Heard Island is a wonderful place for birds. Indeed, Heard Island and the McDonald Islands are the only sub-Antarctic islands without introduced macrofauna, and which have had very little human influence (part of why they are listed as a UNESCO World Heritage Site). Freedom from human influence makes these islands scientifically very interesting, because it is extremely rare to have a site which is that pristine and that isolated.
The species diversity for birds on Heard Island is not very high, even though the number of birds is very large—in the millions.[1,2] Only 19 species breed on the islands, with another 28 species recorded as visitors or seen at sea within the region around the islands. Among the species breeding on the island are four types of penguins (king, gentoo, macaroni, and [my personal favorite,] rockhopper), and three species of albatross (wandering[?], black-browed, and light-mantled sooty). Two species, the Heard Island sheathbill and the Heard Island cormorant, are endemic to Heard Island and the McDonald Islands.
To study the populations of these birds over time, it is necessary to take a census of the populations periodically. On the face, this seems relatively straightforward, and will be familiar to anyone who has participated in the Audubon Society‘s Christmas Bird Count or the Cornell Lab of Ornithology‘s eBird program [ed.: both are excellent citizen science projects you can do in your area, and I highly encourage you to get involved with them.].
On Heard Island, surveying the bird populations is very difficult. Not only do some of the species look similar (e.g. rockhopper and macaroni penguins), but there can be vast colonies of them. Heard Island is home to an estimated 1 million breeding pairs of macaroni penguins alone! Adding to the challenge, some species nest in burrows underground, so a photograph of the area may not help estimate the numbers like it might when the birds and nests are visible. With the exception of the penguins, birds on Heard Island can fly, and will often do so. If you have ever watched birds in your backyard, you may know it can be difficult to count the number of chickadees (or hummingbirds, or other species) visiting, because they move around a lot and look alike.
Another challenge on Heard Island is that many places are quite inaccessible to humans. Sheer cliffs, unstable slopes, and glacial crevasses keep people away from nesting areas.
Even the act of counting birds can put some of them at risk: if a nesting pair is disturbed by a human—even 100 m away—they may fly off the nest long enough for a scavenger to fly in and eat the egg or the chick.
Detailed surveys of the breeding areas can provide important information about the migrations of the birds. Antarctic terns, which had been banded at Bird Island, South Africa, were later observed nesting on Heard Island.
The strategy for counting birds is a little complicated. For small numbers of birds (in my backyard at home, or rare birds on Heard Island), they can be counted individually; this works up to around 50 birds. Beyond that, the numbers are likely to become estimates, though high-resolution photographs of nesting colonies provide a record which can be carefully scrutinized later for more exact numbers. When estimating birds in the field, you would count the number in a small area (one binocular field-of-view, or a 10×10 m region of ground. That gives an estimate of the birds-per-area. Multiplying by the larger area (as multiples of the smaller one) would give an estimated total number of birds.
At sea, another method is used. Because birds are not standing or sitting on a nest, they are counted (species and number) for ten-minute periods, with the location, date, and time noted.
When I go to Heard Island, I will do some birding. My life list has no penguins on it, and I intend to change that. I will not have the time to do a full survey of the birds, but will probably get at least a few estimates of a colony or two. I also intend to do some at-sea counts if the weather and sea-state permit. These observations will be added to the eBird database when I return to civilization after the expedition. One additional challenge I will have is that all of the birds of Heard Island will be life birds for me, and I am not especially good with my field identification of new birds. If you know of a good field guide, please let me know; I’d love to have a good reference to bring with me.
 http://whc.unesco.org/en/list/577 UNESCO organization. Retrieved May 17, 2015.
 Woehler, E. J. “Status and conservation of the seabirds of Heard Island”, in Heard Island: Southern Ocean Sentinel (Eds K. Green and E. Woehler) Surrey Beatey & Sons, 2006, p. 128-165.