you used to need to apply for a permit - https://apps.pittsburghpa.gov/dcp/Urban_Agriculture_Handout_New_Legislation_Version.pdf

But now it seems you don't -

https://firemancreative.net/city-of-pittsburgh-passes-new-urban-agriculture-zoning-code/

https://apps.pittsburghpa.gov/dcp/2015.03.10_-_Urban_Agriculture_Final_Revision.pdf

I'd still call the city anyway to find out the exact requirements. It seems that you need a decent amount of space even for a few chickens within the city, and not many people have that much space especially if you're in an east end neighborhood.