Shaun Micklewright

During a visit to Trimpley Reservoir in mid February 2003 I was surprised to record a significant increase in the numbers of Mallards Anas platyrhynchos present on the main reservoir. Although present throughout the year on the reservoirs and adjacent River Severn, with the maximum number of birds recorded around 30, I was quite surprised to observe approximately 140 feeding around the rocky shore of the reservoir. The water level was approximately two meters below full capacity, exposing a dark tide mark which I first thought was a type of alga, but on closer inspection I was amazed to discover it was caused by thousands of Zebra Mussels Dreissena polymorpha tightly encrusted on the rocks and concrete banks. The Mallards appeared to be prizing them off (no mean feat) with gusto and swallowing them whole in what I can only describe as a feeding frenzy.

The Birds of the Western Palaearctic concise edition describes Mallard food/feeding requirements as 'omnivorous and opportunistic with a range of food and feeding methods'. I have yet to find any reference specifically related to Zebra Mussel as part of Mallard diet although both Tufted Duck Aythya fuligula and Scaup Aythya marila regularly feed on them when they are available.

All records of Zebra Mussels would be most welcome (see Worcestershire Record No 11 November 2001). The Trimpley record is a first for this site and, more worryingly, a potential headache for water abstraction engineers.

Editor's note
The main BWP (Cramp 1977) states animal food includes "insects, molluscs, crustaceans, annelids, amphibians, fish, and occasionally even birds and mammals size range up to 5 cms but usually 1mm to 1 cm". Bulk of diet is usually vegetable material but mallards are nothing if not opportunistic feeders! No mention of zebra mussels although BWP volume one was written 27 years ago and there may be more recent reports.

D.W.SNOW, C.M.PERRINS 1998 The Birds of the Western Palearctic. Concise Edition. OUP
CRAMP S et al 1977 The Birds of the Western Palearctic. Volume 1. OUP

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