More BA Fauna

Argentine Black-and-White Tegu (Salvator merianae) - Photo: Marcelo Gavensky

Birds are the most frequently seen members of the fauna, but there are other remarkable animals from many different groups, vertebrates and invertebrates, which can also be seen in the area.


It is sadly interesting to learn that just a few hundreds years ago Jaguars (Panthera onca) were plentiful in Buenos Aires. They were hunted mainly for their skin and, in addition to the destruction of their habitat, deplation of their natural prey, ilegal hunting and direct persecution for being considered dangerous for the cattle, today the species only survives in Argentina in a few spots of the North West, North East and the Chaco, and its considered critically endangered, with fewer than 300 individuals still left in the country. One of its local names, “tigre”, (Spanish for “tiger”, although a different species) gives its name to a city located just 30 kilometers north of Buenos Aires. Other species of large mammals, such as the Marsh Deer (Blastoceros dichotomus) and the Pampas Deer (Ozotoceros bezoarticus) are endangered, and are not part of Buenos Aires city’s fauna any more, although there is an important population of Marsh Deer not far away from it, in the delta of the Paraná river.

Coypu or "nutria" (Myocastor coypus) - Photo: Roberto Ares

Nowadays the mammals still present in the area are small and very difficult to see, except for some species of rodents. This last group (the rodents) is well represented here, mainly by rats and mice, but with some very remarkable species of the region, such as the Nutria (Myocastor coypus), which name comes from the Spanish word for “otter” although it is not related to real otters, and the Pampas or Brazilian Cavy (Cavia aperea), which is the wild ancestor of the Guinea Pig (domesticated by ancient Incas). Nutrias are common in the lagoons of the region, and cavies are abundant in the areas with grass, which constitutes its main food.

Pampas cavy (Cavia aperea) - Photo: Ignacio A. Chantada

Two species of marsupials are common, the White-eared Opossum (Didelphis albiventris), with a small population living in the Botanic garden of the city, and the Thick-tailed Opossum (Lutreolina crassicaudata), which sometimes can be seen crossing the paths of the Reserva Ecológica Costanera Sur.

Bats are another group of mammals with a good chance to be seen, especially in spring time and in the summer, when they are more active, hunting flying insects (all the Buenos Aires’ bats are insectivorous). Two species are the most common ones: the Hoary Bat (Lasiurus cinereus) and the Brazilian free-tailed Bat (Tadarida brasiliensis).

Reptiles and amphibians

Reptiles are in some way easier to be found and to be seen than mammals, mainly because of their need to lay down at some point during the day and receive warm sunrises to maintain its body temperature.

Argentine Black-and-White Tegus in Costanera Sur (Buenos Aires) - Photo: Marcelo Gavensky

The most remarkable reptile is the Argentine Black-and-White Tegu (Salvator merianae), which is common in spring and summer, crossing the roads and paths of the ecologic reserves. It is the largest lizard in Argentina, and it can reach a length of up to 150 cm, although the commonest findable large size is of around one meter.
                                                 Crossed Pit Viper (Bothrops alternatus) - Photo: Marcelo Gavensky

Detail of the head - Photo: Marcelo Gavensky

There are many species of snakes, been the most notable one the Crossed Pit Viper (Bothrops alternatus), a poisonous viper which inhabits the Reserva Ecológica Costanera Sur (this is the main reason for not leaving the walking paths of the reserve). Another beautiful snake is the Brazilian Green Racer (Philodryas aestivus), with its wonderful emerald color. There are 3 species of aquatic turtles, the Lagoon Turtle (Phrynops hilarii), the Orbigny’s Slider (Trachemys dorbigny) and the Snake-necked Turtle (Hydromedusa tectifera).

Brazilian Green Racer (Philodryas aestivus) - Photo: Marcelo Gavensky

Orbigny's slider (Trachemys dorbigny) - Photo: Marcelo Gavensky

There are also many species of amphibians, which is logic considering the humid conditions of Buenos Aires (sometimes too much humid for its human population...). These amphibians, frogs and toads, are mainly heard when the rain falls, before and after it. The most remarkable species are the native Thin-toed Frog (Leptodactylus latrans), the tree frogs Montevideo Treefrog (Boana pulchella) and Striped Snouted Treefrog (Scinax squalirostris), the Argentine Toad (Rhinella arenarum) and the beautiful Ornate Horned Frog (Ceratophrys ornata), which can be seen only after long periods of strong rains.

Montevideo Treefrog (Boana pulchella) - Photo: Ignacio A. Chantada


This is a group of animals which for sure you won’t see easily, unless you go fishing, but it’s still important to describe them a little bit because of its importance and high diversity. They are present in the La Plata river or "River Plate", and in the many marshes, water streams and lagoons (even in Palermo’s parks) of the region.

