The June, 2008 Airline Pet Travel Report contains pet incidents for the month of April, 2008.
America Airlines lists the death of a dog and a cat on separate flights, but includes very little information on the incidents.
Delta lists the death of an African Grey Parrot. The loading crew in at Hartsfield Jackson Atlanta International failed to notify the captain that there was a live animal loaded in bin four and the bird froze to death in route to the destination city.
Source: June 2008 Air Travel Consumer Report.