Atypical Nest Site of a Semipalmated Plover

—We report on an unusual nest site of a Semipalmated Plover (Charadrius semipalmatus) at La Pérouse Bay, Manitoba, Canada. The nest was located at the base of a 41-cm-high willow (Salix spp.) in a dense willow patch surrounded by coastal mudflats. Vegetation height and percent visual obstruction at the nest site were unusually high compared to height and cover previously described for Semipalmated Plovers. The nest was successful ($2 eggs hatched). The discovery of this unusual nest site in dense vegetation suggests that some Semipalmated Plover nests may be overlooked, emphasizing the need to conduct thorough searches even in non-traditional habitats among shorebird species that typically nest in open habitats. Received 9 October 2003, accepted 1 June 2004. Charadriidae shorebirds nest in unlined to thinly lined, shallow depressions in hardened clay or silt, or in loose stones, pebbles, or sand 1 Watershed Ecosystems Graduate Program, Trent Univ., Peterborough, ON K9J 7B8, Canada. 2 Dept. of Ornithology, American Museum of Natural History, Central Park West, New York, NY 10024, USA. 3 Corresponding author; e-mail: [email protected] in flat areas with sparse vegetation (Cooper and Miller 1997, Nol and Blanken 1999, Nguyen et al. 2003, Amat and Masero 2004). The disruptive effects of a plover’s cryptic plumage and egg coloration against these substrates may enhance concealment from predators (Solı́s and de Lope 1995, Lloyd et al. 2000). Some plovers place their nests near objects or clumps of vegetation, which could provide microclimates that reduce thermoregulatory costs (Wolf and Walsberg 1996, Amat and Masero 2004). Cover, however, reduces visibility around a nest, which may result in a higher risk of predation compared to that of an exposed site (Koivula and Rönkä 1998, Amat and Masero 2004). Nest-site selection among shorebirds, therefore, may be a tradeoff between needing security from predators, minimizing thermoregulatory costs, and having a view of the surrounding area (Wolf and Walsberg 1996, Koivula and Rönkä 1998, Amat and Masero 2004). Here, we report an unusual instance of a Semipalmated Plover (Charadrius semipalmatus) nesting in dense vegetation. 185 SHORT COMMUNICATIONS On 17 July 2003, LPN and DL found the unusual Semipalmated Plover nest site at La Pérouse Bay, Wapusk National Park, Manitoba, Canada (588 459 N, 938 309 W). Several times we observed a plover entering a large patch (6.8 m long 3 5.1 m wide) of willow (Salix spp.) surrounded by coastal mudflats. We found the nest, which contained four eggs, at the base of a willow. The nest was approximately 1.7 m from the outer edge of the willow patch and 10.2 m from the nearest water. RFR observed eggs and adults at the nest on 21 July; 2 days later, the nest contained two chicks and two eggs. On 25 July, neither adults nor young were observed in the immediate area. We used a tape measure at each corner of a 1-m2 quadrat frame to calculate mean height (41 cm) of vegetation within 1 m of the nest site. We used a transparent, 20 3 20 cm density board (100, 2 3 2 cm cells) placed vertically on the ground at the nest site to calculate mean percent visual obstruction by vertical cover (97%) between the nest and the four quadrat corners (Nguyen et al. 2003). Previous descriptions of nest sites used by Semipalmated Plovers (Cooper and Miller 1997, Robinson 1998, Nguyen et al. 2003, Smith 2003) have not mentioned sites in densely vegetated habitat. Vegetation height and percent visual obstruction by vertical cover at the unusual nest site described herein were much greater than those at other Semipalmated Plover nest sites: Akimiski Island, Nunavut (5.8 cm and 21%, respectively, n 5 42; Nguyen et al. 2003); La Pérouse Bay, Manitoba (0 cm and 38%, respectively, n 5 10; RFR unpubl. data); and East Bay, Nunavut (12 cm and 6%, respectively, n 5 24; Smith 2003). Although Cooper and Miller (1997) did not report vegetation height and percent visual obstruction by vertical cover at plover nests in the Queen Charlotte Islands, British Columbia (n 5 71), they described nest sites on open sand, under elevated ends of logs or planks, and on gravel patches, all different from the nest site that we observed. Similarly, Robinson (1998) did not report specific nest-site characteristics at plover nests in Churchill, Manitoba (n 5 32), but his descriptions indicated that nests were found primarily on gravel and stone, or lichen and moss, suggesting that vegetation height and percent visual obstruction by vertical cover were different from those at the nest site we observed. Semipalmated Plovers that nest in open sites with little or no concealment from vegetation may benefit from good visibility and early detection of predators. If true, one would expect a low rate of success among nests in dense vegetation. However, previous studies have shown that nest cover—an indicator of visibility—does not affect shorebird nest success at typical nest sites (Koivula and Rönkä 1998, Nguyen et al. 2003, Amat and Masero 2004). Additionally, nest sites used for renesting by Kentish Plovers (C. alexandrinus) had greater nest cover than those sites where the initial nest was depredated (Amat et al. 1999). We are not certain whether the Semipalmated Plover nest we found was the result of a late-nesting or renesting attempt. The discovery of a nest in dense vegetation, however, indicates that some Semipalmated Plover nests may be overlooked during monitoring or nest searching. We recommend that search efforts be increased in habitats of dense vegetation to assess the frequency of nesting in those types by shorebird species that typically nest in open habitats.