Lead Toxicity in Mute Swans

of pellets had occured.
What is significant is the proportion (42%) of
birds sampled which were suffering from acute poisoning following the
ingestion of lead pellets. Since a largely non-breeding flock composed
of sub-adults and non-breeding adults occurs at Cork Lough, it may have
implications for the population as a whole in the south-west
catchment.
Birkhead and Perrins (1986) consider that non-breeding
flocks are the reservoir of future breeding stock, so any sub-lethal
effects or debilitation caused by lead poisoning at Cork Lough may have
a serious effect on recruitment.
Of the dead birds examined in the present study, 68% had died from
lead poisoning.
This figure has to be treated with caution however, in
that it is based on 1) three incidences in Northern Ireland, two
involving a large number of birds and one involving four birds; 2) an
intensive study of the Lough/ River Lee catchment in south-west Ireland
and 3) a few birds sent to us for examination from other parts of
Ireland (Table II). At Cork Lough and Willis' Pond, Belfast, ingestion
of anglers' weights was the source of le~d
poisoning in swans.
Similiarly Birkhead (1982) working on the River Thames in the U.K.
found that lead poisoning was almost exclusively attributable to
ingestion of anglers' weights.
By contrast, at Lough Neagh, lead
poisoning in swans resulted exclusively from the ingestion of gunshot
at a clay-pigeon shooting site. Deaths of Mute swans at clay-pigeon
shooting sites have also been reported from Denmark (see Clausen and
Wolsrup, 1979).
Gun-shot pellets from wildfowling which had occured
more than 18 years earlier was responsible for the deaths of four
Whooper swans at Kilcolman wildfowl refuge in Co.Cork.
Most hirds affected by lead showed impaction of the oesophagus and
gizzard, two Whooper swans
also Showed impaction of the duodenum.
A
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