understanding population change in migratory songbirds

For nearly 40 years, Richard T. Holmes and a long succession of his students have studied various species, ornithological processes and problems at Dartmouth College in New Hampshire. Professor Holmes has a great paper you can access here, published in the Ibis (journal of the BTO). As expressed in his abstract, his findings in this paper: "clearly demonstrate that to understand changes in abundance of long-distance migrant species requires knowledge of events operating throughout the annual cycle, which presents a challenge to researchers, managers and others concerned with the welfare of these species".