Long‐term continental changes in wing length, but not bill length, of a long‐distance migratory shorebird

Abstract

We compiled a >50‐year record of morphometrics for semipalmated sandpipers (Calidris pusilla), a shorebird species with a Nearctic breeding distribution and intercontinental migration to South America. Our data included >57,000 individuals captured 1972–2015 at five breeding locations and three major stopover sites, plus 139 museum specimens collected in earlier decades. Wing length increased by ca. 1.5 mm (>1%) prior to 1980, followed by a decrease of 3.85 mm (nearly 4%) over the subsequent 35 years. This can account for previously reported changes in metrics at a migratory stopover site from 1985 to 2006. Wing length decreased at a rate of 1,098 darwins, or 0.176 haldanes, within the ranges of other field studies of phenotypic change. Bill length, in contrast, showed no consistent change over the full period of our study. Decreased body size as a universal response of animal populations to climate warming, and several other potential mechanisms, are unable to account for the increasing and decreasing wing length pattern observed. We propose that the post‐WWII near‐extirpation of falcon populations and their post‐1973 recovery driven by the widespread use and subsequent limitation on DDT in North America selected initially for greater flight efficiency and latterly for greater agility. This predation danger hypothesis accounts for many features of the morphometric data and deserves further investigation in this and other species.

Low fitness at low latitudes: Wintering in the tropics increases migratory delays and mortality rates in an Arctic breeding shorebird

“…For Namibia, we used archived data from 1971 to 1979, whereas data from other sites were collected in recent years (Table ). We assumed that no change in size occurred over time (but see (Lank et al, )). As sanderlings of different age classes are of similar size and show only a small degree of sexual dimorphism with a great overlap in size between sexes (Lourenço et al, ), we pooled the ages and sexes.…”

Migrant Semipalmated Sandpipers (Calidris pusilla) Have Over Four Decades Steadily Shifted Towards Safer Stopover Locations

“…Migrant sandpipers also change their behavior seasonally in relation to their temporal proximity to the arrival of migrant peregrines (Hope et al, 2011(Hope et al, , 2014. In a previous paper (Lank et al, 2017) we attributed the shortening wing length measured 1980-2015 in semipalmated sandpipers and other calidridines (Anderson et al, 2019) to selection for better predator escape performance (see also Ydenberg and Hope, 2019).…”

Migrant semipalmated sandpipers (Calidris pusilla) have over four decades steadily shifted towards safer stopover locations

“…The migratory behaviours that shift in response to predation include flock size, vigilance, over-ocean flocking during high tides, length of stay at dangerous locations, location selection, habitat selection within a location, and fuel load (Dekker, 1998; Ydenberg et al , 2004; Pomeroy, 2006; Pomeroy et al , 2008; Sprague, Hamilton & Diamond, 2008). On a longer time scale, wing lengths of semipalmated sandpipers and other small shorebirds utilizing the Bay of Fundy have shortened, enhancing escape performance (Lank et al , 2017; Anderson et al , 2019). Migrant sandpipers also change their behaviour within seasons based on their geographic position relative to that of their temporal proximity to the arrival of migrant peregrines (Hope, Lank & Ydenberg, 2014; Hope et al , 2011).…”

“…Falcon recovery drove Pacific dunlins ( C. alpina pacifica ) to lose their mid-winter fat store (in order to maintain escape performance), and to take up over-ocean flocking in place of roosting at high tide (Ydenberg et al , 2010), and to shift the non-breeding distribution toward greater aggregation at safer sites (Ydenberg et al , 2017). Wing lengths of semipalmated sandpipers ( C. pusilla ) and other calidridines shortened 1980 - 2015 as peregrine numbers increased, potentially due to selection for better predator escape performance (Lank et al , 2017; Anderson et al , 2019). The risk effects, both direct and indirect, of these responses are unstudied as yet, but might be substantial.…”