Birds are the most frequently seen members of the fauna, but there are other remarkable animals from many different groups, vertebrates and invertebrates, that can be also seen in the area.
It is sadly interesting to know that just a couple of hundred years ago there were still Jaguars in Buenos Aires. They were hunted mainly for its fur and, in addition to the destruction of its habitat, today the species only survives in Argentina in some forests of the North West, North East and the Chaco, and it’s critically endangered. One of its local names, “tigre”, (Spanish for “tiger”, although a different species) gives the name to a city, some kilometers north of Buenos Aires. Other species of large mammals, such as the Marsh Deer (Blastoceros dichotomus) and the Pampas Deer (Ozotoceros bezoarticus) are also 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, and a relictual population of Pampas Deer in Samborombon bay area.
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), named after the Spanish word for “otter” although it is not related to real otters (“Coipo” is its proper name), and the Pampa’s Cavy (Cavia aperea), probably the wild ancestor of the Guinea Pig (domesticated by ancient andean people). Nutrias are common in the lagoons of the region and Pampa’s Cavies are abundant in areas with grass, which constitutes its main food.
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 Costanera Sur reserve.
Bats are another group of mammals with a good chance to be seen, especially in spring and the summer when they are more active, hunting flying insects (all Buenos Aires’ bats are insectivores). Two species are the most common ones: the Hoary Bat (Lasiurus cinereus) and the Brazilian free-tailed Bat (Tadarida brasiliensis).
Reptiles & 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.
The most remarkable reptile is the Argentine Black-and-White Tegu (Tupinambis merianae), which is common in spring and summer, crossing the roads and paths of Buenos Aires reserves. It is the largest lizard in Argentina, and it can reach a length of up to 150 cm although the commonest findable size is of less than a meter. A relative of this species, the Rufous Tegu (Tupinambis rufescens) is of similar characteristics, but much less common.
There are many species of snakes, been the most notable one the Crossed Pit Viper (Rhinocerophis 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).
There are also many species of amphibians, which is logical 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 Frog (Leptodactylus ocellatus), the tree frogs Common Tractor Frog (Hypsiboas pulchellus) and Striped Big-Snout Tractor Frog (Scinax squalirostris), the Common Toad (Rhinella arenarum) and the beautiful Common Escuerzo (Ceratophrys ornata), which can be seen only after long periods of strong rains.
This is a group of animals which for sure you won’t see easily, unless you go fishing, but it is still important to describe them a little bit because of its importance and high diversity. They are present in La Plata river and in the many marshes, water streams and lagoons of the region (including the artificial ponds in the city parks).
The fish fauna of La Plata river basin is of sub-tropical/tropical origin, and shares many of its species with the Amazon basin (although much less diverse) in spite of the temperate weather of Buenos Aires latitude. Before the beginning of the twentieth century, with the industrialization of the area originating an intensive pollution activity that continues till today, the La Plata river hosted a wealthy environment with a rich species assemblage now very modified. In addition, the construction of dams 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.
La Plata river and its tributaries are the southernmost limit of distribution for the majority of its fish species. Between the most remarkable ones are the Piranha fish, which are abundant in the summer, with at least three species, including the famous Red-bellied Piranha Fish (Pygoscentrus nattereri) with its local variation which has a golden-yellow belly instead of the red 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 have the same shape but the main difference are their teeth which, instead of being sharp, are more similar to human molars, helping them to chew fruits and seeds that fall to the river. The Pacu (Piaractus mesopotamicus) is one of the species that has disappeared from the area of Buenos Aires. It is still common in the north of Argentina, and can reach a weight of more than 10 kilograms. But there is a related species still findable in the area called “Clock” Pacu (Mylossoma paraguayensis), although much smaller, with an even rounder shape.
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 can 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 Sorubin (Pseudoplatystoma coruscans), which can reach more than 1.5 meters and almost 100 kilograms (or at least it did, back when its population was not as damaged with overfishing as it is today), is another migrant still present in the area of Buenos Aires but only with juvenile individuals, being an uncommon species. It is a carnivore and with its wide mouth can swallows very big preys (mainly other fishes). The Corydoras (Corydoras paleatus) is another member of this group, very common in the area and popular because of its use in aquarium. Loricariids are related to catfishes, and some of their species are among the commonest fishes of the area, such as the “Vieja del agua” (Hypostomus commersoni). There is a migrant silurid that arrives from the sea to the delta of the Parana river for spawning, returning back after it. It’s the White Sea Catfish (Netuma barba), 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 carnivorous fishes) is the Tarpon Prochilodus (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 (Leporinus 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).
