Sceptics notwithstanding, the phenomenon of luminous birds whose lengthy history I surveyed recently on ShukerNature in Part 1 of this two-part review (click here to read Part 1) is assuredly genuine, but how can it be explained? Five principal potential solutions have been suggested by amateur naturalists and professional scientists alike down through the ages, and these are as follows:
1) It is due to the bird having made physical external contact with phosphorescent organisms living on decayed wood in tree holes
The idea behind this suggested solution – the most familiar and extensively documented of the five under consideration here – is that such contact would cause phosphorescent bacteria, plants, and fungi growing on the wood to become attached to the bird's feathers, thereby yielding an area of luminescence upon its plumage.
However, whereas the parts of a bird's body most likely to make contact with wood when entering or exiting a tree hole would be its wings and head (brushing against the rim of the hole), the body region actually exhibiting most (or all) of its perceived luminescence in those specimens that have been reported has tended to be the breast, with the wings and head sometimes giving off little (if any) light.
Also, it must be remembered that glowing examples of extremely large birds, such as North America's great blue heron Ardea herodias, standing 45-54 inches tall, have been recorded – and it seems highly unlikely that birds of this stature would (or could) inhabit tree holes.
In addition, and as its common name suggests, the barn owl, the most popular identity for luminous owls, prefers to roost in barns or deserted out-houses rather than in tree holes (though it will roost in them if need be).
Yet if this option is nonetheless a viable one in relation to certain bird species, a common phosphorescent fungus likely to be involved is the honey fungus Armillaria mellea – a very abundant, widespread, edible species (or species complex, as is nowadays deemed to be the case) that lives on trees and woody shrubs, and sports bioluminescent mycelia yielding an ethereal greenish-blue glow commonly referred to as foxfire.
Indeed, I remember reading long ago a fascinating snippet of information demonstrating just how powerful the foxfire glow of this fungal species can be. Edited by Dilys Breese, and published by the BBC in 1981, the multi-contributor book Wildlife Questions and Answers included the snippet in question, provided by correspondent R. Watling, and which reads as follows:
I have often seen the eerie light of the honey fungus in a tropical rain forest. You see all the leaves and stems and trunks, twenty-five feet tall maybe in an old tree, with this beautiful glow, just like a silver lady among the trees. And these fungi can even take their own photographs! If you set up a camera next to one of them, given enough exposure time, you will get a picture of the fungus all bright and shiny, taken by its own luminescence.
Another species likely to play a part in this particular proffered solution is a phosphorescent plant officially called the luminous moss Schistostega pennata, but also known by such charming colloquial names as goblin gold and rabbit's candle. As noted by bryologist Sean Edwards in a letter published by BBC Wildlife Magazine in April 1994, its luminous portions are the first cells produced by germinating spores, which act like thousands of pear-shaped microscopic cat's eyes, collecting and concentrating even the faintest light. It is often found growing inside (and illuminating) rabbit holes, hence its 'rabbit candle' moniker, yielding a greenish-gold glow.
2) It is due to the bird having ingested phosphorescent microbes
As the luminescence of birds is external, and has actually disappeared in some cases following moulting, one would assume this to be a phenomenon associated exclusively with the bird's external covering, i.e. its plumage, rather than due to any digestive or other metabolic process (but see also Solution #4 for some ostensible exceptions to this statement).
Of course, we could speculate that if any phosphorescent microbes were inadvertently ingested with food, they could pass out of the bird's body within its faeces, which might then in some way become smeared upon its plumage, perhaps during preening, rendering it phosphorescent in turn.
Also, it should be borne in mind that not all phosphorescent bioluminescent fungi are harmless. One such species that is poisonous is Omphalotus olearius, the so-called jack-o'-lantern mushroom. This orange-gilled European fungus grows around the bases, stumps, and buried roots of hardwood trees (a related species, O. illudens, occurs in North America). A bird perching upon it may conceivably find itself with fragments of this fungus attached to its plumage, especially upon its breast feathers, rendering them phosphorescent, but if the bird then attempts to remove such fragments by preening, it could inadvertently swallow some of them and thereby become ill from the toxic nature of this fungus.
