Neotropical Migrant Songbirds

 

What is a Neotropical Migrant?
Flight gives birds tremendous mobility and allows them to make dramatic seasonal movements in response to changing seasons and food availability. Many birds do not remain in Oklahoma throughout the year. Instead, they migrate south to spend winter months in Central and South America or the Caribbean islands. These birds that breed in North America but migrate to the new-world (neo) tropics are known as Neotropical migrants.

Nationwide, approximately 160 species of birds are considered Neotropical migrants. Over 60 of Oklahoma's 180 breeding bird species are migrants. They occur in every habitat from short-grass prairies to moist forests and represent 14 different families and subfamilies as diverse as hummingbirds, flycatchers, thrushes and warblers. Neotropical migrants have one attribute in common: they all feed on insects to some extent and depend upon them to feed their young.

Threats to Neotropical Migrants

Surveys conducted of breeding bird populations have shown significant population declines of 23 (34 percent) of Oklahoma's migrants. No one is certain why these Neotropical migrants have declined, but habitat loss and degradation are considered to be primary factors. With additional perils from habitat loss, predation, cowbird parasitism and pesticides, it appears the migrants' future will become more precarious.

Habitat fragmentation breaks large pieces of habitat into smaller ones, and probably is the migrants' greatest threat. Since settlement days, large tracts of prairie and oak scrub and deciduous forest have been fragmented by crop fields, roads and housing developments. Most migrants are adapted to life in the center of the prairie or woods and are now declining because their habitat is less suitable.

The open, cup-shaped nests built by most migrants leave eggs and young more vulnerable to predators such as raccoons, snakes, blue jays and crows. Unfortunately for most songbirds, these nest predators do well along forest and prairie edges and their impact on migrant nesting success may be increasing.

Brown-headed cowbirds do not build their own nests, but instead lay eggs in unattended nests of other songbirds. Many forest birds are not adapted to cowbird parasitism and as a result, raise the cowbird young as their own, lowering the number of their young raised. In most cases, the growing cowbird chick outcompetes the host bird's chicks.

Pesticides rarely kill birds or other wildlife directly, but their indirect effects are not well understood. They may reduce birds' abilities to withstand the physiological stresses of migration and certainly reduce insect populations, which in turn may reduce the bird's ability to successfully raise young.
 



Common Nighthawk (Chordeiles minor) The common nighthawk, is one of the few nocturnal Neotropical migrants. Male and female plumages are identical; both sexes are mottled brown and in flight, a distinctive white bar can be seen on the underside of each wing. Although not related to hawks, they derive their name from their feeding behavior in which they "hawk" (catch in mid-air) night-flying insects such as moths and beetles. These birds are more closely related to whippoorwills and Chuck-will's widows. Nighthawks do not build a conventional nest; they scrape a shallow depression in the ground for two speckled brown eggs that both adults incubate. If the birds leave the nest, the eggs also are camouflaged. Nighthawks nest throughout the state in pastures, open woodlands, gravel parking lots and flat-roofed houses. In winter, they migrate to Brazil and Argentina.
 

Prairie Warbler (Dendroica discolor) The prairie warbler is an uncommon bird of scrubby woods and thickets in the eastern half of the state. Prairie warblers prefer young forests, thickets and willow scrub along streams. The male has a bright yellow head and breast with bold black streaks, and an olive green back and wings. The female's plumage is a more subtle greenish-yellow. Shrub-dwelling insects, especially caterpillars, comprise most of their diet. Prairie warblers raise one or two broods of three to four young each summer in a small cupped nest of grass and stems constructed in a shrub or sapling. In winter, prairie warblers migrate southeast to the Gulf Coast, Florida and the Caribbean.
 

Blue Grosbeak (Guiraca caerulea) Blue grosbeaks are small songbirds -approximately 6- 7 inches long -with a conical bill adapted for eating seeds. Males are blue with rusty wing bars, while females are brown with faint rusty wing bars. They most frequently are found in thickets, fencerows and riparian scrub along creeks throughout the state but are less common in the northwest and panhandle. They feed upon seeds year- round, but add insects to their summer diet. They normally raise two broods of three to five young each summer in a small cup of grass and weed stems placed 5-15 feet above the ground in a dense shrub or sapling. They form flocks on their Mexico and Central America wintering grounds.
 

Dickcissel (Spiza americana) The dickcissel is a common but often overlooked bird of grasslands and agricultural fields statewide but is un- common in the panhandle and the southeast. They resemble small meadowlarks but have short conical bills. Both males and females have a chestnut patch on the wing, while only males have a yellow breast with a black "V' marking. The adult's diet consists of grass and wildflower seeds, as well as grasshoppers and other insects. One or two broods of young are raised each year and primarily fed insects. The nest is a grass cup that usually is built within 10 feet of the ground in a shrub or clump of tall grass. Dickcissels winter from Mexico to Venezuela
 

Scarlet Tanager (Piranga olivacea) Scarlet tanagers are found in large tracts of mature oak and hickory forests in the eastern fifth of Oklahoma. Males are a brilliant scarlet -red with black wings and tail feathers, and females are a soft yellowish-green with slightly darker wings and tail. Tanagers spend most of their time in tree canopies searching for insects, but will eat small fruits when available, especially on their wintering grounds in forests of Venezuela and northern Brazil. Tanagers raise one brood of three or four young each year. Prior to fall migration, the male molts his red feathers and takes on the female's yellowish color.
 

