Dr Paul Thompson from Aberdeen University's lighthouse field station, near Inverness in the Moray Firth, said the killer whales were doing nothing unusual.
'If there is food where they are, at Catfirth Voe (the Shetland word for bay), then they will be happy. Normally they don't come this close in to shore in Scotland. But as they have, then let's give them some space.'
They have been there since Saturday. It was thought that they might become stranded or that they were trying to protect an injured member of the group.
Calls that boats should be called in to drive the group back to the open sea have been rejected in favour of waiting until early in the new year, when a high tide will deepen the normally shallow entrance to the voe.
The 'sighting season' for killer whales is normally between May and September. However, Dr Thompson said that in countries such as Norway and Canada, killer whales were routinely seen very close to shorelines.
'It should be remembered that cetaceans (the marine mammal group which includes dolphins, porpoises and whales) in places like Florida can live out their entire lives in two or three metres of water. And in fact killer whales - a serious carnivore - can sometimes throw themselves on to land in order to catch a seal.'
The Whale and Dolphin Conservation Society said it was not immediately concerned about them. There was no record in Britain of any being stranded.