His pregnant mother, Mary, had been ill for several days but storms lashing St Kilda in the Outer Hebrides delayed a rescue. By the time she reached hospital it was too late and she died, along with the baby she was carrying.
Her death was a defining moment in the history of the island, which had been inhabited for more than 4,000 years. When he closes his eyes, he can still see his mother with her head covered in a shawl waving from the boat as she was transferred from the island. "It was a very sad moment for me and St Kilda," said Mr Gillies, who now lives in Ipswich. "It changed all our lives."
To mark three-quarters of a century since the last 36 inhabitants were evacuated from the island, the National Trust for Scotland has launched an exhibition charting the beginning of the end for the island said to be "at the edge of the world". Featuring previously unseen photographs, documents and diary entries from the late 1800s to the evacuation on 29 August 1930, the exhibition, at Wemyss House in Charlotte Square, Edinburgh, provides a unique insight into a lost way of life.
The inhabitants of St Kilda, which is 41 miles west of Benbecula, had been self-sufficient since prehistoric times in exploiting the resources of the sea, growing crops and keeping animals. Cut off from the rest of the world, they lived an almost communal lifestyle, sharing in the dangers, hardships and joys of island living. But by the beginning of the 20th century, advances in communication, tourism and the First World War changed their way of life for ever.
As the population became aware of the opportunities outside the island, farming and fowling gave way to tourism and paid employment. By the 1920s, the once sustainable population of 200 people had fallen to just 36.
Seduced by the conveniences of 20th-century living, they had debated long and hard over abandoning their island. But the death of Mary Gillies was the final straw. "The death of such a young woman when it could have been so easily prevented was the end for the remaining islanders," said Susan Bain, archaeologist with the trust and an exhibition organiser.
"They just didn't have the heart to go on. Island life had been changing for some time and by 1930 the people had realised just how cut off from the rest of the world they were."
During the First World War, St Kilda was a naval outpost and the islanders enjoyed daily communications, by telegraph and ship, with the rest of the country. After the war that stopped and they were again on their own.
But for another 12 years, they continued to battle on in the face of poverty, deprivations and the inconvenience caused by the weather. When the islanders finally made the collective decision to leave, it brought to an end thousands of years of human habitation in one of the most important unspoilt natural environments in the world. With its exceptional cliffs and sea stacks St Kilda, a collective name for the four islands of Hoirt, Dun, Soay and Boreray, is the most important seabird breeding site in north-west Europe.
Last month it joined an elite group of 24 locations which have been given two Unesco World Heritage Site listings in recognition of its remote and unspoilt natural environment along with its cultural significance.
It now ranks alongside Ayers Rock in Australia, Mount Athos in Greece and Machu Picchu in Peru. "What makes St Kilda so significant in cultural terms is that it provides evidence of how people lived and evolved since prehistoric times," said Robin Pellew, chief executive for the National Trust for Scotland, which has owned the islands since 1957. "It helps us to understand how people survived in extremely difficult and remote conditions over thousands of years. It is truly a unique and fascinating place."
St Kilda has the largest colony of fulmars in the British Isles, nearly 65,000, and the world's largest colony of gannets. Excavations have uncovered evidence of Bronze Age, Iron Age and early Christian communities. For generations, the men of St Kilda scaled the cliffs and harvested gannets, fulmars and puffins for food, feathers and oil, which they caught by hand or with a fowling rod or a snare.
Using small open boats to move between the islands, they managed flocks of Hebridean sheep, collected puffins on Boreray along with gannets and their eggs from the sea stacks.
In the late 1800s, as increased numbers of tourists began visiting, the islanders produced goods to sell such as sheepskins, tweeds, knitted gloves, stockings and scarves.
"The documents we have on display paint a picture of a society which has been portrayed as almost utopian," said Ms Bain. "It was a harsh but sustainable way of life which was brought to an end by the 20th century. Once communications and travel became easier, the islanders realised what they were missing and didn't want to be so cut off from the rest of the world."