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INTRODUCTION
People’s perception on birds of prey is heavily influenced by their utility, existing myths and traditions, as well as their aesthetic value within a specific social context (Silva et al. 2006). For example, on one side, governments and conservation agencies of different countries often promoted the utilitarian value of some raptors as rodent predators (Whittington & Allen 2008, Servicio Agrícola y Ganadero 2012). On the other hand, cultural myths may generate a negative perception encouraging poaching, persecution and hunting of these birds, affecting their conservation status, particularly in human dominated areas (Jaksic & Jimenez 1986, Martínez 1986, Martínez 2005, Silva et al. 2006, Guerrero 2007, Trinca et al. 2007, Curti & Valdes 2009, Ogada et al. 2012).
One raptor species widely distributed across the world is the Barn owl (Tyto alba, Tytonidae, Taylor 1994). This species is nocturnal and territorial, forming pairs that usually nest in tree holes, cliffs or buildings (Taylor 1994). Its adult length varies between 34-43 cm, and it preys mainly on rodents (Herrera & Jaksic 1980, González et al. 2004, Rivas & Figueroa 2009). In South America, the majority of published studies reported this species inhabiting rural areas or suburban settings but not urban environments (eg. Travaini et al. 1997, González et al. 2004, Trejo & Ojeda 2004, Carmona & Rivadeneira 2006). In Chile, this species is widely distributed from the coast to 1500 m in altitude, typically inhabiting mountains, shrublands and farms (Rivas & Figueroa 2009). However, no study has yet to report this species living strictly in Chilean cities. We report a Barn owl nesting pair into an old native tree within the city boundaries of Valdivia, in southern Chile. As older trees are very scarce in most Chilean cities, this nest represents a good opportunity to understand the feeding ecology of Barn owls in cities as well as to study the perception of urban people with raptors in their immediate vicinity. We predict that urban people will show a combination of negative and positive perceptions to the Barn owls, on one side because of myths and on the other side because of their utilitarian value as rodent predators. In this study, i) we document the feeding habits of Barn owls nesting in urban settings of Valdivia, ii) we analyze the opinions of the local neighbors toward the owls and their nesting tree, and iii) we discuss the potential of these owls as a subject for education and promotion of the conservation of biodiversity in urban areas.
MATERIALS AND METHODS
STUDY AREA
The study was conducted in the city of Valdivia, in Southern Chile (39°50’ S, 73°14’ W, Fig. 1). Valdivia is located at 20 m over sea level, 20 km east from the coast. The city lays at the confluence of the three rivers, surrounded by wetlands and agricultural fields, and has a population of approximately 150,000 people. Climate in the area is temperate, with oceanic influence, an annual mean temperature of 11.9º C, and annual precipitation of 2,540 mm (Luebert & Pliscoff 2005). We studied a pair of T. alba nesting in a large old native tree close to a main street in the Barrio El Bosque, Valdivia. This neighborhood was built around 1990, and surrounded by an array of remaining wetlands and urban areas. The main street has a central floe with two lines of trees, mostly exotic species of English oak (Quercus robur; Fagaceae). However, the nest was located in the only native tree present, a large old Roble tree (Nothofagus obliqua; Nothofagaceae) of 1.2 m diameter and over 300 year old (I.A. Díaz, unpublished data). According to the neighbors, the owl pair has been nesting and living there for over 20 years. To our knowledge, this is the first nest reported in strictly an urban neighborhood in Chile, where the nest is surrounded by transited avenues, electric lines, houses, schools and commercial buildings.
