what does howling mean?

[lbaker]

One of my dogs will howl/sing along whenever she hears a harmonica, she enjoys the attention! I once had a shepard that would start howling if I would even put my head back and make a howling face, even without making a noise He too loved being part of the party

[Kosy]

Renowned dog behavorist Dr. Stanley Coren states that dogs howl to say "Here I am." Responding to a howling-like sound is a natural response, a greeting, as it were.

[elizabethann]

Well Fenway said "here I am" and "how do you do" for quite a bit this morning. There was an accident down the street that had 2 ambulances, a fire truck and 3 or 4 police cars driving by.

[orangegirl]

My dog also howls when she hears the sirens. I work at Doggie Daycare, and when one dog starts to howl, all of the other dogs also join in. They all sit in a circle and howl and/or bark if they are not so good at howling.

[Scooby4]

The answer is that the dogs are responding to a higher frequency than we "humans" can here. Not all sirens produce this higher pitched sound but most do. The sound is about the same as a "dog whistle". Blow a dog whistle and you may have the same results.
I don't think it "hurts" their ears but it may bother them a bit if they have infections. I've never seen dogs get vicious as a result of hearing this noise so I don't think the howling response is terriotorial. It may just fall along the lines of "yawning". You see someone yawning and you will do it a few minutes later. Same with howling.