Have you checked ;Sakuna texts? The only one I have access to at present, namely the Vasanta-raaja, named after its author (in an 1878 edition by Eugen Hultzsch and in a 1997 (reprint?) edition published by ;Srii-ve:nkate;svara Press), has a long section, dvaada;sa varga, devoted to the significance of different types of crow cries. Although it does not explicitly say that "other creatures hall have no power over (a crow)" or (a crow) shall have no fear of death", it seems to presuppose something very close to that proposition. Therefore, you may find what you are looking for in the works of Varaaha-mihira, Sahadeva-and-Bhaa.da.lii, et al.

A Marathi encyclopaedia, Bhaaratiiya Sa.msk.rti-ko;sa (vol 2, p. 307, right column), says kaava.laa amara asato, a;siihii samajuuta aahe = "It is also believed that a crow is immortal.", but it does not provide a text reference. On p. 221 (right column), the same encyclopaedia says that, according to Tulasii's Raamaaya.na, a devotee named Kaaka-bhu;su.n.dii lives in the form of a crow and never dies (no chapter and verse of Tulasii's Raamaaya.na is specified).

On 2014-08-20, at 6:25 PM, Luis Gonzalez-Reimann wrote:

I'm posting this on behalf of Robert Goldman, who has been having trouble sending messages to the list.

Has someone ever come across any references to crows being, if not immortal, then very long lived and not dying of disease or other natural causes?

At Rām. 7.18. 23–25 Dharma (Yama) who had hidden from Rāvaṇa by taking the form of a crow, blesses the bird as follows.

“Then, O Rāma, King Dharma addressed that crow, which now was perched on the beam of the eastern sacrificial hall: ‘O bird, I am pleased with you. Now hear my words of gratitude. Since I am pleased, those various ailments with which I afflict other creatures shall have no power over you. Of this there can be no doubt. ‘Through my boon, O sky-going bird, you shall have no fear of death. Indeed, so long as men do not kill you, you shall live forever."

We haven't been able to locate any other literary or folkloric source for this.