DIET ANALYSIS
Between August 2010 and August 2011, we collected all pellets found around the tree on a monthly basis. We analyzed the pellet’s content in the laboratory, cataloguing the different preys, as they were identifiable. To define to which species the remains belonged, we separated the skulls and bones of vertebrates, classifying them following Reise (1973) and compared them with a reference collection of vertebrate skulls deposited at the Institute of Environmental and Evolutionary Sciences of the Universidad Austral de Chile. In the case of invertebrates, we were able to classify the remains either to the order or family level. Two species of the genus Rattus have been historically introduced in Chile, R. rattus and R. norvegicus (Jaksic 1998), and we simply classified them as Rattus spp. because we were not able to reliably distinguish between these two species within the remains contained in the pellets. Data were pooled by Autumn-Winter and Spring-Summer seasons. The results were expressed as a percentage of the total prey consumed (FREQ) and as a percentage of the total prey mass consumed (BIO). The following equation was used to calculate the percentage of the total prey mass consumed represented by each species in the diet, assuming that the entire body mass of each individual prey species caught was consumed by de Barn owl:
BIO = (100Spi Ni ) / Σ Spi Ni
Where Spi is the mass of the ith species, Ni is the number of individuals of ith species consumed and BIO is the percentage of the total prey mass consumed for each season contributed by the th species. The mass of each prey species was obtained from Díaz (1999).
PEOPLE’S PERCEPTIONS
To document whether the neighbors manifested either a positive or negative perception towards the owls and their nesting tree, we interviewed all the households at a 200 m radius around the nesting tree. The survey was conducted in August 2011, and we asked to only one member within each household to answer three questions regarding the owls. The questions were: 1) Are you aware or have you ever seen the Barn owls that nest in the neighborhood? 2) Do you think owls are a worthy asset, detrimental or do not matter? 3) Can you please explain us why? These same questions were rephrased to known the perception to the owls’ nesting tree. We further classified the answers to the third question “why” as three different arguments following Kellert (1994) with modifications. These were defined as “utilitarian” if the answer was based on the owls’ specific and direct utility to the neighbors (such as preying on rodents), “ethical” if the answers argued about the right of existence of the owls and their nesting tree, and “aesthetical” if the answers focused on the physical attractiveness and magnificence of the owls and their tree.
RESULTS
BARN OWL’S FEEDING HABITS
Overall, 201 pellets were collected during one year, which included 276 individual preys (Table 1). Rodents were the most consumed preys, representing more than 90% of their diet in both seasons of study, whereas only one pellet had invertebrate remains (Gryllidae, Table 1). In addition, the rodents represented 99% of prey biomass in the Barn owl diet (Table 1). The Barn owls preyed upon three native species of rodents: O. longicaudatus (Cricetidae), Abrothrix olivacea brachotis (Cricetidae) and Abrothrix longipilis apta (Cricetidae), in addition to the exotics Rattus spp. (Muridae). The results showed similar proportions of rodent consumption by the Barn owl in both seasons (Table 1). O. longicaudatus was the most consumed prey of the total diet of the owl, representing 80% of their diet in autumn-winter and 76% in spring-summer (Table 1). In addition, O. longicaudatus represented the highest biomass for both seasons, representing 54% of the total biomass prey in autumn- winter and 51% in spring-summer (Table 1). Rattus spp. was the second most consumed and was the second most important biomass, representing 46% of the total biomass prey, while A. longipilis apta and A. olivacea brachotis were represented in lower proportions (Table 1). The remaining 4.4% corresponded to unidentified material (Table 1).
PEOPLE’S PERCEPTION
The majority of the neighbors (67.7%) were unaware of the existence of the owls, but half of them (50.8%) were aware of the existence of the ancient native tree used for nesting (Table 2). Those people aware of the owl’s existence showed a positive perception towards the birds (31%), however people who didn’t know of the owls’ presence were mostly indifferent to them (Table 2). None of the people surveyed expressed a negative perception towards the owls. Most answers indicated a positive opinion about this species. People gave a variety of opinions including utilitarian, ethical and aesthetical reasons; from “being important as a pest control” to “having the right to exist”. One family answered that “children like them”. Overall, 30% of the people interviewed gave an utilitarian reason while 45% gave a combination of ethical and aesthetical reasons for valuing the owls (Table 3).
All of the surveyed people had a positive perception towards the old native Roble tree, regardless if they were or not aware of the tree’s presence (Table 2). Only one person expressed concern about the risk of the tree to falling over the neighboring houses (Table 2). In general, more people (67%) expressed ethical or aesthetical reasons to value the Roble tree (Table 3). The principal reason was appraising the value that the Roble is a native tree. None of the interviewed people manifested utilitarian reasons as a form of evaluating the tree presence (Table 3).
