As gulls are a protected species, it is illegal to harm the birds or disrupt their nests, chicks or eggs.
Newydd Housing Association is developing the site for homes and shops under a £5.4m scheme.
Aberdare Demolition began work in May pulling down the old court house and was scheduled to complete in August. It has now had to down tools until the chicks fly the next, which is expected to be sometime next month.
A spokesperson for the housing association said: “It was a tricky situation for us as we really want to get these homes built but we cannot disturb the nests. After expert advice from the ecologist at the Vale of Glamorgan Council we have decided to stop the demolition until the chicks have happily flown away.”
A contractor for the build element has yet to be appointed. Bids are now being assessed.
Picture below is what the development is expected to look like.