Keepers at the zoo in Worms, Rhineland-Palatinate, said that they tried introducing Gertrud to the rhea babies after their father failed to take care of them properly.
“She's just really relaxed,” zookeeper Karina Decker said on Thursday.
Gertrud has been taking care of the chicks for around six weeks and taught them to drink and to peck for food.
Rhea are flightless birds that grow to around 1.5 metres tall when they reach adulthood – so Gertrud might find herself rushing to keep up with her new brood in very short order.
Male birds are usually responsible for incubating the eggs and raising the chicks among the rhea, which are native to South America.
“Everything was just normal at the beginning,” Decker explains of the abandoned chicks.
But after the first few chicks emerged from their eggs, the male rhea would no longer allow them into his nest.
Since there were storms approaching and the chicks wouldn't have survived a soaking at such a tender age, the zookeepers had to intervene by bringing the chicks indoors.
One of the zoo workers then had the bright idea of bringing Gertrud from home to stand in for the father – and the rhea ended up making her one of their own.