Are the crows there all the time or only during specific times of the day? I listen to this pet behaviorist out here in So Cal who sometimes advises on the use of an airhorn for behaviors you would like your bully to change. Just blow it when Angus starts going nuts over the crows and see how he responds. I've never used one myself but it may be worth trying. You can buy airhorns on Amazon, btw.
Oh, and Angus is a real cutie!!