Product Code Database
The indigo bunting ( Passerina cyanea) is a small seed-eating bird in the cardinal family, Cardinalidae. It is bird migration, ranging from southern Canada to northern Florida during the breeding season, and from southern Florida to northern South America during the winter. It often Bird migration by night, using the stars to navigate. Its habitat is farmland, brush areas, and open woodland. The indigo bunting is closely related to the lazuli bunting and interbreeds with the species where their ranges overlap.
The indigo bunting is a small bird, measuring 11.5–13 cm (4.5–5.1 in) in length. It displays sexual dimorphism in its coloration; the male is vibrant blue in the summer, with brightly colored plumage during the breeding season to attract a mate. It is brown during the winter months, while the female is brown year-round. Nest-building and Avian incubation are done solely by the female. The diet of the indigo bunting consists primarily of insects during the summer months and seeds during the winter months.
The indigo bunting is a close relative of the lazuli bunting and interbreeds with the species where their ranges overlap, in the Great Plains. They were declared to form a superspecies by the American Ornithologists' Union in 1983. However, according to sequencing of the cytochrome-b gene of members of the genus Passerina, it was determined that the indigo bunting and lazuli bunting are not, in fact, sister taxon. The indigo bunting is the sister of two sister groups, a "blue" (lazuli bunting and blue grosbeak) and a "painted" (rose-bellied bunting, orange-breasted bunting, varied bunting, and painted bunting) clade. This genetic study shows these species diverged between 4.1 and 7.3 million years ago. This timing, which is consistent with fossil evidence, coincides with a late-Miocene cooling, which caused the evolution of a variety of western grassland . Evolving to reduce size may have allowed buntings to exploit grass seeds as a food source.
First years and adult males are distinguishable through close observations of the skull and its degree of ossification. Juvenile skulls have a slightly pinkish color that gives under pressure due to its singular layer. Adults instead have a double layer skull, which gives more resistance when applying pressure. First year birds also tend to have a fleshy, yellow gape in the corner of the mouth, apparent in all months except October and November. When comparing males to females that both have brown molt, increased wing length and weight typically indicate a bunting is a male.
As indicated by data collected from Charles H. Blake from his banding experiments in Hillsborough, NC, the Indigo Bunting has a weighted annual survival rate of 0.585. Using his own methods (Blake 1967, p. 5) and a pool of 25 indigo buntings captured and observed, it was determined that approximately two out of twenty-five indigo buntings should live up to six years. Using the calculated annual rate of six-year-old birds obtained (2/25 = 0.08), an annual rate of 0.656 was calculated, 12% higher than the annual rate of 0.585, leading to the 1 out of 25 statistic. The oldest recorded bunting was at least 13 years and 3 months old. However, not much emphasis should be placed on these values since the pool of individuals is small, where any individual can affect the weighted average.
The indigo bunting often migrates during the night, using the stars to navigate. This is not an unusual proposal, for many other birds such as the blackcaps or red-backed shrikes were used to test if birds have orientated migratory behavior or Zugunruhe. Research indicates that indigo buntings placed in funnel cages outside on cloudless autumn nights or in artificial made more southern directional choices. When introduced to increasingly overcast nights, many bunting's abilities to distinctively make southern directional changes decreased, possibly indicating a negative correlation between Zugunruhe and cloud coverage. When in the artificial planetarium scenario and in the presence of a magnetic field similar to Earth's, birds were unable to orientate themselves in a no-star environment, indicating that past hypotheses supporting that birds use geophysical clues as well may be incorrect.
Indigo buntings do not rely on individual stars or the general brightness of groups of stars, but instead use them as clues in navigation. Prior experiments removing certain and stars (Big Dipper, Cassiopeia or Polaris) from the sky had minimal effect on Zugunruhe. Indigo buntings do use the northern sky to help navigate both in the fall and in the spring. It was thought that the bunting has an internal clock, being able to compensate for the movement of stars. However, temporal compensation for stellar motion is not a part of their migratory methods.
In captivity, since it cannot migrate, it experiences disorientation in April and May and in September and October if it cannot see the stars from its enclosure.
While debate has occurred over the years about how birds migrate near the Gulf of Mexico, indigo buntings migrate to South America by flying both over the Gulf of Mexico and around the Gulf of Mexico, with a majority of buntings choosing the trans-Gulf path. Past evidence indicated that indigo buntings did not have a high enough fat content to travel across the Gulf, but that evidence is misleading since most of those birds supporting that study were immature, not having a high body fat content.
Since indigo buntings and many other birds are at their lightest after mating season, questions arose whether increases in overall weight were attributed to fat or other factors such as water weight, or . Research indicates that most if not all weight gain is a gain in fat content.
Quantitative methods of estimating flight range instead look at metabolic rates of the bunting and how much fat it has to use as fuel. Research indicates that the metabolic rate of a lean indigo bunting is 0.64 kcal/hour. With an average speed of 20 mph, 5 extra grams of fat (47.5 kcal of energy) extends a bunting's range to . is equivalent to . Given that the trip across the Gulf of Mexico from Florida is approximately , buntings weighing at least 18 g could make the trip without any stops.
The brown-headed cowbird may brood parasite this species. Indigo buntings abandon their nest if a cowbird egg appears before they lay any of their own eggs, but accept the egg after that point. Pairs with parasitized nests have less reproductive success. The bunting chicks hatch, but have lower survival rates as they must compete with the cowbird chick for food.
|
|
