Lead Toxicity in Mute Swans

Prelin1inary results of
ringing Mute Swans in Ireland
John O'Halloran
Department of Zoology, University College Cork
Richard Collins
10 Biscayne, Malahide, Co. Dublin
Irish Birds 3: 85-89 ( 1985)
Recoveries a~1d .controls of Mute Swans ringed in Ireland are analysed . The longest
nl(l\'emcn.l w1tl111~ the country was ~ 55km. ~fost deaths occurred in spring. The longest
known lilcspan lor an Irish swan 1s at least 12 years 9 months.
Introduction
Detailed studies of Mute Swan Cygnus olor populations in Dublin
and Cork commenced in 1983 (Collins l 985b, O'Halloran et al 1985).
These studies involve intensive colour-ringing of birds, whereas all
Mute Swans ringed in Ireland before 1983 were given only standard
metal rings. Studies on gulls (Laridae) have shown that colour-ringed
birds are much more likely to be reported than birds bearing only a
metal ring (Shedden et al 1985). lt is useful therefore to summarise
this earlier work as its results will not be directly comparable with
those of the Dublin and Cork studies.
The present data have been extracted from the British Trust for
Ornithology's ringing data base. This paper examines the data
available on recovery rates, movements and life-expectancies of
birds.
Ringing Recoveries
The number of Mute Swans ringed in Britain and Ireland up to the
end of 1982 was 37. I 30 (Mead and Hudson 1983). The number
recovered or controlled by that date was 12,688 (a "control" is a
ringed bird recaptured away from its place of ringing and released
again). This represents an overall recovery and control rate for
Britain and Ireland of 34%. From 1975 to 1982, 258 Mute Swans were
ringed in Ireland and during those eight years 31 were recovered or
controlled. This suggests that the Irish recovery and control rate is of
the order of 12%, much lower than the rate for Britain and Ireland as
a whole.
Sixty-one Mute Swans ringed in Ireland before 1983 w~re
recovered or controlled. No Irish Mute Swan bearing a metal rmg
only has been recorded abroad, though a colour-ringed swan was
rec~ntly recovered in Wales (Collins l 985a).
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