SpruceRoots Magazine - February, 2000
Birds Back, Rats Razed
by Mark Drever
The colony of Ancient Murrelets on Langara Island appears to be bouncing back. Biologists working with the Canadian Wildlife Service returned to Langara Island this past summer and surveyed the Ancient Murrelet colony to assess its health following the eradication of rats. The extent of the colony (a potential index of population size) has increased in size since it was last surveyed in 1993. The island at one time was home to an estimated 200,000 pairs of Ancient Murrelets, black and white seabirds that nest in burrows under the mossy soil, but the population had declined to under 20,000 pairs in the mid 1990s. This decline was a result largely due to predation by Norway rats, a species introduced to Haida Gwaii. These large brown rats preyed on eggs and chicks by going into the burrows and they also kill adult birds.
Between 1993 and 1997, the Canadian Wildlife Service eradicated the rats from Langara Island and adjacent Lucy and Cox Islands using a poisoning technique that had been successful on over 40 islands in New Zealand. The Langara eradication was a huge endeavour, with the main effort occurring in the summer of 1995 and involving up to 75 people who worked as camp construction crews, bait operators, cooks and leaders on 5 different camps on the island. The bulk of those employed by the project came from communities throughout Haida Gwaii and Prince Rupert. This effort was led by the Canadian Wildlife Service and used funds from the Nestucca Environmental Recovery Trust Fund, a fund for restoring seabird habitat made available from the settlement of a lawsuit following the Nestucca oil spill which killed approximately 50,000 wintering seabirds along the south-west coast of Vancouver Island in 1988-1989.
When biologists returned to Langara Island in 1999, they found that the colony had greatly increased in size from 22.9 hecatres in 1993 to 35.6 hectares in 1999. Interestingly, the burrow density, that is, the number of burrows per hectare (b/ha), had decreased from 1,800 b/ha in 1993 to 765 b/ha in 1999. The birds seem to be dispersing across the island following release from the predation pressure of the rats.
The total number of birds has decreased from 14,630 pairs in 1993 to 11,520 pairs of nesting birds in 1999. However, these numbers are consistent with a continued decline for two years, due to continued predation by rats between 1993-95 and subsequent recovery after 1995. In addition, biologists found increases in other ground-nesting birds, such as Blue Grouse and Dark-eyed Juncos, but are cautious about attributing these increases to the absence of rats because upland bird populations tend to cycle up and down.
Langara Island appears to be free of rats. Biologists used traps and indicator baits at five sites around the island and found no evidence of rats, such as droppings, tracks, or active rat dens. Numerous old rat burrows had evidence of shrew activity and/or young plants growing at the entrances, indicating an absence of rats. However, it's impossible to be completely certain and detecting low populations of rats remains the central challenge of these types of operations.
The apparent recovery of the Ancient Murrelet colony, and possibly the increase of ground-nesting birds, suggests bird communities have benefited from the eradication of rats. Current efforts to prevent the re-introduction of rats depend entirely on serendipity and the goodwill of current users of the island. Some of the fishing lodges are voluntarily treating their barges before bringing them to the Island. However, a more pro-active approach in the future will ensure Langara Island returns to its place as a productive seabird colony. ·
SpruceRoots Magazine - November, 1999