A few years ago, a particular male cardinal perched outside my dining room window and pecked, pecked, pecked against the pane ... all ... day ... long. Apparently, when some birds robins also apparently display this behavior frequently spot their own reflection, they interpret this as an intruder and begin attacking or pecking at the window to chase the intruder away, according to the website Wild-Bird-Watching.com.
My cardinal hasn't reappeared this season, but he's been replaced by a male bluebird who is just as incessant, and perhaps even more aggressive. I spotted this one dive-bombing a squirrel that ventured too close to its nesting box.
Here's a YouTube video I made of the cardinal several years ago when I was bored one Saturday afternoon ...
... and here's one of the new visitor.
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