Hissing loudly and aggressively, the 1.5 metre-long snakes exchanged lightning strikes at one another's heads for about 15 minutes.

In peak condition, the reptiles moved in parallel to one another with the early afternoon sunlight shooting silver streaks along their coal-black scales.

''When we first came upon them, we were pretty cautious, I'd have to say,'' Mr Green said.

An avid photographer, he had left his Nikon camera at home and borrowed partner Kristina Ortubai's Olympus and 80mm zoom lens. ''It was difficult to tell if they were biting, it all happened pretty quickly. Head strikes were frequent,'' he said.

At first, Mr Green and Ms Ortubai thought the snakes may have been mating.

Later they met ranger Scott Ryan in the reserve, who said it was most likely they were having a territorial dispute.

Generally timid, these red-bellied black snakes had thrown caution to the wind until one chased the other into marsh country near Black Flats dam.

''We stayed a few metres off because we were not quite sure how aggressive they'd be,'' Mr Green said.

''We edged closer, certainly not within striking range, but they were far too involved in fighting for us to be too much of a bother to them.''

Mr Green arrived in the ACT two weeks ago from Sydney to take up a new role as editor of Australian Aviation Magazine.

The keen bushwalker's spirits soared with his welcome to the bush capital.

''It was an uncommon sight and unnerving at times. But being an observer was really a privilege, on the basis that it is not something everyone sees every day.''

National Parks and Catchments, Parks and Conservation Service operations manager Brett McNamara said the observer's photographs highlighted the biodiversity and good supply of food at Tidbinbilla.

''It's a privilege to see something like this, a marvel that is mother nature. Sit back and take it all in,'' Mr McNamara said.