Lead Toxicity in Mute Swans

Swans
effectively, but may not pick up lead weights or line snagged in weed or
stones. Nevertheless. the death of a 2-month-old, flightless cygnet at the
laugh, which was shown to have elevated lead levels and contained ',four
angling shot at post-mortem, implicates the laugh as one of the main
sources of contamination.
Radiological examination of birds has confirmed that elevated levels of
blood lead are due to ingested lead. Seven of the thirty-eight swans
X-rayed showed lead pellets to be present. Three of these birds had
ingested lead and four had been sprayed with gunshot. Interestingly,
'shot-in' lead caused no increase in blood lead level, while ingested lead
caused a considerable elevation. One individual which had one anglers'
weight in its gizzard, as revealed by X-raying, and a blood lead level of
over 4,u.moles Pb/L, had suffered considerable loss of body weight and
metabolic damage (anaemia). Subsequent radiological examination of this
individual ( 8 weeks later) revealed the lead weight had been worn away.
The bird's condition. however (as indicated by plumage condition and
haemoglobin level), remained poor. Although lead levels such as those
mentioned above may not be sufficient to cause death, the birds' reproductive
capacity (Birkhead 1983) and dispersal ability (Bellrose 1959)
may be affected.
Although the levels of lead in the blood of swans in the laugh are high,
the incidence of death as a result of lead poisoning is unknown. While the
presence of anglers' lead in the gizzards of dead birds is presumptive
evidence of lead poisoning, only chemical analysis of body tissues can
1e1u"
F\-(?·c· I > 300'"
FIGURE 2: Recorded movements of swans ringed at Cork City Lough. A
transported to Charleville which later flew back to the lough .
one bird
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I