The Elfin-woods Warbler is endemic to Puerto Rico, where it is uncommon and local. Indeed, it was not observed by ornithologists at all until 1969, when Cameron Kepler and Angela Kay Kepler began to observe a warbler that they could not identify during their regular censuses of birds in the Sierra de Luquillo, eastern Puerto Rico (Kepler 2009). Over time their suspicions that the mystery warbler was a previously unknown species were confirmed, and it was described to science in 1972 (Kepler and Parkes 1972). Since that time it has been reported from four disjunct sites in mountain ranges in the eastern and western ends of the island, and in the interior. These disjunct sites are in the Toro Negro Forest in the center of the Cordillera Central and Maricao Forest at its western end; Carite Forest within Sierra de Cayey in the southeast; and El Yunque Forest in Sierra de Luquillo of eastern Puerto Rico (Kepler and Parkes 1972, Gochfeld et al. 1973, Pérez-Rivera and Maldonado 1977, Woodbury in Pérez-Rivera 1979, Raffaele et al. 1998). Its existence at some of these locations has been questioned (Anadón-Irizarry 2006), and it is now
thought to be restricted to El Yunque Forest in the east and Maricao Forest in the western end of the island. Raúl Pérez-Rivera (pers. comm.) reported the Elfin-woods Warbler in Carite Forest during the 1980's and 1990's in some of the same areas that also were searched by Anadón-Irizarry (2006) in 2003, but the latter did not detect this species. If the Elfin-woods Warbler persists and is sedentary in small isolated pockets of forest, future assessments of the status of this population will require extensive searches covering a much larger area into the fragmented landscape of the Carite Forest. It is unlikelty that there is an extant Elfin-woods Warbler population in the Toro Negro Forest. The only report of this species in the Toro Negro Forest is a sighting of the late botanist Roy O. Woodbury, cited in Pérez-Rivera (1979). I spent two decades (late 1970's to late 1990's) conducting research with the Puerto Rican Sharp-shinned Hawk (Accipiter striatus venator) in the very rugged terrain of the Toro Negro Forest and adjacent lands and never heard or saw the Elfin-woods Warbler.
Anadón-Irizarry (2006) searched for, but had no sightings of, the Elfin-woods Warbler in 2003 and 2004 in Toro Negro Forest, Bosque del Pueblo and Bosque Guilarte in Adjuntas, and in adjacent secondary forests and shaded coffee plantations.
The elevational range of the Elfin-woods Warbler in the two best studied populations is very similar. In El Yunque Forest the species is more common at elevations of 600-800 m, with an altitudinal range that stretches from 250-950 m (Anadón-Irizarry 2006). In Maricao Forest it has an altitudinal range that extends from 150-880 m, being more common at 600-900 m (Delannoy 2007, González 2008).
Distribution outside the Americas
Endemic to Puerto Rico.
Elfin-woods Warblers in El Yunque Forest of eastern Puerto Rico are most abundant in Elfin and Palo Colorado Forest types, and considerably less abundant in Palm and Tabonuco Forests (Wiley and Bauer 1985, Anadón-Irizarry 2006). Habitats adjacent to El Yunque Forest have not been searched to determine the presence and abundance of Elfin-woods Warbler. In the Maricao Forest of western Puerto Rico, Elfin-woods Warblers preferred the Podocarpus forest type, and were significantly less abundant in plantations of Calophyllum brasiliense, Eucalyptus robusta and Pinus caribaea, Dry Slope, and Exposed Woodland forest types (Cruz and Delannoy 1984a, Anadón-Irizarry 2006, Delannoy 2007, González 2008).
The highest Elfin-woods Warbler abundance was recorded in the Podocarpus Forest, a habitat that covers 80 ha (1.9%) of the land area of the Maricao Forest (Silander et al. 1986).
This suggests a very strong preference for a very specific habitat type. The strong preference for Podocarpus Forest could be related to better protection from predators, the presence of a richer food supply (arboreal arthropods), or better reproductive success (Delannoy 2007, González 2008). Both the presence and the abundance of Elfins dropped considerably with distance away from preferred Podocarpus Forest into lower elevations and from the Maricao Forest boundaries, where human modified habitats were prevalent. These lowland habitats were Shaded-Coffee Plantations, Mature Secondary Forests, Young Secondary Forests, Gallery Forests, Pastures, Residential Rural and Dry Slope Forests (Delannoy 2007, González 2008). Elfins were neither recorded in drier habitats (Dry Slope Forests) of the Susúa Forest, located 10 km southeast of the Maricao Forest, nor in humid habitats (Mature Secondary Forests and Shaded-Coffee Plantations) north, northwest, and northeast of the town of Maricao (Delannoy 2007, González 2008). Elfin Forest, Tabonuco Forest, Palm Forest, Granadillo-Caimitillo Forest, Secondary Forest, Timber Plantations, and Shaded-Coffee Plantations along the Cordillera Central (Guilarte, Bosque del Pueblo, Tres Picachos and Toro Negro Forests) and Sierra de Cayey (Carite Forest) were searched for Elfins but yielded negative results (Miranda-Castro et al. 2000, Anadón-Irizarry 2006).
The historical distribution range of the Elfin-woods Warbler apparently has been reduced to two populations, one in El Yunque Forest of eastern Puerto Rico and another in the Maricao Forest of western Puerto Rico (Anadon-Irizarry 2006). Anadon-Irizarry suggested that populations no longer exist in Carite and Toro Negro Forests. However, Anadón-Irizarry was cautious about her remarks and did not rule out the possibility of Elfins being present in isolated pocket of forest habitats not searched. The most important recent finding about the Elfin-woods Warbler distribution is its occupancy of habitats in landscapes outside the borders of protected forest reserves. Elfins can thrive on some human modified and plantation habitats (i.e., timber and shaded-coffee), although abundance on these habitats is much lower than in prime habitat such as Podocarpus Forest (Delannoy 2007, González 2008). Following severe vegetation damage to Elfin Woodland in El Yunque Forest from hurricanes Hugo (1989) and Georges (1998), Elfins made a habitat and elevation shift to occupy Palo Colorado Forest more often (Wayne Arendt pers. comm., Anadon-Irizarry 2006). This was not unexpected, considering that niche shifts in relatively competitor-free insular environments are common among birds, and become adaptive under the high rate of natural and human related disturbance in Caribbean islands (Reagan and Waide 1996, Vilella 2007).
Delannoy-Juliá, C. A. (2009). Elfin-woods Warbler (Setophaga angelae), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.elwwar1.01