Yet, while unusual sightings are thrilling, the park affords everyday species that are often new and equally satisfying to visiting birders. Water is one of the primary resources needed to support birds of this desert park. In an otherwise arid landscape, its presence, even when limited, greatly concentrates bird life. This oasis effect creates excellent birding opportunities in Big Bend at hundreds of desert-surrounded springs, mostly found in the backcountry and hard to reach, and along the prominent Rio Grande. This riparian or river floodplain habitat is the richest for birds in the whole park.
Timing is also very important for seeing specific birds or a diversity of species.
Spring migration is the most popular period for birding with numerous rare and accidental migrants being reported. It begins the last week of February and peaks during the last two weeks of April and first week of May. During this time, diversity is at its height and Rio Grande Village produces the greatest variety of sightings. Many resident species nest as early as April or May even while the neotropical migrants are just arriving or passing through. While surprises are few in summer, many southwestern United States birds, some tropical species, and a couple of Big Bend specialties can be seen with ease.