Perhaps this is why some luminous birds that have been physically examined have been found to be in poor health, such as Rolfe's barn owl, and the specimen documented later here that was captured by a Norfolk engineer in his back garden.
Nevertheless, although such a scenario is not impossible, it is certainly not very plausible as an all-embracing solution.
3) It is due to the growth of feather-specific phosphorescent microbes upon the bird's breast plumage
In some ways paralleling the previous two proffered solutions, this third one proposes that phosphorescent bacteria or fungi may grow upon a bird's breast feathers if they have become damp or dirty. Propounded by British zoologist William P. Pycraft (1868-1942) among others during and beyond the Norfolk luminous owl 'flap', it derives support from the fact that breast feathers are often particularly dense (as with those of pigeons, for instance), thereby encouraging microbial proliferation upon them. Also, the breast is a difficult region for many birds, especially short-billed ones, to reach satisfactorily when preening.
Furthermore, in his article, de Sibour noted that avian luminescence is particularly powerful during flight. He sought to explain this occurrence as an effect of superoxygenation, pointing out that if a medium containing phosphorescent particles is agitated, that medium's luminescence does increase.
Consequently, this third suggested solution to the enigma of luminous birds would seem to be the most tenable of the three considered by me here so far. Even so, in view of the comparative rarity of glowing birds while concomitantly bearing in mind that a very great many birds must at some time or another possess damp and/or dirty breast feathers, this solution still falls some way short of providing a wholly satisfactory explanation.
4) It is due to some internal light-generating metabolic process
There are certain especially mystifying cases in the luminous bird files that if accurate seem to indicate that those individual birds' luminosity was directly linked not to any externally-sited phenomenon but instead to their own internal metabolism. For in each case, its external luminosity vanished once the bird itself had died. The earlier-mentioned gamekeeper Fred Rolfe who in 1897 had shot down a luminous sphere in Norfolk and found it to have been a barn owl in very poor condition made no mention of any such occurrence, but it was a notable feature of the two incidents now documented by me here.
The July 1911 issue of The Irish Naturalist contained several reports and reviews by different writers appertaining to luminous birds, especially luminous owls, but the report of especial interest here concerned a luminous specimen of North America's afore-mentioned great blue heron, as I'll be documenting below shortly.
In his own Irish Naturalist survey of reports, C.B. Moffat referred to a very interesting rural belief apparently prevalent in both Europe and North America that I hadn't previously encountered but which is very pertinent to the luminous great blue heron specimen. Here is what Moffat revealed:
A belief has long prevailed ascribing similar luminosity [to that of owls] to several of the herons and bitterns, which are supposed to be assisted in their nocturnal fishing operations by a phosphorescent light emitted from the "powder-down patches" of the breast-feathers, a light that is thought to serve, perhaps, the double purpose of attracting fish to the vicinity and helping the watchful bird to see them.
Powder-down feathers are specialized down feathers that grow continuously, in specific tracts, but are only produced by four taxonomically-unrelated bird groups (parrots, herons, bustards, and tinamous). In some such species, the tips of these feathers' barbules disintegrate, yielding fine powdery grains resembling dust or talc but composed of keratin; in others, the powder grains originate from cells surrounding the barbules of growing powder-down feathers. When a bird spreads these grains over its body during preening, they assist in protecting, ridding of parasites, and waterproofing the bird's plumage and skin, but well worth noting here is that they also confer upon its feathers a noticeable sheen.
Moffat then stated that wildlife observer James E. Harting had presented a resume of the principal evidence relating to this belief within a chapter entitled 'The Fascination of Light' contained in his book Recreations of a Naturalist (1906). In particular, Harting had referred to a detailed account by Philadelphia-based hunter W.J. Worrall of how he had shot a luminous specimen of the great blue heron. According to Worrall, the heron had possessed three phosphorescent spots – "one in front, and one on each side of the hips between the hips and the tail". The description went on to state that as the fatally-wounded bird expired, so too did its luminescence, its lustre "disappearing entirely with death".
