I have a 3-year-old Gerbian Shepsky who whenever he hears fire truck, ambulance, or police car sirens he just starts howling (he does not howl at car horns, but he will bark at them) he started doing this at 1yr and has kept doing it since. I don't know if this is normal at all. (Note: A gerbian shepsky is a German Shepard husky mix, but mine also has a bit of Alaskan malamute)
Many dogs howl at sirens, so it's nothing to be concerned about. There are a few reasons we think this happens, though experts aren't sure:
- To communicate with what they may think is another dog (The Spruce Pets)
- To alert you to an abnormal sound they think you should know about (Hill's)
- To scare the sound away, which in their mind may work because the siren does move away from them—this can in turn reinforce the behavior and make them do it more
Given that your dog reserves the howling for the sirens but barks at other loud things, it could be that either your dog perceives one as a threat but not the other, one as another dog howling and not the other, or something altogether different! While a normal behavior, it's still a mysterious one.