Red-bellied Piranha (Pygoscentrus nattereri) - Photo: Marcelo Gavensky
The fish fauna of the River Plate basin is of sub-tropical/tropical origin, and shares many of its species with the Amazon basin, although less biodiverse, especially in this latitude with a temperate weather. Before the beginning of the twentieth century, with the industrialization of the area originating an intensive pollution activity that continues till today, the Río de la Plata hosted a wealthy environment with a rich species assemblage now very modified. In addition, the construction of damns in several points of the main basin’s rivers (Paraná and Uruguay) has interrupted the natural migration of many species that used to migrate southward in the summer, and the opposite direction in winter. This has damaged very much their populations.
The jaw of a piranha - Photo: Marcelo Gavensky

The Río de la Plata and its tributaries are the southernmost limit of distribution for the majority of its fish species. Between the most remarkable ones are the Piranhas, which are abundant in the summer, with three species present in the area, including the famous Red-bellied Piranha (Pygoscentrus nattereri) with its local variation which has a golden/yellow belly instead of the red-bellied Amazon type. In Argentina these species are popularly known as “Palometas” or “Palometas bravas” although the first name is also used for other species with a tall and flat body. Very related to the piranha fish are the Pacus. Their body has the same shape but the main difference are their teeth which, instead of being sharp, they are more similar to human molars, and help them to chew fruits and seeds that fall to the river. The Small-scaled Pacu (Piaractus mesopotamicus) is one of the species that has disappeared from the area of Buenos Aires. It’s still common in the north of Argentina, and can reach a weight of more than 10 kilograms. But there’s a relative species still findable in the area, called “Clock” Pacu (Mylossoma duriventre). It’s much smaller, with an even rounder shape.

Serrasalmus maculatus, another species of piranha in the area - Photo: Marcelo Gavensky

The “tiger of the river”, as it’s sometimes mentioned in a poetic manner, is the Golden Dorado (Salminus brasiliensis) named after its color, which is golden yellow. It grows up to 1 meter and more than 30 kilograms (very rare to find nowadays), but in the area the average is much smaller, constituted by juvenile specimens. It is the species in the area with the longest migration movements, with records of more than 1000 kilometers. It’s a hunter of other fishes, even big ones.

The silurids (“catfishes”) and their relatives are well represented here. The huge Spotted Sorubim (Pseudoplatystoma coruscans), which can reach more than 1.5 meters and almost 100 kilograms (or at least it did, back when its population wasn’t as damaged with over fishing as it is today), is still present in the area of Buenos Aires but only with juvenile individuals, being an uncommon species. It is also a migrant. It is a carnivore, and with its wide mouth can swallows very big preys (mainly other fishes). The Peppered Corydoras (Corydoras paleatus) is another member of this group, very common in the area, and popular too because of its use in aquarium. Loricarids are relatives of the catfishes, and some of their species are among the commonest fishes of the area, such as the “plecos” (Hypostomus commersoni).
There is a migrant silurid that arrives to the delta of the Parana river for spawning, returning then to the sea, where it lives during the rest of the year. It’s the White Sea Catfish (Genidens barbus), which can size a length of 70 centimeters and even more. One of the most important species, in terms of biomass and position in the food chain (been, in their different stages –eggs, larvae, juvenile and adults– the main source of food for carnivore fishes) is the Streaked Prochilod (Prochilodus lineatus), called “Sábalo” by the locals . It is a migrant that grows up to 70 centimeters and feeds on the organic components of the mud. A similar species in shape, although different in its feeding habits, is the "Boga" (Megaleporinus obtusidens) which is an omnivore that reaches 80 centimeters and up to 10 kilograms. These two species are very common in the region (especially the first one).

One of the many species of fish popularly known as "mojarras" in Argentina - Photo: Marcelo Gavensky

The Carp fish (Cyprinus carpio) is an exotic species (introduced by humans) that has become very common in the Río de la Plata and in the lagoons of Buenos Aires province. As other exotic species, they can compete with the local fauna and affect them in many ways, sometimes too harmfully.

A very representative carnivore fish, common in all the water bodies of the area, is the Argentine Wolf Fish, locally called "Tararira" (Hoplias argentinensis). With up to 50 centimeters and big sharp teeth, is the main predator fish of Buenos Aires lagoons and rivers.

The Spotfin hatchetfish (Thoracocharax stellatus) belongs to one of the most remarkable fresh water fish families of South America: Gasteropelecidae. They are among the very few fish species that can do something similar to fly. It’s a tiny fish with very big pectoral fins, which escapes from its predators by jumping out of the water (several meters above the surface) and “flying” by flapping its fins as if they were wings. They arrive to the Río de la Plata in the summer, as many of the other species. Another remarkable fish is the Biara, locally called "Chafalote" (Rhaphiodon vulpinus), a predator with a long narrow body and two long and sharp conspicuous fangs in its lower jaw, which they use for hunting small fish. There is a family of fishes which is particularly diverse in the Neotropc and (even more) in Africa: the Cichlids. They are very territorial and take good care of their offspring, in some cases carrying them inside their mouths. In the area of Buenos Aires one of the commonest cichlid is the Chameleon Cichlid (Australoheros facetus), present even in Palermo’s lakes. A similar looking species, although more colorful, is the Small Rainbow Eartheater (Gymnogeophagus meridionalis). Then there is a gender of cichlids with a long shape and a characteristic spot in its caudal fin that resembles an eye, and functions as a defense by not letting know to their predators where the real head is. This is the gender Crenicichla, known as "pike cichlids", whose members are mainly predators of small fish. Crenicichla lepidota is one of the species in the area.