The Carp fish (Cyprinus carpio) is an exotic species (introduced by humans) that has became very common in La Plata river and 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 Tararira (Hoplias malabaricus). 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) is among the most remarkable freshwater fishes of South America, being one of the very few species that can do something similar to fly. It is 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 moving its fins as if they were wings. It arrives to La Plata river in the summer, as many of the other species.
Another species to quote is the Chafalote (Rhaphiodon vulpinus),a predator with a long thin body and two long and sharp conspicuous teeth in its jaw, which they use while hunting small fishes.
There is a family of fishes that belongs to the continents of South America and Africa, with a very high diversity of species: the Cichlids. They are very territorial and take good care of their offspring, in some cases carrying them inside of their mouths. In the area of Buenos Aires the commonest cichlid is the “Chanchita” (Australoheros facetus), present even in Palermo’s lakes. There is a similar species called “Siete colores” (Gymnogeophagus meridionalis) which is more colorful. Then there is a genus 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 Crenicichla, whose members are mainly predators of small fish. The Pike Cichlid (Crenicichla lepidota) is one of the species in the area.
A special mention deserves a group of tiny fish with a particular way to adapt to the environment. They are called “Killys” and live on shallow bodies of water that depends 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), called Silverside (Odontesthes bonariensis) or “Pejerrey”, its Spanish local name. They move in schools and usually swim not far from the surface. It grows 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). They arrive to La Plata river in the summer and are among the world’s largest freshwater fish species, although in the area there are mainly small juveniles. As their name suggests they have poisonous stings (two) in their tails, which can be very painful (although not deadly) for humans if stinged.
The group of the invertebrates is well represented in Buenos Aires. Following are just some of the most notable common (or easy to see) insects and arachnids.
There is a group among the insects that must be mentioned separately: the diurnal butterflies. Many of them find their southernmost limit of distribution in this area. That is the case of the Morpho genera, which finds its southernmost limit in the continent with the Argentine Flag (Morpho epistrophus argentina), consider to be Argentina’s national butterfly, although not officially. With nearly 10 centimeters of length between the tips of their white/light blue colored wings, it is one of the largest butterflies in Buenos Aires. It is specially common in the riverside forest and “talares” of the delta of the Paraná River, Martin Garcia Island, and the Natural Reserve of Punta Lara (near the city of La Plata). Best places for finding it in BA city are the reserves of Ribera Norte and Vicente López, only in a not very long period of time during the summer.
Another remarkable Neotropical genus of butterflies represented in the area is Diaethria. One species of this genus reaches the riverside forests of La Plata river: the “Eighty” (Diaethria candrena), named after the number “80” legible in the ventral side of its hind wings.
The group of the Helicons has some conspicuous representatives in the area too. 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 Crimson-patched Longwing (Heliconius erato phyllis) and the Gulf Fritillary (Agraulis vanillae maculosa) are present in the area of the city, been the last one the most common (even abundant) species. Another typical representative from the riverside forest is the Crystalline (Episcada hymenaea), with transparent wings. They live in the deep of the forest, avoiding sunny areas.
In the Espinal forest, there is one of the most beautiful butterflies of the province, which depends very much on the Tala trees. This is the Sapphire (Doxocopa laurentia). The male of this species has two greenish blue bands in the dorsal side of their wings.
Other beautiful butterflies are the Polysticto (Battus polystictus), the Thoas Swallowtail (Heraclides thoas thoantides), both of them from the Papilionidae family, the Crimson-banded Black (Biblis hyperia nectanabis), and the Monarch (Danaus plexippus erippus).
There are also some interesting species of moths, including members of the Sphingid family (Hawk Moths).
Besides the butterflies there are many other remarkable insects in the area such as the Camoati Wasps (Polybia scutellaris), a species of black and very small social wasp that builds a very characteristic huge nest, and the Rhinoceros Beetle (Diloboderus abderus).
Finally, from the plenty of arachnid species in Buenos Aires area, we can quote the big Tarantulas, with several species in the area, and the wonderful Golden Orb-web Spider (Nephila clavipes), which lives in the riverside forests of the Río de la Plata. Scorpions are also present in the city.