Herons in North America, Central America and the West Indies
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Book chapter↗
Geology topics
Robert W. Butler
Publications and source records attributed to Robert W. Butler.
Wind assistance: A requirement for migration of shorebirds?
We investigated the importance of wind-assisted flight for northward (spring) migration by Western Sandpipers ( Calidris mauri ) along the Pacific Coast of North America. Using current models of energy costs of flight and recent data on the phenology of migration, we estimated the energy (fat) requirements for migration in calm winds and with wind-assisted flight for different rates of fat deposition: (1) a variable rate, assuming that birds deposit the minimum amount of fat required to reach the next stopover site; (2) a constant maximum rate of 1.0 g/day; and (3) a lower constant rate of 0.4 g/day. We tested these models by comparing conservative estimates of predicted body mass along the migration route with empirical data on body mass of Western Sandpipers at different stopover sites and upon arrival at the breeding grounds. In calm conditions, birds would have to deposit unrealistically high amounts of fat (up to 330% of observed values) to maintain body mass above absolute lean mass values. Fat-deposition rates of 1.0 g/day and 0.4 g/day, in calm conditions, resulted in a steady decline in body mass along the migration route, with predicted body masses on arrival in Alaska of only 60% (13.6 g) and 26% (5.9 g) of average lean mass (22.7 g). Conversely, birds migrating with wind assistance would be able to complete migration with fat-deposition rates as low as 0.4 g/day, similar to values reported for this size bird from field studies. Our results extend the conclusion of the importance of winds for large, long-distance migrants to a small, short-distance migrant. We suggest that the migratory decisions of birds are more strongly influenced by the frequency and duration of winds aloft, i.e. by events during the flight phase, than by events during the stopover phase of migration, such as fat-deposition rate, that have been the focus of much recent migration theory.
The Auk↗
Conservation of North Pacific shorebirds
In his introduction to the 1979 Symposium proceedings entitled “Shorebirds in Marine Environments," Frank Pitelka stressed the need for studies and conservation programs that spanned the western hemisphere (Pitelka 1979). In the 15 years since Pitelka's call to arms, the locations of many important migratory and wintering sites for shorebirds have been identified in the Americas (Senner and Howe 1984, Morrison and Ross 1989, Morrison and Butler 1994) and in the East Asian-Australasian flyway (Lane and Parish 1991, Mundkur 1993, Watkins 1993). However, assessments for Central America, the Russian Far East and most of Oceania remain incomplete or lacking. The recognition that shorebird conservation required the protection of habitats throughout the birds' range (e.g., Morrison 1984, Davidson and Evans 1989 in Ens et al. 1990) prompted the establishment of the Western Hemisphere Shorebird Reserve Network (WHSRN) in the Americas in 1985 (Joyce 1986). This program complemented the 1971 Convention on Wetlands of International Importance Especially for Waterbirds (Ramsar Convention, Smart 1987), recognized by more that 50 countries world-wide. Our purpose for writing this paper is to: (1) describe the distribution of North Pacific shorebirds throughout their annual cycle; (2) review the locations of and threats to important sites used by North Pacific shorebirds during the breeding, migration, and wintering periods, and (3) outline a program for international conservation of Pacific shorebirds.
Transactions of the North American Wildlife and Na↗