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An estimate of the breeding population of royal albatrosses (Diomedea epomophora sanfordi) on the eastern islet of The Sisters group of the Chatham Islands in January 1954 was between 400 and 450 birds. In October 1964 the breeding birds were considered to be occupying only one-quarter of the area as seen in January and the count of birds was accordingly multiplied by four giving a theoretical peak breeding population of 360 pairs.

Similarly, Buller’s mollymawk (D. bulleri) at the corresponding dates in 1954 and 1964 was considered to have a breeding population of 250 and 240 pairs respectively. A preliminary count from RNZAF aerial photographs (fide C.J.R. Robertson) indicated the presence of 630 pairs of royal albatrosses on the eastern Sister at the end of November 1973, and more detailed results are expected from current field studies.

At The Pyramid, a southern outlier of the Chatham Islands, counts of birds along strips of rock faces suggested a total population for the Chatham Island mollymawk (D. cauta eremita) of 2,500 pairs, a figure comparing favourably with earlier estimates of “several thousand” and “between two and three thousand” pairs.

Based on all the information from visits made up to 1969, tentative timetables have been drawn up for the breeding cycles of the Chatham Islands populations of the royal albatross and Buller’s mollymawk, both of which also breed elsewhere, and of the Chatham Island mollymawk which is known to breed only on The Pyramid.