miércoles, 10 de mayo de 2017

The Marshland Barn Owls of Doñana

Doñana evokes the image of endangered species such as Lynx or Imperial Eagle and magnificent landscapes renowned around the world. But in fact this protected piece of Spain amasses additional wonders the general public is not so aware of. If we wish to know these hidden secrets, all we have to do is take a closer and deeper look and soon we will discover one of the most fascinating natural treasures. But we have to do it while most humans are sleeping, when the night comes and there are no colours or lights, only stealth creatures in the kingdom of shadows. Today, we are talking about the Barn Owls of Doñana marshlands.

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.

Most people in the region are not aware of Barn Owls. However owls come in every year in high numbers for the winter months, becoming one of this protected area’s most interesting natural events. If we want to get a closer look, we will have to do it when the night comes and get ready to forego sleep. This Barn Owl was photographed from inside our vehicle as it hunted a shrew, Bon appétit!

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.

Doñana's marshes homes birds of different origins. Locals are joined by young birds from Germany, France, Belgium and the Netherlands, as evidenced by ringing schemes. Some of them are larger and darker, fitting in the Central European subspecies Tyto alba guttata. The owl of the image can regarded as intermediate in between the darker race and ours Tyto alba alba.

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.

The main cause of mortality of the species in Europe is from car collisions on roads. Every year thousands are killed everywhere across the continent. Casualty figures are overwhelming, to the point that it contributes largely to the population decline  throughout the distribution range. It is one of the wildlife side effects derived from having fast roads in developed areas.

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.

Hungry birds do not hesitate to walk on the ground in search of toads and other amphibians, which occurs mostly after consecutive days of non-stop rain. The quality of this image is poor as one hand was holding the camera while the other steered the car.

Any higher elevation from the ground seems good for an owl searching for prey. This particular owl was so hungry that it was not bothered by our close presence. Obviously this is a high-risk behaviour that takes many lives where roads have fast and dense traffic.

This owl did well throughout the winter.

Marshes provide an excellent array of perches for the owls to look for prey. They can choose whichever are the most suitable according to the grass cover thickness, where the prey dwell. Furthermore, there is plenty of food in the area and this perfectly explains the high numbers of Barns Owls coming in each winter.

Barn Owls love hunting on the wing. Long wings and low wing-load enable this behaviour like no other European owl in a very similar fashion to kestrels. It doesn't matter if there are perches around, they seem to enjoy flying buoyantly back and forth and hovering every now and then over the grass to nose-dive on unsuspecting prey.

Surprisingly, it is not a rare occurrence for Barn Owls to take advantage of cars moving on the road. When vehicles drive slowly (like that of mine), car lights and engine noise flashes up small prey at the road sides, good enough for birds who rise to the occasion. Many birds of different origin display this interesting hunting behaviour.

An explicit example of the high risk this practice poses by exposing the owl to car collisions. Javier took this shot of a wintering owl who arrived at the marshes and spent most of its time hunting like this. Fortunately this reckless bird made it through the winter, indeed a lucky one!

A dark-breasted wintering Barn Owl takes advantage of this vehicle while moving on the unpaved road at Brazo de la Torre. The owls which inhabit this area have higher survival rates, since vehicles drive at lower speeds. This owl gave us wonderful moments and pictures throughout the whole 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.

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.

If buildings are not available for roosting, Barn Owls do not hesitate to spend the daytime hours inside the canopies of Tamarix trees along water bodies. We must be careful to avoid disturbing them away in this vulnerable moment, as they can be attacked by diurnal birds of prey, specially Marsh Harriers, Peregrines and Buzzards.

So sad to see, but that is the way it is. Marshlands can be a safe Haven but in less than the blink of an eye may turn into hell for an unwary and inexperienced owl. This is what scholars call habitat-trap; birds perceive a good quality habitat with plenty of easy available food, but seem unable to identify severe mortality risk from human factors

The cycle of life rules in the marshes too. A run over Barn Owl is scavenged by a rat. Roles are reversed now. There are countless numbers of rats and this is the reason why so many owls meet here every winter.

There is also good news and these is the type we are most happy to broadcast. This owl was double lucky. The car it collided with did not kill it immediately and more importantly, it was brought in for rehabilitation to Celia Sanchez's capable hands, in Doñana National Park.

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?

A world without Barn Owls is not a good world. Let us support those NGOs doing a great job like GREFA, BRINZAL, AMUS and other rehabilitation centres spread across our country, or others abroad like The Barn Owl Trust in the UK, devoted to conserve the species and its environment. Their work is amazing and very much needed if we want to keep watching Barn Owls in the future.

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