Keepers at a bird sanctuary in West Sussex hoped that the last remaining female Blue Duck in the country - called Cherry - might mate with either of the drakes, Ben or Jerry.
But neither male duck appeared interested and are now inseparable at the Arundel Wetland Centre, leaving Cherry to her own devices.
Centre warden Paul Stevens said he was disappointed that efforts to produce new Blue Duck offspring had failed but said the two male birds made "a lovely couple".
"They stay together all the time, parading up and down their enclosure and whistling to each other as a male might do with a female he wants to mate with," he said.