Growing up, I didn't think much about birds. To me there were only three kinds of birds: robins, ducks and seagulls. It wasn't until my twenty-first year that birds diversified for me. It started with my second course at U.Vic. It was officially called Biology 329: Biology of the Vertebrates of B.C., but most people called it the "Bird Watching Course". Our instructor was Salt Spring's David Fraser. Dave's contagious passion changed my life forever. A few days into the course, we went on a jam packed multiday field trip to the Nicola Valley. I never quite recovered from that trip. I was hooked; for the next few years I carried binoculars everywhere.
So what is it that's got me squawking praise for birds. Well, for one thing, many
paleontologists believe that they are the only living descendents of dinosaurs. While the mighty T.rex was chasing it prey, other theropod dinosaurs were quickly getting smaller. It was at this time that feathers started to evolve. These early feathers may have been used for
insulation or for colour. Another flight adaptation, the furcula (wish bone) evolved. While the fossil record is sparse, it is generally believed that close relatives of the T.rex evolved into birds over a relatively short evolutionary period of about 10 million years.
What else is so hot about these modern day dinosaurs? Well their body temperature for one. Birds run about 2 to 3⁰C hotter than humans. Flying is a lot of work. Higher temperature means higher metabolism and more energy for flying. Another cool thing
about birds is their respiratory system. Take a deep breath and hold it. You have 5 or 6 liters of air in your lungs. Now exhale as much as you can. There is still about 1 liter of air left in your lungs. This residual liter of air is low in oxygen and has a lot of CO2. When you take your next breath it mixes and dilutes the incoming air. Birds use a system of air sacs that send air through their lungs in a single direction. This reduces the residual, allowing birds to extract more oxygen and eliminate more CO2. The system takes up a lot of space, about 20% of a birds body volume. Whereas in humans it is only about 5%. Another feature that most birds have is hollow bones. Most of the strength of a cylinder is in the outer layer. This is the reason bicycles are made of tubes, not solid bars. It gives maximum strength for weight. Contrary to what you might expect, bird skeletons are heavier than those of a similar sized mammal, but the demands of flight create the need for an extra strong skeleton. Having hollow bones maximizes this strength while adding the least amount of weight.
So what about Salt Spring birds? They fly south for the winter right? Well, the answer is yes and no. Here on the BC south coast, vultures, osprey, rufous hummingbirds and a few others head south in the fall. We have our year round residents like ravens, eagles and oystercatchers. But, while many of us are California dreaming on dark December days, some birds come here for their winter vacations. As inland lakes freeze over in the fall, waterfowl go looking for some place warm, and they find it right here!
The Common Loon and Bufflehead are two examples of water birds that are more common in the winter.
Speaking of frozen lakes, even here on coast we get our cold spells. Go to frozen pond on
winter day and what do you see? Ducks standing on the ice, BAREFOOT! What the heck? How does a small animal with a high body temperature stay warm standing on ice? Well, there are two ways. One, they have physiological adaptations allow their feet function at cooler temperatures. Two, something called 'counter current exchange'. You see, the artery that carries blood to the feet runs right next to vein that carries blood back. The artery gradually cools giving most of its heat to blood returning in the vein. By the time the blood gets to feet it has cooled considerable and is then re-warmed on the way back. The foot operating at much cooler temperatures looses little heat to the ice.
Those little theropods have come a long way in the last 200 million years. They've come to live on every continent, in environments ranging from desert, to rainforest, open ocean and arctic tundra. They have diversified into 82 families and about 10 000 species, 588 in BC. They have evolved a higher body temperature, hollow bones and a highly efficient respiratory system. So the next time you hear a thunk in the living room, consider the possibility. Maybe a dinosaur just flew into your window.
Photo Credits
First dinosaur: Tirriko at pixabay.com/illustrations/velociraptor-dinosaur-utahraptor-5860316/
Second dinosaur: DariuszSankowski at pixabay.com/photos/dinosaur-gad-mammal-dino-extinct-958004/
Loon: J-photos at unsplash.com/photos/wNrRNR-9xd0
Bufflehead: Rodney Saigeon at unsplash.com/photos/6KzWYSZ7VZk
My sources include various books and that inhabit the natural history section of my bookshelf and the webpages shown below.