Island bird population slowly increasing
The eradication of cats followed by the recent blitz on mice and rats has rolled out a welcome mat to burrowing seabirds which are now returning to Macquarie Island to breed.
Although it is too early to quantify numbers of all species winging their way back to their sub-Antarctic nesting ground, wildlife ranger Bree Hunter is buoyed by the number of active burrows she has discovered this summer.
Most of her time is spent monitoring wildlife population trends on the island, with an emphasis on burrowing petrel species. An island-wide census of both northern and southern giant petrels will be completed annually for three years until 2013. Rangers count nests at the beginning of the breeding season, and re-visit them later to record breeding success.
Bree says that the eradication has certainly benefited Macquarie Island’s burrowing petrel population. Although it is too early this summer for statistics on breeding success, Bree was able to provide data for one species of burrowing petrel which indicates an increase in population.
Prior to cat eradication, grey petrels had not been confirmed as breeding on the island for over 100 years. After cats were removed from the island, the first active burrows were found in April 2000 and some chicks fledged that year. The grey petrel is Macquarie’s only winter breeding petrel. Last winter it had the highest breeding success rate (87 per cent) since monitoring began in 2005, and was also found nesting in new locations.
The burrow occupancy of sooty shearwaters and white headed petrels also appears to be higher. Blue petrels have been breeding for a number of years in low numbers on off-shore islands, with low fledging rates as a result of rat predation. This year there is quite a difference as hundreds of active burrows have been found on the main island. There is plenty of evidence for optimism about Macquarie Island’s future if the eradication of introduced pests is ultimately successful.