There are no squirrel species native to Puerto Rico. While squirrels are present, their appearance is a relatively recent phenomenon tied to human activity. Any true squirrel population found on the island is non-native, invasive, and extremely localized.
The Status of Squirrels in Puerto Rico
The specific rodent that has established small, isolated populations is the Indian Palm Squirrel (Funambulus palmarum). This species is distinguished by its small size, typically weighing around 3.5 to 4.2 ounces, and its distinctive coat pattern. Its grayish-brown fur is marked by three prominent pale stripes running longitudinally down its back.
These squirrel populations are not widespread across the main island or its archipelagos. They are confined to small, concentrated pockets within specific urban and suburban areas. The Indian Palm Squirrel is highly adaptable, thriving in gardens, parks, and human-modified landscapes. The species is diurnal, meaning it is active during the day, which makes it a visible, though uncommon, sight in these localized areas.
Origin and Geography of Establishment
The Indian Palm Squirrel’s presence is a result of the exotic pet trade and accidental releases or escapes. These animals were not intentionally introduced for biological control, unlike other invasive species on the island. The timeline for their establishment is not clearly documented, but it is a contemporary issue, distinguishing it from historical introductions like the mongoose.
Successful establishment requires favorable micro-habitats and a consistent food supply. The small groups of squirrels are concentrated in areas with dense ornamental vegetation, such as certain municipalities and private estates. This limited geographical concentration suggests that initial introduction events were few, and the species has not managed to colonize the dense interior forests or spread widely across the island.
Ecological Impact and Management
As an invasive species, the Indian Palm Squirrel presents several ecological concerns for native flora and fauna. They possess a broad, opportunistic diet, consuming seeds, fruits, and vegetative matter, which places them in direct competition with native frugivores and seed dispersers. Their omnivorous nature also extends to animal matter, including bird eggs and nestlings, posing a threat to native bird populations.
The species is highly commensal with humans, readily adapting to urban settings where they can become a nuisance. Damage to agricultural crops, utility infrastructure, and garden plants are recognized problems where this species has naturalized elsewhere. Local environmental agencies classify non-native species like this as restricted or prohibited. Management strategies focus on preventing further spread and containing existing localized populations.
Common Look-Alikes
Many people who believe they have seen a squirrel are likely observing a different non-native mammal entirely. The most significant source of confusion is the widespread Small Indian Mongoose (Herpestes auropunctatus), often referred to by the Spanish term for squirrel, ardilla. The mongoose is a slender, weasel-like carnivore with a pointed snout and a long, bushy tail often mistaken for a squirrel’s tail.
A clear distinction is that the mongoose is a ground dweller, rarely climbing trees, and lacks the three pale stripes characteristic of the Indian Palm Squirrel. Misidentification is also possible with various species of rats present. These rodents generally lack the large, bushy tail and the diurnal, highly arboreal behavior typical of true squirrels. The Indian Palm Squirrel is a true rodent of the family Sciuridae, setting it apart from the mongoose (family Herpestidae).