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American White Pelican Foraging Areas and Movement Strategies in Nevada and South Dakota

  • Bates, K.K. and M.A. Yates, Boise State University / Raptor Research Center
  • Fuller, M.R. and S. Hanser, U.S. Geological Survey, Boise

Sky filled with American white pelicansWe instrumented 17 American White Pelicans (Pelecanus erythrorhynchos) in Nevada (1996-97) and 10 in South Dakota (1998) with Platform Transmitter Terminals (PTTs) and/or VHF transmitters during the nesting season to identify movements, foraging areas and flight altitude ranges. The instrumented individuals we tracked always moved in flocks with other non-marked pelicans. We occasionally tracked flocks containing one or more instrumented pelicans to and from foraging areas in excess of 100 km from their nesting colonies. During foraging flights instrumented pelicans achieved maximum above ground level (AGL) altitudes of approximately 3.0 km and 1.5 km in Nevada and South Dakota, respectively.

After the Pyramid Lake (NV) nesting period, but before migration, some birds moved several hundred kilometers. For example, one individual left the capture area in early July, flew to northern California, then to southern Oregon, southern Idaho, and arrived at the Great Salt Lake in Utah by mid-August. In early/mid-September it returned to north central Nevada then flew to north central Wyoming before migrating south in late September (Fig. 1).

Map of pelican movements

Figure 1. Movements of one American White Pelican instrumented with PTT 5717 from 2 May 1997 through 9 November 1997.

These movements provide an example of connectivity among the wetlands of the Great Basin and adjacent regions and to migratory and wintering areas, and are representative of the useful information that can be obtained using the Argos satellite telemetry system. The data are giving us an understanding of the timing and possible impetus for such movements and a better handle on why and how pelicans are able to exploit temporal resources throughout their range.

Along those lines, we looked more closely at local movements during the breeding season. Sharp declines in breeding success at Pyramid Lake through 2004 corresponded with regional drought conditions, raising questions about the availability and quality of forage available to breeders. Managers particularly wanted to know the effective foraging range and presumed foraging sites of Pyramid Lake birds. We assembled GIS products, defined presumed foraging trips and locales for our Nevada subjects, and made ground visits to assess current viability of some sites suggested by our data as ephemeral or marginal resources. We found that, although many presumed foraging trips were less lengthy, it was not unusual for Pyramid Lake breeders to forage 160 kilometers or more from the nesting island.