The deer subsequently populated other neighboring locales in Micronesia, including the islands of Rota, Saipan and Pohnpei.

However, in the absence of a natural predator, its population is rapidly expanding in Guam, posing serious threats to the native ecosystem and agricultural lands due to overgrazing.

[13] Philippine deer are generally nocturnal, foraging for food (grasses, leaves, fallen fruits and berries) at night.

Many tense encounters between males result in nothing more than bluff charges, and the loser willingly retreats or is chased off of the boundaries of the territory.

These boundaries are constantly updated through urinating, defecating in key spots, and rubbing oil scent glands on surrounding plants.

[citation needed] After approximately six months, females give birth to a single fawn with light-colored spots, which will eventually disappear after several weeks.

[citation needed] The Bagobo-Tagabawa tribe in Barangay Sibulan, Toril, Davao City identified the Philippine brown deer as a "cultural keystone species" (CKS).

Habitat loss and fragmentation drive the deer to hide in the remaining patches of forest with scarce food to eat.

This is because of the rapid population decline estimated to be more than 30% in the last 24 years or three generations due to excessive hunting, shrinkage in distribution, and habitat loss and fragmentation.

[1] In prehistoric times, the Sunda island of Borneo might have been connected to Palawan during the penultimate and previous glacial events, judging from the molecular phylogeny of murids.

The other animal fossils were ascribed to deer, macaques, bearded pigs, small mammals, lizards, snakes and turtles.

However, the Philippine brown deer shows significant variation across its range, with populations on Mindanao Island being smaller than those of Luzon.

Thus, it is possible that the overlap between the Luzonese brown deer and the archaeological material is coincidental, and that the fossils could belonged to another species of Cervus that had occurred in Palawan, with the taxonomic classification being unresolved.