Of interest, the location of this heron's three phosphorescent spots matches the location of some of the paired, dense patches of powder-down feathers in herons, which occur on their breast, flanks, and rump. So, might those phosphorescent spots simply have been extra-powdery (thence unusually pale and shiny) patches of powder-down feathers? Worth noting here is that in a Forest & Stream article written by American naturalist Charles S. Westcott and published in 1874, Westcott stated that he had experimented in a dark room with the powder from the powder-down feathers of least bitterns Botaurus exillis, the New World's smallest species of heron, "and found it to be of the same nature as 'fox-fire'". Moreover, J.P. Giraud, Jr., author of The Birds of Long Island (1844), affirmed that the powder-down of dead herons "gives out a pale glow, not unlike that produced by decayed timber, familiarly termed 'light wood,' or 'fox fire'".
How, then, can we not only reconcile the above evidence provided independently by Westcott and Giraud that powder-down luminescence is not linked to a bird's life or death with Worrall's contradictory claim that the luminescence of the glowing heron that he had shot faded away once the bird itself died, but also (assuming its veracity) explain his latter claim?
The fundamental biological problem that Worrall's claim poses was highlighted by none other than Charles Fort – America's premier collector and chronicler of newspaper cuttings reporting anomalies across the entire spectrum of "damned" (i.e. scientifically-rejected or ignored) phenomena – when reporting in his book Lo! (1931) a second case in which this same luminescence-themed incongruity featured.
Fort referred to a report published on 7 February 1908 in Norwich's Eastern Daily Press newspaper (Norwich being a major city in Norfolk), in which engineer Edward S. Cannell of Lower Hellesdon, Norwich, claimed that on the early morning of 5 February when still dark he had seen something shining on a grass bank in his back garden, and that when it fluttered down a path there he discovered that it was a "bright and luminous" owl. He was able to capture the owl, which seemed to him to be ailing, and took it indoors, where it soon died. According to Cannell: "It was still luminous, but perhaps the glow was not as strong as when I saw it first" – i.e. its luminescence began fading following the owl's death. Moreover, in a sequel report, published by the same newspaper on 8 February, it was revealed that Cannell had taken the dead bird to a Mr Roberts, of Norwich-based taxidermists Roberts & Son, who claimed in an interview: "I have seen nothing luminous about it".
Needless to say, if both Cannell and Roberts were telling the truth, i.e. regarding the former's claim concerning the owl's brighter luminocity when alive than when newly dead and the latter's claim that when he later examined its corpse there was no luminosity at all, this is a most unexpected turn of events. For as Fort astutely pointed out:
Of course a phosphorescence of a bird, whether from decayed wood, or feather fungi, would be independent of life or death of the bird.
Indeed it would. Consequently, the only plausible explanation for any cases like Worrall's heron and Cannell's owl that feature synchronicity between a luminous bird's death and the disappearance of its luminescence would seem to be that the latter characteristic was caused by some intrinsic physiological, bioluminescent process – whereby the living bird was actively generating its luminescence via a specialised metabolic process, which obviously would therefore cease once the bird died.
Yet although bioluminescence
is well-documented from a wide range of organisms, it is currently unknown from
any birds. (What has been confirmed,
meanwhile, is that many bird species possess plumage that glows in the
ultraviolet section of the electromagnetic radiation spectrum; but as human
eyes cannot detect ultraviolet light, this particular type of plumage glow
remains invisible to us.) Nor has this physiological condition been confirmed from any other tetrapod vertebrate (but click here for my investigation of a highly-controversial Trinidad lizard claimed by some researchers to be bioluminescent).
Of significance, furthermore, as revealed in his earlier-cited American Midland Naturalist article from 1947, is that during his researches into glowing birds, McAtee requested fellow American scientist Edwin R. Kalmbach to send him some specimens of the powder-down tracts from American black-crowned night herons Nycticorax nycticorax, a nocturnal species often claimed by eyewitnesses to be luminescent. He duly tested these tract specimens for the presence of luciferin and luciferase, the compounds inducing bioluminescence in known bioluminescent species, but he found no traces of them.
