Lead Toxicity in Mute Swans

in blood. In general, healthy birds have blood lead levels below
40µg/100mls. (Simpson et al 1979 and Birkhead 1981). Forty-one
percent of the birds sampled at The Lough had blood lead levels
above this limit. By contrast the level at the country sites was well
below maximum tolerable limits.
The estimated values in the blood of the birds sampled on the Lee
must be treated with caution for two reasons. Firstly, less than 12%
of the birds present were sampled and these results may not be
representative of the whole flock. Secondly, as mentioned, the Lee
population is heterogenous in that an as yet unquantified proportion
utilise the Lough from time to time. Nevertheless, the blood lead
levels of the River Lee sample were consistently lower than those of
population at The Lough.
It is clear from the sample at The Lough, and perhaps somewhat
unexpected, that adults have lower blood lead levels than sub-adults
(Table 2). One possible explanation for this might be that there are
differences in the extent to which both age-classes utilize The Lough.
It might be surmised therefore, that because of the artificial food
supply sub-adults (i.e. non-breeders) congregate and occupy The
Lough continuously for ·prolonged periods of time. In contrast and
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