Local Birding

Last week, on my birthday, I went out to bird along the Clarksberg Branchline Trail in West Sacramento, Ca. I was out on the trail at 6:30 just before dawn and wandered around for about an hour. The section of the trail that I was birding is really close to my condo and as such is a spot that I bird pretty frequently. This morning was one of those mornings that reminded me of why it so special, and important, to get out to places close to where you live and see what is happening in the world.

It was a great morning of birding. I saw a Red-breasted Sapsucker searching for food high in a oak, found many Varied Thrushes foraging in the leaf litter for insects and worms, watched a pair of Red-shouldered Hawks as they flew screaming across an open field straight towards me to land in a tree right over my head, and found a White-throated Sparrow (an unusual winter visitor to the west coast and my favorite member of the genus Zonotrichia) hanging out with a group of Golden-crowned Sparrows! The birds were wonderful, and I was right around the corner from my house, and only there for an hour! You do not need to work hard for great birding.

These small, local birding explorations are not grand adventures. They are not exhilarating chases to see some incredibly rare species. They do not generally produce stupendously high species totals. But what they are is the bread and butter of birding experiences. They keep us in touch with the movements and pulses of the natural world right around where we live. Pulses that can go unnoticed all too easily in our modern busy lives. These local explorations give us the one-the-ground knowledge of what creatures are living next door, of how the environment changes from season to season and year to year, of exactly where a given bird can be found and what they like in a habitat. This is not knowledge that can be obtained easily, and it is knowledge that can be of great import. So get out to visit the local spots that are close to you and keep an eye on what is going on. you never know what you are going to find!

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Powered Flight in Vertebrates

Powered flight, the ability to propel oneself through the air against the force of gravity, requires a great deal. From specialized bones to specialized skin, and everything in between, the demands of flight penetrate all aspects of an animals’ life. And yet, despite how mechanically difficult powered flight is to achieve, it has evolved three different times in vertebrate evolution, once in birds, once in bats, and once in the now extinct pterosaurs. One of the things that make the three different evolutions of flight especially interesting is that the three different groups accomplished the feat is such different ways.

A pterosaur wing has a large upper arm bone, two smaller forearm bones, a few wrist bones, and then four fingers. The first three are small fingers that have small claws at their tips and are free to move and grasp objects. The fourth finger is extremely long, extending all the way to the tip of the wing. The bones of this fourth finger are longer and thicker than the bones of the other fingers, and this is because this fourth finger supports the entire wing membrane. The wing membrane attaches all along the rear surface of the fourth finger, the rear surface of the arm, and then to the side of the trunk of the animal and even to the leading edge of the hind legs. That means that, when a pterosaur is in flight, the whole weight of the animal is being supported on once finger of each hand! Some pterosaurs got to an estimated 550 lbs (although most were about 25 lbs) with a 10 or 11 meter wingspan, so those are some strong fourth fingers!

A bat wing is the same upper arm bones of the pterosaur, but the hand is very different. Instead of supporting al the body weight of the animal on just one finger, all five of the fingers of a bat are elongated (the thumb is the only finger that is small and clawed and free to grasp). In between each of these fingers, and extending from the pinky finger to the body are membranes that the bat can stretch or fold as needed by moving the bones in its fingers, hands, and arm. Since all the fingers are sharing the load, each one is proportionately much finer and thinner than the fourth finger of a pterosaur. Additionally, bats have thin muscles that cover the surfaces of the membranes just beneath the skin. By tensing or relaxing these muscles, the bat has very fine control over the sharp and tension of the wing membranes, and this turns out to be very important in bat flight. It is not known if pterosaurs had similar muscles on the membranes of their wings, but it seems likely that they did.

A bird wing also has the same basic upper arm bones seen in the other groups, but instead of elongating bones and making them delicate and distinct, birds go the opposite direction. Most of the bones in the hand and fingers of a bird are fused together. This makes a structure that is short, thick, and strong. Out of this support structure extends feathers. Not a membrane made of skin like a pterosaur or a bat, but a completely different evolutionary innovation. Feathers, and flight feathers in particular, are strong and thin and light. Flexible enough to bend a bit to change shape, but rigid enough to support the weight of the bird and the forces of air-speed, drag, lift and gravity that all flying organisms have to contend with. In modern birds, muscles in the skin at the base of the feathers allow for independent control of each feather. This allows birds to have amazing control over the shape of their wing.

Flight is a fascinating example of how a complex structure or function can arise by natural selection. In these three cases, natural selection favored three very different, and ultimately successful, experiments in how to get an animal airborne. All three were very different solutions, which is worth remembering. Most of the problems out there, even really hard ones, probably have many different solutions, you just have to tinker and figure them out.

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The Ethogram: Creature Feature: Megamouth Shark

Check out my post on the Ethogram about these really cool, really rare, plankton eating shark!

http://theethogram.com/2015/02/02/creature-feature-megamouth-shark/

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