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THE BARN OWL by Walter L. Meagher Wayne and Susan saw the barn owl at twilight in El Charco. On another evening, the night watchmen saw a barn owl near the canyon, more than once since then. Not only is it beautiful – all owls are beautiful – but, like the barn swallow, the barn owl lives in alliance with human settlements. There are no barns in our neighborhood, or near El Charco; it would take some sleuthing to find where they nest.

Pellets are a clue to roosting sites. Barn owls swallow prey whole. A single mouse, shrew or vole - one at a time. Later, the owl regurgitates fur and bones in a neat bundle called an owl pellet. An inquiring young naturalist might find a site of pellets, bring them home, and reassemble a vole, with all its bony parts. Evidence from studies of barn owls in the U.S. suggests voles are preferred to mice. The Mexican vole is tiny and feeds mostly in the daytime; if it were the principal component of the barn owl’s diet, adaptations for night predation would be unnecessary.      

It was surprising to learn, from Mario Mendoza, Director of the Botanical Garden, ‘El Charco del Ingenio’, that: ‘en las comunidades rurales en esta parte del pais, el tecolote (owl) tiene una connotación “mala” tal vez porque hay un dicho que dice, “Cuando el tecolote canta, el indio muere.”’ More likely it is a vole that dies.

Most birds observe ordinary hours of the working day, and roost at sundown, as snowy egrets and great-tailed grackles do; but owls, like bats, have evolved ways to exploit food available in the dark. Barn owls locate prey by sound alone. The concave surface of the facial ruff, so singular in appearance and worn by no other family of birds, collects and amplifies sound.

        Collection alone does not fix location. The barn owl needs to know whether the sound (a mouse snuffling along its grassy trail) comes from left, right or straight ahead. Sound travels at a different rate depending on direction. How loud the sound is, its time and intensity are all recorded in neural cells in the owl’s midbrain, and that information is processed – and frankly, the details of this are not fully known – making a ‘neural map’. With this ‘map’ the barn owl flies directly to the source of the sound, without ‘seeing’ the sound source, and seizes a rodent. This remarkable system is so reliable that the barn owl lives comfortably all round the world, and is one of the world’s most successful predators.

Yet it is not enough to locate prey. Prey must not hear the advance of the predator. Solving this problem, the barn owl approaches silently, flight without a whisper. Usually birds in flight make some kind of sound. Given that the barn owl is a big bird, it should make more sound in flying than smaller birds make. Any sound, giving notice of an oncoming predator, is warning enough for a small rodent to scamper away. However, owls do not make a sound in flying: their wings have a ‘silencer’. The first primary feather is serrated rather than smooth. Air flowing over a smooth surface, surprisingly perhaps, always makes a sound, whereas serrations on feathers disrupt airflow, creating the silence that gives the owl its second advantage as a hunter in the night.     

Neural maps and feather serrations – these are all matters of biology. Long before they were known, the owl held a place in human cultures. An ill omen for the campesino, but an emblem of wisdom, the little owl (a different species from the barn owl) was the goddess Athena’s associate. But in Europe, as well as in Mexico, many people feared the night-flying bird as an omen of death. Could it be that the belief of the campesino originated in Europe and arrived with the Conquistadors? We prefer the bright side, and are glad the bird’s presence is honoured in the name of our largest bookstore in town, El Tecolote.