Lead Toxicity in Mute Swans

I
ingested lead pellets in gizzards.
Grass lead levels at Cork Lough were variable with lowest values in
summer.
Furthermore, in Canada geese which are largely grazers, there
was no relationship to the blood lead level despite a seasonal pattern
of lead levels in grass.
No large increase in blood lead or no acute
lead poisoning occurred in the geese.
Infact, the median lead level
for Canada geese at Cork Lough only once exceeded that of background
levels in Mute swans.
It is probable that fresh grass growth after
mowing is responsible for the lower grass lead levels in summer.
No
boating is carried out at Cork Lough, so this activity did not have any
influence on the birds or their susceptibility to picking up lead
pellets. The sampling methods employed for the recovery of lead
pellets and their patchy distribution in the mud may have been
responsible for the low recovery of angling lead pellets from Cork
Lough.
Nevertheless, the death through lead poisoning from ingesting
anglers' weights of a flightless two month old cygnet in 1985
implicates the Lough as one of the contaminating sites. It is unlikely
that the birds picked up angling lead from the river Lee.
This river,
which is part of the Lough catchment, is relatively fast flowing and
this, coupled with tidal action in locations of high swan density and
angling, is likely to 'wash away'any angling lead pellets. However, as
mentioned earlier, because the Lough is only part of a catchment area
within which the swans are resident (O'Halloran et al., 1987a), the
possibility of Mute swans picking up lead pellets from other ponds
cannot be dismissed.
The concentration of lead pellets at Lough Neagh
(2,500/m 2 ) was due to the presence of a clay pigeon shooting site
adjacent to a swan feeding area, which lead to the Mute swans ingesting
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