Lead Toxicity in Mute Swans

INTRODUCTION
Lead poisoning through the ingestion of discarded anglers' weights
or spent gunshot is known to be a major cause of mortality in Mute
swans [Cygnus olor, (Gmelin), Birkhead, 1982; O'Halloran et al.,
1987a)]. Conclusive evidence that death i·s due to lead · · poisoning,
however, can only be achieved through chemical analyses of tissues.
The most widely used tissue for the diagnosis of lead poisoning in
birds is the liver and frequently only a single tissue sample is
taken.
Roscoe et al., (1979); and Anders et al., (1982) attempted to
determine the flux of lead in the bodies of caged birds by feeding them
lead.
They then extrapolated the results to the field situation. The
validity of extrapolating experimental results to the field situation
has been questioned, because of the contrasting pattern and duration of
exposure to pollutants in the two situations (Hutton, 1980).
While high tissue lead levels are diagnostic of birds which have
died from lead poisoning, there is a need to investigate sub-lethal
effects.
Some workers have demonstrated the immuno-suppressive effects
of lead in birds (Franson, 1986), while others have shown a change in
reproductive performance (e.g. Elder, 1954).
Hunter and Wobesser
(1980) found encephalopathy and peripheral neuropathy in lead poisoned
M a 11 ar d A nas p 1 a t yrync h os (L) • These Changes preceded anaemia which
was induced following the feeding of lead pellets.
Acute lead poisoning is considered to be responsible for the deaths
of a large proportion of Mute swans, but an additional cause of
mortality is collision wit h over-h ea d power c ables · Bi.rkhead and
Perrins (1986) suggest that sub-lethal doses of lead may have an effect
on high degree co-ordination in Mute swans.
Sub-lethal levels
- 114 -