  In this paper, we present the identification of five previously unknown giant
radio galaxies (GRGs) using Data Release 1 of the Radio Galaxy Zoo citizen
science project and a selection method appropriate to the training and
validation of deep learning algorithms for new radio surveys. We associate one
of these new GRGs with the brightest cluster galaxy (BCG) in the galaxy cluster
GMBCG J251.67741+36.45295 and use literature data to identify a further 13
previously known GRGs as BCG candidates, increasing the number of known BCG
GRGs by >60%. By examining local galaxy number densities for the number of all
known BCG GRGs, we suggest that the existence of this growing number implies
that GRGs are able to reside in the centers of rich ($\sim 10^{14}$
M$_{\odot}$) galaxy clusters and challenges the hypothesis that GRGs grow to
such sizes only in locally under-dense environments.
