I have heard that crows and blue jays are very susceptible to West Nile Virus, a disease that is deadly for horses if they are bitten by infected mosquitoes. So if you find dead blue jays or crows, you may want to eradicate mosquitoes in your environment through proper management techniques.
You also should make sure that your horses are regularly vaccinated against WNV.
For a wonderful discussion and essay on how to prevent Wile Virus, go to The Green Equestrian: West Nile Virus - Join the "Swat-Team".
Debbie Solano, CRS, ABR, CDPE, CHMS, e-PRO, GRI, REOS, SRES
Coldwell Banker Select, Realtors -- Land & Ranch Division
4408 S. Harvard Avenue
Tulsa, OK 74135