Bird Skull Mystery

While taking measurements at roost sites recently, there was a morbid find under a Calophyllum in an urban area on Andersen Airforce Base. It is generally a popular roost site for starlings, sparrows, and doves, but the birds above in the canopy just make the scene below them at the base of the tree seem more chilling. What looked like a graveyard for nearly 50 birds could have been a cache made by some predator lurking around base of the tree. Let us know what you think could have caused this mass grave.