Lead Toxicity in Mute Swans

differences [see O'Halloran et al. (A) in ]
~ ~ ' press • In the present
study, changes in haematological parameters were detected in live swans
with elevated lead.
X-ray examination of birds revealed that the
elevated lead was due to the ingestion of lead weights.
O'Halloran et
al., (B) [in press] reported that 22% of swans x-rayed at Cork Lough in
S.W. Ireland had ingested lead weights in their gizzards.
In this
study, in two of the x-rayed birds, a lead weight was present in the
gizzard and elevated blood lead levels.
Swan no. 1 (Table 4), x-rayed
a few weeks later, had lost it's lead weight and blood parameters had
returned to normal.
A third bird, (specimen no 9, Table 4) had no lead
weights and a low blood lead level, but at some time between then and
day 21, at least one lead weight was ingested.
The elevated lead
levels resulted in a decrease in circulating haemoglobin in the cell
(hypochromic anaemia, specimens 6,7,8, Table 4), while in other swans,
there was a reduction in the number of circulating red blood cells.
Despite the drop in haemoglobin levels, most birds recovered.
In one
swan, (specimen 1), the plumage remained poor for a year and the
over-all condition of the bird was poor.
Though haematological damage
was found in these birds, it is likely that other metabolic damage had
also been caused by elevated lead.
Hunter and Wobesser (1980) reported
that in a lead poisoned Mallard, anaemia w&s preceded by damage to the
nervous system and this is likely to be true also for Mute swans.
Location of waterways, numbers of pylons/wires and degree of
urbanisation may be contributing factors in causing collisions.
However, this study does suggest that sub-lethal effects of lead cause
anaemia and other pathological damage which may lead to increased risk
of colliding with objects.
- 127 -