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title: "White-chinned Petrels show only modest increases two decades after removal of cats at Marion Island: are House Mice the problem?"
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# White-chinned Petrels show only modest increases two decades after removal of cats at Marion Island: are House Mice the problem?

Ben Dilley ([Percy FitzPatrick Institute of African Ornithology](http://www.fitzpatrick.uct.ac.za/), DST/NRF Centre of Excellence, University of Cape Town, South Africa) and colleagues have published in the journal [Polar Biology](http://link.springer.com/journal/300) on burrow density changes of ACAP-listed White-chinned Petrels *Procellaria aequinoctialis*and other burrowing petrels at Marion Island after the eradication of feral cats.

 The paper’s abstract follows:

 “Introduced predators are one of the main threats facing seabirds breeding on oceanic islands. Cats (*Felis catus*) were introduced to subantarctic Marion Island (290 km²) in 1949, and by the 1970s some 2000 cats were killing about 450,000 seabirds per year, greatly reducing burrowing petrel populations.  Cats were eradicated by 1991, but house mice (*Mus musculus*) remain.  The densities of utilised petrel burrows were estimated in 2013 by systematically searching for their burrows in 741 10 9 10 m sample quadrats in the north-eastern sector of Marion Island, repeating the sampling design and methods used by Schramm in 1979.  The mean burrow densities and 95 % CIs were compared between surveys by species for the different habitat and vegetation types, with non-overlapping CIs considered indicative of an increase in burrow density.  With cats eradicated and the potential for immigration from nearby Prince Edward Island (free of introduced mammals), we could expect a multi-fold increase in petrel numbers over the last two decades; however, burrow densities at Marion have increased by only 56 % since 1979.  White-chinned petrels (*Procellaria aequinoctialis*) showed the greatest increase, despite being listed as vulnerable due to incidental mortality on fishing gear at sea.”

 ![](https://acap.aq/images/stories/acap/Birds/Petrels/W/White_chinned_Petrel_by_Ben_Phalan.jpg)

 White-chinnd Petrels, photograph by Ben Phalan 

 **Reference:**

 Dilley, B.J., Schramm, M. & Ryan, P.G. 2016.  Modest increases in densities of burrow-nesting petrels following the removal of cats (*Felis catus*) from Marion Island.  [*Polar Biology*.  doi:10.1007/s00300-016-1985-z](https://www.researchgate.net/profile/Ben_Dilley3/publication/303890749_Modest_increases_in_densities_of_burrow-nesting_petrels_following_the_removal_of_cats_Felis_catus_from_Marion_Island/links/575e1c2308aec91374aefb12.pdf).

 *John Cooper, ACAP Information Officer,  15 August 2016*