I have read many articles over the years about why a Roller rolls. But, I do not recall ever reading one about the aerodynamics the Roller needs to master in order to roll. From a practical standpoint it strikes me that the aerodynamics is an important subject. After all, if we understand the aerodynamics a bit it might just tell us something about how to breed a better Roller.
Today both video and high speed photography are readily available of Rollers performing. If you know what to look for these tools are a great help in understanding what a Roller does when it rolls. But, if you do not understand aerodynamics you can watch these tools as long as you wish and you are not at all likely to ever see the important factors. For instance I have heard that the roll is initiated by the Roller sticking its tail straight up. Yes, during a roll a Roller does stick its tail straight up. But that has nothing at all to do with how the bird generates the angular momentum in the roll.
were designed after birds in general. A
major key to making an airplane or making a
bird fly in a stable manner is to place the center of gravity and
lift in proper places with respect to each other. In
both birds and planes the major lifting
surface is the wing.
A minor lifting
surface in both cases is the tail.
Either a airplane or a bird
can rotate on three axis.
These three axis are called
the pitch, roll
and yaw axis.
For purposes of
understanding a bird rolling only the pitch axis is important so I will
the other two.
If you draw a line from one wing tip to the other wing tip rotation around this line is a pitch rotation. This is the rotation a Roller makes when it rolls. Modest changes in the pitch axis are made in an airplane by adjustment to the angle of the tail control surfaces. In a bird the whole tail is moved up or down a bit. In either a plane or a bird simply adjusting this control surface is able to cause the object to fly a loop providing it has enough air speed at the start. But, it will not cause the rapid spin we see in a Roller.
There are well understood design criteria for airplanes that lead to stable flight. If you violate these designs you will have a plane that is either very hard or impossible for a human to fly. These same design criteria apply to birds. An important design criteria to worry about is where the center of gravity happens to be relative to the center of lift. The center of gravity of any object is simply that point from which you could hang the object on a string and it would not rotate nose down or nose up. The center of lift is that point on a flying object where you could treat all lift as simply being a vertical vector. In order to have an airplane or a bird that fly's in a stable manner, the center of gravity must be slightly forward of the center of lift. As you move the center of gravity back towards the center of lift, the flying object becomes less and less stable in the pitch axis. Very small corrections with the tail control surface, leads to a very large pitch axis response. If you move the center of lift in front of the center of gravity, stable flight is impossible. The flying object will roll in the pitch axis.
In an airplane, a pilot who wishes to stay alive worries a lot about where his center of gravity is relative to his center of lift. There are some controls a pilot has, to move the center of gravity forward or backwards. He can adjust how the plane is loaded and which fuel tanks are used. He can seat heavy passengers close to the wing. A bird is stuck and does not have the ability to move weight forwards or backwards. A crop full of food moves the birds center of gravity forward and the bird can not shift other weight to compensate. However, a bird can do something an airplane can not do. A bird can rotate its wings forwards or backwards at the shoulder to adjust the center of lift, relative to the center of gravity. This ability to rotate at the shoulder is very important for a bird; if it could not do this, it would have a hard time flying. Birds simply must be able to make such compensations to accommodate full versus empty crops. A full crop would call for a more forward wing angle than an empty crop. A Homer burns a significant amount of abdominal fat during a race moving its center of gravity forwards, from where it was at the start of a race. So during the race, the Homer needs to be able to swing its wings slightly forward to keep the center of gravity and center of lift in the correct relationship. A hen can be carrying an unlaid egg one hour, then lay the egg the next hour and need to fly again even though the center of gravity has been shifted. The hen needs to shift her wing angle slightly forward to compensate for laying an egg. There is nothing in the slightest unnatural about this ability. All birds have it.
When a Roller is going to do the first flip it may tilt its body very slightly up from level flight and flare its tail. At that point its tail is straight out behind the bird. Picture 1 of a Roller right at initiation of the roll shows this clearly.
