Download e-book for iPad: Arctic Shorebirds in North America : a Decade of Monitoring by Jonathan Robert Bart, Victoria Helen Johnston

By Jonathan Robert Bart, Victoria Helen Johnston

ISBN-10: 0520273109

ISBN-13: 9780520273108

ISBN-10: 0520953495

ISBN-13: 9780520953499

Each 12 months shorebirds from North and South the United States migrate hundreds of thousands of miles to spend the summer season within the Arctic. There they feed in coastline marshes and estuaries alongside the most effective and pristine coasts at any place. With lots on hand foodstuff they may be able to reproduce nearly explosively; and as wintry weather methods, they retreat south besides their offspring, to come to the Arctic the subsequent spring. This striking trend of move and job has been the item of in depth learn by means of a world group of ornithologists who've spent a decade counting, surveying, and staring at those shorebirds. during this vital artificial paintings, they tackle a number of questions on those migratory poultry populations. what percentage birds occupy Arctic ecosystems each one summer season? How lengthy do vacationing shorebirds linger ahead of heading south? How fecund are those birds? the place precisely do they migrate and the place precisely do they go back? Are their populations growing to be or shrinking? the result of this learn are the most important for larger realizing how environmental guidelines will impression Arctic habitats in addition to the far-ranging wintry weather habitats utilized by migratory shorebirds.

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Within a single stratum we −^ have simple random sampling. From (6), Xuh ϭ −^ − Zuh/auh. The estimated variance has the same −^ 2 ^ ^(Z structure as expression (7), but V uh) ϭ s (Zuhi)/ 2 ^ − nuh, V(auh) ϭ s (auhi)/nuh. For the mean within one habitat, across Ͼ1 region, expressions (6)–(10) apply, except that g and h are equal and constant, so expressions (8)–(10) simplify: (10) When nugh ϭ 1, the corresponding term in expressions (8)–(10) cannot be evaluated even though the variance or covariance the term represents does exist.

2. , the bias) would be much smaller. If we used plot sizes of 1 and 9 but increased the sample size to 2, then the bias would also be smaller. More generally, the bias in a ratio estimate decreases with sample size and when the variance of the random variable in the denominator decreases. With ratio estimates in stratified sampling, and either small sample sizes or large variance of the METHODS 15 random variable in the denominator, the bias in each stratum can be considerable. If an overall estimate is computed by adding up stratumspecific estimates, the bias also sums and can become quite large when estimates are summed over several strata.

62), considerably higher than other recent estimates (Tibbitts et al. 2005, Morrison et al. 2006). 3). On the YDSA, where we distinguished between wet and moist habitats, most sightings were in moist areas. These data are consistent with previous observations of breeding birds on the Yukon–Kuskokwim Delta (Gill et al. 2002, Johnson and McCaffery 2004, Johnson et al. 2009). The estimated number of pairs breeding on surveyed plots was 35. 63) on the AMSA. These values virtually bracket the range of densities reported in most other studies throughout this species’ range (Gill et al.

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Arctic Shorebirds in North America : a Decade of Monitoring by Jonathan Robert Bart, Victoria Helen Johnston


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