reached when acceleration due to gravity is matched by air resistance. A more general definition is the second one on the list, which is “The velocity at which the driving forces are cancelled out by the resistive forces,” in which driving forces could include those other than gravity (e.g. wing propulsion). In my first quote above, what I had in mind was distinguishing the first definition from the second. > [@mischevious](#): > > This velocity is not dependent on previous acceleration. The fact that falcons may accelerate first only means that they will hit their terminal velocity sooner in the dive. > > My understanding of the situation is this (and if I’m wrong, I’m willing to be educated): In the start of a dive, a falcon is moving relatively slowly. It starts flying actively (powered dive) downward to push its initial acceleration up. At some speed, the added air resistance of having its wings open cancels out the acceleration it can provide with wingpower. So, it folds its wings into the most streamlined form it can, and allows gravity to continue to accelerate it (passive drop). Gravity will continue to accelerate it until the acceration of gravity is canceled out by the increased air resistance, which would be when the bird hits terminal velocity. The bird cannot go faster than this. > > If this is correct, than the point of the initial wing-powered boost is so that the bird can hit terminal velocity (or at least a high velocity) in the space between it and the ground - which is not infinite. Yes, that is basically correct, except that if **Darwin’s Finch’s** figure is right, birds rarely if ever achieve terminal velocity. My basic point is that the falcon achieves a faster speed at any point in time during its dive by using powered flight during the first phase than it would by using gravity alone. Compare it to a bobsled, say, in which one that receives a powerful push by its crew on takeoff will get to the end of its run faster than one which is merely nudged over the edge, despite the fact that it is only powered by gravity through most of its run. (Not a strict analogy, since we are dealing with contact friction rather than air resistance; however, I think the point holds.) > [@Tuckerfan](#): > > Altitude can determine terminal velocity, and one human has broken the sound barrier on his way down. > > > [@](#): > > > > Joseph Kittinger, for example, rode a balloon up to 103,000 feet in an open gondola and then stepped out and freefell to Earth, becoming the only person to break the sound barrier without a vehicle. As the first link in my post indicates, Kittinger evidently reached 9/10 the speed of sound, but did not exceed it. The reason he was able to achieve such a high speed was the virtual absence of air resistance at such altitudes. He did not “freefall to Earth,” but only for about 7,000 feet of his descent. ---
**Author:** ![Improv\_Geek](https://avatars.discourse-cdn.com/v4/letter/i/b3f665/32.png) [@Improv\_Geek](https://boards.straightdope.com/u/Improv_Geek)\ **Post date:** [June 26, 2004, 8:59pm UTC](https://boards.straightdope.com/t/peregrine-falcons/251652/15 "2004-06-26T20:59:51Z")
Since the factual discussion is well underway I feel somewhat allowed to make a horrible joke. I think you all are ignoring the obvious question here, is it a laden or unladen peregrine falcon?