Consequently, even if certain bird species are indeed somehow bioluminescent, they nonetheless must also be externally luminescent if like herons they possess powder-downs, judging not only from McAtee's failure to link these feathers to metabolically-induced bioluminescence, but also to the above-reported findings of Westcott and Giraud that samples of these feathers' powder derived from dead birds continue to be luminescent. To my mind, however, this seems a superfluous and therefore impractical, implausible duplication of glowing ability.
5) It is due not to birds at all but features non-living BOLs instead
Investigators of the unexplained will be well aware that all manner of anomalous non-living phenomena involving mysterious glowing balls of light (frequently abbreviated to BOLs or BoLs) have been reported from many parts of the world, and include spooklights, foo fighters, ball lightning, and min-min lights, as well as more familiar, scientifically-resolved examples like the will-o'-the-wisp or ignis fatuus (resulting from the oxidation of phosphine, diphosphane, and methane, compounds produced via organic decay in marshes, bogs, and swamps). So might reports of luminous birds in reality involve BOL phenomena and not feature birds at all? Whereas it is certainly possible that some may have done, examples of such entities being shot down and found to be birds obviously cannot be explained away like this. Moreover, whereas it is true that the Haddiscoe sightings took place in marshes, where will-o'-the-wisp activity would not be surprising, others have occurred far from such terrain.
Equally problematic for a BOL explanation regarding luminous birds are those examples in which the luminous entities have been observed moving in an evidently conscious, self-aware manner. Relevant here is that in an exact reversal of the above-mentioned suggestion that luminous birds may be BOLs, many investigators of Australia's most famous unexplained BOL phenomenon, the mysterious min-min lights long encountered in Queensland, nowadays deem it more likely that these glowing enigmas are not of any meteorological or chemical-based origin but are actually living creatures, specifically barn owls, precisely because of the ostensible curiosity and inquisitiveness that min-mins demonstrate towards their human observers. Here is a prime example, as documented by me in my book The Unexplained (1996):
For example: You Kids Count Your Shadows, a collection of Wiradjuri aboriginal lore and beliefs from New South Wales compiled by Frank Povah [and published in 1990], contains an account of a sheep drover who was checking his flock on horseback one evening when a blue min-min light appeared over his shoulder, and persistently followed him during his work. In exasperation, he chased after it, still on horseback, but was unable to catch up with it – until he gave up, and began riding home, whereupon the min-min cheekily appeared over his shoulder again!
It is sad that such a captivating phenomenon as luminous birds has fallen out of scientific favour in modern times, especially as science is now equipped with so much readily-available sophisticated technology with which to investigate it thoroughly. Of course, this is due in no small way to the equally sad scarcity of reports nowadays. Saddest of all, however, as noted by David Clarke in his Fortean Studies article chronicling the luminous owls 'flap' reported in Norfolk during the early 1900s (referenced by me in Part 1 of this review), is that this scarcity may well be due in turn to how much rarer, as a result of habitat destruction and poisoning by pesticides, the barn owl has become in Britain and elsewhere during the century or more that has passed since the Norfolk 'flap'. Then again, if the numbers of this species, now extensively protected, do eventually re-attain their former level, perhaps this most delightful and whimsical of wildlife anomalies may once again attract the attention of professional and amateur enthusiasts and eyewitnesses all over again, back in fashion at long last.
Finally: worth noting here is that phosphorescent bacteria were declared the official answer to the anomaly of a leg of lamb that glowed in the dark and which had recently been purchased in the Worcestershire town of Kidderminster, England, during spring 1988. As reported by the Sandwell Express & Star newspaper on 12 March 1988, when the discovery was first announced there were fears of Chernobyl-derived radioactive fall-out from its nuclear power station's explosion two years earlier. However, Hereford-Worcester's county analyst and scientific advisor Geoffrey Keen rightly rejected this melodramatic notion in favour of phosphorescent bacteria being responsible, thereby solving with Sherlockian skills of deduction the curious case of the luminous leg of lamb.
If you haven't already done so, be sure to check out Part 1 of my luminous birds review article here on ShukerNature.
NB – All images of luminous owls included here were created by me using Grok X1.
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