Nest and breeding population abundance of Least Terns: assessing bias and variation in survey timing and methods

作者：Hillman Matthew D; Karpanty Sarah M^*; Fraser James D

来源：Journal of Field Ornithology, 2013, 84(3): 287-298.

DOI：10.1111/jofo.12027

• ground-nest counts
• incubating-adult counts
• North Carolina
• Sternula antillarum

Methods commonly used to estimate the number of nests and size of the breeding population at colonies of Least Terns (Sternula antillarum) and other waterbirds include walk-through counts of nests (ground-nest counts) and counts of incubating adults from the colony perimeter (incubating-adult counts). The bias and variance of different methods and the comparability of repeated surveys versus once-annual censuses are poorly understood. Our objectives were to assess (1) the potential bias and variation of the more rapid incubating-adult counts compared to the time-intensive, and presumably more accurate, ground-nest counts, and (2) how accurately a once-annual census captured peak nesting abundance. We studied nine Least Tern colonies at Cape Lookout National Seashore (CALO), North Carolina, from April to August 2010-2012. We analyzed observer and survey method agreement with concordance correlation coefficients ((c)). We deployed time-lapse cameras at 156 nests and used repeated-measures logistic regression to determine if the proportion of time spent incubating varied with colony, time of day, or time of season. We found substantial agreement in abundance estimates of Least Tern nests and incubating adults between observers and survey methods, and among different times of day and seasons (all comparisons (c) %26gt; 0.97). Least Terns incubated eggs 94% of the time on average during daylight hours, irrespective of colony, nesting stage, or month. Although the nesting peak at CALO occurred during the recommended census period for Least Terns, abundance estimates for surveys conducted at different times during that period varied by as much as 39%. We recommend conducting incubating-adult counts to estimate nest and breeding population abundance of Least Terns or other waterbirds when vegetation or dunes do not obstruct views of nesting colonies. In addition, given the variation in abundance estimates for surveys conducted at different times during the recommended survey period, incubating-adult counts should be performed at least twice during the census period, with the maximum count reported as peak nest abundance.

• 出版日期2013-9
• 单位美国弗吉尼亚理工大学(Virginia Tech)