The least bittern (Ixobrychus exilis) is a small heron, the smallest member of the family Ardeidae found in the Americas.
The Least Bittern occurs from North America through Central and South America including the West Indies (Raffaele and others 1998), where it is an uncommon to locally common resident in Puerto Rico (J.A. Salguero-Faría, personal observation 2009). It is regularly seen at the Humacao Natural Reserve (Oberle 2018). It is present on Vieques, where it ranges from rare to extremely rare (Gemmill 2015), and is also present on Culebra. It usually inhabits shallow marshes, pond edges, mangroves (Oberle 2018), and freshwater swamps with dense emergent vegetation, often cattails (Typha spp.) (Raffaele and others 1998). The atlas fieldwork yielded a total of 44 records within 29 hexagons or 6 percent of the 479 total hexagons (see map). Of the 29 hexagons where this species was found, breeding met the atlas definition of confirmed in 24 percent (7) of the hexagons, probable in 7 percent (2), and possible in 62 percent (18), while the species was observed in 7 percent (2) of the hexagons but without evidence of breeding (see map).Least Bittern 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. 145Least Bittern/Martinetito
Previously published reports indicate that the Least Bittern breeds from May to August (Raffaele and others 1998). The nest is usually constructed above standing water on aquatic vegetation, and it is made mostly of twigs, weeds, cattails, and other swamp plants (Biaggi 1997, Raffaele and others 1998). Atlas results suggest that this species breeds mostly from December to August with peak breeding activity in February, March, and May (see chart). The breeding activity mostly takes place within the subtropical moist forest life zone (see chart). Results (see table and map) show that this species breeds mostly on the coastal plain or lowlands within the subtropical moist forest life zone (74 percent of the hexagons) with some evidence for breeding found in the subtropical dry forest life zone (26 percent of the hexagons).
The current population trend of the Least Bittern is described as stable (Butcher and Niven 2007). This species is currently listed as a species of least concern by the IUCN (BirdLife International 2016). Locally, this species is not listed in any of the threatened categories of PRDNER and USFWS. In Puerto Rico, the Least Bittern has a protected habitat in land of 14 percent or 91 km2 of the total area covered by the hexagons where evidence of breeding was found for this species (645 km2).