BirdWalk Newsletter

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1 BirdWalk Newsletter Walk Conducted By Perry Nugent And Ray Swagerty Newsletter Written by Jayne J. Matney Cover Photo by Jim Betz Notice the special wing posture at the elbows and wrists allowing for the Osprey s ability to hover Wings: Aerodynamics, Shapes, and Abilities Even before the Wright brothers, wings of birds have been analyzed and copied to allow humans to do what they are gifted to do- fly. Because the function and physics are basically the same for planes as it is in birds, the aerodynamics are basically of the same principles. Flight requires streamlined, rigid, lightweight structures. Maneuverability requires flexibility and panels. Mass (weight and gravity forces), lift, drag, and thrust are all elements involved in flight. Anatomical adjustments have been made to help in this endeavor for birds. Included in these adjustments are: #1. Their bones are strong, but hollow. This allows strength against forces involved and nicely set bones and joints as levers for strong muscles, yet have the consolation of a lightweight skeleton for being airborne. #2. Birds possess smoothly arranged feathers for better aerodynamics.

2 (See article Feathers, in the newsletter) #3. They usually have enlarged breastbones for strength against outside forces during flight and for attachment of strong breast muscles for flight. #4. Birds have beaks instead of heavy jaw bones and teeth which reduces overall weight. #5. Birds generally have streamlined bodies for better aerodynamics, therefore, aiding in flight. #6. Last, but not least, birds have wings. There are several physics/aerodynamic terms needed to understand how wings work. Weight- Force due to gravity acting on an object Lift- Upward force produced by a difference in pressure along surfaces due to airflow Drag- air resistance or forces that oppose the relative motion of an object Thrust- Forces which moves an object forward Force- Causes an object to change its shape, stops or stops motion, or changes direction of motion Air pressure- Force exerted by the weight of a column of air over a given surface area wing loading - weight of the bird or plane divided by the total surface area of the wing angle of attack - the angle at which the wing meets the airflow. Adjusting this angle can decrease or increase lift. high aspect ratio and low aspect ratio wing tips- the lack of large wing slots or fingered wing tips versus the narrow pointed wings with noneto-little wing slotting or fingers. Wings vary in sizes and shapes. These two factors, as well as the angle of those wings during flight, aid the bird in flight. The lift that the bird gets is directly affected by these factors. Have you ever put your hand outside the window of your car while it is moving and felt your hand get pushed upward from the air flow and pressure on the bottom of your hand when you tilted it up? When you angled your hand downward, it was forced downward? Aerodynamics for airplanes and birds function in the same way. If the front edge of the bird s wing

3 is tilted upward, that will put more air flow and more pressure onto the bottom side of the wing. This will cause the bird to go upward by providing lift. If the front edge of the wing is shifted downward, this is going to cause downward flight, because more air flow and pressure will be on the top surface of the wing. Birds which dart about and change direction in flight are masters of this type of air physics. Depending upon all of the other aspects of the bird s physical features, such as weight and size, the lift mechanics can be calculated by what is called wing loading. Wing loading calculates how fast a bird needs to be traveling to maintain lift according to those other physical aspects. It is measured in kilograms per square meter. Larger wings provide greater lift, therefore lower wing loading. This lower wing loading means that the bird does not have to put out as much effort or fly as fast to get lift. The counter to that is that smaller winged birds need to fly faster in order to get or maintain lift. When birds flap their wings, they are using size, shape, and muscle power to propel them forward. This is called thrust. Lift and thrust work together during the down-stroke. This forces air downward and back. During the up-stroke, the bird adjusts its wing partially in order to lessen wind resistance and get back into position for the next down-stroke. Navigation is highly dependent upon the twisting and repositioning ability of the wing joints and tail feathers. The type of wing depends upon the functions needed for the bird s lifestyle. Resources vary slightly on how they distinguish the different types or styles of flight. Basically, large wingspans are best for soaring, gliding, and speed, while more streamlined wings are best suited for diving at high speed and darting around with high maneuverability. But there is also the wing tip characteristics that come into play. The larger the slotting or fingers at the wing tip the more drag that can be produced with them to aid in soaring and stalling thrust. This would be considered wings with a low aspect ratio. Vultures, eagles, and hawks, for example, will fit into this category. Pointed wings with little to no slotting on the tips would be considered high aspect ratio wings. Examples of these birds would be swifts, terns, and sandpipers. Photos above are by Guenter Weber

4 With the many ways to break down the types or shapes of wings, for our purposes, I am going to categorize them according to the below list: Large Wing Span: There are actually 3 kinds of large wing span birds. The practice of gliding in flight is used by birds which are conserving energy by not working the wing muscles all the time. The typical glider will eventually need to adjust the wing to a new position in order to maintain or gain altitude but continue the forward motion. Gliders which are considered the slow flappers have large wing spans, broad feather surface and arched shaped wings. These birds are the egrets, herons, etc. See photo below by Guenter Weber. Also considered gliding birds, the soaring birds use external features such as air currents and thermals. Soaring birds will not typically lose altitude or have to make up for the adjustment needed as with the slow flapping birds.

