Red Kites are a protected species
Police believe rare birds of prey found dead in Northumberland may have been deliberately poisoned.
Two red kites were found by a landowner in Hexham and initial examinations showed no obvious cause of death.
Laboratory tests and post-mortem examinations are now being carried out by experts from Defra.
A spokesman for Northumbria police said Red Kites had been targeted in the past it was possible the birds, which are a protected species, had been poisoned.
The birds were found close to each other on 12 February and showed no evidence of bullet injuries.
A Northumbria force spokesman said: "This is an unusual incident and it's a possibility that these birds may have been poisoned, as Red Kites have in the past been persecuted.
"If this is the case then we need to find out who, and how they have done this.
"Red Kites are a protected species under current legislation and anyone found guilty of killing them can expect a custodial sentence or a heavy fine."