 At university Gillham fell in love with the coast and began a lifelong study of seabird islands, with research on Skomer and Skokholm.In 1953 she completed her PhD in Island Ecology at the University of Wales, Bangor, with her thesis researching the effects of seabirds on the vegetation of islands, based on research carried out on the islands off the Pembroke coast.Her PhD was supervised by Professor Lily Newton, who Gillham later dedicated her book 'Sub-Antarctic Sanctuary