In November and December, 2016, we used aerial photography and satellite imagery to determine the population size of Northern royal albatross breeding and Northern Buller's albatross on the Forty-Fours and The Sisters, Chatham Islands, and to compare the estimates derived from these techniques with ground counts. In addition, we also used the opportunity to test the feasibility of using aerial photography to estimate population size of Northern giant petrels, which also breed on the two island groups.
The estimated annual count of royal albatross derived from aerial survey after adjustment to account for the presence of loafing birds in the colony was of 4,772 annual breeding pairs after correction using aerial close-up photos, and 4,406 annual breeding pairs after correction using ground counts.
The count derived from satellite imagery for The Sisters and The Forty-Fours was 2,578 and 2,533 Apparently Occupied Sites, respectively, which was 21% lower than the raw aerial count for The Sisters (3,269 birds) and 38% higher than the raw aerial count for the Forty-Fours (1,830 birds). The ground count for the Forty-Fours was 1,404 annual breeding pairs.
The estimated annual count of Buller's albatross derived from aerial survey after adjustment to
account for the presence of loafing birds in the colony was 17,969 annual breeding pairs after correction
using aerial close-up photos, and 16,138 annual breeding pairs after correction using ground counts (correction factor 0.121). Most birds (85.3%) were breeding on The Forty-Fours.
The ground count for the Forty-Fours was 16,492 annual breeding pairs, which included an estimate of 3,445 nesting attempts that had failed. Adjusted aerial counts for The Forty-Fours were 7.1% and 16.5% lower than the ground count, although a direct comparison is difficult due to the 14-day difference between the ground and aerial counts, and the inclusion of failed nests in the ground counts, which would not have been detectable from the air.
There were no counts derived from satellite imagery for Buller's albatross as the resolution of the imagery is unsuitable for counting this species.
Aerial counting of northern giant petrels was not effective at either The Sisters or The Forty-Fours. Birds were not clearly visible in most images and detecting birds was difficult. An aerial count of 370 chicks at The Forty-Fours, was 30% of the 1,235 giant petrel chicks counted on the ground.
The use of WorldView-3 satellite imagery to count albatross populations is a new phenomenon which has potential application to the other greater albatross species. The mixed results obtained in this study indicate there may be more to be learnt to refine the technique. At this stage use of either aerial photographic surveys or on-ground counts remain the preferred methods for estimating population size and monitoring in the Chatham Islands.
Baker, G.B., Jensz, K., Bell, M., Fretwell, P.T. & Phillips, R.A. 2017. Seabird Population Research, Chatham Islands 2016/17 aerial photographic survey. Report prepared by Latitude 42 for the Conservation Services Programme, Department of Conservation, Wellington. 20p.