Farming users of rodenticides are being urged to follow product label instructions diligently after the chemical's residues were found in barn owls.
Two-thirds of barn owls analysed were found with detectable liver residues of two or more second generation anticoagulant rodenticides (SGARs).
Another 21% were positive for one SGAR, according to a report conducted by the Campaign for Responsible Rodenticide Use (CRRU).
The highest frequency detections were of bromadiolone, difenacoum and brodifacoum.
For the first time in four years since CRRU began annual reporting of ‘SGAR residues in barn owls’, one specimen was identified in which SGAR exposure was a possible contributor to the cause of death.
Of 100-a-year analysed, the other 399 had died mainly from either road traffic trauma or starvation.
CRRU chairman Dr Alan Buckle said: "Compared with a 2006 to 2012 benchmark, several years before the CRRU-operated UK Rodenticide Stewardship Regime was established, these latest results show no significant rise nor fall in total SGAR residues.
"Moreover, the latest analysis was of birds that died during only the second year of fully operational rodenticide stewardship controls."
Even so, the results come at a sensitive time, Dr Buckle said: "The stewardship regime will be reviewed formally by its HSE-led government Oversight Group during the next two to three months."