We used roadside surveys to examine abundance trends and spatial patterns for 11 terrestrial bird species from 1991 to 2010 on Saipan, Northern Mariana Islands. Relative abundances of the White-throated Ground-Dove, Mariana Fruit-Dove, Collared Kingfisher, Micronesian Starling, and Micronesian Myzomela all increased during the study period. Abundances of the Golden White-eye and Rufous Fantail followed a curvilinear trend that increased during the first half of the survey period (1991–2000) and decreased in the second half (2001–2010). Abundances of the remaining species (Island Collared-Dove, Bridled White-eye, Nightingale Reed-Warbler, and Eurasian Tree Sparrow) showed no significant trends. The most numerous species (over 40 individuals detected per survey), in decreasing order of abundance, were the Bridled White-eye, Rufous Fantail, Golden White-eye, Micronesian Starling, and Micronesian Myzomela. The total abundance of birds increased on average by 0.27 birds per year, per survey station, island-wide. Three stations out of 47 (6.4%) recorded a significant loss of total birds over the time period, and bird numbers increased significantly at only one station (2.1%). Stations at which we detected declines were clustered in the northern, less-populated, region of Saipan. We explored the relationship between typhoon frequency/severity and bird abundance to explain trend patterns but found no significant correlation. We suggest ways to improve roadside surveys as a management tool to aid in detecting avian declines that are of conservation concern.


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pp. 81-93
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