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  • The surveys are conducted along the sandspit and within a 96 ha lagoon that encompasses mudflats, eelgrass beds, and saltmarsh at the northwest end of Sidney Island, located in the Strait of Georgia, British Columbia. The survey counts numerate two species, Western Sandpiper (Calidris mauri) and Least Sandpiper (Calidris minutilla), during a portion of the southern migration period (July, August, and early September), and have been conducted intermittently since 1990. Sidney Island (48°37’39’N, 123°19’30”W) is located within the Salish Sea (Strait of Georgia), 4 km off the coast of Vancouver Island in southwestern British Columbia, Canada. Southbound Western and Least Sandpipers stop over within Sidney Spit Marine Park (part of the Gulf Islands National Park Reserve), roosting and feeding along the sandspit and within a 96 ha lagoon that encompasses mudflats, eelgrass beds, and saltmarsh at the northwest end of the island. These species are the most numerous shorebird species using the area during southern migration. Adults precede juveniles, arriving at the end of June and throughout July. Juveniles reach the site in early August, with their numbers trailing off in early September. As a result, the site experiences a transition from purely adult to purely juvenile flocks over the course of the season. Daily counts, beginning in early July and ending in early September, were conducted in 1990 and from 1992-2001 (no counts occurred in 1991). Effort was reduced to weekly surveys between 2002 and 2013. Over the entire monitoring period median survey effort was 9 counts annually. All counts were conducted at the low tide of the day, when shorebirds were feeding in the exposed mudflat of the lagoon. Observers walked along the shore of the lagoon stopping periodically at vantage points to look for birds. For ease of data recording and to keep track of individual flocks, the survey area was divided into separate units demarcated by prominent geographical features. Counts were made with the unaided eye, through binoculars, and with a 20 – 60x zoom spotting scope, depending on the proximity of the birds. All individuals in small flocks were counted and individuals in large flocks were estimated by counting in groups of 5, 10, 50 or 100 according to flock size in each successive field of view across a scan of the entire flock. Between 1990 and 2001, when daily counts were conducted, birds were occasionally counted more than once in a day. The largest count value obtained was used as the daily estimate for these days. For smaller flocks, we were able to identify all individual birds to species and age-class. Sub-samples from larger flocks were also aged (adult or juvenile) and identified to species. Birds were aged by plumage characteristics. Adult Western Sandpipers are distinguished from juveniles by the dark chevron markings present along the sides and breast. Juvenile Least Sandpipers have a buffy breast compared to the distinct, darker one of the adult, and juveniles have bright rufous scapulars compared to the drab feather-edges of the adults. In both species, juvenile plumage appears brighter and cleaner than adult plumage, which is more worn and tattered.

  • Average grid cell density is a polygon feature class containing the average density value for each grid cell per species/groups and season.

  • Grids surveyed is a polygon feature class containing the 5’ latitude by 5’ longitude grid cells surveyed for all seasons combined including the grids that were surveyed but where no species were seen. In order to produce maps for a specific season a selection for these grids must be performed.

  • Surveyor shorebird bird observations and counts for all years.

  • Study area is a polygon feature class showing the extent of where most of the bird sightings were recorded and then used in the atlas. A few rare species have been included as well that go beyond this area.

  • These shorebird surveys are conducted intermittently at a series of sites near the town of Tofino on the west coast of Vancouver Island, British Columbia, during northward (April to May) and southward migration (July to November). This survey includes all shorebird species. Surveyors used binoculars or a spotting scope to count the total number of shorebirds present within the natural boundaries of each survey site during the northward and/or southward migration periods. They used a boat to count birds within the entire area of Arakun Flats and Ducking Flats by traveling along the outer edge of the mudflats, and by stopping at standardized vantage points on land. They also used a boat to view as much area as possible within Maltby Slough, South Bay and Grice Bay from the openings to each of these bays. Surveyors walked the entire length of Chesterman Beach including the tombolo to Frank Island. Surveys were done at least twice a week at each site. Most boat surveys began at low tide when the mudflats were exposed and continued on the rising tide. Road accessible sites were usually surveyed during the hour before high tide or at high tide in 2011. Surveys were not conducted in weather that reduced visibility or made boat travel unsafe (heavy rain or high wind). Surveyors counted birds individually when they were within flocks of fewer than 200 birds. They estimated the size of larger flocks by counting 50 or 100 birds and then judged how many similar-sized groups made up the entire flock. Distant flocks were recorded as small or large shorebirds and assumed to have the same species composition as those closer to shore in 1995 or identified to species group and recorded as either “dowitchers” or “peeps” in 2011.

  • Rare species is a point feature class containing rare species sightings.

  • Survey effort is a polygon feature class with the original transects – for reference.