A grey and white bird made a nest in my tree? What type of bird is it?

There has been this very loud peeping sound that has been waking me up early in the morning. Today, by chance, I saw a grey and white bird that was about the size of a seagull or small hawk, fly up to the very top of my eucalyptus tree. I saw it land at one of the very high branches with its wings spread. It looked kind of like it was feeding its young. I only got a small glimpse of it because it came fed its baby then flew away. I live in San Diego, CA. Does anyone know what this specie men is?