1. Lead poisoning of waterfowl
2. table ～The number of dead birds at Miyajima-numa [spring]
- In recent years there have been a number of reports from all over the
country about waterfowl being poisoned and killed after using lead shot
and fishing weights as grit (stones to aid digestion).
The number of reported incidents increased nationwide after concern was
raised in 1989 when it was discovered that lead poisoning by the Faculty
of Veterinary Medicine of Hokkaido University was responsible for the deaths
of a great number of swans at Miyajima-numa. Prior to that, dead swans
had been discovered in Miyajima-numa and neighboring Tegata and Oyako Marshes.
The suffering that these birds were seen to endure before dying supports
the conclusion that the cause of death was lead poisoning.
Details of the birds’ deaths, mainly swans, during spring are collated
in the table below.
There are cases where birds have died before winter ice has cleared from
the marsh in the spring (April 2nd, 1992), and it is thought that in such
instances the birds picked up lead where they wintered or during migration
to Miyajima where symptoms developed.
There are also many cases in the ponds, marshes and lakes along the Ishikari
River (Chashinai Marsh in Naie, Urausu Marsh in Urausu, Fukuroji Marsh
in Sunagawa, Tsukigaura Lake in Tsukigawa, and so on). Although the swans
only stay for a period of about a month in Miyajima and other waypoints,
they spend a total of five months where they winter, so it is thought that
the total number of deaths nationwide is quite high.
The reason that the number of dead birds at Miyajima-numa seems so great
is not that the level of lead pollution is particularly high, but because
the ratio of fallen birds that are discovered is high. The damage to wild
geese and ducks that do not stand out because of their protective plumage
is also thought to be serious.
In autumn, which begins shortly after the birds come from Siberia where
there is no lead shot, there are very few fallen birds, also because their
stay is short.
|(( In Consideration of the Large Number of Deaths))
- In autumn 1984, harvesting of the rice fields, which are a feeding ground
for the geese, was finished unusually early due to a spell of good weather.
Straw was burned and the fields were plowed. As a result, in spring the
following year, 1985, there was not nearly enough fallen rice and the geese
and swans alike fed on the marsh’s plant life. Furthermore, strong agricultural
chemicals had been used.
- In autumn 1989, the Hokkaido Hunter Association of Hokkaido voluntarily
refrained from any hunting of waterfowl with guns because of the high number
of deaths of swans (33-4) in spring of that year. For that reason, geese
and ducks from other lakes and marshes gathered at Miyajima-numa as a kind
of refuge, and exhausted the supply of fallen rice. It is thought that
in the following spring, white-fronted geese ingested lead when they made
up for the shortage by eating plants in the marsh. It is thought that the
birds have taken less lead from the matsh since 1991 because of fine gravel
scattered around the lake and the birds’ own extension of their feeding
grounds. However, with the increase in the number of migrating birds, there
is no end to the deaths.
- It is possible that the increase in the number of swans which fell victim
in spring 1997 was due to a decrease in the water level which allowed their
necks to reach the bottom of the marsh easily, and ingest remaining lead