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POP2016-01: Objective 6: Chatham Island shag census 2014-2016. (PDF, 545K)
Summary
A survey of all of the rocky coastline of the Chatham Islands was carried out between Oct-Dec 2016 to undertake a census of breeding Pitt Island shag.
A total of 682 pairs of Pitt Island shag were recorded at 90 breeding sites throughout the islands. These results are similar to that recorded in 1997 (729 pairs) and suggest that the Pitt Island shag population has been stable for at least 20 years.
Most birds breed in small colonies, with mean colony size 7.6 pairs (range 1-36 nests) and 77% of colonies having ≤10 breeding pairs.
Significantly lower counts recorded in 2003 and 2011 are believed to be an artefact of the timing of a single survey missing the peak of breeding at most colonies, hence underestimating the breeding population.
The distribution of Pitt Island shag has changed since 1997. Previously only 47% of birds were found on Main Chatham, now 72% where recorded here. This reflects both an increase in numbers on Main Chatham, and a decline on Pitt and surrounding offshore islands. However, this may also be an artefact of later breeding on Pitt Island and surrounding off shore islands resulting in underestimating the population here.
Pitt Island shag numbers have increased in Te Whanga Lagoon, with birds spreading from Shag Rock onto Motuhinahina Island and breeding with Chatham Island shags at a new colony at Waikato Point.
Ground and boat based surveys (supported by aerial surveys of more isolated offshore reefs and albatross islands) is the most effective method at censusing Pitt Island shags, and is recommended for ongoing monitoring of this species and multiple surveys each season to cover peak breeding is highly recommended to get accurate results.
Publication information
Bell, M.D., Bell, D.J., Boyle, D.P. & Tuanui-Chisholm, H. 2017. Pitt Island Shag census 2016, POP2016-01 Chatham Islands seabird population research 2016/17. Technical report prepared by Wildlife Managment Ltd for the Conservation Services Programme, Department of Conservation, Wellington. 9 p.