Well, you should have. Because it's the best thing ever. Seriously. (Read the New York Times article about it)
eBird is a citizen-science intiative from the Cornell Lab of Ornithology to get birders across North America, (and now, the world!) to report their bird sightings and build a huge, detailed dataset of where and when birds are seen. Along with the many brilliant uses for this data for science, it's also a great help for wannabe birders like myself to identify and learn more about birds.
Luckily, there are a lot of great sources online for helping develop birding skills. Having only really started watching birds when I moved overseas, learning how to take advantage of broad categories to narrow down what an unknown bird might be, was a huge breakthrough for helping me improve my ability to recognize new species. Visually categorizing a bird based on relative size and shape, color patterns, behavior, and habitat are all steps in narrowing down what a streak of color flying past or foliage-obscured bird might be.
Just this morning, I was distracted from my work by a fast-moving raptor that flashed past my parent's apartment as it was mobbed by about 8 American crows. With only about 3 seconds of blurry viewing time, a glimpse of a barred-tail, somewhat pale underside and brownish streaky back, I quickly jumped online to determine what I'd seen.
First stop, a look at the eBird bar charts for NYC to see which species of hawk are spotted in the area at this time of the year. In November, the options were Sharp-shinned hawk, Cooper's hawk, Red-shouldered hawk and Red-tailed hawk. I knew it wasn't a Northern harrier already because I've seen them in California and it didn't have the characteristic white rump.
Take a look at the 'life-history' tab for the Cooper's hawk, Sharp-shinned hawk and American Crow on the All About Birds website from the Cornell Lab of Ornithology.
Here's a great image by Chuck Roberts- a juxtaposition of Sharp-shinned (left) and Cooper's hawk (right) on same fence (two separate images of immature birds on the same fence).
This video, from the Cornell Lab of Ornithology's Inside Birding series, has Jessie Barry and Chris Wood explaining how to use size and shape to determine which bird you're looking at. All of the videos in this series are great for learning birding basics.
[Side bar: I was lucky enough to meet these two awesome birders last week- they are incredibly nice people, have an amazing knowledge of birds, ecology and technology, and Chris is even good at imitating people's accents. Good storytelling and birding!]