Sediment Mobility in the Severn Estuary and its Influence upon the Distribution of Shorebirds

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Author: Ferns, Peter N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1983
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Dunlin
• Online Access: http://dx.doi.org/10.1139/f83-294; http://www.nrcresearchpress.com/doi/pdf/10.1139/f83-294

In December 1979, superficial muddy sediments were eroded from considerable areas of the intertidal zone of the southern shores of the Severn Estuary during a period of prolonged westerly gales. Shorebird numbers at the affected sites showed an immediate decline as a result of the depletion of their mud-dwelling invertebrate food resources, and there was a corresponding increase in the numbers of birds along the northern shores of the estuary where no such erosion had occurred. Detailed monthly counts of 14 species of shorebirds in the Severn Estuary during 1971/72 to 1975/76 were therefore examined to determine if any of the previously unexplained anomalies in their distribution coincided with weather conditions likely to have given rise to similar losses of intertidal sediment. Although the 5 yr in question were relatively calm compared with the 1960s, there were five individual months during which the mean hourly windspeeds exceeded 13 m∙s −1 on more than 25 occasions. During these periods, the average deviations in the numbers of Shelduck, Grey Plover, Dunlin, Curlew, and Redshank from those predicted by a log-linear model taking seasonal, annual, and regional trends into account, were particularly large. Furthermore, the sites which were involved in each case were those that were directly exposed to the prevailing winds during the windiest periods of the month in question. High winds, by propagating waves that mobilize fine sediments in the intertidal zone, are thus implicated as a significant factor influencing the distribution of some shorebirds.Key words: Severn Estuary, sediment mobility, shorebird distribution, wading birds, local migration