Striated heron

Butorides striata is a small heron of the family Ardeidae, described by Linnaeus in 1758 ^[1]. In English it is called «striated heron» ^[1]. It is nearly cosmopolitan: it lives in South America, Africa, Madagascar, southern and eastern Asia, Australia and many islands, and 28 subspecies are recognised ^[2]. The IUCN Red List classifies it as Least Concern ^[3]. In Peru it is among the birds recorded in Los Manglares de Tumbes National Sanctuary ^[4].

The nominate subspecies, Butorides striata striata, occupies nearly all of South America except its far south, and interbreeds with the North American Butorides virescens where their ranges meet, in central Panama and on Tobago ^[5]. West of the Andes, by contrast, that study describes it as a non-breeding vagrant in northern Chile; the southernmost records there come from the mouth of the Elqui River, at about 30° S ^[5].

On the Peruvian coast, a bird census of the San Andrés beaches, in Pisco, classifies it as a resident and links it to the shrubs and grassy patches of that shore, which lies north of the Paracas National Reserve ^[6]. Further north, the species appears on the bird list of Los Manglares de Tumbes National Sanctuary, where 158 species were recorded between 1996 and 2020 ^[4]. In the Lima metropolitan area there is at least one breeding record ^[7].

According to the introduction of a nesting study in Brazil, it lives in damp places with trees or thick vegetation beside rivers, lakes and estuaries, and at times on open ground such as swamps, pasture, rice paddies or exposed coral reefs; in Brazil it is even found on lakes in urban areas ^[8].

In northern and central Argentina it nests from October to March, and confirmed breeding reaches 37° S ^[5]. In the Lima metropolitan area, an analysis of citizen-science data from 2000 to 2020 gathered a single breeding record of the species, dated January, and the authors found no earlier data on its breeding season on Peru's central coast ^[7].

A nesting study in Mato Grosso, Brazil, followed 115 active nests during the 2010 season at a seasonally flooded pond inside the urban perimeter of Porto Esperidião: the first in early January and the last one active until 21 April, with a peak of 89 active nests in March ^[8]. The nest is an open platform of dry twigs 20 to 30 cm long; incubation lasted 24.88 days on average and the chicks stayed in the nest about 20.83 days ^[8]. Of the nests with eggs, 60% held 3 eggs, bluish and matt ^[8].

Chicks hatch with open eyes and grey down, and at 6 days they already walk along the branches ^[8]. Even so, breeding success was only 16.43% by the Mayfield method, and 84.34% of the nests were preyed upon ^[8].

At the southern edge of its range it is a partial migrant: south of 24° S fewer than 10% of eBird records fall in the austral winter months, and density maps suggest that most birds winter in eastern Bolivia and central Brazil ^[5]. No ringing or satellite-tracking data exist to confirm its routes ^[5].

According to a note on its predation of frogs, it eats mainly fish, and also amphibians, assorted invertebrates (insects, spiders, leeches, crustaceans, molluscs and worms), small reptiles, birds and mice ^[2]. In the Brazilian Pantanal, on 12 January 2023, an adult was seen pulling a harlequin frog (Lysapsus limellum) from among water plants at a lagoon edge and swallowing it; the authors present it as the first record of a vertebrate as a potential predator of that frog ^[2].

Its abundance is tied to water level: along the Paraguay and Paraná rivers it is inversely related to water height, which indicates that herons move away from the big rivers during floods ^[5]. In Mato Grosso, by contrast, breeding activity coincided with the peak of the local flood ^[8].

Nests suffer heavy predation. Three nests held pierced eggshells, probably the work of passerines, and birds of the vulture, falcon and accipitrid families are mentioned as visiting heron colonies when the adults leave ^[8].

Its global category on the IUCN Red List is Least Concern ^[3].

In Peru, the bird table of the master plan of Los Manglares de Tumbes National Sanctuary lists it with IUCN category LC and with no category in the D.S. 004-2014-MINAGRI column ^[4]. The sanctuary was recognised as a Ramsar site in 1997 for the richness of its resident and migratory birds ^[4].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In Belo Horizonte, Brazil, a juvenile found dead on the shore of a reservoir in May 2010 harboured 7 species of trematodes, among them Posthodiplostomum nanum in the small intestine, with 183 individuals, and two species of Clinostomum in the mouth cavity ^[9]. For four of those species it was a new host, and Centrocestus formosanus was recorded for the first time in South America in a naturally infected definitive host ^[9]. The literature review in that work gathered 31 trematode species known from Butorides striata ^[9].

These parasites complete their cycle through snails and fish: metacercariae of Clinostomum marginatum have been found in more than 20 fish species in Brazil, and those of Posthodiplostomum nanum in poeciliid fishes ^[9]. It is a study of a single bird, so it does not show how frequent these parasites are in the species ^[9].

In the censuses of the San Andrés beaches, in Pisco, north of the Paracas National Reserve, the species was classed as a resident tied to the shrubs and grassy patches of the shore; the study was published in 2025 ^[6]. In the Lima metropolitan area, its only documented breeding record in data from 2000 to 2020 is dated January ^[7].

Further north, it is on the bird list of Los Manglares de Tumbes National Sanctuary, with records from 1996 to 2020 for the area's birds as a whole ^[4].