Lead Toxicity in Mute Swans

MATERIALS AND METHODS
Study sites.
The main sampling site was at Cork Lough, in the western suburbs of
Cork city (Fig.l). This location was selected because of the relatively
large flock of Mute swans present there.
The number of swans varies
seasonally with a maximum of 160 birds in winter and a minimum of 60 in
summer.
The birds, a heterogenous assemblage of non-breeders, immatures
and breeding birds, congregate there as a result of artifical feeding.
Cork Lough includes two areas of open water and an island where the
birds roost.
The maximum depth at Cork Lough is l.5m in the northern
basin and the substrate is soft and silty throughout, with very little
grit. The area is an internationally renowned coarse angling site
(Anon, 1986).
A second site was selected at the Gearagh, Macroom,
Co.Cork where a number (~.100)
of swans annually congregate for moulting
(Fig.l).
Collection of blood samples.
Over 823 blood samples were taken from 456 uniquely ringed Mute
swans between December 1984 and November 1986.
Groups of birds were
caught each week by hand;
each bird was fitted with a numbered metal
ring and a unique yellow 'Darvic' ring for individual recognition.
Blood samples (5ml) were obtained using a 23 gauge 1 inch needle either
from the brachial vein or , in the case of cygnets, from the tarsal
vein.
Blood was immediately placed in a low lead sodium heparin tube
and placed in a polystyrene ice box for transportation and then stored
at -20°c before analysis.
An aliquot was also placed in dipotassium
ethylene diamine tetra-acetate (EDTA) tube for haemoglobin estimation.
- 17 -