| Summary: | An area over schist held a higher mean spring density of Dotterel Charadrius morinellus than two areas over granite . Spring density varied little between years . Density washighest on ground dominated by Juncus trifidus or Carex bigelowii, especially where there were ridges, terraces, hummocks or boulders, and was low on Nardus stricta or heath. Most clutches with fresh eggs hatched. After losses of clutches or broods up to mid July, some pairs formed, clutches were laid in a few days and some late young fledged . Most chick losses occurred before two weeks. Breeding success varied much. It was associated positively with July temperature and negatively with July precipitation . Birds over granite bred more poorly than over schist. On each area, flocks after arrival and before departure favoured the upper parts of the largest block of favoured habitat. Early spring flocks did not comprise pairs, but later spring flocks did. On each study area the spring sex ratio was close to 1 :1 . Nearly all agonistic encounters involved birds in flocks . and pairs close together on snow-free patches. On the area over schist, more birds were seen after arrival than just before egg laying . When snow lay late on high parts, pairs there waited to nest late after the thaw . Nearly all incubating birds, and all birds attending dependent young, were cocks.
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