The western sandpiper, Calidris mauri, is one of a few Florida shorebirds belonging to a group known as ‘stints’ (small sandpipers belonging to the genera Erolia or Calidris). Distinguishing characteristics include a black bill and legs (Paulson 2005). Like similar species, sex can be determined in part by bill length. In general, female bills measure at least 2.5 cm longer than those of males (Paulson 2005), a difference thought to be derived from intersexual competition for food at wintering locations (Stein et al. 2008). Plumage and body coloration vary with age and season, and descriptions are divided accordingly below.
Reddish-brown plumage of varying degrees is concentrated on the crown, ears and along the upper back (Paulson 2005). The breast is streaked, and the sides are marked with several black streaks and chevrons. In the fall after breeding, individuals are often faded and patchier.
Coloration is nearly identical to that of the semipalmated sandpiper, C. pusilla. Plumage is plain grayish-brown above and white below, the eyebrow feathers (supercilium) are white and the breast is lightly streaked (Paulson 2005).
Legs are olive, darkening to black in adults (Paulson 2005). Plumage coloration on the head is similar to that of non-breeding adults, but darker and more distinct. Wing feathers are grayish-brown to reddish-brown with buff fringes. Underparts are mostly unmarked, and the sides of the breast are streaked. Breasts of the youngest individuals are tan, fading to white during the first migration.
Potentially Misidentified Species
The western sandpiper is most easily confused with the semipalmated sandpiper, C. pusilla. As mentioned above, non-breeding adults are very similar in coloration (e.g. Paulson 2005). On average, western sandpipers are larger than C. pusilla and have longer, more curved bills. In flight, the two species are distinguished only by their calls (Peterson 1980) (see 'Voice' below).
HABITAT AND DISTRIBUTION
Like many shorebirds, C. mauri is found throughout a large range extended by long seasonal migrations. Wintering and migratory stopover populations occur from Washington in the west and Delaware in the east south throughout the Americas to Peru (e.g. Terres 1980). Depending on the season, individuals may be abundant both inland and along the coast. Despite its broad migratory range, this species is known to breed only in western and northern Alaska (Terres 1980; Paulson 2005).
Little information is available on the distribution of the western sandpiper in the IRL, but birds are found throughout Florida on tidal flats and sandy beaches (Kale 1990).
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
The western sandpiper is the largest of the stints, with a body length of about 16.5 cm and a wingspan ranging from 30 to 36 cm (Terres 1980; Paulson 2005). Lifespan varies with environmental conditions and other factors. Little information is available on the maximum age of C. mauri, but similar species live up to 7 years under certain conditions (Terres 1980).
The western sandpiper is a common stint, considered abundant despite its limited breeding range (Paulson 2005) (see 'Regional Occurrence' above). Detailed abundance records for sandpiper populations within the IRL are scarce. However, birds are known to stopover in Florida from July through May, and some non-breeding individuals extend their stay throughout the summer (Kale 1990). With the exception of the spring season, the western sandpiper is more abundant in the southeastern U.S. than its prolific relative, C. pusilla (Paulson 2005).
The leaf and grass-lined nests of C. mauri are typically built in ground depressions on moist to dry arctic tundra or on mossy mountain slopes near sedges and low-lying plants (Terres 1980). Clutch size is generally four eggs per nest. Eggs are cream to light brown and marked with reddish-brown spots and blotches (Terres 1980). Both parents incubate the eggs until they hatch, a period of about 18-19 days. After hatching, chicks are brooded for 5-7 days, and further parental investment includes leading chicks out of the nest and offering protection from predators via territorial displays and parent-offspring signal calls for an additional 2-3 week period (Johnson et al. 2008) (see “Voice” below).
Studies have revealed some degree of nesting site and mate fidelity from one breeding season to the next. Of the population surveyed from the Yukon-Kuskokwim River Delta in Alaska, 40-60 % of breeding adults returned to the same nesting site, and 4-29 % returned to the same mate (Johnson & Walters 2008). Results indicated that site and mate fidelity lead to faster clutch initiation and higher nest survival rates.
