Are disproportionate losses of eastern breeding Semipalmated Sandpipers (Calidris pusilla) driving declines in the upper Bay of Fundy, Canada?

Abstract

Large numbers of Semipalmated Sandpipers (Calidris pusilla) use the Bay of Fundy, Canada, as a stopover site during their southbound migration from breeding to wintering grounds. The species exhibits a geographic cline in bill length on the breeding grounds (larger in east). Based on a previous analysis of morphometric traits that detected a small temporal decline in bill length, it has been suggested that observed declines in the Semipalmated Sandpiper population staging in the Bay of Fundy were driven by a disproportionate loss from the eastern breeding population. New data collected in the Bay of Fundy has made it possible to reassess this suggestion. We compared new bill length data from the Bay of Fundy (2009Fundy ( -2014 to historical data (1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) to examine temporal changes in bill length at this stopover site.We also examined count data at a major roost site from 1981 to 2014 to assess temporal changes in migratory passage. Variation in median passage date is explained best by a combination of year and Arctic climate data. Birds are now migrating through the region later in the season; median passage date has advanced approximately 5 d from 1980s values. Our analyses suggest that while there was a small decline in bill length between the 1980s and early 2000s, it has since reversed and bills are now comparable to historical values. Given this reversal in mean bill length, coupled with population estimates that are still low relative to historical values, there is now little evidence to support the hypothesis that the decline between the 1980s and today in birds passing through the Bay of Fundy is linked to disproportionate losses of eastern breeders. We therefore suggest that population declines may be distributed more broadly across the breeding range of birds that use the Bay of Fundy as a stopover site.

Intra- and interannual regional fidelity of Semipalmated Sandpipers (Calidris pusilla) during migratory stopover in the upper Bay of Fundy, Canada

“…However, we have no evidence that breeding populations are segregating within the bay. Bills of all birds banded in our study were on average 0.14 mm longer in Chignecto Bay than in the Minas Basin (Bliss 2015). Although statistically significant, this difference is well within the range of calculated measurement error for bill measurements (Bliss et al 2019).…”

“…Bills of all birds banded in our study were on average 0.14 mm longer in Chignecto Bay than in the Minas Basin (Bliss 2015). Although statistically significant, this difference is well within the range of calculated measurement error for bill measurements (Bliss et al 2019). Although additional data on breeding origin, perhaps obtained based on feather isotopes from hatch year birds, are needed to draw firm conclusions, based on our data we suggest that fidelity to particular regions of the bay occurs on an individual basis and not based on breeding origin, and birds of multiple origins are present in each region of the bay.…”

“…In all cases, we required three consecutive hits to filter out false detections (Crewe et al 2019). We assessed variation among regions and years in mean number of movements per bird per day using a generalized linear mixed effects model (R package lme4, Bates et al 2015) with number of movements per bird per day as the dependent variable, region and year as fixed factors, and bird as a random factor. We modeled data using a negative binomial distribution to accommodate our non-normal count data and to account for overdispersion.…”

“…Peregrine Falcons (Falco peregrinus) are now much more prevalent and are known to affect shorebird movement and habitat use (Dekker et al 2011, Hope et al 2020. Semipalmated Sandpipers are migrating through the region later (Bliss et al 2019), and the population of sandpipers using the bay is now estimated to be less than half of what it was in the 1970s (Neima 2017). We revisited Hicklin's (1987) hypothesis and predicted that birds now are likely to require increased flexibility in movement and habitat use relative to what was previously observed.…”

Migration tactics and connectivity of a Nearctic–Neotropical migratory shorebird

“…We recommend future studies during the winter attempt to further investigate stable isotope signatures for this species and other shorebirds, which will enhance the connectivity throughout the annual cycle (Rushing et al, 2014). Our connectivity results suggest a more widespread migratory pattern is occurring from SESA departing the NGOM coast than previously thought, and the NGOM is thus supporting concentrations of the entire breeding population that is currently declining (Bliss et al, 2019;Brown et al, 2017;Withers, 2002). Further research is needed to investigate a more in-depth landscape and habitatscale analysis of migratory patterns on the NGOM coast for this species (Martin et al, 2007;Moore et al, 2005).…”