Downward trophic shift during breeding migration in the shorebird Calidris mauri (western sandpiper)

Abstract

The recent demonstration of mudflat surficial biofilm feeding by western sandpiper Calidris mauri has provided new insight into the feeding ecology of shorebirds. We assessed feeding modes over the migratory cycle, and specifically whether a downward shift in trophic position occurred during the 2004 northward migration from their overwintering areas to the Arctic breeding grounds. We used stable isotope composition and calculated trophic positions of adult western sandpiper at their northward migratory stopover on Roberts Bank, British Columbia, Canada, in 3 animal compartments with increasing turnover times (stomach contents, liver, and muscle). This allowed the retrospective determination of their major diet source types over time frames encompassing the geographical ranges of their previous migratory stopovers and arrival on the Roberts Bank stopover. Detailed taxonomic and photopigment determinations were also performed on stomach contents and surficial biofilm. The Roberts Bank biofilm showed high taxonomic homogeneity among sampling sites, suggesting a qualitatively consistent food source during western sandpiper stopover. A statistically significant downward shift in mean trophic position (TP) occurred between previous migratory stopovers (TP = 3.0 ± 0.5, mean ± SD) and arrival on the Roberts Bank stopover, where the maximum probability densities showed > 70% dietary contribution of benthic diatoms, with a TP = 2.3 ± 0.4, close to the diet of the suspension-feeding bivalves Tapes philippinarum and Mya sp. (TP = 2). Advantages of biofilm over macrofaunal feeding during migration may include decreased handling and search time, as well as greater availability and digestibility of the high-energy carbohydrates needed for flight.

Intertidal biofilm distribution underpins differential tide-following behavior of two sandpiper species (Calidris mauri and Calidris alpina) during northward migration

“…First, the intensive use of the upper intertidal by western sandpiper aligns with biofilm being the major component of their diet at Roberts Bank (Kuwae et al 2008;Beninger et al 2011;Kuwae et al 2012). Secondly, rapid pecking is the predominant feeding mode used by western sandpipers on Roberts Bank (Mathot and Elner, 2004), and is also reflective of biofilm grazing and stomach contents Kuwae et al 2008Kuwae et al , 2012.…”

Peak Abundance of Fatty Acids From Intertidal Biofilm in Relation to the Breeding Migration of Shorebirds

“…and Nitzschia spp. (Beninger et al, 2011;Schnurr et al, 2019). Based on fatty acid markers, we suggest that the overall diatom biomass within the biofilm declines from spring to summer (Figure 3), a change accompanied by an increase in bacteria, cyanobacteria, and dinoflagellates.…”

“…These higher photon flux densities (Jensen and Revsbech, 1989;Schnurr and Allen, 2015;Schnurr et al, 2016b) and temperatures (Blanchard et al, 1997;Kudo et al, 2000;Jiang and Gao, 2004;Scholz and Liebezeit, 2013) result in enhanced rates of photosynthesis and growth in microphytobenthos. Since diatoms are the main primary producers in intertidal biofilm at our study site (Beninger et al, 2011;Schnurr et al, 2019), increases in photosynthetic activity likely cause increases in overall diatom biomass in the biofilm. Thus, we found a positive correlation between organic content and temperature (24 h) 50th percentile (Table 3).…”

On the tip of the tongue: natural history observations that transformed shorebird ecology

“…In addition, microbial mat and film feeding only became important at one of the last stopover sites (Roberts Bank, British Columbia, Canada), prior to breeding in Alaska, prompting the birds to descend a full trophic level overall. These observations suggested that this particular food resource is critical to reproductive success in western sandpipers (Beninger et al 2011, Schnurr et al 2019).…”