Detail of the tail of Crenicichla lepidota - Photo: Marcelo Gavensky

A special mention deserves a group of tiny fish with a particular way to adapt to the environment. They are called Killifish and live on shallow bodies of water that depend on the rains. Their eggs can survive long periods of drawings until it rains again and the larvae hatch. They are considered by many aquarists as the most beautiful freshwater fishes, with very conspicuous colors. One of the species is the Argentine Pearlfish (Austrolebias bellotti) which can be found in some areas of the city and its surroundings.
In winter there is one species that becomes common (the opposite of the rest of the species), and it’s the Argentinian Silverside (Odontesthes bonariensis). They move in schools and swim not far from the surface. They grow up to 50 centimeters but the average length is much smaller.

Finally, some of the most remarkable species are the South American Freshwater Stingrays, in the area Potamotrygon motoro and Potamotrygon brachyura. This last species is the heaviest freshwater fish in South America, with recorded weights of over 200 kilograms, although in Buenos Aires area there are mainly smaller individuals. As their name suggests they have poisoned stings (two) in their tails, which can be extremely painful (although not deadly) for humans if stinged.


The group of the invertebrates is well represented here, with some very remarkable species. Following are just some of the most notable common (or easy to see) invertebrates, among the insects and the arachnids.

Caterpillars of White Morpho butterfly (Morpho epistrophus argentina) - Photo: Marcelo Gavensky
Among the insects there is a group that must be mentioned separately: the diurnal butterflies. Many of them find their southernmost limit of distribution here. That’s the case of the Morpho genera, which finds its southernmost limit in the continent with the White Morpho (Morpho epistrophus argentina). With around 10 centimeters of length between the tips of their white/light blue colored wings, it’s one of the largest diurnal butterflies in the area. It is common in the riverine forest of the delta of the Paraná River, Martin Garcia Island, and the Natural Reserve of Punta Lara (near the city of La Plata). In the reserves of Buenos Aires it's possible to find it in Ribera Norte and Vicente López, although its presence is occasional in Costanera Sur reserve. Among the most remarkable Neotropical genera of butterflies is the Diaethria. One species of this genus reaches the riverside forests of the Río de la Plata: the Candrena Eighty-eight (Diaethria candrena). Its name comes from the number “88” legible in the ventral side of most Diaethrias hind wings, although in this species the number seems more like an "80".

Candrena Eighty-eight (Diaethria candrena) dorsal and ventral faces - Photo: Marcelo Gavensky

The group of the Helicons has some conspicuous representatives in the area. Their host plants (for their caterpillars) are the Passiflora, from which they take the toxicity that gives them an effective protection against predators. The Julia (Dryas iulia alcionea), the Common Longwing (Heliconius erato phyllis) and the Gulf Fritillary (Agraulis vanillae maculosa) are present in the area of the city, being the last one the most common (even abundant) species. Another typical representative from the riverine forest is the Hymenaea Clearwing (Episcada hymenaea), with transparent wings. They live in the deep of the forest, avoiding sunny areas.

Male of Laurentia Emperor (Doxocopa laurentia) - Photo: Marcelo Gavensky

In the Espinal forest, there is one of the most beautiful species of the province, which depends very much on the Tala (Celtis spp.) trees. This is the Laurentia Emperor (Doxocopa laurentia). The male of this species has two greenish blue bands in the dorsal side of their wings.
Other remarkable butterfly species are the Polystictus Swallowtail (Battus polystictus), the Thoas Swallowtail (Heraclides thoas thoantides), both of them from the Papilionid family, the crepuscular Lowland Owlet (Opsiphanes invirae amplificatus), and the Southern Monarch (Danaus erippus), an abundant species that can be seen throughout the year.

Southern Monarch (Danaus erippus) - Photo: Ignacio A. Chantada
There are also some interesting species of moths, including members of the Sphingid family ("Hawk Moths"), and the large Black Witch Moth (Ascalapha odorata).
Other remarkable insects in the area, among a plethora of others, are the "Camoati" wasp (Polybia scutellaris), a species of social wasp which is black and very small, but builds a very characteristic huge nest; and the Horned Beetle (Diloboderus abderus).
Horned beetle (Diloboderus abderus) - Photo: Marcelo Gavensky

Finally, from the plenty of arachnid species in Buenos Aires area, we can quote the big Tarantulas, with the endangered Grammostola burzaquensis in the area, and the wonderful Golden orb-web spider (Trichonephila clavipes), which lives among the riverine forests of the River Plate and its tributaries. Scorpions are also present in the city.

Golden orb-web spider (Trichonephila clavipes) - Photo: Marcelo Gavensky