UBC Theses and Dissertations
Foods and habitat of four anatinids wintering on the Fraser Delta tidal marshes Burgess , Thomas Edward
The Fraser delta tidal marshes are important for migrating and wintering ducks, in particular, Mallard, Pintail, Widgeon, and Green-winged Teal. Agricultural, residential, and industrial development threaten the tidal marshes with destruction and quality loss. In order to preserve and protect the most valuable areas, and perhaps improve the characteristics which attract ducks, it was considered necessary to determine areas of most value, and the environmental characteristics which could be improved. A study of the occurrence and food habits of ducks on the tidal marshes was considered to be the best means of determining the importance of each unit. The relative importance of the tidal marshes for loafing and feeding habitat was indicated from a synthesis of all available information on duck use of the entire delta area. Aerial censuses conducted throughout two winters provided data on the distribution and abundance of Mallard, Pintail, Widgeon, and Green-winged Teal on the foreshore and adjacent upland. It was found that an annually variable population of ducks was present from September until May, with the largest numbers occurring during fall and spring migrations. The tidal marshes attracted approximately one-half the ducks on the deltas— with the largest proportions occurring in September, early October, late March, April, and May.. All four census units of the tidal marsh attracted similar winter totals of ducks although the relative number at each unit varied throughout the winter. As all of the tidal marshes appeared important to ducks, the features of all of them were studied. Area was determined from aerial photographs, and topographical relationships were determined from known tide levels. Composition and distribution of vegetation was determined from line transects. Relative production of seeds was determined from line transects and seed samples. The tidal marshes were found to cover approximately 3,733 acres, sloping from the approximately thirteen foot to the seven foot tide level. A six to eighteen inch "drop-off", which usually occurred near the ten foot tide level, separated the tidal marsh into an upper and lower zone, each with a different vegetative composition. Fourteen plant species were found, of which five Cyperaceae species, Scirpus americanus , Carex lyngbyei , Eleocharis macrostachya , Scirpus paludosus , and Scirpus validus composed ninety-three percent of all plants. The first two species, dominant on the lower and upper zones respectively, formed seventy percent of all plants. Distribution appears to be determined by the degree of tidal flooding, the degree of local drainage, and possibly by undemonstrated differences in soil and water salinity. Seed production varied annually, and was related to the degree of tidal flooding. Scirpus validus and Carex Lyngbyei produced the most seeds, followed next by Scirpus americanus. Ducks were collected on the tidal marshes and adjacent agricultural areas. Analysis of their stomach contents revealed that Carex Lyngbyei, Scirpus validus and Scirpus americanus were the most important- tidal marsh food items. Polygonum lapathifolium and P. persicaria were the most important seed foods taken on the agricultural areas. Although Mallard, Pintail, and Green-winged Teal consumed mostly seeds, Widgeon consumed primarily green vegetation, including winter rye, Lolium sp., and several Gramineae species. A synthesis of the available information indicates that the tidal marshes were most important as loafing areas from October until January, while during the remainder of the period, from September until May, they were also important for the provision of food. The control of water levels, by diking and pumping, appears to be essential for the improvement and protection of the tidal marshes.
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