Shorebird surveys
Surveys were conducted as part of the Arctic PRISM shorebird monitoring
program (Bart and Johnston 2012). These surveys were designed to
estimate population sizes and habitat relationships for shorebirds
breeding across the whole of the North American Arctic, only recently
completing the first round of surveys that covers each of the 19 PRISM
survey regions. Here, we include data from the first two regions to be
surveyed for a second time in the Canadian Arctic. We surveyed 25,000
km2 in the Rasmussen Lowlands, a coastal plain wetland
complex located at the base of the Boothia Peninsula, designated as a
Ramsar Wetland of International Importance (Carp 1980) and a Canadian
Important Bird Area (Aguilar Mugica et al. 2009). We also surveyed a
25,000 km2 area in Foxe Basin including the coastal
wetlands and inland dry areas on Prince Charles Island, several nearby
islands, and a portion of western Baffin Island (Figure 2). Both
regions, approximately 750km apart, include a wide variety of land cover
types, such as intertidal flats, low-lying salt marshes, flat marshy
tundra, heath tundra, dry grasslands, beach ridge complexes and
unvegetated broken shale (Bart and Johnston 2012). Each region was
stratified by habitat type, and plots were randomly sampled within each
habitat type, with a greater proportion of plots located in wetland
habitats (Bart and Johnston 2012).
We included habitat type as a
factor in our models, but did not use a design-based approach for
calculating the means and variances. These two regions are well suited
for the current study because they are high quality shorebird habitat,
containing a good diversity and abundance of shorebirds, and because
they are located at mid-Arctic latitudes, therefore hosting both colder-
and warmer-breeding species.
Each region was surveyed twice, 22-25 years apart. The Rasmussen
Lowlands region was surveyed in 1994-95 and 2019, while the Foxe Basin
region was surveyed in 1996-97 and 2019. While the earlier surveys of
each region were completed over sequential two-year periods, the later
surveys in both regions were completed simultaneously in one season
owing to increased funding and resources. We excluded the 1996 data
because of unusually poor weather and flooding that disrupted the normal
behaviour of the birds (Bart and Johnston 2012). Each plot was surveyed
once per survey period (1994-1997 and 2019). Surveys were conducted
between June 18 and July 15, during late courtship and early incubation,
when breeding territories could be identified from the birds’
territorial displays. The detectability of birds is believed to change
throughout the season, as birds settle on their nests and incubation
progresses. The late-courtship to early incubation period maximizes
detectability. Detectability could vary slightly even within this time
window, and most certainly varies due to weather and other factors.
This variability in detection could introduce imprecision into the
estimates. However, we do not expect that this would contribute to bias
because surveys in both time periods occurred over a number of days
during late courtship-early incubation. In both time periods, 28 plots
were surveyed in the Rasmussen Lowlands and 36 plots were surveyed in
Foxe Basin (64 plots total). Plots were 16 ha (400m by 400m). Surveyors
recorded the proportion of each plot covered by upland habitat (e.g.
mesic grasslands or heath habitats, sparsely vegetated xeric habitats)
or lowland habitat (e.g., hydric areas of grass/sedge, polygonal
wetlands, saltmarsh). In our analyses, we categorized a plot as upland
or lowland depending on which habitat type was predominant.
Following PRISM protocols (Bart and Johnston 2012), surveyors searched
the plot walking straight-line transects, covering a breadth of 50m with
the observers situated 25m apart, using a GPS to ensure complete
coverage of the entire plot. Surveys took approximately 90 mins.
Observers recorded the number and species of all birds observed within
each plot. Altogether we observed 12 species of shorebirds: American
Golden-Plover (Pluvialus dominica ), Baird’s Sandpiper
(Calidris bairdii ), Black-bellied Plover (Pluvialis
squatrola ), Buff-breasted Sandpiper (Tryngites subruficollis ),
Dunlin (Calidris alpina ), Pectoral Sandpiper (Calidris
melanotos ), Red Knot (Calidris cantus ), Red Phalarope
(Phalaropus fulicarius ), Ruddy Turnstone (Arenaria
interpres ), Semipalmated Sandpiper (Calidris pusilla) , Stilt
Sandpiper (Calidris himantopus ), and White-rumped Sandpiper
(Calidris fuscicollis ).