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Factors Affecting Survival in Mediterranean Populations of the Eurasian Eagle Owl

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Factors Affecting Survival in Mediterranean Populations of the Eurasian Eagle Owl Factors affecting survival in Mediterranean populations of the Eurasian eagle owl Mario León-Ortega, María del Mar Delgado, José E. Martínez, Vincenzo Penteriani & José F. Calvo European Journal of Wildlife Research ISSN 1612-4642 Volume 62 Number 6 Eur J Wildl Res (2016) 62:643-651 DOI 10.1007/s10344-016-1036-7 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Eur J Wildl Res (2016) 62:643–651 DOI 10.1007/s10344-016-1036-7 ORIGINAL ARTICLE Factors affecting survival in Mediterranean populations of the Eurasian eagle owl Mario León-Ortega1 & María del Mar Delgado2 & José E. Martínez1,3 & Vincenzo Penteriani 2,4 & José F. Calvo1 Received: 21 March 2016 /Revised: 6 July 2016 /Accepted: 27 July 2016 /Published online: 12 August 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract The survival rate is a key parameter for population significantly between the two populations, gunshot being the management and the monitoring of populations. Thus, an main cause in Seville and electrocution in Murcia. analysis of survival rate variations and the factors influencing the same is essential for understanding population dynamics. Keywords Home range . Human-induced mortality . Here, we study the factors determining the survival and the Known-fate model . Sex-biased mortality causes of mortality of the Eurasian eagle owl (Bubo bubo)in two Spanish Mediterranean populations (Murcia and Seville) where the species has a high population density and breeding Introduction success; yet its survival rates and the factors that affect them are unknown. Between 2003 and 2010, 63 breeding owls were The study of demographic parameters is essential for under- captured and radio-tracked. Three monthly (quarterly) surviv- standing the trends and changes of wild populations (Moyes al rates were estimated using known-fate models in the pro- et al. 2006;Schaubetal.2010; Smith et al. 2010; Tenan et al. gram MARK. The mean overall annual survival rate was 2012). Among various vital rates that affect population change 0.776 (95 % CI: 0.677, 0.875). We observed survival differ- (i.e. survival, productivity, immigration/emigration), survival ences between sexes, and between the breeding and non- is usually considered the most important driver of population breeding periods, although no overwhelming support was dynamics, because this parameter is usually the greatest con- found for any particular model. We concluded that (i) females tributor to the population growth rate in K-selected organisms have a lower survival rate than males, probably due to their (Sibly and Hone 2002;Grandeetal.2009; Margalida et al. larger home ranges, which increase the risk of mortality; (ii) 2014). Thus, annual survival can be a key parameter for mon- the survival rates of both sexes were lower during the non- itoring and managing populations of conservation concern, breeding period; and (iii) the causes of mortality differed especially in the case of long-lived species (Wisdom et al. 2000; Hernández-Matías et al. 2011). Thus, understanding patterns of variation in survival is necessary to interpret both life history variation and the mechanisms driving population * Mario León-Ortega change (Robinson et al. 2010; Smith et al. 2014). [email protected] To our knowledge, although few estimates on owl survival in Mediterranean European regions have been published (e.g. 1 Departamento de Ecología e Hidrología, Universidad de Murcia, Boano and Silvano 2015), owl survival estimates are available Campus de Espinardo, Murcia, Spain for several species in boreal and temperate regions of Europe 2 Research Unit of Biodiversity (UMIB, UO-CSIC-PA), Oviedo and North America (Newton et al. 2016). These studies re- University - Campus Mieres, 33600 Mieres, Spain vealed that owl survival (i) shows temporal patterns of varia- 3 Bonelli’s Eagle Study and Conservation Group, Apdo. 4009, tion related to cyclic food abundance and climatic factors E-30080 Murcia, Spain (Seamans et al. 2002;FrancisandSaurola2004; Lehikoinen 4 Department of Conservation Biology, Estación Biológica de Doñana, et al. 2011; Pavón-Jordán et al. 2013;Duggeretal.2016); (ii) C.S.I.C., c ⁄ Americo Vespucio s ⁄ n, 41092 Sevilla, Spain is influenced by habitat structure (Franklin et al. 2000; Author's personal copy 644 Eur J Wildl Res (2016) 62:643–651 Hakkarainen et al. 2008;Duggeretal.2005); (iii) decreases 2013). The objectives of this study were (1) to determine with the presence of human infrastructures (Grilo et al. 2012; temporal patterns of survival, (2) to examine the effects of Thorup et al. 2013; Borda de Água