I determined the highway zone over which 42 radio tagged female northern pintails (Anas acuta) flew on their way from daytime roost sites in the north to nocturnal feeding sites in the south part of the Grassland Ecological Area (EA), California, during 4 and 11 November and 9 December, 1992. My objectives were to identify important pintail flight corridors along a highway where increased urbanization is projected, gather baseline flight path information so that impacts of future urbanization and other landscape changes can be evaluated, and provide insight into how urbanization and wetland habitat impact pintail flight paths. Most pintails flew fairly direct routes from their roost to feeding sites but some apparently followed routes over wetlands they encountered early in their trip and ended up taking indirect routes. No pintails flew over and 1 pintail diverted around the most heavily urbanized zone, providing weak evidence that urbanization may have acted as a partial barrier to pintail flight. Urban expansion eastward from the City of Los Banos into the path used by most pintails should be avoided to maintain direct waterfowl flight paths between habitats in the north and south Grassland EA. Open-space corridors should be incorporated into conservation planning in urban-wetland landscapes to facilitate direct flight paths between wetlands, which may be important to daily energetic of wintering pintails during hunting season, when they must fly considerable distances between sanctuaries and some feeding areas.
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