Hi All,
My apologies for one more message concerning Macquarie Island and the
eradication program for rabbits and rodents (birds get mentioned in the last
paragraph!). There have been a couple of emails to birding-aus suggesting
that the successful removal of cats (last one was shot in 2000) from
Macquarie Island is the cause of the rabbit and rodent problem. While it may
be a contributing factor, I don?t believe that cats were likely to suppress
rabbit numbers to the extent implied.
I?ve just come across a reference that adds an interesting historical
perspective as rabbits and cats were both established on the island prior to
1900. It was published in 1956 (Law, P. and Burstall, T. Macquarie Island,
ANARE Interim report #14). The relevant paragraph for rabbits reads??Rabbits
are now firmly established and are extremely abundant in many localities
over the southern two-thirds of the island. In 1949-50, in many parts of
this area, they completely destroyed much of the natural vegetation, leaving
little but mosses and roots. In the Pleurophyllum bogs, when they have eaten
the leaves and heart of the plant, they even dig out the roots, a method of
attack first noted by Hamilton in 1884.? The report goes on to speculate
that cats may have suppressed rabbit numbers on the north of the island in
1884 (quoted from Hamilton) but also suggests that skuas probably take a far
greater toll on other vertebrates such as prions than cats do. As
Sub-Antarctic skuas also take rabbits, including cooperative hunting of
adult rabbits by pairs of skuas, there are clearly other dimensions to the
predator-prey interactions on the island.
In addition to flightless or flight limited species such as rails and
parakeets that are now extinct, one species that is likely to have been
influenced by cat predation is the Grey Petrel. Being the only truly winter
breeding species of bird on the island was bad news for the species. In
winter several million other seabirds are absent and fat Grey Petrel chicks
may be the only easy pickings. As a breeding species they were extinct on
the island by about 1950 (possibly much earlier). Since the removal of cats
though Grey Petrels have bounced back. While I am not aware of the latest
counts, at least tens of pairs have nested in recent years, and the
population appears to be increasing rapidly.
Rohan Clarke
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