Coleman (9) will throw his head back and howl along with Tootsie (7). Bailey and Sarah do not howl when the siren goes off. My little Annie used to "sing" to me too when the siren would go off too. The next door neighbors GS sings with my two as well.
I used to think it was because the noise hurt there ears but did some research and came up with an alternative - the siren sounds like another dog calling? So they are supposedly talking back and forth.
Koko howls when we go upstairs (she not allowed, cat zone!) and leave her downstairs. she will get in her crate and howl until someone comes downstairs with her. She will also do a quite howl if she is told to "sing" she almost sounds like she is doing the scales a bit off key!
Lily and Legend howl when they are outside and hear sirens. The sirens can be heard as far as 5 miles away. We live in Mt. Pleasant, SC, and there is quite a bit of marsh that the sounds travel across. Once they start to howl, they keep each other going; they actually are close enough to howl in each other's face. Now that's an "in your face" experience!
I had heard it was due to the their ears hurting, but read enough online to decide it's probably just their method of communicating with other dogs, especially across distances (like when hearing a siren or a coyote some distance away). But at our house, Rocket howls every time my son cries. It's really funny, but can be annoying because my son will cry louder to be heard over Rocket, then Rocket howls louder to be heard over Aaron, etc., etc., etc. In the meantime my husband and I are competing with them both in trying to get Aaron to stop so Rocket will stop. Then there's Rocket climbing over all of us to get to Aaron so he can lick him in his face. SU and I are usually laughing so hard that it only makes my son angry so he cries even more. What a fiasco!
Fortunately my son doesn't cry very much since he's six, but since I never had a dog howl to a crying child before. Harmonica playing and sirens, yes, but not this. It's funny.
Then there's the happy howl; Duke howls when he's happy, whenever we get up in the morning, when we are going outside, when I come home. It's so sweet. Labs howl much less that other breeds. I never heard Mitz or Judy howl, but once when I took Mitz for a walk and left Judy behind, neighbors said Judy gave the most mournful howl.
Well after doing some research on the internet about it, the answer seems to be that they are communicating their position. One website was talking about how a wolfes howl means "I'm here", and thats how they communicate their position over long distances because a howl can be heard further then a bark. Maybe the dog thinks the sirens is another dog, and he is letting the percieved dog know that he is there. My last dog used to howl all the time when he heard sirens, murphy is only about 7 months now, but he hasnt howled at all.