Scientist Masakazu Konishi evaluates how barn owls catch their prey in complete darkness. By testing their auditory localization skills in a variety of tests the Barn Owls accurate localization becomes better understood.

   The ability to hunt in complete darkness is an incredible feat that requires excellent hearing and motor senses. This nocturnal behaviour is rare among birds. This habit is seen in less than 250 species and within those species some may only be considered crepuscular (active at dawn and/or dusk) (Martin, 1985). This point alone makes the study of nocturnal behaviour fascinating for any bird fanatics. Payne and Drury were the first to demonstrate the acoustic hearing abilities of Barn Owls in 1958 (Konishi, 1973). Masakazu Konishi revisited their observations in his own study in order to gain further information.

 

    There are two important points in Konishi’s experiment. First is that the Barn Owl does not depend on scent or body heat to track prey and that an owl will not strike prey whose sounds are unfamiliar. The first point was determined by attaching a piece of crumpled paper behind a mouse. When the lights were turned off and the owl was cued to attack, it striked the paper instead of the mouse. This indicates that the mouse body heat and scent was not a determinant for mouse location by the Barn Owl. The second point was determined by noticing that new sounds that did not ensure an award, were ignored. In order to move forward in experiments of the auditory capability, the frequency threshold of the Barn Owl needed to be determined. Three owls were used for this experiment: the owls were trained to leave their perch when they heard certain cues for a reward. In the end it was found that the Barn Owl could hear in a range of 500 Hz to 10 kHz. This range is much larger when compared to other birds. In addition the Barn Owl has specializations that help in its localization of prey by acoustic cues alone which other birds and even other owls do not possess (Dyson, 1998).

     Three experiments were created to further test the Barn Owls ability of sound localization: locating artificial sounds, locating pure tones and locating noises. To determine accuracy of location of artificial sounds (electronically developed sounds), a ‘chess-board’ set up was created consisting 10cm x 10 cm squares and 20 cm x 20 cm squares making up 100 squares. Loud speakers were set up under certain squares. When the owl heard the sound cue it would land on the square and the accuracy of measurement was determined by sensory pads in the squares. It was determined that the midpoint between the owl’s feet was always near the centre of the plate square, indicating almost perfect accuracy throughout trials. In locating pure tones barn owls seemed less able to accurately track sounds at low and high frequency tones, such as 3 kHz and 10 kHz whereas intermediate tones were more easily detected (6-9 kHz). For locating noise sounds with varying bandwidths were played, the sound would last from the time the owl left the perch until it landed on the ground. It was determined that the owls tracked best when provided sounds with frequencies ranging 5.5-9.5 kHz and a frequency range of 4-7.5 kHz was sufficient for accurate location. In short, the Barn Owl is able to locate a mouse based on a small section of the frequency spectrum. Since mice make a variety of frequency noises while moving through their habitat, owls are able to be very successful nocturnal hunters (Konishi, 1973).

The ability of the Barn Owl to locate sound is complex. Accurate localization depends on a variety of spatial cues or spatial information which is reliant on the right size and shape of the owl’s head and ears (Knudsen, 1985). It was also proven relevant that prey continues to move after the owl takes off for accurate localization. In Konishi’s experiment the prey was missed 69 times out of 86 when a spatial cue did not persist from the time of leaving the perch to landing. Whereas the same bird hit the target 46 times of 58 trials when the cues persisted through takeoff to landing (Konishi, 1973). Finally, a well known factor of sounds localization is the use of the facial shaped disk of the Barn Owl. This facial disk helps in funneling sound into the ear holes and helping with sound localization (Martin, 2005).

Many birds make use of perch- and flight hunting techniques besides the Barn Owl (i.e. Kestrels). However the grace and beauty of the Barn Owls soundless and seemingly weightless flight is unmatched by many birds (Taylor, 1994). There is a vast amount of research on different aspects of auditory localizations in bird species and the Barn Owl specifically. The Barn Owls ability to hunt successfully in complete darkness is remarkably unique among bird species and deserves attention among ornithology researchers.

 

   

    References

1. Konishi, Masakazu. How the Owl Tracks its Prey: Experiments with trained barn owls reveals how their acute sense of hearing enables them to catch prey in the dark. American Scientist, 61.4 (1973): 414-424. Print.
2. Martin, G.R. Sensory capacities and the nocturnal habit of owls (Strigiformes).Ibis, 128.2 (2008): 266-277. Print.
3. Dyson, M.L., Klump, G.M. & Gauger, B. Absolute hearing thresholds and critical masking ratios in the European barn owl: a comparison with other owls. J Comp Physiol A, 182 (1998): 695-702. Print.
4. Taylor, Iain. 1994. Barn Owls- Predator-Prey Relationships and Conservation. University of Edinburgh. Web. 22 Oct. 2015.
5. Knudson, E.I. & Knudsen, P.F. Vision Guides the Adjustment of Auditory Localization in Young Barn Owls. Science, 230.4725 (1985): 545-548. Print.
6. Martin, J.M., Raid, R.N. & Branch, L.C. 2009. Barn Owl (Tyto alba). University of Florida, IFAS. Web. 17 Oct. 2015.