Forekomst af antikoagulante rodenticider i danske rovfugle, ugler og ...

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aeruginosus and 3.0 in eagle owl Bubo bubo. Overall more than 60% of
birds and 80% of mustelids had two or more anticoagulants in their body.
For the kestrel Falco tinnunculus, common buzzard Buteo buteo, tawny
owl, barn owl Tyto alba and little owl Athene noctua the average cumulative
concentration of all anticoagulants in the liver ranged between 35
and 58 ng/g. For the red kite Milvus milvus and the eagle owl, the average
concentration was 152 and 162 ng/g, respectively, while concentrations
in rough-legged buzzard Buteo lagopus, marsh harrier, long-eared
owl Asio otus and short-eared owl Asio flammeus ranged between 9 and
24 ng/g. There was no obvious explanation for the observed differences,
but these may be due to the degree to which the species exploit urbanised
areas and farmland. The higher concentrations in red kite and eagle
owl may relate to their predation of carrion and rats, respectively. The
average concentrations of anticoagulant rodenticides in stoat Mustela nivalis
and weasel Mustela erminea were 58 and 63 ng/g, respectively. The
highest levels of anticoagulants were measured in stoats and weasels.
Studies suggest that 200 ng/g anticoagulants in the liver represent a critical
contamination level for raptors and owls. Between 5.7% and 22% of
the examined kestrel, common buzzard, tawny owl, barn owl, little owl,
stoat and weasel had concentrations higher than 200 ng/g. Amongst red
kite and the eagle owl the proportion of individuals with more than 200
ng/g liver were 66% and 70%, respectively, while there were no critically
high concentrations recorded in rough-legged buzzard, marsh harrier,
long-eared owl and short-eared owl, although small sample size for the
last species prevents firm conclusions.
Overall no differences in frequency and level of contamination were detected
between sex and age groups, between time of year, or in relation
to the registered cause of death, which could indicate a systematic pattern
in the risk of poisoning. For stoat and weasel, concentrations of anticoagulants
increased from spring to winter, a trend reflected amongst
some of the bird species. Higher concentrations were also present in
stoats and weasels found dead, compared to other causes of death, and
for both species, body condition were weakly, but significantly correlated
with rodenticide burdens.
The recorded frequencies of anticoagulant poisoning in Danish birds of
prey, owls and mustelids, were markedly higher for most species than
those from British studies. The number of anticoagulants recorded per
individual was also higher in Danish birds and mustelids than found in
Great Britain. Higher sensitivity of the HPLC analysis used in the present
study cannot explain this difference. Possible explanations for the
differences between Denmark and Great Britain may include differences
in landscape structure, in application policies and methods for authorized
rodent control and in private use of the anticoagulants available on
the open market.
The use of anticoagulants over the past 10-20 years to control rodents in
Denmark has not had any documented adverse effect on the populations
of raptors and owls, as most species have increased in abundance during
this period. However, it can not be ruled out that the use of anticoagulants
locally or even nationally has elevated chick mortality in some