Puerto Rican Nightjar (Guabairo): the endemic nightjar of the dry forest

How to recognize the guabairo by its song

The most reliable way to detect a guabairo is by ear. The male gives a rapid series of emphatic, high-pitched whistles, 'whip, whip, whip, whip', usually shortly after dusk and again before first light. Males hold territories and sing year-round, but singing increases in the second half of December, when territorial encounters become more frequent, and peaks in April and May.

Watch for one common mix-up: the Puerto Rican Bullfinch (Comeñame) also gives a whistled 'whip-whip-whip', but it sings by day from trees and shrubs and often ends with a buzz. If you hear the series in full darkness inside southern dry forest, the nightjar is the main candidate. The species page has a recording from Yauco with its spectrogram so you can compare the rhythm.

Where it lives: from Guánica Forest to Cabo Rojo and Guayama

The core population is in and around Guánica State Forest, where the guabairo is rare to locally common. It also lives in the limestone hills of Guayanilla and Peñuelas, in Susúa and Maricao state forests, at La Parguera and Sierra Bermeja (Lajas), and at Guaniquilla, El Combate, and Peñones de Melones (Cabo Rojo). In November and December 2021, at least two birds were documented singing on the Cabo Rojo National Wildlife Refuge, where the species had not been reported before, and since 2017 there have been new records in Ponce and Guayama.

Typical habitat is semideciduous dry forest with deep leaf litter and an open understory, plus evergreen forest and sometimes riparian strips and plantations. The breeding bird atlas found it in 46 of the archipelago's 479 hexagons (10%), with 60% of breeding hexagons in the subtropical dry forest life zone and the rest in moist and wet forest at higher elevations.

From 'extinct' bird to rediscovered species

The earliest guabairo records come from the moist northern karst: a specimen collected at Bayamón in 1888, subfossil bones from caves in Morovis, and a bird seen at Río Piedras in 1911. Then half a century passed with no records, and it was presumed extinct, partly because of the mongoose introduced around 1877.

In 1961 it was rediscovered in Guánica Forest, 62 km (39 mi) southwest of the last sighting. Surveys from 1985 to 1992 found no relict populations in the northern karst but confirmed three southwestern strongholds: Guánica-Ensenada, Susúa-Maricao, and Guayanilla-Peñuelas. That history is why the guabairo appears both among the living endemics and on lists of species we nearly lost.

Nesting on the ground: why it is so vulnerable

The guabairo builds no nest. The female lays one or two spotted buff-brown eggs directly on leaf litter, often at the base of a small tree or under a low shrub. Both parents incubate for 18 to 20 days and use distraction displays toward predators. The literature places nesting from late February to early July; the atlas found activity from December to August, with most records from February to May and a peak in May.

Laying on the ground exposes eggs and chicks to mongooses, feral cats and dogs, and fire ants, which can kill chicks. The Pearly-eyed Thrasher (Zorzal Pardo) also takes eggs and young, and Short-eared Owls have been seen hunting young nightjars. Even so, the federal agency and researchers identify habitat loss and degradation, especially on private land, as the main threat.

How many guabairos there are and what 'Vulnerable' means

There is no recent island-wide count. In 1969–1971, 450–500 pairs were estimated, mostly at Guánica. Between 1985 and 1992, surveys counted about 1,400–2,000 singing males across roughly 10,000 hectares; because not every singing male is paired, that figure can overstate pairs. 2010 models suggested more habitat and more birds than previously thought, and the IUCN moved it from Endangered to Vulnerable in 2023 because of that wider distribution, not because recovery was confirmed.

Federally it remains endangered: the 1984 recovery plan calls for 600 pairs in Guánica, 400 in Guayanilla-Tallaboa, and 200 in Susúa before delisting can be considered, and those targets have not been documented. Between 47% and 81.4% of its habitat is privately owned, and only 14% of the area where breeding is likely or confirmed is formally protected.

Other nightjars and nighthawks: what not to confuse it with

The Puerto Rico Ornithological Society catalog lists two other 'guabairos': the Guabairo de la Carolina (Chuck-will's-widow), a larger North American migrant, and the Guabairo Coliblanco (White-tailed Nightjar). Both are accidental in Puerto Rico, so a record needs solid documentation. The Antillean Nighthawk (Querequequé), by contrast, is common in season and is seen flying high over clearings, pastures, and towns at dusk with an insistent call.

The practical rule: a repeated song from inside southern dry forest in full darkness points to the guabairo; a long, pointed-winged bird hunting in open sky points to the nighthawk. To listen responsibly, stay on trails and roads, avoid shining lights on the bird, and do not use repeated playback to lure it.

What is a guabairo?

A guabairo is the Puerto Rican Nightjar (Antrostomus noctitherus), a nocturnal nightjar endemic to the island. It lives in dry and lower montane forests of the south, from Cabo Rojo to Guayama, and is mostly detected by its 'whip, whip, whip' song at dusk.

What does the Puerto Rican Nightjar sound like?

The Puerto Rican Nightjar gives a rapid series of emphatic, high-pitched whistles, 'whip, whip, whip', shortly after dusk and before dawn. Males sing year-round, with more activity from late December into spring and a peak in April and May.

Is the Puerto Rican Nightjar endangered?

Yes. It has been federally listed as endangered since 1973 and is also endangered under Puerto Rico regulations. The IUCN reclassified it as Vulnerable in 2023 because its range proved wider, but only 14% of its breeding area is protected.

Where can you hear the Puerto Rican Nightjar?

The best-known place is Guánica State Forest and its surroundings. It also lives in Guayanilla-Peñuelas, Susúa, Maricao, La Parguera, Sierra Bermeja, and several parts of Cabo Rojo. Listen from permitted roads and trails without spotlighting the bird or luring it with playback.

Is the guabairo an owl?

No. The guabairo is a nightjar (family Caprimulgidae): it has a very wide gape and cryptic plumage, and it catches insects in flight. Puerto Rico's owls, such as the Puerto Rican Owl (Múcaro), belong to a different order of birds.

How many Puerto Rican Nightjars are left?

There is no recent island-wide estimate. Surveys from 1985 to 1992 counted about 1,400–2,000 singing males across roughly 10,000 hectares in the southwest, and 2010 models suggest there may be more birds and habitat than previously thought.