About Zenaida asiatica (Linnaeus, 1758)
White-winged doves (Zenaida asiatica) are plump, medium-sized birds, larger than average doves. They measure 29 cm (11 in) from bill to tail, weigh 150 g (5.3 oz), and have a wingspan between 48 and 58 cm (18.9 to 22.8 in). Their upperparts are brownish-gray, while their underparts are gray, with a bold white wing patch that forms a brilliant white crescent when flying and is still visible when the bird is at rest. Adult individuals have a ring of blue, featherless skin around each eye, a long dark mark on the lower face, brighter pink-red legs and feet, and bright crimson eyes. Juveniles have brown eyes, are duller and grayer than adults, and lack iridescence; juvenile plumage is typically seen between March and October. It is difficult to tell male and female white-winged doves apart, and this usually requires examination of the cloaca. Males do have slightly more iridescent purple color on the crown, neck, and nape, as well as a more distinctive ear spot, but these differences are very subtle. Males are heavier on average, but daily weight changes from feeding make this an unreliable identifier for field observation, so most observers cannot tell sexes apart reliably from external characteristics alone. The species' defining feature is its namesake white-edged wing, which similar dove species do not have. It is easily confused with the mourning dove, which it closely resembles. Compared to the mourning dove, the white-winged dove is larger and heavier, with a short, rounded tail, while the mourning dove has a long, tapered, triangular tail. Mourning doves have several black spots on the wings, which white-winged doves lack. While similar to the white-tipped dove, the white-winged dove can be distinguished by the presence of its white wing edging that the white-tipped dove lacks. The invasive Eurasian collared dove is also similar, but lacks the white wing edging, and is further differentiated by its overall grayish color and black neck band. The molting pattern of white-winged doves is similar to that of mourning doves. Molting occurs from June through November, and takes place on summer breeding grounds unless interrupted by migration. Some populations of white-winged doves are migratory, and winter in Mexico, Central America, and the Caribbean. They live year-round in Texas; in 2001, San Antonio, Texas hosted a year-round population of over a million doves. The species inhabits scrub, woodlands, desert, urban, and cultivated areas. They are increasingly found farther north, and now occur as visitors to most of the United States and small parts of southern Canada. In recent decades, increasing urbanization and backyard bird feeding have allowed the species to expand throughout Texas, into Oklahoma, Louisiana, and coastal Mississippi. It has also been introduced to Florida, and continues to expand outside its historic range into Kansas, Arkansas, Oklahoma, and northern New Mexico. It has been increasingly reported as far north as Canada and Alaska. Within Arizona, populations are effectively divided between agricultural and desert groups. It shares its habitat with the mourning dove, but white-winged doves fly at higher elevations than mourning doves. They generally nest at low densities in the desert, but gather in high concentrations near riparian areas. Nesting in riparian zones is colonial behavior, while nesting in harsher desert environments is noncolonial. These nesting colonies vary widely in size, and can become very large, ranging from 5 hectares (0.019 mi²) to over 1,000 hectares (3.9 mi²). Outside of colonies, nest density is less than 10 nests per hectare, while colonies hold 500 to 1,000 nests per hectare. Before widespread agriculture developed across its current range, white-winged doves may not have been widely present in what is now the United States, supported by a lack of fossil remains and no mentions in the journals of early European explorers. Their presence in California is likely recent, resulting from the human-created filling of the Salton Sea at the start of the 20th century. The species' historical range closely matches the range of the saguaro cactus, which it relies heavily on for nectar and fruit in areas where both occur. Modern agriculture has greatly expanded the species' range by providing a reliable source of forage. The urban heat island effect may also allow the species to live farther north than it could naturally. White-winged doves typically begin migrating into Arizona in March. In California, birds arrive in April and depart by August. Migrations through Texas run from April through June, peaking in May, with departures occurring from September to October. Migratory groups can include up to 4,000 individuals, though most groups hold fewer than 50 birds. Timing of migration is affected by a combination of weather, food availability, and hunting pressure. As populations have expanded in Texas, the species is becoming less migratory, with around one-third of birds now overwintering in Texas. Migrations are tracked through traditional bird banding, but the isotope composition of hydrogen and carbon in feathers can also be used. A 2015 study found that tracking the amount of different isotopes allowed researchers to accurately identify the migration origin of a white-winged dove. Researchers could also identify if a bird had fed on saguaros, due to the unique carbon signature produced by cactus photosynthesis. Normally, migrating flocks number up to 4,000 birds, but a flock of up to a million individuals has been recorded in Texas. Zenaida asiatica may fly 25 or more miles to find water, though they can survive entirely on the water contained in saguaro cactus fruit.
