Northern Prairie Wildlife Research Center
The increase in the numbers of flooded gravel pits is an obvious feature of many river valleys in the southern half of England. Mute swans (Cygnus olor) have colonized many of them, where water sports have not kept them away. Pleasure boating has shown tremendous growth on many river and canal systems in recent years, to the detriment of underwater weed growth and the security of many mute swan resting places. Lead poisoning has recently been found to be a major cause of mortality of mute swans on certain Midlands rivers, such as the Trent and the Avon, where almost every mute swan found dead has been shown to have ingested lead weights discarded by anglers.
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/resource/literatr/disturb/bibli146.htm
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