Bird Size and Bird-Brained Math
Oh, you're going to love this one - determining bird size from a photograph. For the backyard birder, this is pretty easy as long as you have a known reference. (Though for a nature birdwatcher, I'd imagine the task is a bit more formidable.) Alrighty then... Where to begin? Well, how about at the beginning Beguine? Here's the pic and we want to know the length of the crow...
(Before we get to truly rocking and rolling, be forewarned that I'm using a digital microscope and a digital caliper, so if the following photograph strikes you as odd, that's OK. I'm just trying to introduce as much accuracy into the process as possible. There's no reason why you can't use a magnifying glass and a decent rule to perform the same steps...)
And away we go!
- Right off the bat, we're going to have to relate the unknown length of the beastie to a known length in the image. Well, it just so happens that I built that crow feeding tray and know that the rail that goes around the top is .75" tall. So now we have a reference.
- Next, I used the microscope and found the length of the bird in the picture.
Hmmm... Looks to be about 31 mm
- I repeated the step above and found that the .75" rail was about 1.4 mm
- So what is the ratio of the image railing to the real railing? It's about 13.25.
- Onward! To get the real length of the creature, we'll have to multiply the picture length of 31 mm by 13.25 and that gives us 410 mm, or about 16.125". That sounds right and looks right. Granted, the bird might be crouching or the snapshot angle may not be at a true 90 degrees... But close enough.
See you by the feeders,
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