Birds of Mona Island

The Red-footed Booby colony at Cabo Norte

Red-footed Booby nests in trees rather than on the ground, and Mona's main colony lies in the Cabo Norte area. A georeferenced survey published in Caribbean Naturalist counted 1,351 perched birds and 652 nests on 364 trees spread over 19.6 hectares. More than 90% of nests were in two tree species, Guapira discolor and Ficus citrifolia, which shows how closely the colony depends on a particular forest.

A later study in Wildlife Society Bulletin used point counts in 2019 and estimated about 6,130 birds in the colony, more than double earlier estimates. The authors found that night counts yield higher densities because many boobies are fishing at sea during the day. For a birder the lesson is simple: an empty tree at midday does not mean the colony is gone.

Mona Yellow-shouldered Blackbird: the island subspecies

Yellow-shouldered Blackbird (Agelaius xanthomus) is endemic to Puerto Rico and listed as endangered by both the federal government and DRNA. The U.S. Fish and Wildlife Service (FWS) describes four areas where the species survives; one is Mona and Monito, where the subspecies A. x. monensis developed. That population is roughly 150 birds, the second largest after southwestern Puerto Rico.

Island Conservation explains that nest predation by rats restricts the Mona blackbird to nesting on inaccessible cliffs. That is why the FWS recovery plan requires the Mona population to show a stable or increasing trend before the species can be delisted. If you see one, it is a black bird with a yellow shoulder patch; watch it without approaching the cliff edge.

Caves, shearwaters, and terns: what almost no one sees

A Journal of Caribbean Ornithology paper documented that Sargasso Shearwater (formerly treated as Audubon's Shearwater) and Bridled Tern still breed in caves on northern Mona, more than 80 years after their last recorded observation. The authors argue that these remnant populations could be key to seabird recovery on the island once invasive mammals are removed.

That does not make the caves a destination. DRNA prohibits camping in or making expeditions into caves and bans rappelling and climbing anywhere in the reserve. Sargasso Shearwater is mostly pelagic and is best detected from the sea; Bridled Tern may be seen flying near the coast. Both can be appreciated without entering their refuges.

Land birds and migrants in the dry scrub

Open records aggregated by GBIF for Mona are led by Pearly-eyed Thrasher, Brown Booby, Common Ground Dove, American Kestrel, Magnificent Frigatebird, Zenaida Dove, and Gray Kingbird. Mangrove Cuckoo, White-crowned Pigeon, and White-tailed Tropicbird, which uses the cliffs, also appear.

During migration the island works as a stopover in the Mona Passage. Records include warblers such as Prairie Warbler, Northern Waterthrush, and Blackpoll Warbler, plus raptors such as Peregrine Falcon and Merlin. A rare migrant on Mona deserves documentation with photos, date, and exact location, because observer coverage is very low.

DRNA permits and rules for visiting Mona

DRNA requires the permit to be processed at least five working days in advance through its Land Use and Forest Permits Section. You check space, make a reservation valid for 24 hours, and then submit the application, payment, and documents at a DRNA office. Camping costs $10 per person per night and is allowed only at Playa Pájaros (capacity 50) and Playa Sardinera (capacity 60).

Visiting Monito islet, lighting fires, bringing pets, feeding or disturbing wildlife, and cutting vegetation are all prohibited, and all trash must be carried back to Puerto Rico. The permit page does not arrange transport: crossing the Mona Passage is arranged separately. DRNA also opens goat and pig hunting seasons (in 2024-2025, December through April, Monday to Thursday), so check the current calendar before planning.

What birds live on Mona Island?

Mona is known for its Red-footed Booby colony at Cabo Norte, Brown Booby, Magnificent Frigatebird, White-tailed Tropicbird, and the Mona Yellow-shouldered Blackbird, a subspecies unique to Mona and Monito. Island Conservation reports habitat for 117 bird species, many of them passing migrants.

Do you need a permit to visit Mona Island?

Yes. DRNA requires a prior permit, processed at least five working days in advance through its Land Use and Forest Permits Section. Camping costs $10 per person per night and is allowed only at Playa Pájaros and Playa Sardinera.

Can you visit Monito Island?

No. DRNA's rules for the reserve prohibit visits to Monito islet. Its birds, including the Mona blackbird, are protected by keeping people off it.

How many boobies are on Mona Island?

A study based on 2019 counts, published in 2023, estimated about 6,130 birds in the Red-footed Booby colony, more than double earlier estimates. An earlier survey counted 652 nests on 364 trees at Cabo Norte.

What is the Mona Yellow-shouldered Blackbird?

It is the subspecies Agelaius xanthomus monensis of the Yellow-shouldered Blackbird, endemic to Mona and Monito. FWS estimates about 150 birds in that population, and because of rat predation it nests mostly on inaccessible cliffs.

Can you enter the caves on Mona?

DRNA camping rules prohibit camping in or making expeditions into caves, as well as rappelling and climbing. Some northern caves are breeding refuges for Sargasso Shearwater and Bridled Tern.