Picture 1 also shows the wings rotated forwards from normal flying position. In normal flying position the leading edge of both wings is nearly a straight line rather than a V as shown in this picture. This picture and the rest of the pictures in this sequence were all of the same bird during 70% of one initial rotation.
Then the Roller starts a wing flap. During this wing flap it keeps both wings rotated forwards at the shoulder from the normal flight position. This moves the center of lift forward of the center of gravity. The net result is the bird is not in stable flight. Rather, the lift from that single wing flap starts a violent backwards rotation. Think about hanging a one foot long ruler from a string tied on the six inch position. The six inch position is the center of gravity. Now, if you tied a second string on the ruler at the five and one half inch position and jerked up sharply what would happen? Obviously the ruler would rotate violently about its center of gravity. That five and a half inch point is the equivalent of the center of lift. If you watch flying Rollers and know what to look for you can see this forward swing of the wings for that first wing beat at the start of a flip. If you watch slow motion of a Roller the wings swinging forwards is a lot easier to see. What you can not see without slow motion is what the tail is doing during establishment of the angular momentum needed for the flip. Picture 2 clearly shows the tail is still extended straight out behind the bird. Yet the bird is already starting to be in a head up attitude.
Picture 3. First Down Flap Finished and Wings Again Over Back
Picture 4. Body is Now Vertical. Tail is Raised.
Picture 5. Body Now Rotated about 120 Degrees. Tail Now Fully Lifted.
5 shows the bird just a little farther along in the
first flip of the roll.
The wings are
still fully extended over the back and the tail is now fully lifted to
At this point all the angular
momentum needed to roll is established.
However, drag forces during
the roll will wear away this angular
So the bird will continue to
flap its wings about one time per flip as long as it wishes the roll to
It will also keep it tail
as long as it wishes to continue the roll.
To stop the roll the bird
simply extends its tail to normal flying
position and does one wing flap with the wings swung slightly behind
This will cancel the
stored angular momentum of the roll.
do these pictures tell us about what the best Roller should
One obvious thing is the
shorter the birds body is the less angular momentum it needs to
allow a given rotation speed.
So a short
backed bird should be able to roll faster than a long backed bird. Likewise
a smaller overall bird has less mass
thus requires less energy to establish the needed angular momentum. Flying
Rollers typically are small
I suspect breeders have done
good job of selecting for proper size pigeons simply by selecting for
All birds have the ability
to swing their wings forwards at the shoulder to put them in position
initiate a roll.
But not all birds are
willing to roll.
So the breeder is mainly
selecting for an attitude on the birds part that rolling is desirable. All
the breeder can select for is parents
that have this attitude based on their performance and hope the
passed to offspring.
may still feel the tail is important in establishing
the angular momentum regardless of what photography so clearly shows. Well,
we all know a bird can fly without a
In fact they can fly
So I took a young roller that
been flying a month.
This bird was doing
a lot of single flips and occasionally doing short rolls of three or
On day one I pulled the two
tail feathers and released it to fly with the kit.
was zero change in its
It could still flip just as
good and just as often with only 10 tail feathers as it could with 12. Each
subsequent day I
pulled the two outer tail
I saw no change in the speed
of this birds
flips as I pulled tail feathers. Nor
it perform less as it lost tail feathers.
On the day I pulled the last
two tail feathers the first couple of times
it performed it lost a lot of altitude.
Up until that point it would
generally gain altitude during a one or two
But after it had
adapted to zero tail feathers, which only took less than five minutes
time, its performance was just as good as it had been six days before
It turned over just as fast
and it performed just as often and it no longer lost altitude.
one occasion I have seen one of my birds do a fair flip
without even doing a wing flap.
birds had been flying for some time and were getting tired. They
were doing a lot of gliding.
One of them, during a glide,
its wings well forward from normal glide position.
result was a single flip.
