Age Differences in Flight Feathers
There are often substantial differences between the remiges and rectrices of adults and juveniles of the same species. Because all juvenile feathers are grown at once—a tremendous energy burden to the developing bird—they are softer and of poorer quality than the equivalent feathers of adults, which are moulted over a longer period of time (as long as several years in some cases). As a result, they wear more quickly.
As feathers grow at variable rates, these variations lead to visible dark and light bands in the fully formed feather. These so-called growth bars and their widths have been used to determine the daily nutritional status of birds. Each light and dark bar correspond to around 24 hours and the use of this technique has been called ptilochronology (analogous to dendrochronology).
In general, juveniles have feathers which are narrower and more sharply pointed at the tip. This can be particularly visible when the bird is in flight, especially in the case of raptors. The trailing edge of the wing of a juvenile bird can appear almost serrated, due to the feathers' sharp tips, while that of an older bird will be straighter-edged. The flight feathers of a juvenile bird will also be uniform in length, since they all grew at the same time. Those of adults will be of various lengths and levels of wear, since each is moulted at a different time.
The flight feathers of adults and juveniles can differ considerably in length, particularly among the raptors. Overall, juveniles tend to have slightly longer rectrices, and shorter, broader wings (with shorter outer primaries, and longer inner primaries and secondaries) than do adults of the same species. However, there are many exceptions. In longer-tailed species, such as Swallow-tailed Kite, Secretary Bird and European Honey Buzzard, for example, juveniles have shorter rectrices than adults do. Juveniles of some Buteo buzzards have narrower wings than adults do, while those of large juvenile falcons are longer. It is theorized that the differences help young birds compensate for their inexperience, weaker flight muscles and poorer flying ability.
Read more about this topic: Flight Feather
Famous quotes containing the words age, differences, flight and/or feathers:
“Youth demands more than ordinary life. Age clings to it.”
—Mason Cooley (b. 1927)
“The country is fed up with children and their problems. For the first time in history, the differences in outlook between people raising children and those who are not are beginning to assume some political significance. This difference is already a part of the conflicts in local school politics. It may spread to other levels of government. Society has less time for the concerns of those who raise the young or try to teach them.”
—Joseph Featherstone (20th century)
“Its shrill scream seems yet to linger in its throat, and the roar of the sea in its wings. There is the tyranny of Jove in its claws, and his wrath in the erectile feathers of the head and neck. It reminds me of the Argonautic expedition, and would inspire the dullest to take flight over Parnassus.”
—Henry David Thoreau (1817–1862)
“You may call a jay a bird. Well, so he is, in a measure—because he’s got feathers on him, and don’t belong to no church, perhaps; but otherwise he is just as much a human as you be. And I’ll tell you for why. A jay’s gifts and instincts, and feelings, and interests, cover the whole ground. A jay hasn’t got any more principle than a Congressman.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)