A Review of accounts of luminosity in Barn Owls Tyto alba
| Paper by Fred Silcock 2004-06-04, last updated 2006-06-07 |  Page 3 of 6  | Properties of the Min Min Light
The so-called Min Min Light is distinctive, has a character all its own and should not be confused
with other kinds of light phenomena, including light refraction during
atmospheric temperature inversions, that may be seen in Australia. There is
much about the behaviour of this light resembling that of a bird. It has a
propulsion system and the ability to move against the wind. One of the
Light's common behaviour patterns is very similar to that of a Barn Owl in
hunting mode. Typically, a Min Min is reported as about the size and shape
of a football, sometimes round, sometimes oblong. Some observers have spoken
of it seeming to have a core about the size of a hen egg (several observers
and correspondents: notably Della Lenahan's many sightings around Julia
Creek, Qld, over 10 years since 1951; also James Young, fencer of Hawker,
SA). The strength of the light may vary in individual cases from strong to
weak and the colours range from whitish to orange, red and blue. Mostly, the
light appears within about two metres of the ground, often descending to
below a metre.
Sometimes its proximity to the ground will cause a reflection. Typically, in
this mode it proceeds slowly and in a curious rising and falling manner,
often referred to as 'bobbing', occasionally punctuated by short bouts of hovering. It may at times appear
to the onlooker to be swaying from side to side.
It is able to navigate to the extent that it does not bump into obstacles,
easily threads its way through plantations of trees and rises to pass over
fences in its path. Lights have generally been reported from open country,
and may be seen following fence-lines and sitting on posts. Reports show
that lights are capable of speeds of more than 70 km/h (cf. 80 km/h for Barn
Owl in Bunn et al. 1982), and if approached they react evasively, retreating
and/or cutting out, sometimes reappearing nearby. A light may appear in
approximately the same location on a number of consecutive nights and follow
regular flight paths. No audible sound of its movement through the air was
noted.
One observer, sitting in a motor car, had a Min Min come to within about 7 metres (near Julia Creek,
Old, undated). At this distance she described the shape as being like an
inverted pyramid, 'longer that it was deep'. She tooted the horn and the
light vanished. If one draws the shape described, there is no trouble in
fitting inside it the form of a bird with out-stretched wings.
Another observer, looking through a telescope from an undetermined distance,
noted that the shape of the light constantly changed from an orb to a
flattened form with one straight side, like a 'D'. Such a shape might
represent the varying angle of view presented by a bird in flight: the
rounded breast at times obscured by part of a wing.
A problem with interpreting informant's information is their perception of
scale at night. There can be difficulty in focussing and determining the
size and distance of a moving light in the dark, and a common error is
judging a light to be large and distant when it is small and close.
'Explanations' for luminescing Barn Owls
The existence of luminous Barn Owls is readily accepted, but commonly
attributed to the birds having come in contact with luminous fungus inside
the tree hollows in which the owls roost. In England, the fungus usually
mentioned is the well-known Honey Fungus Armillaria mellea which
causes wood to glow. Bunn et al. (1982) stated:
Sightings of apparently
phosphorescent Barn Owls have elicited several notes in the ornithological
journals and, improbable as those claims may seem, there can be no doubt
that such phenomena have occurred. The most satisfactory explanation is
that Barn Owls must occasionally roost in tree hollows where luminous
bacteria or the common fungus Armillaria niellea (Honey Fungus), which is
sometimes also luminous, are saprophytic on the rotten wood inside.
However, the glowing part of this
fungus is the mycelium growing in the wood, not external fruiting parts or
spores or exudation (McAlpine 1901). For feather contamination to take place
by this means, the wood would have to be broken up into particles. Wood
fragments and fungal fibres are unlikely to adhere to feathers for long,
given the frequent feather maintenance of birds by preening, in order to
ensure aerodynamic properties and insulation. Also, the breaking of the wood
would likely damage the mycelia and reduce their capacity to glow (McAlpine
1901). At least the birds observed by 'A Country
Teacher' (Anon. 1907) were not at the time roosting in a tree hollow.
Perhaps a bird could become contaminated by residue, maybe dust, from
luminous wood in tree hollows. Dust has some suggestion of dryness and most,
if not all, luminous fungi require humid conditions in order to function or
stay alive, even if dust is present. The Honey Fungus is no exception.
McAlpine (1901) stated, 'As we have seen, only a few fungi become luminous,
and it is found that as respiration becomes feebler the light decreases in
intensity and ceases entirely at death.' Speaking of the Honey Fungus in
particular, Brefeld (in McAlpine 1901) stated that in the mycelial strands
only the youngest and softest portions were phosphorescent, whereas the
older brown and hard strands were no longer capable of it. If the Honey
Fungus in connection with avian luminosity has any credence in Britain, it
has none in Australia where this fungus does not occur (although it was
thought to at one time).
Mycologist Dr Tom May (in Iitt.) has strong views against the likelihood of
birds becoming luminous as a result of contact with luminous fungi, and
knows of no fungus able to emit light anywhere near the strength of that
said to come from Mimi Min Lights. He adds: 'If fungal contact were an
option, why don't we see luminosity in other animals that at times inhabit
tree hollows?', and further: 'I have seen no records at all of any luminous
fungi from the arid areas of Australia'. The Min Min Light has an extensive
distribution throughout the arid areas of the continent.
Perhaps there is fungal contamination other than that by Armillaria
mellea? Other fungi there may be, but to what extent they are found
amongst birds, if at all, and how they behave, I have not yet been able to
discover. Or perhaps bacterial contamination? According to Professor J. Lee
(University Of Georgia, USA, in litt.), on luminous bacteria: 'Although most
types of these bacteria are found in the ocean, there is also known one
terrestrial species, Photorhabdus (Xenorhabdus) luminescens, that
infects nematodes.'
Harvey (1920) remarked, 'Most luminous bacteria grow best at relatively low
temperatures and would not thrive in warm-blooded animals such as birds and
mammals even though no defensive mechanisms were developed by the host.'
Luminous bacteria are known to infect meat stored in chillers, but their
origin is contamination from sea fish stored therein (Andriessen 1987).
Fungal contamination of the owls' feathers is inconsistent with the owls'
apparent ability to switch the light off suddenly, as when alarmed.
Similarly, a symbiotic relationship with luminous bacteria would require
structures in the owl's anatomy for revealing or hiding the bacterial
colonies. Prev | Next
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