The Puerto Rican owl (Gymnasio nudipes) or múcaro (Spanish via Taino), formerly known as the Puerto Rican screech owl, is a nocturnal endemic owl of the archipelago of Puerto Rico. It is the only species placed in the genus Gymnasio of the family Strigidae. The subspecies G. n. newtoni, which was endemic to the Virgin Islands, was locally referred to as the cuckoo bird. The Puerto Rican owl is a small owl possessing a brown upperside, a light-brown to white underside, white brown lines and white eyebrows. Sexual dimorphism is minor in this species with females being slightly larger than males. It is usually 20 centimetres (7.9 in) to 23 centimetres (9.1 in) in length with a wingspan of 154 centimetres (61 in) to 171 centimetres (67 in) for both sexes, and weighs about 103 grams (3.6 oz) to 154 grams (5.4 oz).
The Puerto Rican Owl is endemic to Puerto Rico and the Virgin Islands (Oberle 2018), but recent playback surveys using acoustic recorders in the Virgin Islands and in Vieques elicited no response (Gemmill 2015), suggesting that this species has been extirpated or is extremely rare on those islands. The species occurs in all forest types at all elevations from wet forests in the mountains to dry forests in coastal areas (Raffaele and others 1998), woodlots, forest edges, and tree-filled gardens (Oberle 2018). The owl occurs in both small and large forest fragments (Pardieck and others 1996). The atlas fieldwork yielded a total of 364 records within 284 hexagons or 59 percent of the 479 total hexagons (see map). Of the 284 hexagons where this species was found, breeding met the atlas definition of confirmed in 1 percent (4) of the hexagons, probable in 31 percent (89), and possible in 67 percent (190), while this species was observed in an additional hexagon but without evidence of breeding (see map). Puerto Rican Owl distribution. The map shows the highest breeding code by hexagon and overlaying the ecological life zones in Puerto Rico. Note: percentages may not total 100 due to rounding. 175Puerto Rican Owl/Mucarito de Puerto Rico
The Puerto Rican Owl nests in cavities in large hardwood trees and palms from April to June, according to previously published reports (Raffaele and others 1998). Atlas findings indicate breeding activity for this species occurs throughout the year, but increases from December to July and peaks in June (see chart). Results confirm that this species breeds in all ecological life zones, but it is mostly associated with the subtropical moist and subtropical wet forest life zones (63 and 28 percent of the hexagons, respectively) (see table and map).
Population trends for the Puerto Rican Owl are stable in Puerto Rico, but the subspecies (M.fin.finewtoni) is apparently extinct in the Virgin Islands and Vieques (Thorstrom and Gallardo 2017). Globally, it is listed as a species of least concern by the IUCN (BirdLife International 2016), and locally, this species is not listed in any of the threatened categories of PRDNER or USFWS. In Puerto Rico, the Puerto Rican Owl has a protected habitat in land of 11 percent or 729 km2 of the total area covered by the hexagons where evidence of breeding was found for this species (6770 km2).