Cedar Waxwings.. toxic berries?


At least 8 Cedar Waxwings were found dead, close proximity and no external injuries, at the Claremont Golf Course.
Not clear if a plant/berry is responsible or some other toxin in the area. 
For example, Heavenly Bamboo(Nandina domestica) berries are toxic and CEWAs are known to fall victim poisoning.
I don't know if the Claremont GC has these non-native plants on their grounds. 

Has anyone recently encountered dead CEWAs lacking external injuries?
GGAS, Lindsay Wildlife, Cali F&W have been contacted.
The Claremont GC has been notified. The CGC state that they are "very environmentally conscious, use organic fertilizer, have a special area for bees etc." They have asked to be kept informed.

Saved a couple CEWA specimens if further analysis is needed.
heartbreaking... they are such elegant birds.

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