-
Views
-
Cite
Cite
Robert W. Russell, Paul E. Lehman, Spring Migration of Pacific Loons Through the Southern California Bight: Nearshore Flights, Seasonal Timing and Distribution at Sea, The Condor: Ornithological Applications, Volume 96, Issue 2, 1 May 1994, Pages 300–315, https://doi.org/10.2307/1369316
Close - Share Icon Share
Abstract
We studied the spring migration of Pacific Loons (Gavia pacifica) from a coastal promontory and during shipboard transects in the Southern California Bight. The coastline in the northern part of the bight acts as a leading line that diverts northbound migrants toward the west. We detected no effect of the onshore wind component on migration traffic rates along the coast and rejected the hypothesis that nearshore flights resulted from wind drift. Migration of Pacific Loons proceeded in headwinds up to 13 m/sec, but traffic rates decreased with increasing headwind strength, suggesting that loons avoided flying in the most energetically unfavorable conditions. The timing of peak migratory flights varied from mid-April to early May in different years, perhaps reflecting constraints imposed by the availability of food in wintering areas, at premigratory staging sites, and/or at en-route stopover sites. At sea, migrant loons were concentrated in cool waters in the northern part of the bight, and observations of loons on the water were associated with high densities of zooplankton at nearby sampling stations. We hypothesize that many northbound loons stop in the northern bight to feed on macrofauna attracted by concentrations of zooplankton near the frontal boundaries of upwelling plumes. Such stopovers should allow migrant loons to replenish energy stores efficiently and to resume northward migration rapidly.
