Habitat use and movements of Northern Pintails wintering in the Suisun Marsh, California
During the past fifteen years there has been a significant decline in the Northern Pintail (Anas acuta) population, and a disproportionate delcline in the number of pintails wintering in the Suisun Marsh. In order to investigate the reasons for this decline we captured and radio-marked 100 female northern pintails on Grizzly Island State Wildlife Area in the Suisun Marsh and monitored habitat use and movements of the birds from September to March during 1991-92 and 1992-93. Vegetation types of Suisun Marsh were mapped from aerial photos with a geographic information system (ARC/INFO) and nine habitat classifications were developed on the basis of dominant vegetation types. Comparison of habitat use versus availability was completed with Chi-square goodness-of-fit analyses which tested for preference or avoidance of particular habitat classifications using the Bonferroni Z-statistic. Analyses were conducted on bird locations taken between sunset and sunrise, and pooled over all birds in three time periods each year. Suisun Marsh pintails preferred habitats dominated with Brass Buttons (Cotula coronopifolia) and never preferred Alkali Bulrush (Scirpus robustus) or Fat Hen (Atriplex triangularis) dominated habitats. Pickleweed (Salicornia virginica) dominated habitats were preferred in some time periods. Soil types were mapped and classified into nine groups. Chi-square tests were completed on bird use in these nine soil classifications during each of three time intervals. Soil type Suisun Peaty Muck was preferred in all but the first time period of the first year while Valdez Silty Clay Loam was preferred only during the initial time interval. The length of time the radio-marked birds spent in the Suisun Marsh varied but many began to leave the Suisun Marsh soon after marking and in both years less than 10% of them remained in Suisun Marsh on 15 December. The birds primarily moved into the Sacramento-San Joaquin River Delta and later into the Sacramento Valley. By the middle of January over 70% of the birds were in the Sacramento Valley with relatively few birds having moved into the San Joaquin Valley (less than 7%). Future management of Suisun Marsh for Brass Button dominated habitats may encourage more pintails to remain in the Suisun Marsh for longer periods of time by providing a preferred habitat type.
For more information, contact Mike Casazza.