Western sandpipers emit a variety of calls, depending on the circumstance. During flight, vocal communication consists of a high-pitched, squeaky dzheet, jeet or cheep. While in flight, call variation is the only method for distinguishing C. mauri from the semipalmated sandpiper, which often trills repeatedly and emits a duller sound (Peterson 1980; Paulson 2005). Breeding adults produce a crescendoed trill of brr-eee brr-eee brr-eee breee-urrrrr that drops at the end (Paulson 2005). After hatchlings leave the nest, parents have been documented to use four distinct calls for communicating with offspring, categorized as ‘brood’, ‘alarm’, ‘freeze’ and ‘gather’ (Johnson et al. 2008). Chicks respond in varying ways, depending on the type of call. In some instances, juveniles notify parents of their location, while others remain silent as an antipredatory response.
Temperature & Salinity
The natural range of the western sandpiper extends from arctic to tropical climate zones, suggesting that the species has a broad thermal tolerance, which is regulated in part by seasonal migration (see ’Habitat & Distribution’ above). Individuals may stopover and feed in terrestrial, freshwater and/or coastal marine ecosystems, depending on season and migratory route (e.g. Terres 1980).
The western sandpiper feeds and forages in a similar fashion to the semipalmated sandpiper, walking with its head down while snapping or probing through the sand in search of prey (Terres 1980). This species may also submerge its head to catch a variety of invertebrate prey, and utilize the surface tension of the surrounding water to transport food down the beak (Estrella et al. 2007).
Little information is available concerning predators of the western sandpiper, but birds of prey, alligators and larger mammals probably consume eggs, hatchlings and adults.
Like many other bird species, the red knot acts as a terminal or final host for several parasites acquired from a variety of prey items, including the parasitic worms, Bartolius pierrei (Cremonte 2004), Skrjabinocerca canutus, Viktorocara capillaries, and V. limosae (Diaz et al. 2005).
Although there are no obligate associations documented between the western sandpiper and other species, C. mauri is commonly found alongside other organisms from the tidal flat and sandy beach habitats in which it resides. For more extensive information on these ecosystems and their associated species found in and around the IRL, please visit the Tidal Flat and Beach Habitat pages.
Threats & Conservation
Unlike the related red knot, Calidris canutus rufa, populations of the western sandpiper are strong and no special status has been issued for the species. However, C. mauri is protected under the Migratory Bird Treaty Act of 1918, which prohibits the harassment, capture, kill and/or possession of listed migratory species (e.g. USFWS 2010).
Estrella, SM, Masero, JA & A Pérez-Hurtado. 2007. Small-prey profitability: field analysis of shorebirds’ use of surface tension of water to transport prey. The Auk 124: 1244-1253.
Farrand Jr., J (Ed.). 1983. The Audubon Society Master Guide to Birding Volume 1: Loons to Sandpipers. Alfred A. Knopf. New York. USA. 447 pp.
Fernández, G & DB Lank. 2007. Variation in the wing morphology of western sandpipers (Calidris mauri) in relation to sex, age class, and annual cycle. The Auk 124: 1037-1046.
Johnson, M, Araf, S & JR Walters. 2008. Parent-offspring communication in the western sandpiper. Behav. Ecol. 19: 489-501.
Johnson, M & JR Walters. 2008. Effects of mate and site fidelity on nest survival of western sandpipers (Calidris mauri). The Auk 125: 76-86.
Kale II, HW & DS Maehr. 1990. Florida’s Birds. Pineapple Press. Sarasota, FL. USA. 288 pp.
Norris, DR, Lank, DB, Pither, J, Chipley, D, Ydenberg, RC & TK Kyser. 2007. Trace element profiles as unique identifiers of western sandpiper (Calidris mauri) populations. Can. J. Zool. 85: 579-583.
Paulson, D. 2005. Shorebirds of North America: A Photographic Guide. Princeton Univ. Press. Princeton, NJ. USA. 361 pp.
Peterson, RT. 1980. A Field Guide to the Birds: A Completely New Guide to All the Birds of Eastern and Central North America. Houghton Mifflin. Boston, MA. USA. 384 pp.
Stein, RW, Fernandez, G, de la Cueva, H & RW Elner. 2008. Disproportionate bill length dimorphism and niche differentiation in wintering western sandpipers (Calidris mauri). Can. J. Zool. 86: 601-609.
Terres, JK. 1980. The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf. New York. USA. 1109 pp.
USFWS. 2010. Migratory Birds and Habitat Programs. U.S. Fish and Wildlife Service. Online at http://www.fws.gov/laws/lawsdigest/migtrea.html (Date accessed: 08/10/2010).