TABLE 1 Food habits of the Barn owl (T. alba) in Valdivia, Southern Chile. The data were grouped in Autumn-Winter and Spring-Summer. N total= 276 individuals in a total of 201 pellets. FREQ is the percentage of each prey calculated over the total prey items consumed. BIO is the percentage of total prey mass consumed. / Hábitos alimenticios de la lechuza blanca (T. alba) en Valdivia, Sur de Chile. Los datos fueron agrupados en temporada Otoño-Invierno y Primavera-Verano. N total= 276 individuos en un total de 201 egagrópilas. FREQ es un porcentaje calculado sobre el número total de ítems consumidos. BIO es el porcentaje del total de la biomasa de las presas consumidas.
TABLE 2 People perception (%) about Barn owl (Tyto alba) and the Roble (Nothofagus obliqua). N surveys= 65 houses. / Percepción de la población (%) sobre la lechuza blanca (Tyto alba) y el roble (Nothofagus obliqua). N encuestas=65 casas.
TABLE 3 Answers (%) provided by the interviewed neighbors about their perception of the Barn owl and the native nesting tree. Answers were classified as aesthetical, ethical or utilitarian value. / Respuestas (%) proporcionadas por los vecinos entrevistados sobre su percepción hacia la lechuza blanca y hacia el árbol nativo en donde nidificó. Las respuestas fueron clasificadas como valor estético, ético o utilitario.
DISCUSSION
FEEDING HABITS OF THE BARN OWL
The primary prey consumed by the Barn owl in Valdivia was O. longicaudatus, in concordance with diet analyses from rural areas in Chile and Argentina (Herrera & Jaksic 1980; Gonzalez et al. 2004; Udrizar et al. 2005). This study is the first one to report the food habits of Barn owls in urban settings in Chile. Most studies in the southern cone have been carried out in rural and suburban areas, showing that Barn owl also consume a larger variety of animal preys in addition to O. longicaudatus, such as birds, bats, reptiles, amphibians and invertebrates (Romano et al. 2002; Gonzalez et al. 2004; Carmona & Rivadeneira 2006). In Valdivia, the diet of Barn owl was based almost exclusively on rodents in both seasons, maintaining similar proportions of consumption, which is very intriguing. We found only four species of rodent within the owls’ pellets examined (considering Rattus spp. as one species). We argue that three non-mutually excluding possible causes may explain the prevalence of rodents as preys, and particularly on O. longicaudatus in Valdivian Barn owls: i) O. longicaudatus may be the most abundant species in urban and rural areas, ii) their behavior makes them more visible to the owls, and iii) Barn owls may select for a specific type of prey.
Several studies have proposed that the most abundant rodents in urban settings, should be Rattus rattus, Rattus norvegicus and M. musculus; at least in Chilean cities (Jaksic 1998; Torres-Pérez et al. 2004, González et al. 2004; Fernández & Simonetti 2012). Unfortunately, studies that assess the diversity and abundance of rodents in urban areas of Chile are scarce (Fernández & Simonetti 2012) and just one ongoing study in the nearby city of Temuco (170 km north of Valdivia) has found a large variety of rodent species in urban settings, including O. longicaudatus (Muñoz-Pedreros et al. unpublished data). If Barn owls prey based on abundance, then O. longicaudatus should be an abundant species in Valdivian urban settings contrary to that is widely believed or accepted for Chilean rodents despite the lack of studies (Iriarte 2007, Fernández & Simonetti 2012). On the other hand, the foraging ranges of Barn owls are around 4 km around the nest (Smith et al. 1974) and O. longicaudatus is a rodent with large home ranges (Murúa et al. 1986), which could favor the consumption of O. longicaudatus by Barn owl. Valdivia is located within a matrix of natural wetlands densely covered by large grasses such as Cyperus spp. and Juncus spp., and surrounded by a mix of native or exotic shrubs. Most urban wetlands are immerse in an urban matrix of residential and commercial development, and are threatened by a strong pressure for urbanization (González et al. 2003). Barn owls could easily prey within the surrounding wetlands, however the lack of populations’ studies about rodents living in these wetlands limited our ability to understand where and how this species is feeding on rodents.
