The yellow baboon, Papio cynocephalus, is a medium-sized primate known for its yellow-brown coat and elongated face. It primarily inhabits the savannas and open woodlands of East Africa. Yellow baboons are social animals, living in groups that can number up to 200 individuals. They have a complex social structure with well-established hierarchies. Omnivorous, they feed on fruits, seeds, insects, and small vertebrates. Their behavior is marked by great adaptability, allowing them to thrive in various environments. Yellow baboons play a crucial role in their ecosystem, particularly in seed dispersal.

The baiji, or Yangtze river dolphin, was a freshwater mammal endemic to China’s Yangtze River, measuring 2–2.5 m in length and weighing 135–230 kg, with a streamlined pale grey-blue body and a long, slightly upturned beak. It relied on echolocation to feed on fish and shrimp in the river’s turbulent, silt-laden waters.

The yellow wagtail is a small migratory passerine bird found primarily in meadows, cultivated fields, and riverbanks across Europe, Asia, and North Africa. It is easily recognized by its bright yellow plumage on the belly and chest, its slender legs, and its quick movements. This bird primarily feeds on insects and invertebrates, which it captures by running on the ground or pecking at the grass.

The yellowhammer is a small passerine, 15–16 cm long, with bright yellow head and breast in males and duller, brown-streaked plumage in females. It inhabits open fields, hedgerows, and edges, feeding on seeds and insects while foraging on the ground. During breeding (April to July), the male sings from a perch or in flight to mark territory and attract the female.

The yellowhammer is a small passerine bird found primarily in fields, meadows, and hedgerows across Europe and Asia. It is easily recognized by its bright yellow plumage, brown striped head, and pale yellow belly. This bunting is mainly insectivorous, but it also feeds on seeds and berries. It is often heard singing, especially during the breeding season, where it defends its territory with a clear and distinct song.

The yacare caiman is a medium-sized semi-aquatic reptile (up to 2 m long), recognizable by the bony ridge between its eyes that resembles eyeglasses. Found in South America (northern Argentina, Brazil, Paraguay), it inhabits freshwater marshes, lakes, rivers, and floodplains. An opportunistic omnivore, it feeds on fish, crustaceans, birds, and small mammals. During the breeding season, males produce deep grunts and aggressively defend aquatic territories, while females build vegetation nests and lay 20–40 eggs.

The Yellow-casqued Hornbill is a characteristic bird of the open forests and savannas of sub-Saharan Africa. It is easily recognizable by its large curved bill, adorned with a bright yellow casque that gives it a distinctive appearance. Despite its massive size, the bill is lightweight and hollow, allowing this bird to fly with agility despite its size. Its plumage is primarily black and white, with yellow accents around the bill and casque. The Yellow-casqued Hornbill is primarily frugivorous, feeding on fruits, berries, and insects found in trees. It is often seen in pairs or small groups, moving from branch to branch and emitting loud and distinct calls. While it is relatively widespread in its habitat, it may be threatened by deforestation and habitat loss due to agricultural expansion.

The Yellow-headed Caracara, Milvago ferrugineus, is a medium-sized raptor known for its pale head and rusty-brown plumage. It primarily inhabits open regions of South America, from savannas to agricultural areas. An opportunistic feeder, it consumes carrion, insects, and occasionally small vertebrates. Its flight is often slow and gliding, and it is frequently seen walking on the ground in search of food. Although a bird of prey, it is less aggressive than other raptors. Its adaptability to various environments has allowed it to thrive despite environmental changes.

The Gubernatrix cristata, commonly known as the Yellow Cardinal, is a medium-sized songbird recognizable by its distinctive crest and bright yellow plumage. Native to South America, it primarily inhabits the wooded regions and open savannas of Argentina, Uruguay, and Brazil. Unfortunately, this species is endangered due to illegal capture for the pet trade and habitat loss. The Yellow Cardinal is a social bird, often observed in small groups. Its melodious and powerful song is a characteristic trait that attracts the attention of ornithologists and bird enthusiasts. Conservation efforts are underway to ensure its survival, including the protection of its natural habitat and captive breeding programs.

The yellow-bellied toad is a small amphibian 30–40 mm long, with olive-brown dorsal coloration and bright yellow belly mottled with black. It inhabits temporary shallow wetlands at forest edges and meadows, feeding on insects, spiders and worms. During breeding, males emit high-pitched calls near shallow pools and females lay clusters of eggs on aquatic vegetation.

The Yellow-banded Poison Dart Frog, or Dendrobates leucomelas, is a small, vividly colored frog native to the humid tropical forests of Venezuela, Guyana, and Brazil. It is easily recognizable by its bright yellow bands contrasting with its black body. This coloration serves as a warning to potential predators of its toxicity. Measuring about 3 to 4 cm in length, this species is diurnal and primarily feeds on small insects. It plays a crucial role in the ecosystem by regulating insect populations. Although its skin is toxic, it is prized by terrarium enthusiasts for its striking colors and fascinating behavior.

The yellow-legged gull is a large seabird found primarily along the Mediterranean and Atlantic coasts. It is easily recognized by its white plumage, gray wings, and yellow legs. This gull is omnivorous and feeds on fish, marine invertebrates, and food waste, making it an opportunist. It is also known for its nesting behaviors on rocky coastlines and cliffs and can occasionally be seen in urban areas.

The yellow-eyed penguin, native to New Zealand, is easily identified by its striking yellow eyes and the yellow band of feathers around its head. This medium-sized penguin stands about 65 to 70 cm tall and weighs between 5 and 8 kg. It inhabits rocky shores and coastal forests, feeding primarily on fish and squid. Sadly, it is critically endangered due to habitat loss, predation by introduced species, and human disturbance. Conservation efforts are vital for its long-term survival.

The Yunnan snub-nosed monkey (Rhinopithecus bieti) is a large arboreal primate measuring 74–83 cm in body length (excluding tail) and weighing 14–17 kg, distinguished by its striking black-and-white coat, pink lips and flattened nose lacking nasal bones. Endemic to the alpine coniferous and mixed forests of southwestern China at elevations between 3000 and 4500 m, it feeds mainly on tree lichens, supplemented by bamboo leaves, buds and occasional fruits. This dietary specialization and dense, insulating fur enable survival in subzero temperatures. Living in cohesive troops often exceeding 400 individuals, these monkeys exhibit synchronized group displays and vocal congregations that reinforce social bonds during long, harsh winters.

The yellow-necked mouse, Apodemus flavicollis, is a small rodent belonging to the Muridae family. It is characterized by a distinctive yellow band around its neck, contrasting with its reddish-brown back and white belly. Primarily nocturnal, it inhabits forests, hedgerows, and sometimes gardens. Its diet includes seeds, fruits, and insects. Agile and fast, it can evade predators effectively. It reproduces several times a year, with litters of 4 to 7 young. Although common, it plays a crucial role in the ecosystem by dispersing seeds and controlling insect populations.

The Yellow-throated Toucan is a colorful bird found primarily in the tropical forests of Central America, notably in Costa Rica, Panama, Nicaragua, and Honduras. It typically measures about 50 cm in length and weighs between 400 and 600 g. Its plumage is mainly black, with a bright yellow throat and chest, and it has a wide, colorful bill, typically yellow with touches of red and orange. The Yellow-throated Toucan is primarily frugivorous, feeding on fruits, berries, and nuts, but it can also consume insects and small vertebrates. It generally lives in small social groups and is an excellent climber, spending much of its time in trees. While it remains relatively stable in certain areas, it is sometimes threatened by deforestation and habitat loss.