4 Answers

Howling is a form of communication, but it is not always easy to determine what the dog is trying to say; it may be a sign of distress or it may be intended as a signal to other dogs. Two main explanations for howling at sirens have been suggested. One is that the sound is painful todogs and the other is that it is instinctive behavior: a response to a noise that sounds — to the dog — like another dog howling. The second theory is more generally accepted.

Read more >>>http://www.wisegeek.org/why-do-dogs-howl-at-sirens.htm#slideshow

I take my grand son out to Howl at the moon on some full moons, he loves it, he is almost 5, we have done it since he was 2! 

The only reason dogs do not respond to humans in speech is because they lack the facility to talk. But maybe they can learn to type if the keys were bigger. They do communicate through thought, gestures and vocal noises and some dogs can pronounce words that are understandable by humans. Usually less than 100 words. The potential contributions dogs and other animals have made has barely been tapped. Animal brains, are a product of evolution and thus express keen reserves of deeper comprehension than humans do in some areas. Breaking down the barriers to our mutual understanding has been an on-going process.   

Sometimes dog howls but most of all wolves howls at the full moon.Dogs howl because that is the form of their communicate to other.Sometimes they howl because they are crying.That is when the dogs howls.