There are currently underway censuses, but there were counting's before in the island. What were the goals and results of field work?
PS: In terms of methodology presents some difficulties to calculate the number of individuals, censuses are made to monitor the population, but not with absolute data. The purpose of the census is compared with the previous, if the species is increasing or decreasing. Being a nocturnal bird is difficult to observe and the methodologies for absolute estimating of the number of individuals requires a large number of data, accurate contacts and very large in terms of how these contacts occur. Because it is a nocturnal species the estimated contacts is low and the data has a large margin of error. Therefore we did not use this kind of analysis, we used the method by comparison. From 100 observation points, then we have to analyze case by case, among the several points, since several factors such as the weather, which at first glance may indicate that the population is decreasing, but when analyzed in depth we can determine temperature differences from one census to the other, the breeding season may have been displaced due to these oscillations and the conditions of the current census are not the same of the previous. The conclusions have to take into account a number of indicators that are not linear. The basis of comparison is made from a census to another, but the conclusions take into account these factors. We have a smaller number of individuals, which may indicate a population decline, but after we may reach the conclusion that there are indicators that conditioned this descent of contacts.
Natural factors rather than human-induced?
PS: Yes, exactly the natural or induced by man also. For example, the contact points are distributed around the island and that repeat 3 in 3 years. What you do is repeat the points of the previous years, but as we know, building, fire, climatic factors can alter the environment surrounding the very point of contagion, I will give an example, there is a point where it is now the Madeira Forum, 12 years ago that spot was not a shopping center, formerly was an agricultural area, had banana trees, and then it was a great area for nesting and occurrence of owls. This stage is an area more difficult to observe, I am not saying that the population of these birds has disappeared, they may have shifted, but is now more difficult to observe them. It may even happen that one night the wind conditions influence the results, an outstanding evening in some censuses, but during the three years following the temperature is lower and if there is some wind becomes more difficult for the observer to detect a bird that is singing in the distance . We must also take into account other indicator that is the observer, imagine that one of the volunteers is sick, and may be it less attentive that day. We are not able to eliminate most of these factors, of course we tried to make the census the same time, in the same time of year, with the same climatic factors and even with the same observers if possible. However, there are aspects that may not vary and depend on the species. The data we obtain must be filtered to reach safer conclusions. We can say that visualize fewer individuals and the population declined, but to say that this form of raw maybe we are changing the truth of the facts.
After these censuses in 2013 we can say that the owls of the towers are a sustainable species on the island?
PS: Yes, clearly. This species is well set in all habitats, is a viable species i.e. that is not in danger. An estimate that was made, not based on these works, but it is an article indicates that the population is between 2,500 up to 10.000000 individuals. It is quite a sustainable number for the island of Madeira. It is a bird that has several food supplies, which indiscriminately uses various types of habitats, is not a species that requires great care. Suffers from habitat changes since it is an island, or off factors, such as a rodent control on agricultural land, it is obvious that this will affect indiscriminately the raptors. And the owl is also a bird of prey. It is not because of this change that the bird will die. It is a species that spans multiple habitats, including forest where there are no such these chemicals and the owl of the towers can survive these impacts that are localized. Does not compare with seabirds, petrel of Madeira, exists in small numbers in a small space, and if this area is eroding the species suffers. In the case of owls is not so, is a species that must be monitored to know the state of ecosystems, it is a predator, because everything that happens under the food chain is already reflected at the top. Controlling the bird we control what is below.
So what were the other objectives of the census of 2013?
PS: For the first time we have extended the work to the rest of the archipelago, the island of Porto Santo, Desert and Wild islands using the same methodology, points of contagion over these territories, trying to include all habitats and present a methodology for conducting passive listening, to learn if the species is present and then active listening that is causing the bird to react to the sound output to check for response and how many individuals are there. And relate this to the habitats to try to understand if there is any behavioral change.
