The Merced National Wildlife Refuge, located in California, covers a vast area of 10,262 acres (41.53 km2) comprising wetlands, native grasslands, vernal pools, and riparian areas. Its inception dates back to 1951 when the Lea Act was established to provide a winter home to waterfowl, which were causing crop damage in the adjacent farmland. In recent years, advancements in agricultural practices and the management of the refuge have contributed to reducing wildlife/crop issues.

The refuge is home to the largest wintering population of lesser sandhill cranes and Ross's geese within the Pacific Flyway, as over 20,000 cranes and 60,000 arctic nesting geese make their annual migration from Alaska and Canada to reside in the refuge for six months. The presence of these birds draws thousands of other visiting waterfowl, waterbirds, and shorebirds, making it a true winter phenomenon.

Apart from providing a wintering ground, the Merced National Wildlife Refuge also provides crucial breeding habitats for a variety of species, including Swainson's hawks, tri-colored blackbirds, marsh wrens, mallards, gadwall, cinnamon teal, and burrowing owls. Tri-colored blackbirds, a colonial-nesting songbird, breed in colonies of over 25,000 pairs. The refuge is also home to year-round wildlife such as coyotes, ground squirrels, desert cottontail rabbits, beaver, and long-tailed weasels.

Vernal pools are another fascinating feature of the Merced National Wildlife Refuge. These special pools emerge when natural shallow depressions underlaid with clay soils fill with winter rainwater. The pools come to life as fairy and tadpole shrimp emerge from cysts embedded in the soil from the previous year. The endangered tiger salamander, alongside other amphibians, lays eggs and rears tadpoles in these pools. The vast number of aquatic invertebrates found in these pools provides a crucial food source for wintering and migrating birds as they prepare for the long flight north to their breeding grounds.