In a statement posted to their social media account, the San Diego Zoo Safari Park wrote that the two male lesser flamingos are now fostering a chick after "showing off their parenting skills with a dummy egg earlier this year”.

Earlier this year, the two lesser flamingos were spotted sitting on a nest, according to the zoo.

Care specialists gave them a fake egg as a way to keep them occupied and stop them from interfering with other nests. The flamingos did such a good job caring for their fake egg that the wildlife specialists decided to give them a real, fertile egg.

"Wildlife care specialists sneakily swapped a fertile egg into their nest, allowing another pair of flamingos to double-clutch and raise a second hatchling,” the zoo explained.

"The pair have perfected their fatherly duties by alternating brooding responsibilities and keeping the chick satisfied thanks to a hearty helping of crop milk every day”.

Crop milk comes from the parents' upper digestive tract, and the zoo explains that "both males and females can feed the chick this way, and even flamingos that are not the parents can act as foster feeders”.

"The begging calls the hungry chick makes are believed to stimulate the secretion of the milk. As the parents feed their chicks the crop milk, they are drained of their colour—so much so that their plumage turns a pale pink or white! The parents gain this color back eventually as the chicks become independent and eat on their own."

The two foster dads are both in their 40s and are lesser flamingos, a species found in sub-Saharan Africa and western India.