Male swan 'adopts' eggs at Abbotsbury Swannery
A male swan at Abbotsbury Swannery in Dorset has "adopted" the eggs of a female whose mate had died.
Swanherds said it was "highly unusual" for a cob not to to kill young that are not his own.
The first of hundreds of cygnets have begun hatching at the swannery, the only managed colony of nesting mute swans in the world.
It was established in the 11th Century, when Benedictine monks began farming the birds for their banquets.
The pen (female swan) recently lost her mate when it was killed in a territorial dispute.
Swanherds put up a fence to protect her nest but another neighbouring cob swam downstream and has adopted her eggs as his own.
Deputy Swanherd Steve Groves said he had not seen such "very odd" behaviour in 25 years of working on the lagoon near Chesil Beach.
"This seems to go against what scientists call the 'selfish gene', where you would expect a cob to kill young that don't belong to him," he said.
"Staying true to the old adage that swans mate for life, we believe she will stay paired with him and next year he will be able to father his own cygnets with her."
The eggs are expected to hatch overnight.
About 100 breeding pairs of swans at Abbotsbury Swannery have produced about 500 eggs.
The hatching of the first cygnet is traditionally taken as a sign that summer has arrived.
This year first cygnet was born early on 16 May, while in 2012 the first one was born at the end of April.