5 Soaring birds are subdivided into passive or active soaring. Active soaring birds have large wing spans but their wings vary from others by having a narrow feather surface with pointed tips. These are the birds which soar the wind currents, especially useful for long distance migrators across the ocean such as an albatross. Passive soaring birds make use of thermals which are air currents which travel vertically due to heat rising. These birds have a much wider feather surface such as the eagles and vultures. They will usually have more distinct slotting at the tips than the active soaring birds. Osprey photo above by Chuck Fuhrman Elliptical Wings: These wings are wide, but shorter than the soaring or gliding type of wings with respect to body size. This enables them to be able to maneuver better for quick movements. They are generally fast at take-off and can be considered the dodging birds. These birds usually have slotting on the tips or edges of the wings as well. Therefore, they have a low aspect ratio wing. Birds of this category include the crows, thrushes, and sparrows. Crow wings are elliptical in type- notice slotted tips Photo by Guenter Weber High Speed Wings: High speed goes hand-in-hand with high aspect ratio wings. The wings are narrow and pointed. Many are also back-swept wings and are more flattened. These birds can dive quickly, and dart about in the air with fast aerial acrobatics. Examples of birds following this directive are swifts, tern, and pipers. Ducks can also be categorized in this grouping. Hovering Wings: Hovering wings are very specialized and usually small. However, there are a few exceptions such as the Osprey which is quite large and

6 has the ability to hover. The body is held almost vertical and the elbow joint is flexed to bring that portion of the wing back and forth at a horizontal plain. Another example would be the Belted Kingfisher. But when thinking of the bulk of hovering birds, we usually think of the hummingbirds. The wings are small, and the nervous system and musculature on these birds are fine-tuned for rapid wing beats. The flexibility of the joints in the wing are also key elements to this skill. The hummingbirds can rotate their shoulders unlike most birds. Because of these features and skills, these birds are sometimes referred to have motionless flight. This is when the downward stroke cancels out the upward stroke of the wings. Hummingbird Photo by Guenter Weber Of course not all birds will fit into one specific category. This is a human-made scheme and we cannot expect nature to follow all of our schemes. However, this gives you a foundational place to start. Food for Thought: Research was done by Jonathan Kennedy (Post Doc) through the Center for Macroecology, Evolution and Climate, University of Copenhagen on the differences in birds wings geographically as you move away from the equator. The research shows that the birds living nearest the equator have shorter, rounder wings than those further away from the equator. The reason for this is the fact that the birds nearest the equator do not have to migrate. Therefore, they have not evolved for the need to fly long distances. Going along with that, those that don t live near the equator have narrower, pointed wings. They are generally those birds which will need to migrate and take advantage of the long distance soaring type wing structure. Information Gathered for this article came from: Education at the Lab, The Cornell Lab of Ornithology; Ehrlich, Paul R., Dobkin, David S., and Wheye, Darryl, Wing Shapes and Flight, Stanford.edu; How Birds Fly Science Learning Hub,

7 Sunday 21 st, 2018 was a wonderful day for bird watching! 57 species were accounted for with the help of 8 participants. The duck varieties are still here, but the numbers seen are lower, probably because of the fact that the birds moved closer to the river and near Bubba s Pond when the snow storm came through last week. Many have yet to return to Ravenswood and the Audubon Swamp since the storm. Bubba s Pond is not on the survey. However, Wood Duck, Gadwall, Mallard, and Blue-winged Teal were all accounted for on this particular morning. Also in Ravenswood and Audubon Swamp were Pied-billed Carolina Chickadee on popcorn plant Grebe, Anhinga, Great Blue Photo by Guenter Weber Heron, Great Egret, Little Blue Heron, White Ibis, and Common Moorhen. In addition, an immature Bald Eagle made itself known twice during the day in the area between Ravenswood, the front parking lot, and the exit road. Near the cabins, the 8 participants viewed a White-throated Sparrow and a Killdeer along with other birds which were scattered throughout the property such as Eastern Phoebe, White-eyed Vireo, American Crow, Fish Crow, Carolina Chickadee, Tufted Titmouse, Carolina Wren, Ruby-crowned Kinglet, Eastern Bluebird, Hermit Thrush, American Robin, Northern Mockingbird, Yellow-rumped Warbler, Pine Warbler, Swamp Sparrow, Northern Cardinal, Red-winged Blackbird, and Common Grackle. Eastern Towhee were seen near the maintenance barns, and Chipping Sparrow were seen near the pavilion area. Along the exit road, a Gray Catbird and a Song Sparrow made the list. Along Oak Grove, the participants had a couple of excellent sightings: An Orange-crowned Warbler and an American Goldfinch.

8 In the woodpecker category, higher numbers than usual were seen of the Red-bellied Woodpecker, Downy Woodpecker, Pileated Woodpecker, Yellow-bellied Sapsucker, and Northern Flicker. Another highlight on the walk were some good looks at the Golden-crowned Kinglets. In the gardens, a Brown Thrasher was observed, and near the office Downy Woodpecker Photo by Cathy Padgett were some Cedar Waxwings. One, lone Mourning Dove was seen. Double Crested Cormorant and American Coot were located on the large, boat pond and the Perry Field Pond. Tri-colored Heron, Laughing Gulls, and Ring-billed Gulls were seen as fly-by species. Two Red-shouldered Hawk were calling out loudly to each other in the morning. A Blue-headed Vireo was spotted perched near the picnic tables at the end of the walk. Quick note: The elusive American Bittern was spotted and photographed out in the grasses of the large boat pond today as well. Of course, it was caught doing its I am a part of the grasses imitation, but to no avail. Guenter was able to capture this fun bird regardless. See Guenter s photo right.