This Antarctic territory is a land claim unrecognised by most other countries,[6] meaning that Mawson Peak is the highest mountain with undisputed Australian sovereignty.

From 1855 to 1882 a number of American sealers spent a year or more on the island, living in appalling conditions in dark smelly huts, also at Oil Barrel Point.

The first recorded aircraft landing on McDonald Island was made by Australian scientists Grahame Budd and Hugh Thelander on 12 February 1971, using a helicopter.

A July 2000 satellite image from the University of Hawaii's Institute of Geophysics and Planetology (HIGP) Thermal Alert Team showed an active 2-kilometre-long (1.2 mi) and 50- to 90-metre-wide (164–295 ft) lava flow trending south-west from the summit of Big Ben.

Some wetland areas have been recorded on McDonald Island but, due to substantial volcanic activity since the last landing was made in 1980, their present extent is unknown.

These include the southern elephant seal and macaroni, gentoo, king and eastern rockhopper penguins, considered to be wetland species under the Ramsar Convention.

The weather is marked by low seasonal and daily temperature ranges; persistent and generally low-lying cloud cover; frequent precipitation and strong winds.

At Heard Island, exposure to salt spray and the presence of breeding and moulting seabirds and seals is a particularly strong influence on vegetation composition and structure in coastal areas.

Evidence from microfossil records indicates that ferns and woody plants were present on Heard Island during the Tertiary (a period with a cool and moist climate).

The vascular flora comprises the smallest number of species of any major subantarctic island group, reflecting its isolation, small ice-free area and severe climate.

Areas available for plant colonisation on Heard Island are generally the result of retreating glaciers or new ice-free land created by lava flows.

Today, substantial vegetation covers over 20 km2 of Heard Island, and is best developed on coastal areas at elevations below 250 m. Bryophytes (mosses and liverworts) contribute substantially to the overall biodiversity of Heard Island, with 43 mosses and 19 liverworts being recorded, often occupying habitats unsuitable for vascular plants, such as cliff faces.

Forests of the giant Antarctic kelp Durvillaea antarctica occur at a number of sites around Heard Island and at least 17 other species of seaweed are known, with more to be added following the identification of recent collections.

Low seaweed diversity is due to the island's isolation from other land masses, unsuitable beach habitat, constant abrasion by waves, tides and small stones, and the extension of glaciers into the sea in many areas.

[citation needed] The consequent increase in habitat available for plant colonisation, plus the coalescing of previously discrete ice-free areas, has led to marked changes in the vegetation of Heard Island in the last 20 years or so.

Expeditioner boot traffic during the Australian Antarctic program expedition in 1987 may be at least partly responsible for the spread, but it is probably mainly due to dispersal by wind and the movement of seabirds and seals around the island.

Only one small specimen was found growing on a coastal river terrace that had experienced substantial development and expansion of vegetation over the past decade.

[36] As with plants, a 1980 survey of McDonald Island found lower diversity there, with just eight lichen species and a number of non-lichenized fungi recorded.

A paper reviewing population data for the black-browed albatross between 1947 and 2000/01 suggested that the breeding population had increased to about three times that present in the late 1940s,[44] although a Convention for the Conservation of Antarctic Marine Living Resources CCAMLR) Working Group was cautious about the interpretation of the increasing trend given the disparate nature of the data,[45] as discussed in the paper.

Two species, including the thrips Apterothrips apteris and the mite Tyrophagus putrescentiae are thought to be recent, possibly natural, introductions.

A study over summer at Atlas Cove in 1987/88 showed overall densities of up to 60 000 individual springtails per square metre in soil under stands of Pringlea antiscorbutica.

Distinct differences in relative abundances of species between habitats has also been shown, including a negative relationship between altitude and body size for Heard Island weevils.

The large macro-alga Durvillaea antarctica supports a diverse array of invertebrate taxa and may play an important role in transporting some of this fauna to Heard Island.

[47] The presence of glaciers on Heard Island provides an excellent opportunity to measure the rate of glacial retreat as an indicator of climate change.

Between 1949 and 1954, marked changes were observed to have occurred in the ice formations above 5000 feet on the southwestern slopes of Big Ben, possibly as a result of volcanic activity.

[49] Retreat of glacier fronts across Heard Island is evident when comparing aerial photographs taken in December 1947 with those taken on a return visit in early 1980.

The increase in the rate of ice loss suggests that the glaciers of Heard Island are reacting to ongoing climate change, rather than approaching dynamic equilibrium.

[46] The United Kingdom formally established its claim to Heard Island in 1910, marked by the raising of the Union Flag and the erection of a beacon by Captain Evensen, master of the Mangoro.

[53] The islands are contained within a 65,000-square-kilometre (25,000 sq mi) marine reserve and are primarily visited for research, meaning that there is no permanent human habitation.

[54] In part to carry out this mission, as of 2023, the Navy's Armidale-class boats are in the process of being replaced by larger Arafura-class offshore patrol vessels.