et al. 2014); and (iv) is sex and age on the survival rates of Eurasian eagle owls, (3) reduced by the predation of young individuals (Sunde 2005). to compare survival rates between the two populations, living In addition to age, other individual-related variables, such as in areas characterised by different human pressures and envi- sex or physical condition, are expected to be important factors ronmental characteristics and (4) to document the causes of affecting survival. For example, age- and sex-biased mortality mortality and analyse the factors influencing it. has been observed in many wild bird populations (Tavecchia et al. 2001;Martínetal.2007; Rymešová et al. 2012), and other studies have documented higher survival rates for indi- Methods viduals with better body condition or health status (Dinsmore and Collazo 2003;Hyltonetal.2006). Differences in survival Study areas rates between males and females are usually associated to differences in behaviour and energetic investment during the The study was carried out from January 2003 to December reproduction period (Liker and Székely 2005; Rymešová et al. 2010 in two populations in southern Spain: (i) the Sierras of 2012), but also to differences in habitat use or foraging activ- Columbares, Altaona and Escalona, a hilly area ranging from ities (Lambertucci et al. 2012). 40 to 646 m a.s.l. in the province of Murcia (south-eastern The Eurasian eagle owl Bubo bubo (Linnaeus, 1758) is Spain 37°45′ N, 0°57′ W; hereafter Murcia), which includes socially monogamous, long-lived (>15 years in the field a special protection area (SPA) ‘Monte El Valle y Sierras de and >60 years in captivity; Penteriani et al. 2010), non- Altaona y Escalona’ (ES0000269; León-Ortega et al. 2014); migratory and territorial, life history traits that would pre- and (ii) the Sierra Norte of Seville (Sierra Morena massif, dict high adult survival rates. Previous research suggests south-western Spain; 37°30′ N, 06°03′ W; hereafter Seville), that Eurasian eagle owls may experience high mortality a hilly area 60–200 m a.s.l. (Penteriani et al. 2005). by electrocution and direct persecution from humans Both study areas share a Mediterranean climate and have (Marchesi et al. 2002;Sergioetal.2004;Martínezetal. high densities of rabbits and Eurasian eagle owl pairs (ca. 40 2006;Rubolinietal.2001), and two studies suggest that territories per 100 km2 over the whole study area; Penteriani survival rates increase with age (Olsson 1997;Schaub et al. 2010; León-Ortega et al. 2014). The landscape in Murcia et al. 2010), although other possible factors such as sex is a mosaic of forest of Aleppo Pines Pinus halepensis,scrub- were not taken into account. lands, irrigated and rainfed crops, hunting enclosures and Survival is frequently estimated using capture-mark- urbanised areas. In contrast, the Seville landscape is dominat- recapture techniques based on recaptures and/or recoveries ed by sparse woodlands composed of Holm Oaks Quercus of birds ringed with metal or coloured rings, or a combination ilex, Gall Oaks Quercus faginea, Stone Pine Pinus pinea, of both (Lebreton et al. 1992), or by radio-tracking (Kenward Olive Trees Olea europaea, Mastic Tree Pistacea lentiscus 2001). These methods have been widely used in population and small plantations of Eucalyptus sideroxylon. In many monitoring studies, which determine general demographic pa- areas, scrubland has replaced woodland. Most of the area is rameters in wildlife, such as immigration, emigration, survival managed for game species (mainly partridges and rabbits). and population size (Altwegg et al. 2003,Newtonetal.2016). In particular, the use of radio telemetry represents an ideal Trapping and radio-tracking method for survival studies, as it provides unbiased results for relatively long periods of an individual’slife(Smithetal. Owls were trapped using two methods: (i) simulation of a 2010;Thorupetal.2013,Newtonetal.2016). territorial intrusion using a combination of a taxidermy mount In this paper, we aim to assess the factors associated with of an Eurasian eagle owl and a mist-net to capture the territo- variation in survival and attempt to identify the causes of death rial bird when it responds to the simulated intruder (Penteriani in two Spanish populations of the Eurasian eagle owl, using et al. 2007); (ii) placement of a bow-net in the nest when radio-tracking methods and known-fate survival models. The nestlings were 20–35 days old (i.e. when they were already two populations studied are located in areas characterised by able to thermoregulate; Campioni et al. 2013)sothatadults the high availability of rabbits Oryctolagus cuniculus (the could be captured when they returned to care for chicks at the main prey of the Eurasian eagle owl; Penteriani et al.
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