On the other hand, O. longicaudatus has a fleeing behavior characterized by alternating running and jumping (Kittlein 1994, Iriarte 2007), which may render this species much more visible to the Barn owls compared to other rodents (Kittlein 1994). Furthermore, O. longicaudatus activity occurs at the same time as the Barn owl, which may also explain their prevalence in the Barn owls’ diet (Kittlen 1994, Iriarte 2007, Rivas & Figueroa 2009).
Last, Barn owls may actively select their prey as suggested by Simonetti & Walkowiak (1979). Bozinovic & Medel (1988) analyzed the energetic requirements of this and other raptors, proposing that preys of the size of O. longicaudatus provide the best energetic return at minimal effort for the Barn owl. This reason may explain why Barn owl was preying mainly on O. longicaudatus, and this owl may prey on other items when the abundance of O. longicaudatus decreases below a threshold level despite the larger biomass of other preys such as Rattus spp. which is more aggressive than smaller native rodents (Simonetti & Walkowiak 1979, Muñoz & Murúa 1990).
These results correspond to the first records of the diet of Barn owls in urban settings in Chile, and until our knowledge, no other nest of Barn Owl have been found inside the urban perimeter of this or another Chilean city. Our results should be complemented with further studies focused on finding and documenting other owls’ nests inside the urban perimeter, and to characterize the rodent communities that live in urban areas.
PEOPLE’S PERCEPTION
Our result showed that the Barn owl provides an important ecosystem service in the city of Valdivia, by preying an important amount of rodents, particularly O. longicaudatus; the main vector of Hantavirus in Chile (Castillo et al. 2000, Figueroa et al. 2001, Table 1). Therefore, we expected that Barn owl where strongly valued by its utilitarian importance. The neighbors’ perception to the owls pair and to the nesting tree was mostly favorable (Table 2), however it was driven mainly from aesthetic and ethical reasons, and not by utilitarian reasons (Table 3). This is contrary to the strong utilitarian value reported for this species in rural areas of Chile (Silva et al. 2006) and evidence a different type of relationships between wildlife in urban settings vs. rural settings. The fact that most neighbors were unaware of the owls’ presence in their neighborhood is similar to that reported for other urban areas in the world, where people living in urbanized areas are more likely to be uninformed about the wildlife that surrounds them (Clergeau et al. 2001, Gilbert 2012). People who were not aware of the owl’s presence in their neighborhood expressed indifference, whereas everybody else had a positive opinion about the owls (Table 2), suggesting that exposure and interaction with biodiversity would influence the people appreciation towards local wildlife (Clergeau et al. 2001, Gilbert 2012).
IMPLICATIONS FOR CONSERVATION
In Chile, no previous study have showed Barn owls living in urban settings, despite this is a common factor in European and North American cities (Smith et al. 1974, Ramsden 1998, Kasprzykowski & Golawski 2006). The subspecies inhabiting southern Chile is of different color, and maybe the local species are not use to live in cities. In fact, urban settings of Valdivia are very different of what is known and assumed for urban areas in the developed world (Silva et al. 2015). Based in our field observations and data from Silva et al. (2015), we hypothesize that the presence of Barn owls in this city is strongly influenced by the matrix of wetlands and the remnants of native forest vegetation such as the old native tree where owls were nesting. Then, legacies and the local matrix can provide and explanation of why this species is nesting in the middle of a street.
Therefore, the owls and the nesting tree can represent important biological legacies in this city, and in addition valued by the neighbors mainly for aesthetical reasons independently of the utilitarian reasons. These biological legacies should be protected as a local and unique patrimony of the city, and emphasized as first-hand contacts with nature and wildlife in urban areas. As several studies suggest, first- hand positive experience with wildlife contribute to develop concern and participation to the protection of species and ecosystems (e.g., Mittelstaedt et al. 1999, Hine et al. 2009). In the future, most of the human population will concentrate in urban areas (United Nations 2011), then biological legacies including relevant, charismatic native species in cities can provide these first-hand experience to the neighbors, increasing their awareness for wildlife, favoring a positive relationships between the natural environment and people (e.g., Llanos-Pineda 2013). These legacies represent an opportunity to develop integrative educational programs, focused on species and ecosystems, favoring the awareness for local wildlife such as the raptors in places where people conduct their daily lives.
