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is not known and keepers aren't sure yet whether it is fertilised

A pair of gay vultures have adopted an egg abandoned by its mother at a zoo and are trying to incubate it themselves in a nest they have built.

Animal keepers had collected the egg in the muddy ground under a tree where it had been dropped by a griffon vulture called Lisa at Nordhorn zoo in Germany.

Zoo spokeswoman Ina Deiting said Lisa had made no attempt to build a nest.

Birds of a feather: Gay vultures ISIS and Nordham are seen in their compound at Nordham Zoo where they have adopted an egg abandoned by its mother in the hope of incubating the chick and raising it themselves

Incubation period: The egg was temporarily placed in an incubator before being entrusted to the male couple who 'promptly sat on it' in a nest they have built. However, it is not known whether the egg is fertilised

The egg was temporarily placed in an incubator before being entrusted to the male couple, named ISIS and Nordhorn, it was reported by national news agency DPA.

Deiting said the couple 'promptly sat on it' in the hope of incubating the egg.

The biological parentage of the egg is unclear and zoo keepers also don't know yet whether it is fertilised.

The story of ISIS and Nordhorn is the second involving gay birds to make news in Germany this month.

Several days ago, newspapers reported that the gay king penguin couple Stan and Olli had been moved from a Berlin zoo to an all-male enclosure in Hamburg.

Zoo keepers were intrigued by the lack of fertilised eggs after Stan and Olli joined the breeding programme.

Animal keepers had collected the egg in the muddy ground under a tree where it had been dropped by a griffon vulture called Lisa at Nordhorn zoo (above) in Germany

The birds were chosen specifically to participate in the programme to ensure the survival of the species, but their lack of interest in the opposite sex proved a major problem.

Speaking earlier this month, Berlin Zoo spokeswoman Christiane Reiss told The Local.de: 'They're gay, as far as we know.

'They never bred. And when it came to courtship, they only mated with one another.'

Previously, it was reported that two male lions were seen mating in a Botswana game reserve.

The two adult lions were photographed becoming more than affectionate in the Lagoon area of the Kwando Concession.

Lawyer Nicole Cambré, who took the pictures during a safari trip, said she saw the two male lions 'mating' and was told by her guide that this behaviour had been evident for a week.