Bias in density estimations using strip transects in dry open-country environments in the Canary Islands

We studied bias in density estimations derived from strip transects in dry open-country in the Canary Islands. We also present some critical remarks on García-del-Rey’s (2005) paper regarding strip transects and the validity of comparisons based on population densities of birds in scrublands on Tenerife island using two different methods: territory mapping and strip transect sampling. Although strip transects with census belts of 25 m do not account for detectability, this method only slightly undervalues true density estimates, and allowed to detect more than 85% of birds present in poorly vegetated environments in the Canary Islands. Previously published works on distribution and abundance of terrestrial birds in the Canary Islands using the strip transect sampling with belts of 25 m on both sides of the observer, thus provide reliable information that only slightly underestimates true densities

Teoría y praxis de modelos generalizados: infiriendo patrones con el paquete estadístico R

Curso de la Sociedad de Amigos del Museo Nacional de Ciencias Naturales - CSICEjemplo de análisis con variables predictoras muy relacionadasEjemplo de análisis con una variable respuesta con elevada carga de cerosEjemplo de análisis con variables predictoras muy relacionadas: -Partial Least Squares (PLS) regression analysis -Similitudes y diferencias con modelos de regresión lineales -Soluciones robustas mediante el uso de bootstrapping -PLS con los paquetes “plsdepot” y “plsRglm”.-- Ejemplo de análisis con una variable respuesta con elevada carga de ceros: -Modelo Generalizado Lineal con una respuesta Binomial Negativa -Modelo Generalizado Lineal “Hurdle” asumiendo inflado de ceros -Modelo Generalizado Lineal Logístico, con una respuesta Binomial estimada como frecuencia -Modelo Generalizado Aditivo con una respuesta Binomial estimada como frecuencia -Revisión de los supuestos canónicos de los modelos -Estimas robustas de los parámetros y significación del modelo -Estimas frecuentistas y multimodelo basadas en la Teoría de la Información -Visualización de los efectos parciales de las predictoras sobre la respuesta -Modelos nulos para estima de significaciónN

Curso práctico de estadística exploratoria. Patrones naturales obtenidos mediante regresión.

Peer Reviewe

Variación geográfica de la riqueza de especies invernantes en la península Ibérica. Estacionalidad y determinismo ambiental.

Peer Reviewe

Occurrence data may provide unreliable thermal preferences and breadth of species

Accurate information on the thermal preference and specialization of species is needed to understand and predict species geographical range size and vulnerability to climate change. Here we estimate the position and breadth of species within thermal gradients based on the shape of the response curve of species abundance to temperature. The objective of the study is to compare the measurements of this approach based on abundance data with those of the classical approach using species’ occurrence data. The relationship between species’ relative abundance and minimum winter temperature of 106 bird species wintering in the Iberian Peninsula is modeled at 100 Km2 resolution with quadratic logistic regressions. From these models we calculated the preferred temperature of species as the temperature at which the abundance is maximized, and the thermal breadth of species as the relative area under the temperature-abundance curve. We also estimated the thermal preferences and breadth of species as the average temperature and temperature range of the UTM cells in which the species are present. The abundance-temperature response curves reveal that birds prefer higher temperatures to overwinter, and are more thermally selective, than is measured by the classical approach. Moreover, response curves detect a higher inter-specific variability in both thermal preferences and thermal breadth of species. As occurrence data gives the same weight to cells with one or many individuals, the average temperature of the cells in which the species is present roughly reflects the average temperature in the region of study and not the environmental preferences of species.This paper is a contribution to projects CGL2008-02211/BOS and CGL2011-28177/BOS of the Spanish Ministry of Education and Science.Peer reviewe

Relaciones entre avifauna y estructura de la vegetación en el País Vasco

Tesis Univ. Complutense de Madrid.Fac. de Ciencias BiológicasTRUEProQuestpu

Foraging patch selection in winter: A balance between predation risk and thermoregulation benefit

In winter, foraging activity is intended to optimize food search while minimizing both thermoregulation costs and predation risk. Here we quantify the relative importance of thermoregulation and predation in foraging patch selection of woodland birds wintering in a Mediterranean montane forest. Specifically, we account for thermoregulation benefits related to temperature, and predation risk associated with both illumination of the feeding patch and distance to the nearest refuge provided by vegetation. We measured the amount of time that 38 marked individual birds belonging to five small passerine species spent foraging at artificial feeders. Feeders were located in forest patches that vary in distance to protective cover and exposure to sun radiation; temperature and illumination were registered locally by data loggers. Our results support the influence of both thermoregulation benefits and predation costs on feeding patch choice. The influence of distance to refuge (negative relationship) was nearly three times higher than that of temperature (positive relationship) in determining total foraging time spent at a patch. Light intensity had a negligible and no significant effect. This pattern was generalizable among species and individuals within species, and highlights the preponderance of latent predation risk over thermoregulation benefits on foraging decisions of birds wintering in temperate Mediterranean forests. © 2013 Villén-Pérez et al.This paper was funded by project CGL2008-02211/BOS of the Spanish Ministry of Educación y Ciencia.Peer Reviewe

Local habitat and landscape influence high predation of bird nests on afforested Mediterranean cropland

Afforestation programs such as the one promoted by the EU Common Agrarian Policy have contributed to spread tree plantations on former cropland. Nevertheless these afforestations may cause severe damage to open habitat species, especially birds of high conservation value. We investigated predation of artificial bird nests at young tree plantations and at the open farmland habitat adjacent to the tree plantations in central Spain. Predation rates were very high at both tree plantations (95.6%) and open farmland habitat (94.2%) after two and three week exposure. Plantation edge/area ratio and development of the tree canopy decreased predation rates and plantation area and magpie (Pica pica) abundance increased predation rates within tree plantations, which were also affected by land use types around plantations. The area of nearby tree plantations (positive effect), distance to the tree plantation edge (negative effect), and habitat type (mainly attributable to the location of nests in vineyards) explained predation rates at open farmland habitat. We conclude that predation rates on artificial nests were particularly high and rapid at or nearby large plantations, with high numbers of magpies and low tree development, and located in homogenous landscapes dominated by herbaceous crops and pastures with no remnants of semi-natural woody vegetation. Landscape planning should not favour tree plantations as the ones studied here in Mediterranean agricultural areas that are highly valuable for ground-nesting bird species.Ministerio de Ciencia y EducaciónComunidad de Madri

Estornino negro – Sturnus unicolor Temminck, 1820

Aves - Orden Passeriformes - Familia Sturnidae en la Enciclopedia Virtual de Vertebrados Españoles, http://www.vertebradosibericos.org/. Versiones anteriores: 20-06-2003; 9-02-2007; 7-03-2008; 28-10-2011; 14-11-2011A comprehensive review of the natural history of the Spotless Starling Sturnus unicolor in Spain.Peer reviewe