I live in Sofia more than a year and I can tell you the main bird species here.
The first bird you will see here is the Magpie. There are very large numbers of them in almost every place in the city.There are also many grey crows.
Other bird that you can see here in Sofia is the great tit. In the winter they group with other small birds to find food and often "attack" food that is left on the terraces.
One of the most interesting birds that I see here is the Green Woodpecker. But all the birds that I saw were male.
I don't count the birds that I saw in the parks in Sofia because there is different habitat and the birds there are like the birds in any small forest in Bulgaria. From what I saw here for the last year I can say that the bird variety is very poor inside the town except the park of course.
The pictures in this post are from http://en.wikipedia.org.