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Aleutian Tern Onychoprion aleuticus numbers in Alaska appear to be in decline; however, colonies are difficult to count for the purposes of monitoring due to their co-occurrence with Arctic Terns Sterna paradisaea, low nesting densities, high variability in attendance, sensitivity to human disturbance, and remote terrain. We paired visual observations with unmanned aerial systems (UASs) to test the feasibility of using this technology to survey a small colony of nesting Arctic and Aleutian terns in southcentral Alaska. We used counts of terns in the air and nest attendance to test for disturbance from UAS flights. We conducted 11 UAS flights over seven days at altitudes ranging from 15-30 m and located 23 nests in the 4.1 ha (0.041 km²) colony site (5.6 nests ha-1) by systematically searching the orthomosaics. We were most likely to distinguish tern species in the 18-m and 15-m altitude photos; the white forehead was most visible in side angle rather than top-down. Nest attendance and the number of aerial birds were not influenced by the UAS in this colony, which experiences high Larus gull activity. Aleutian Terns arrived on 19 May and were attending nests by 02 June; nest attendance declined throughout June. We believe the best approximation of total nesting pairs will be achieved by counting nests 7-10 d after first initiation. In mixed species colonies, we recommend that UASs fly in a 'lawn mower' pattern with overlap to maximize side angle images and aim for an image resolution of < 4 mm (which was achieved by 15-m altitude flights with our camera setup). In single species colonies, 30 m is sufficient and can be achieved more efficiently. [ABSTRACT FROM AUTHOR]

We compiled survey data on 202 Aleutian Tern colonies throughout Alaska and Russia to assess the current status and colony sizes and to evaluate whether there had been changes in recent decades. We fit a Poisson generalized linear mixed model to all available counts of Alaskan colonies since 1960, excluding colonies in which the temporal spread of counts was < 6 years. Russian data were not included in the trend model due to our inability to resolve dates on a number of counts. We estimate that numbers at known colonies in Alaska have declined 8.1% annually since 1960 or 92.9% over three generations (33 years; 95% CI = 83.3%-97%), with large colonies experiencing greater declines than small colonies. Trends at known colonies within discrete geographic regions of Alaska (Aleutian Islands, Bering Sea, Chukchi Sea, Gulf of Alaska and Kodiak Island) were consistently negative. The most recent counts of all known Alaskan colonies summed to 5 529 birds. This estimate should be considered a rough minimum because it does not account for colonies that have not been surveyed in recent years -- the size of which may have changed -- or for the fact that the surveys conducted were neither systematic nor inclusive of all potential habitats. In Russia, the sum of the most recent count of all colonies was 25 602 individuals, indicating that Russia may host approximately 80% of the world population. Numbers in some regions in Russia appear to have increased substantially in recent decades, especially on Sakhalin Island and the southern coast of the Koryak Highland. We have no data to identify any population-level stressor that could explain the apparent reduction in numbers in Alaska. However, predation, egging and other anthropogenic disturbances, and degraded habitat may cause population change at local levels. If this overall pattern cannot be explained by other possible but unlikely factors (e.g. establishment of large colonies in new locations within Alaska, or major shifts between Alaska and Russia), then the observed trends in Alaska are, indeed, alarming. Therefore, we urge close monitoring of known colonies within Alaska, studies of dispersal, establishment of management practices to insulate colonies from human disturbance, and more concerted efforts among Alaskan and Russian partners. [ABSTRACT FROM AUTHOR]