Ignis fatuus

“The foolish fire, is an Exhalation kindled by meanes of violent moving, when by cold of the night, in the lowest region of the ayre, it is beaten downe, and then commonly, if it be light, seeketh to ascend upward, and is sent downe agayne; so it banceth up and downe: Els if it move not up and downe, it is a great lumpe of glewish or oyly matter, that by moving of the heat in it selfe, is enflamed of it selfe, as moyst hay will be kindled of it selfe.”

- William Fulke (1563), A Goodly Gallerye: William Fulke's Book of Meteors, pp.10-13.

“There is some evidence that phenomena such as the Will o' the Wisp in England and Min Min Light in Australia are luminescing Barn Owls Tyto alba (e.g. Purdy 1908; Gurney 1908; McAtee 1947; Bunn et at 1982; Macnamara 1989). However, the source of the luminescence is yet to be resolved. The most common explanation for such luminescence is that the owls have become contaminated with luminous fungi that grow inside hollow trees (e.g. Bunn et al. 1982) although, for reasons discussed herein, that explanation is unsatisfactory. 

[...] 

Is there any reason why birds could not bioluminesce? In a private letter Peter J. Herring, editor of Bioluminescence in Action (Academic Press, London 1978) said, 'There is no fundamental reason why there should not he a self-luminous bird (or mammal or reptile) but none has been reported'... 

This paper considers four premises: 

1. There is sufficient evidence to suggest that one or more of the following are true.
2. Barn Owls are indeed luminous, as has been often reported.
3. Luminescence is intrinsic to the owls and does not arise from contamination with luminous fungi.
4. Luminous natural phenomena, such as the Will o' the Wisp and Min Min Light, represent sightings of luminous owls. 

Only the Barn Owl is considered in this paper, because all the evidence gathered points to that species…”

- Fred Silcock, "A Review of accounts of luminosity in Barn Owls Tyto alba," Australian Raptor Studies II - Birds Australia Monograph 3 (1997).