|
Article Excerpt
The Rock Sandpiper (Calidris ptilocnemis) is one of the most polytypic shorebird species in the family Scolopacidae (Charadriiformes) and has one of the most northerly non-breeding distributions of all shorebirds. It is the only breeding species endemic to Beringia with recognized subspecies (AOU 1957) and is generally considered to form a super-species with Purple Sandpiper (C. maritima) of the north Atlantic (Conover 1944, Cramp and Simmons 1983, Sibley and Monroe 1990). Rock Sandpipers are distinct among North American shorebird species as they exhibit an intraspecific leapfrog migration pattern (Boland 1990). C. p. quarta and C. p. couesi are essentially sedentary with the latter undertaking temporary movements in response to harsh climatic conditions (Fig. 1, Gill et al. 2002). C. p. ptilocnemis is a short- to intermediate-distance migrant that moves between breeding sites on Bering Sea islands and non-breeding sites in upper Cook Inlet and, to a lesser extent, along other shorelines from the Alaska Peninsula south to the Alexander Archipelago (Gill and Tibbitts 1999, Gill et al. 2002). In contrast, some populations of C. p. tschuktschorum undertake annual round-trip flights of 7,000 km (Gill et al. 2002). However, understanding timing of migration and specific routes is complicated by subspecies having partially sympatric molting and wintering areas (Gill et al. 2002).
There have been few studies of Rock Sandpiper breeding behavior in North America (Hanna 1921, Miller 1996, Gill et al. 2002, Johnson and McCaffery 2004), and none with color-marked individuals. Previous work focused on subspecific classification and distribution, post-breeding and winter ecology, and feeding (Preble and McAtee 1923, Smith 1952, Gill and Jorgensen 1979, Gill and Handel 1990, Gill 1997, Gill and Tibbitts 1999, Gill et al. 2002, Pruett and Winker 2005). Bent (1927) summarized descriptions of breeding behavior of Rock Sandpipers from 19th century explorers, and Hanna (1921) provided early accounts of breeding behavior for C. p. ptilocnemis. Breeding behavior of color-marked individuals has only been studied for C. p. tschuktschorum on the Chukotsky Peninsula, Russia (Kondratyev 1982; Tomkovich 1994, 2003). Males in this population established and defended territories on upland tundra habitat from which they advertised for mates (Myers et al. 1982; Tomkovich 1985, 1994). Nests were initiated from mid-May through mid-June (P. S. Tomkovich in Gill et al. 2002), and some pairs initiated replacement clutches if nest loss occurred early in the season (Tomkovich 1994, 2003). Rock Sandpipers were socially monogamous and commonly exhibited biparental care of eggs and young. However, one member of the pair, usually the female, deserted its mate and brood shortly after hatch, or rarely, even before hatch (Myers et al. 1982; Tomkovich 1994, 2003).
[FIGURE 1 OMITTED]
The Rock Sandpiper is listed as a species of high concern in the U.S. Shorebird Conservation Plan (Brown et al. 2001, USSCP 2004) due to restricted breeding distribution, limited population size (Morrison et al. 2006), and threats to nonbreeding sites (Gill and Tibbitts 1999). Thus, identifying the extent of variation in life history and behavior among/ within subspecies is critical for effective conservation, yet this has not been reported from North America, where three of the four subspecies occur. Our objectives were to: (1) describe breeding phenology and habitat use; (2) measure mate and breeding site fidelity rates; (3) quantify hatching and fledging success, and parental care in a color-marked breeding population on the Yukon-Kuskokwim River Delta, Alaska; and (4) compare our results with those from studies 600 km west in Chukotka, Russia.
METHODS
Study Area and General Methods.--Our study area was at the Yukon Delta National Wildlife Refuge's Kanaryarmiut Field Station, Yukon-Kuskokwim River Delta (YKD), Alaska (Fig. 1; 61[degrees] 22' N, 165[degrees] 07' W). We located and monitored Rock Sandpiper nests opportunistically during 1998-2002 on and around a 36-ha plot while gathering data for other avian studies (mean [+ or -] SD number nests located annually = 4.0 [+ or -] 1.6, 4 adults banded). We systematically studied Rock Sandpipers during 2003-2005 (mean [+ or -] SD number nests located annually = 10.7 [+ or -] 1.5, 20 adults banded), monitoring nests and recording individual behavior on an additional 12 ha surrounding the original plot (48 ha total).
Two to four observers surveyed daily for banded birds, nests, and broods from late April through late July (2003-2005). We marked adults and chicks at the nest with a U.S. Geological Survey federal bird band and with unique combinations of UV-stable color bands. We measured morphological features during banding including: mass; length of closed, flattened wing (Stiles and Altshuler 2004); exposed culmen (Baldwin et al. 1931); and total tarsus (including lateral condyle of tibiotarsus). We assigned gender of adults by culmen length. Female Rock Sandpipers average larger than males in all measurements, but culmen length overlaps between males and females (males: range = 23.1-30.8 mm; females: range = 28.1-34.0 mm; Tomkovich 1982, Gill et al. 2002). When culmen length was inconclusive (28.1-30.8 mm, 30% of females, 60% of males), we assigned gender by comparing culmen length and mass with their mates (females > males) and/or behavior (courtship displays, copulation position).
We mapped locations of banded individuals (2003-2005) and nests (2000-2005) using ArcMAP GIS software (ESRI, Redlands, CA, USA). We produced vegetation maps in the field by manually delineating vegetation patches on aerial photographs, and digitized and geo-referenced habitat polygons using ArcMAP. The upland tundra vegetation community was a mosaic of patches which we classified into three basic types: (1) upland tundra that contained graminoid species (hereafter tundra-grass); (2) upland tundra that lacked a graminoid...
|
