The Owl Pages

A Review of accounts of luminosity in Barn Owls Tyto alba

By Fred Silcock (Page 3 of 5)

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.

Page updated 2006-06-07