The best-known Scriptural description of the nesher is also the most problematic to understand. It occurs in reference to God bringing the Jewish People out of Egypt:
"You have seen what I did to the Egyptians, and how I carried you (va'esa eschem) on the wings of nesharim, and brought you to Myself." (Exodus 19:4)The conventional translation of va'esa eschem is "I carried you." However, some translate it as "I elevated you." The explanation is that the nesher is the highest-flying bird, and God raised the Jewish People to spiritual heights above anything in the natural world with His miraculous redemption. The highest flying birds are griffon vultures.
But many explain this verse instead to refer to God poetically carrying the Jewish People like a nesher carrying its young on its back (see Rashi ad loc.). This relates to a description of the vulture later in the Torah:
"As a nesher stirs up its nest, flutters over its young, spreads out its wings, takes them, bears them on its pinions; So did God guide them, and there was no strange god with them." (Deuteronomy 32:11-12)The description here is of the nesher carrying its young upon its wings while flying. Many have considered this verse to present us with a great difficulty and to require some kind of allegorical or poetic interpretation, since neither vultures or eagles are generally known to carry their young on their wings. Swans and other waterfowl sometimes carry their young on their backs while swimming, and jacanas and bustards may sometimes carry their young between wing and body while walking. There are reports of some ducks taking flight while their young are on their backs. A further report concerns an obscure water bird from Central and Southern America called the sungrebe, which carries its twin young in pouches under both wings.
But eagles and vultures, despite being widely studied, are not generally described as displaying such behavior. However, unbeknownst to many, reports do indeed exist of eagles carrying their young on their backs. One ornithologist writes:
"Many ornithologists have thought that the Bible picture of an eagle carrying her young was merely figurative, but in recent years certain reliable observers have actually seen a parent bird let its young rest for a moment on the feathered back - especially when there was no other roosting place in sight. When an eagle nests on the ledge of a sheer-walled canyon, many feet above the earth, with no jutting tree or protruding rock to break the fall, the quick movement of a mother bird to offer her own back to a frightened fledgling may be the only way to let it live to try its wings again." (V.C. Holmgren, Bird Walk Through The Bible [New York: Dover Publications 1988] p. 98)One report of this behavior is as follows:
"Our guide was one of the small company who have seen the golden eagle teaching the young to fly. He could support the belief that the parent birds, after urging and sometimes shoving the youngster into the air, will swoop underneath and rest the struggler for a moment on their wings and back. ... Our guide, when questioned, said that every phrase of the verse [Deut. xxxii, I I] (which was new to him) was accurate, save the first; he had seen it all except the stirring up of the nest." (W.B. Thomas, Yeoman's England , pp. 135-6)Another report concerning the golden eagle comes from Arthur Cleveland Bent, one of America's greatest ornithologists, on the authority of Dr. L. Miller:
"The mother started from the nest in the crags and, roughly hand-ling the youngster, she allowed him to drop, I should say, about ninety feet; then she would swoop down under him, wings spread, and he would alight on her back. She would soar to the top of the range with him and repeat the process. Once perhaps she waited fifteen minutes between flights. I should say the farthest she let him fall was a hundred and fifty feet. My father and I watched him, spellbound, for over an hour." (A. C. Bent, Bulletin of the Smithsonian Institution CLXVII , 302)nesher to be the griffon vulture rather than the eagle. However, it is possible that such rare behavior likewise occurs with griffon vultures, or that nesher is a generic term encompassing both eagles and griffon vultures.
Another solution to the entire question is to posit that "the Torah speaks in the language of men," which, according to one school of thought, means that it packages its messages within the scientific worldview of the generation that received the Torah. For more on this approach, which has been used by several recent and modern authorities to explain other phrases in the Torah that are scientifically inaccurate (such as references to the "firmament," the hare bringing up its cud, the dew falling, and so on), see my essay "The Question of the Kidneys' Counsel."
If referring to a griffon vulture, these verses show that the vulture is regarded by the Torah very differently from the way that it is perceived in contemporary culture. While people today view the vulture in a negative light, the Torah presents it as an example of a loving and caring parent. This also relates to the vulture's entire parenting process. Female griffon vultures usually lay one egg, which both parents incubate for an unusually long period of around seven weeks until it hatches. The young are slow to develop and do not leave the nest until three or four months of age. The long devotion of the vulture to its young symbolizes God's deep dedication to the Jewish People.
 See HaKesav VeHaKabbalah ad loc.
 See Johnsgard, Paul A. and Kear, Janet, "A Review of Parental Carrying of Young by Waterfowl" (1968). Papers in Ornithology. Paper 32. http://digitalcommons.unl.edu/biosciornithology/32. Also Celia K. Falzone. 1992. “First Observations of Chick Carrying Behavior by the Buff-crested Bustard”. The Wilson Bulletin 104 (1). Wilson Ornithological Society: 190–92. http://www.jstor.org/stable/4163135.
 See Johnsgard and Kear, ibid.
 This remarkable phenomenon was first reported in 1833 by the German ornithologist M.A. Wied. Subsequent generations of ornithologists viewed this report with skepticism or ridicule. However in 1969 Mexican ornithologist Miguel Alvarez del Toro confirmed that soon after hatching, the male sungrebe places each of the two chicks in pouches under his wings and departs. An article by B. Bertrand explains: "M. Alvarez del Toro, who observed a nesting pair in Mexico, discovered that the male has a shallow pocket under each wing into which the two young can fit. The pocket is formed by a pleat of skin, and made more secure by the feathers on the side of the body just below. The heads of the chicks could be seen from below as the bird flew. Alvarez del Toro collected the bird in order to examine it and confirm the unlikely discovery. Subsequently, he found it confirmed also by a report published by Prince Maximilian of Wied 138 years earlier but apparently ignored, forgotten or not believed. This adaptation is unique among birds: in no other species is there any mechanism whereby altricial young can be transported...." Bertrand, B. C. R. (1996) Family Heliornithidae (Finfoots) in del Hoyo, J., Elliott, A., & Sargatal, J., eds. Handbook of the Birds of the World. Vol. 3. Lynx Edicions, Barcelona.