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Victoria Johnston

Publications and source records attributed to Victoria Johnston.

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USGS2012

Methods

Detecting declines in population size is one of the highest priorities of the shorebird initiatives in Canada and the United States. The quantitative goal is 80% power to detect a 50% decline, occurring during no more than 20 years, with a significance level of 0.15, using a two-tailed test, and incorporating effects of potential bias into the estimator. The Arctic PRISM program was designed to achieve this goal for arctic-nesting shorebird populations. The survey methods are an application of double sampling. Rapid surveys were made on a large number of plots selected from throughout arctic Alaska and Canada using stratified random sampling. Intensive surveys were made on a subsample of the plots to obtain detection rates, which were used to calibrate results from rapidly surveyed plots. Surveys will be made of the entire arctic region, each lasting several years and producing an estimate of average population size during the survey period. Results from two or more survey periods will be used to estimate change, or trend, in population size.

Book chapter↗
USGS2012

Goals and objectives

We report results from shorebird surveys in the North American Arctic, defined here as Bird Conservation Regions 2 and 3 of the North American Bird Conservation Initiative (http://www.nabci.net/International/English/bcrmap.html). The surveys estimate population size and trend, and provide information on habitat relationships, at the regional and Arctic-wide scale (Table 1, Fig 1). Of the 53 species of shorebirds that breed in the United States and Canada, 26 (47%) breed in the arctic in sufficient numbers that arctic surveys are an important part of monitoring programs for them (Brown et al. 2001, Donaldson et al. 2000; Table 1). Arctic-breeding shorebirds are a diverse group that exhibits a wide range of migration, reproductive, and wintering strategies (Table 1.1). Some species migrate a short distance to the northern United States and southern Canada (e.g. Purple Sandpiper; for scientific names, see Appendix D), while others undertake epic migrations to West Africa (e.g. Red Phalarope) or southern South America (e.g. Hudsonian Godwit, Red Knot). Some migrate in huge flocks, while others trickle south singly or in small groups. There are monogamous, polygamous, and polyandrous breeders, and most habitats in the Arctic provide nesting opportunities for shorebird species. Despite their different life history characteristics, all Arctic shorebird species share two traits: 1) they are all are migrants (none inhabit the Arctic year-round) and 2) because of their migratory behavior, all are exposed to anthropogenic hazards at some point(s) in their life cycle.

Book chapter↗
USGS2012

Small-scale and reconnaissance surveys

This brief chapter addresses two related issues: how effort should be allocated to different parts of the sampling plan and, given optimal allocation, how large a sample will be required to achieve the PRISM accuracy target. Simulations based on data collected to date showed that 2 plots per cluster on rapid surveys, 2 intensive camps per field crew-year, 2-4 intensive plots per intensive camp, and 2-3 rapid surveys per intensive plot is the most efficient allocation of resources. Using this design, we investigated how crew-years should be allocated to each region in order to meet the PRISM accuracy target most efficiently. The analysis indicated that 40-50 crew-years would achieve the accuracy target for 18-24 of the 26 species breeding widely in the Arctic. This analysis was based on assuming that two rounds of surveys were conducted and that a 50% decline occurred between them. We discuss the complexity of making these estimates and why they should be viewed as first approximations.

Book chapter↗