It was not a very fast flip. But
it was a well controlled flip.
It seems clear from the photos that any pigeon that can fly is capable of rolling. All they need to do is rotate the wing forward a bit at the shoulder and the roll is automatic. Thus the genetics we need to put in the bird are not structural changes. They are aimed at making the bird enjoy rolling. The bird needs to want to roll or it is not going to roll.
1972 Journal of Heredity paper indicates rolling
is a multi gene trait.
support this idea.
I started with Joe
These birds did not perform
at all unless they were flown every single day for months.
of these birds would do a single flip
occasionally if flown long enough. But
even two year old birds did not really roll.
The very best of them might
turn over three or four times rarely and
most only single flipped.
frequency of performance was very low.
Quite often I would watch a
kit of 20 birds and see no more than one
bird flip in ten minutes.
year I got some stock from a strain that has been bred
strictly for performance.
will start to do flips within a month of flying daily.
are doing flips while still squeakers. They
progress much more rapidly than the
From the first tail rides
to the first flip is generally only two or three days.
do good tight flips and quite often by
two months of flying are doing triple and quadruple flips.
also perform at a higher air speed than
the Quinn birds.
The Quinn birds need to
really slow air speed down to perform.
The high performance birds
will perform at normal air speed and
routinely exit a single or double flip at higher altitude than they had
they entered the sequence.
performance is orders of magnitude higher than Quinn birds.
date crosses between the Quinn birds and high performance
birds have given performance no better than pure Quinn birds. They
have now been flying for two months and
are not even doing tail rides yet.
states in his CD on Rollers that it took as much as
six generations of back crosses to pure Rollers to put the roll back in
birds after an outcross to a nonperforming breed. Lee
Faecking has told me this fits with his
A lot depends on how often
birds are flown as well as how long they have flown.
flown daily perform more than birds
flown only two or three times a week.
The same bird will perform
more as a two year old than as a one year
It has often been noted that
siblings can differ greatly in performance, even in inbred strains. It
is also a lot harder to judge rolling
performance than it is to look at a crest or some other show trait and
the quality of the crest or the other show trait. I
suspect that some of the many back crosses
needed to recover the roll is simply that roll is hard to judge and
also due to
performance variation in individual birds that are quite alike
Six generations of back
crosses would indicate roll is quite a lot of genes.
over half a dozen at least.
On the other hand when you
think about the
difficulty of judging rolling and the individual variation, my guess is
dozen genes is more like the maximum number.
It seems clear that rolling
is a multi gene complex just like most
physical traits in pigeons.
also indicates that some of these genes are codominants.
observation has been that Rollers are quite calm birds
relative to many breeds.
I have to
wonder if calmness is not an important part of good rolling performance? A
bird that felt stress during its first
attempts to roll, as a flighty bird might, would naturally resist
As I feel performance is
wholly voluntary and the bird must enjoy it calmness and a low tendency
excited or stressed may be important.
Rollers also seem to have a low degree of homing ability. Attempts were documented to train a variety of breeds to home in the Hollander years of the Newsletter. Rollers were the poorest homing breed tested. Even with considerable training few would come home from 25 miles. Last year I flew some birds from May 1 until about October 1. I culled 20 of these birds in early October by cutting their bands off and releasing them 15 miles air distance from my house. Only one of these birds came home and it took that bird several days to return. It was a three year old bird. Homer guys tell me that they would expect 100% return if they did such a test with Homers. I think Rollers may have been selected for non homing ability. It is highly desirable for Rollers to fly close enough to the loft so they can be seen most of the time. I live in a pretty heavily wooded area. So I can only see my birds fly when they are close to the loft. If they go more than 1/8 mile horizontal distance from the loft they are going to be behind trees. I can see them about 75% of the time when they are flying. By contrast, when I flew Homers they were often out of sight for an hour or more. Selection for poor homing ability probably induces Rollers to fly much closer to the loft so they do not get lost.
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