The dead raptors were discovered in April, but toxicology test results which prove they had ingested poison have only just been returned.
An RSPB officer had to abseil 30 metres down the face of the quarry to retrieve the bodies after a birdwatcher spotted the corpse of the male bird on a ledge next to a dead pigeon which is believed to have been baited. The female was then found submerged in the water at the base of the pit.
Peregrine falcons are protected by law and killing them is illegal. North Yorkshire Police are now investigating the incident.
The toxicology report found that the birds had eaten bait laced with the highly toxic insecticide bendiocarb.
The RSPB had already expressed concerns about the increasing number of raptor persecution incidents reported in North Yorkshire during the lockdown spring, when it was thought that perpetrators felt they were less likely to be observed by witnesses.
RSPB senior investigations officer Guy Shorrock said: “We believe the pigeon on the ledge was poisoned bait, laced with the highly toxic substance in order to deliberately kill these two birds. This was a criminal act, at the height of lockdown, resulting not only in the loss of two magnificent birds but any chicks they might have raised.
“North Yorkshire sadly has a diabolical reputation for the illegal shooting, trapping and poisoning of birds of prey. I have been picking up the bodies of raptors for nearly 30 years, and in the current ecological emergency, this cannot continue. Our wildlife needs better protection.”
North Yorkshire Police's Rural Task Force lead Inspector Matt Hagen added:
“Poisoning a bird of prey is a crime and it is saddening each time we have another incident reported to us. Every investigation is thoroughly carried out with all lines of enquiry followed to try and find those responsible, but we cannot do this without the public’s help, please be our eyes and ears and report this type of incident to the police.
“I’m urging anyone who has any information about bird of prey persecution to get in touch with the police, someone out there knows who is committing these crimes and we need that information to ensure they are stopped.”
If you have any information relating to this incident, call North Yorkshire Police on 101 and quote the crime reference number 12200057190.