In the desert and in the Wild Island, the owls have habitable conditions? Taking into account that these are areas with no vegetation, which has no trees,
PS: This is another of the adaptations that this bird can do. In fact, the species nests primarily on the mainland in old buildings, hence the name of the owl of the towers because it built nests in the towers of the church. Here in Madeira it can make nests in the rocks, but would not be expected to be present in these islands, where there is no woody vegetation, but it is present. In the Desert was a period of rodent control and removal of rabbits and this led to the species disappeared temporarily, in recent years several individuals have been sighted regularly and still were visualized nests. The species is back and this despite the fact that there are neither Bugio in rabbits or rats. It is a species that has adapted that environment and the existing conditions, which leads that the danger level is lower.
But in the case of the Wild islands?
SP: The case of the Wild is different while in this Desert island is proven nesting and it lives there all year, on these islets is a sporadic presence may be individuals who come from nearby islands, the Canaries who come to hunt, more than nest, nests on these islands are not confirmed, although the records. It is a species regularly present.
The curious fact is that we do not link the owl of the towers that ability to travel great distances, even at sea. It is an achievement that we associate to the Atlantic birds, which mostly are migratory, further taking into account the small size of the bird.
SP: In fact is not a species that usually go through these oceanic distances to come hunt. Its migration is not very large, and is sedentary does not deviate much from their areas but they came here, as well as some very small Passeriformes and they were not expected to make great migration. What can happen? At a time when the juveniles leave the nest the territory is already occupied by the parents, then the young birds have to look for other areas, some more daring individuals go further and adapt, can live, reproduce in these areas and colonize new ones. This is what happens with these species. Some eagles also travel long distances to hunt and then return to their origin. This is not a species of this genus, but sometimes some individuals have moved away from certain areas and colonized these new ones. The arrival of the owl to the Desert islands may be one of those cases.
Recently been proved by studying a set of fossils that a kind of owl became extinct at the beginning of the colonization of the islands, there is some similarity between both species, or they are different?
PS: They are different, although they are of the same order. The species that disappeared is a nighthawk, is close, which had different habits and what is believed that this species has been identified is that in fact disappeared at the time of colonization, because it had nesting habits of land use. It is believed that this species has suffered from large fires and the introduction of predators that did not exist at the time, like cats and rats. It is the story of many species that disappeared in island environments, the arrival of man and the entrance of these very aggressive predators led to the extinction of these birds. It is believed that happened not only with this owl from Madeira, but with other species found in the same areas in the dunes of the piety of St. Lawrence and Porto Santo, which have adapted to live, feed and nest in the ground. The owl of the towers despite living on an island, and that should be impacted with these predators, was sustainable because nests off the ground. We do not know your date of arrival of this bird islands, we do not know the evolutionary history of this species in the archipelagos, so you cannot determine if was already here in the era of colonization and had adapted, or appeared later with the arrival of these small rodents which are their food base. There is still a lot to study.
This work is not an isolated act comes under the Atlas of breeding birds of Madeira?
PS: Yes, this atlas is being developed since 2009 by the department of the Natural Park of Madeira in collaboration with SPEA (Portuguese Society for the Study of Birds) and a group of researchers associated with forming the management team of this project. The aim is to study the birds that nest on the island, it is a continuous work, and we want to do a specific work for a new atlas of the birds, where the scale is smaller and scale the fieldwork done in Madeira. As the owl is different has a specific methodology, was a work aside the project. The baseline studies included in the atlas was completed in 2012 and now we are in a phase of data processing and can point to other species. SPEA held in 2011 census of woodcocks and we have until the end of this year for another rallidae, which are the moorhens and coots that nest on the island streams. That is, if there is room for maneuver to bring these work to the ground.
The purpose of the atlas is to put the information at the disposal of national researchers, and other scientists who wish to visit the island and the population in general?
PS: Yes, the idea of the atlas of breeding birds of Madeira is to provide information that can be used both by researchers, and ordinary citizens, also in terms of tourism. It is a space where they can see what kind of birds are in which zones, densities and if they are or not nests in their respective areas. In general, the scale of the atlas covers 10x10 square kilometers, a grid of 100 square kilometers. The idea was to make 2x2 square kilometers, is a small scale, where people can know what is not in the center of Funchal, but in Parque Santa Catarina, for example, for the Owl of the towers as for other species occurring. That's the idea. It is a scale that has never been attempted. The data are online, except for the year 2012, because they are being treated.
