| Summary: | I studied patterns of nest site choice and reproductive success in tundra nesting shorebirds at East Bay, Nunavut, to determine the factors that affect nest success in habitats with limited structural complexity. From 2000-2002,1 monitored the nests of five species: Black-bellied Plover (Pluvialis squatarola), Red Phalarope (Phalaropus fulicaria), Ruddy Turnstone (Arenaria interpres), White-rumped Sandpiper (Calidris fuscicollis) and Semipalmated Plover (Charadrius semipalmatus). For all species, I evaluated the influence of habitat, food availability, nest distribution and parental behaviour on nest success. I found strong patterns of non-random nest placement and clear evidence of habitat preferences. However, I found little evidence that variation in nest habitat was related to variation in success within or between species. Shorebirds did not prefer to nest in habitats where food was most abundant. Nest success was not consistently higher in preferred nest habitats. Instead, reproductive success may be related to the amount of parental activity near the nest. Red Phalaropes displayed considerable variation in nest site choice; they nested in grass/sedge marshes and also in rocky coastal habitats. I studied their distribution, behaviour and nest success to determine if their use of coastal nest sites reflects a protective nesting association with an aggressive larid, the Sabine's Gull (Xema sabini). I found and monitored 29 phalarope nests with nearby (< 150 m) Sabine's Gull nests and 26 nests without nearby Sabine's Gulls. Coastal phalarope nests were nearer to Sabine's Gulls than expected by chance. Although I detected no habitat differences between coastal sites with and without Sabine's Gulls, only 3 phalarope nests were found in coastal areas without gulls. Approach experiments and incubation monitoring suggested that phalaropes without nearby gulls behaved more secretively. Phalaropes with nearby gulls had 17-20% higher hatch success in 2000 and 2001. In 2002, lemmings were scarce, predation was high, and phalaropes with nearby Sabine's Gulls did not have increased reproductive success. I found evidence that nest success may be influenced by parental behaviour and nesting associations, but the most significant variation in reproductive success was attributable to cycles of predators and lemmings. Science, Faculty of Zoology, Department of Graduate
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