Doñana homes an interesting breeding population of Barn Owls (Tyto alba) but this comes as no surprise whatsoever, since the owl breeds throughout Spain, with the only exception of the highlands. What makes Doñana a singular place, is that winter densities rise up and sometimes dramatically. From mid-late November the marshlands receive large numbers of owls. Not only resident individuals can be found here, making up 10-20% of the whole winter population, also first year birds from Andalusia and other Spanish regions show up as well. However, it is the considerable number of owls from Central Europe arriving after a long journey that increases the population more importantly. The marshes turn out into a natural Tower of Babel, where birds from Andalusia, Spain, France, Belgium, Germany and the Netherlands meet to cope with the colder months of the year.
But why do so many Barn Owls come together every year? How can they all fit in such a small place? What is the population dynamic? Are there any behavioural differences between resident and foreign owls? I dedicated my PhD thesis to find the answers to these and many other questions, which kept me busy for nearly ten years and brought me so many sleepless nights. Every time one enigma unveiled another one arose, yet more intriguing than the one before.
The melting pot of wintering owls we are talking about, become spectacular in those years when birds come to the marshes in largest numbers, which happens following the concurrence of different factors occurring in Central Europe. When the cyclic vole populations collapse –which used to happen every 3-5 years before the climate warming emerged- and this in turn happens to meet particularly harsh winters, then the major dispersal of the post-fledged young is forced to head for the South West in search of areas with high prey availability and habitats where access to prey is easier. This occurrence is Known as “wanderyear o wanderjahren” and implies that fledged owls that fail to find suitable hunting grounds near the territory where they were born, have to move in large amounts Southward bound, till they come across the Andalusian marshlands. First they have to face the trial of their lives and complete an arduous journey of up to 2000km and nearly half-a-year adventurous trip across the most dangerous and hostile continent for the species. In compensation of this challenge they settle down in a Barn Owl Garden of Eden.
But many will not to survive, dying mainly as a consequence of collisions with vehicles in the thick network of roads and highways across Europe. Once in the safer sections of the marshes, they will be rewarded with a natural paradise: an abundance in food supply and open areas where their main competitor is absent, the so-powerful Tawny Owl, not to mention to be free from the most feared enemy, the Eagle Owl; indeed a true paradise on earth. For a young inexperienced Barn Owl, exhausted after a strenuous journey that is full of hazards and dangers, this is far more than can be hoped for.
As a matter of fact the marshlands of Guadalquivir River, either natural or rice fields, constitute one of the most favourable habitats for the species. Rats thrive and small mammals and insects are plentiful at the sides of ditches and water channels, thanks to the benevolence of mild temperatures during the winter, while the other rest of Europe freezes up. Owls enjoy plenty of roosting sites and good availability of perches to sit and search for prey or should they prefer, there are countless areas of long grass corridors to hunt on the wing, as they love to do.
This year we have enjoyed one of the best winters for the Barn Owl to be remembered. Accordingly it was not unusual to see owls born and ringed in Andalusia as well as others from outside the country, as suggested by their bigger size and darker coloration. For owl enthusiasts, the darker and more robust birds fit in the subespecies Tyto alba guttata, from Central Europe, while the smaller and paler locals are regarded as T.a.alba, from South-Western Europe and the British Isles.
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This owl had arrived into the marshland three days before my friend Javier took the picture while I was driving in December a few years ago. Luckily the bird survived the whole winter. |
Going out to the marshes at night in search of Barn Owls opens us up to a fascinating world, a world that is not always understood and known for quite an obvious reason: the night is the time when most humans are sleeping. But if we are willing to enjoy a unique experience and have handy a good Thermos of coffee (or any other substance to keep you awake throughout the night), then there is nothing else like a winter night-drive in the marshlands. Certainly we will see things otherwise overlooked and that will change our minds about these mysterious birds, which have nothing to do with the general image of lazy birds dozing off inside hollow trees and barns.
On arrival from their long journey, the owls are frantically searching for food. On rainy nights they can even be observed walking on the ground looking for toads and salamanders and if they are really hungry, can also be spotted in daylight, always aware of the other enemies they fear: diurnal birds of prey.
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This owl did well throughout the winter. |
Not surprisingly, on favourable winters it is possible to count up to five owls in an area of safe path of no more than 1 km, provided there is water on one or both sides. Research has revealed that the presence of one individual works a luring effect on other wintering owls nearby, in what scientists call a density-dependent process. According to this, one Barn Owl hunting successfully on a particular spot is broadcasting visual clues, revealing that the habitat is suitable to newcomers searching for good foraging habitats in the vicinity. In a similar way Griffon Vultures communicate to one another when one of them finds a carcass to feed upon. This interesting behaviour may end up in several birds hunting close by on the same area.
One of the things that draws our attention the most is that sometimes owls seem unwary when approached by human observers, to the point they can nearly be caught by hand. This is particularly remarkable when potential preys have just been detected and the owls are absorbed obtaining the accurate location to make the capture attempt. They are hungry and this action keeps them literally focussed in one thing only: finding food. Our birds spend the night hunting and flying back and forth and when the sun appears, they retire back into rice farms scattered around the marshland or inside the canopy of Tamarix trees alongside water bodies.
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This individual was active in broad daylight last wintering season. We took the pic with the cellphone without even taking any notice of our presence. |
And so goes the winter for a young Barn Owl here in Eden. But time is merciless and does not stop for anything or anyone and as weeks go by, the owl’s behaviour becomes more and more elusive and nocturnal, similar to local bird’s behaviour. Now they are no longer the inexperienced birds they were upon arrival to Doñana. They have learnt to survive the most critical period of their lives, the first winter, and now are ready to find a partner and defend a breeding territory by themselves.
By mid February the owls leave and the marshland turns empty; we will have to wait impatiently, looking forward to the next year to see them returned once again. As far as we know, they go back to their home grounds, but science still has not fully confirmed this point.
In Spring the only screech echoing in the marshes is that from native Barn Owls, those who chose to settle down in this magic land we call Doñana.
¿Would you like to join us to watch Barn Owls?
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