Variation in diet of Semipalmated Sandpipers (Calidris pusilla) during stopover in the upper Bay of Fundy, Canada

Abstract

Semipalmated Sandpipers ( Calidris pusilla (L., 1766)) use the upper Bay of Fundy, Canada, as a critical stopover site during their annual fall migration to wintering grounds in South America. While in the area, they feed extensively on mudflat invertebrates. Historically the amphipod Corophium volutator (Pallas, 1766) has been thought to make up the majority of their diet. However, we have recently observed flexibility in foraging behaviour and prey selection by sandpipers. The extent of this flexibility and the current diet composition is unknown. To address these knowledge gaps, we assessed Semipalmated Sandpiper diets using stable isotope analyses of blood plasma and available prey items. Data were collected in two arms of the Bay of Fundy during summer 2009 and 2010. Diets fluctuated between years and sites, but in all cases the diet was much more diverse than previously thought. Polychaetes and biofilm made substantial contributions, and C. volutator was still present in the diet, but at much reduced levels than previously noted. This previously unrecognized inclusion of biofilm in the diet is consistent with recent observations of other calidrid shorebirds. Based on measures of prey availability, there is little evidence of preference for C. volutator.

Fatty acid composition and concentration of alternative food of Semipalmated Sandpipers (Calidrispusilla) in the upper Bay of Fundy, Canada

“…FA levels in C. volutator in our study correspond well with those found in previous work (Ackman et al 1979;Maillet and Weber 2006), suggesting that these animals are a consistent source of essential FAs in the Bay of Fundy. Given recent evidence that Semipalmated Sandpipers in the region consume a broad diet (MacDonald et al 2012;Quinn and Hamilton 2012;Gerwing et al 2016), FA concentrations and profiles of alternate food items, relative to C. volutator, should be considered.…”

“…Information on relative abundance of the different taxa at each site is provided in Gerwing et al (2015). We collected biofilm by scraping it from the surface in areas in which it was visible (appearing as a thin green or green-brown mat on the surface of the mud) using a thin spatula and stored it in scintillation vials (Quinn and Hamilton 2012). Some sediment was unavoidably collected with the biofilm, but this was minimized as much as possible, and birds are also known to consume considerable sediment while feeding (Reeder 1951) so what was sampled likely resembles what birds would consume.…”

“…Although they have historically been a limited part of the diet of Semipalmated Sandpipers in the Bay of Fundy region (Hicklin andSmith 1979, 1984), recent work suggests that polychaetes now form a large component of the sandpiper diet (Ginn 2009;Quinn and Hamilton 2012;Neima 2017). This is not surprising because relative availability of C. volutator and polychaetes has changed over the past several decades.…”

“…This is not surprising and has also been documented in other areas of their range (e.g., Skagen and Oman 1996). In the Bay of Fundy, both polychaete worms and biofilm (consisting primarily of diatoms and the extracellular polymeric substances that they produce; Trites et al 2005) now appear to contribute substantially to the diet (Quinn and Hamilton 2012), and other prey such as ostracods can be important if present in sufficient quantities (MacDonald et al 2012). The inclusion of biofilm is consistent with recent studies of related shorebird species (Kuwae et al 2008(Kuwae et al , 2012Jardine et al 2015), in which it has been found to be an important dietary component.…”

Benthic food distribution as a predictor of the spatial distribution for shorebirds in a wetland of central Chile

“…Shorebirds detect prey by visual and tactile sensory mechanisms, been pecking and probing the main methods (Baker & Baker 1973), and flexible foraging strategies that can shift their diet to exploit locally abundant invertebrate resources (Skagen & Oman 1996, Quinn & Hamilton 2012. During nonbreeding seasons many shorebirds often forage across flats following tidal exposure and generally distribute themselves on specific habitats based on availability, distribution and abundance of macrobenthic invertebrates (Wilson 1990, Colwell & Landrum 1993, Butler et al 2001, according to the physical characteristics of tidal flats (Yates et al 1993, Colwell 1993, Finn et al 2008.…”