Black-capped Vireo (Vireo atricapillus) The black-capped vireo is one example of a Neotropical migrant that has declined to the point where it now is classified as an endangered species. This small bird once was common in western and central Oklahoma, but only a few hundred remain today, mostly in the scrub oak-covered hillsides of the Wichita Mountains. Males have a black cap and neck. The female's cap is gray but both sexes have white spectacles and yellowish sides. They mostly eat caterpillars and other insects. The vireo's nest is a small hanging cup of grass, lichen and spider webs, suspended from a shrub's branch two to five feet above the ground. They may raise one or two broods of three or four chicks before migrating to western Mexico for the winter.
 

Cliff Swallow (Hirundo pyrrhonota) Cliff swallows nest in colonies throughout Oklahoma, where each pair constructs an oven-shaped nest of mud on the side of a cliff or under abridge or building eaves. They are most common in Oklahoma's western and central counties. Their diet is made up of small flying insects. This species can be distinguished by its long pointed wings, square tail, orange rump patch and buff-colored forehead. Cliff swallows have one of the longest migration routes, traveling to southern Brazil and Argentina for the winter.
 

Baltimore Oriole (Icterus galbula) The Baltimore oriole perhaps is best known for its hanging, basket-like nest. The female constructs the intricately woven nest on the end of a tall tree branch. Orioles inhabit deciduous woodlands of elm and cotton- wood along streams and around towns and farms statewide but are uncommon in the southeast and far west. Caterpillars, beetles arid other tree- dwelling insects comprise most of the oriole's diet, but they also eat small fruits and nectar of some flowers. The oriole is well known for the male's fiery orange and black plumage. Females have an orange-yellow breast and olive-brown back and wings. They spend the winter from southern Mexico to northern South America.
 

Painted Bunting (Passerina ciris) The male painted bunting is one of Oklahoma's most colorful songbirds, with his metallic blue head, brilliant red breast and belly and bright green back. Females are a soft yellow-green that blends in well with the oak thickets they frequent. Painted buntings are most common in scrubby, blackjack/post oak woods in the central half of the state. They mostly eat seeds, but insects also are important, especially to their growing young. The nest is a cup-shaped bowl of grass built a few feet off the ground in a shrub or sapling. Unlike many Neotropical migrants, male painted buntings retain their colorful plumage while on Mexico and Central America wintering grounds.
 

Why Do Some Songbirds Migrate?

Birds migrate primarily to find food. The shortage of insects, rather than cold weather, is the main factor that forces Neotropical migrants to move. Biologists once believed that these migrants originated in the Northern hemisphere and were forced south with the advent of winter. How- ever, most now believe that these birds originated in the tropics and began to move northward each summer to take advantage of the abundant insect population of our northern summer. The longer day length of the temperate summer allows for rapid plant growth and as a consequence, insects become abundant. This abundance draws the tropical birds north.

Searching for Summer’s Winged Jewels

For the most part, Neotropical migrants are not common backyard birds. Some colorful species, such as the Northern oriole, dickcissel, barn swallow and scissor-tailed flycatcher, are common along roadsides and around pastures and farms. However, most Neotropical migrants are found in forests, thickets and prairies away from human development. Except during migration, many of these species are rarely seen by most people.

The spring return of migrants to Oklahoma begins with the purple martin's arrival during the first weeks of March, and builds slowly to a peak in early May. In almost any wooded park on a spring morning, you may see small flocks of brightly colored birds foraging voraciously in the trees, often ignoring the birdwatchers eager to see these winged jewels. This brief window of time provides unparalleled opportunities to see otherwise hard-to-see species, yet we are only experiencing a tiny portion of a massive continental wave. By late May, migration is complete and the birds have set up their summer territories. Within three months they'll complete their nesting cycle and begin their long journey south.

Most Neotropical migrants winter in Central America and the larger islands of the Caribbean. Geography dictates that millions of birds are packed into a small area each winter. While the potential . breeding grounds in the U.S. and Canada encompass nearly 25 million square miles, the entire land mass from Mexico to Panama is less than 4 million square miles. More than half of all Neotropical migrants funnel into this small area.

Always on the Move

Migration often is a long ordeal and one that requires a great deal of energy. Migrant songbirds primarily fly at night and spend the day finding food to build fat reserves for the next leg of their journey. Most migrants embark on a 20-hour nonstop flight over as much as 650 miles from coastal Louisiana and Mississippi across the Gulf of Mexico and to the Yucatan peninsula. Some migrants, including Oklahoma's, follow a route along the west coast of the Gulf of Mexico through Mexico and into Central America. While birds can stop to rest and feed along the way, this route may be up to three times longer.

You Can Help Migratory Birds

Some of the problems facing migratory songbirds start in our own backyards and communities. Habitat loss and fragmentation from real estate development, agriculture and other activities are the single greatest causes of declining songbird populations in the United States. Development slowly chips away at Oklahoma' s last large tracts of forest and grasslands and is a tremendous threat to migratory birds. Many areas now lack the minimum habitat birds use for stopovers along their migration routes.

Protecting these areas requires local action and provides many opportunities for citizen activists to preserve habitat at community and state levels. Identification of high-priority songbird species and habitats, development of conservation strategies, and protection and management of lands through purchase, easement and zoning all can be carried out by citizens working through county and state jurisdictions. Each of us also can do the following:

  • Create habitat and provide food sources by planting native trees, shrubs and flowering plants; leave snag trees as potential nesting sites.
  • Educate others about the threats migratory songbirds face in two continents.
  • Volunteer to participate in monitoring projects such as Breeding Bird Surveys and Migration Counts, which census songbird populations.
  • Donate money to groups that purchase habitat in North and South America, including the Oklahoma Department of Wildlife Conservation's Habitat Donor Program.
  • "Search for the Scissortail" on the state tax form and donate part of your tax refund to the Nongame Wildlife Program to assist other groups through "Partners in Flight."