I'm just going off a post that was done here in 2012. From that information, my understanding would be that you could have 10 pets, no matter the breed/species, but that was all the animals you could have. Either way, I'm only planning to have 3 hens.
So, I just got off the phone with the City Zoning Officer for Marlborough, MA and she was VERY helpful. She told me that my zone isn't the right zone but she wouldn't care if I got chickens as long as:
1) there weren't a ton of them
2) I got no complaints from neighbors
3) they had cute little names and came when called
In her words, she can't tell me what kind of an animal I can have as a pet :-D
She also said that:
1) she would be the person enforcing the zoning of the city if there were any issues
2) she would work with me if that was the case and there were complaints/issues
3) I cannot have roosters (I wasn't planning to anyway)
I feel like she would be very supportive of my efforts, especially because the lot I have is 750 sqft short of being a Rural Residential Zone that has no issues with chicken keeping, the Health Inspector's sister has a flock of chickens, and the houses across the street and behind me ARE Rural Residential Zone properties.
Finally, she helped me figure out who my Ward Councilor is and how to reach him so that if I wanted to propose making some tweaks to the current ordinances, I could contact him. 750 sqft seems like an awful little amount to zone differently than the properties in front of and behind mine in order to disallow something, especially when the area behind me is wooded before the next yard and a brook runs through it.