Bias in little owl population estimates using playback techniques during surveys

Problemas en las estimas poblacionales de mochuelos cuando se realizan censos con reclamos Se desarrollaron dos estudios diferentes para probar la eficiencia de los censos por medio de reclamos de mochuelos (Athene noctua): (1) un seguimiento intensivo de las respuestas a los reclamos de mochuelos radio–marcados en una pequeña área, (2) un estudio extensivo utilizando reclamos para estimar la eficiencia del método como herramienta para detectar la presencia de mochuelos. En el primer caso, se detectaron 8,12 mochuelos de media en un periodo de censo de 30′, número cercano al tamaño de población real; además, se detectaron esplazamientos significativos de los mochuelos desde la posición inicial (antes de conectar el reclamo) a las posiciones siguientes durante la ejecución del reclamo. Sin embargo, tan sólo se detectó una media de 2,25 y 5,37 mochuelos en los primeros 5′ y 10′ respectivamente. En el segundo caso, se detectaron 137 territorios de mochuelos en 105 unidades de muestreo positivas. La tasa de ocupación fue de 0,35, la ocupación estimada de 0,393 y la probabilidad de detección de 0,439. La probabilidad acumulada estimada de detección sugiere que se precisarían de al menos cuatro muestreos en un estudio extensivo si se pretende detectar el 95% de las áreas ocupadas por mochuelos. Palabras clave: Mochuelo común, Métodos de censo, Programa Presence, Eficacia de detección, Actividad vocal.To test the efficiency of playback methods to survey little owl (Athene noctua) populations we carried out two studies: (1) we recorded the replies of radio–tagged little owls to calls in a small area; (2) we recorded call broadcasts to estimate the effectiveness of the method to detect the presence of little owl. In the first study, we detected an average of 8.12 owls in the 30' survey period, a number that is close to the real population; we also detected significant little owl movements from the initial location (before the playback) to the next locations during the survey eriod. However, we only detected an average of 2.25 and 5.37 little owls in the first 5' and 10', respectively, of the survey time. In the second study, we detected 137 little owl territories in 105 positive sample units. The occupation rate was 0.35, the estimated occupancy was 0.393, and the probability of detection was 0.439. The estimated cumulative probability of detection suggests that a minimum of four sampling times would be needed in an extensive survey to detect 95% of the areas occupied by little owls. Key words: Little owl, Survey methods, Presence Program, Detection efficiency, Vocal activity.Problemas en las estimas poblacionales de mochuelos cuando se realizan censos con reclamos Se desarrollaron dos estudios diferentes para probar la eficiencia de los censos por medio de reclamos de mochuelos (Athene noctua): (1) un seguimiento intensivo de las respuestas a los reclamos de mochuelos radio–marcados en una pequeña área, (2) un estudio extensivo utilizando reclamos para estimar la eficiencia del método como herramienta para detectar la presencia de mochuelos. En el primer caso, se detectaron 8,12 mochuelos de media en un periodo de censo de 30′, número cercano al tamaño de población real; además, se detectaron esplazamientos significativos de los mochuelos desde la posición inicial (antes de conectar el reclamo) a las posiciones siguientes durante la ejecución del reclamo. Sin embargo, tan sólo se detectó una media de 2,25 y 5,37 mochuelos en los primeros 5′ y 10′ respectivamente. En el segundo caso, se detectaron 137 territorios de mochuelos en 105 unidades de muestreo positivas. La tasa de ocupación fue de 0,35, la ocupación estimada de 0,393 y la probabilidad de detección de 0,439. La probabilidad acumulada estimada de detección sugiere que se precisarían de al menos cuatro muestreos en un estudio extensivo si se pretende detectar el 95% de las áreas ocupadas por mochuelos. Palabras clave: Mochuelo común, Métodos de censo, Programa Presence, Eficacia de detección, Actividad vocal

Magnetism in Atomic-Sized Palladium Contacts and Nanowires

We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monoatomic wires, we find a spin moment of 0.7 Bohr magnetons per atom, whereas for short, monoatomic wires between bulk leads, the predicted moment is about 0.3 Bohr magnetons per wire atom. In contrast, a coaxial (6,1) wire was found to be nonmagnetic. The origin of the wire magnetism is analyzed.Comment: 6 pages, including 4 figure

Target Geometry Dependence of Electron Energy Loss Spectra in Scanning Transmission Electron Microscopy (STEM)

In the frame of the Self-Energy formalism, we study the interaction between STEM electrons and small particles in the range of the valence electron excitations. We first calculate the energy loss probability for an isolated sphere and study the loss spectrum dependence on the size of the particle and on the relative impact parameter. Then we analyze the loss spectra in more realistic situations: (a) the effect of the coupling between the particle and supporting surface is studied in a simple geometrical model; and (b) we analyze the dependence of the losses on the geometrical shape of the target by considering hemispherical particle. Our results are in a good qualitative (and in simple cases, quantitative too) agreement with several experimental results which show anomalous excitations. We restate the suitability of the dielectric theory to study the surface excitations of these systems

Numerical study of bound states for point charges shielded by the response of a homogeneous two-dimensional electron gas

We study numerically the existence and character of bound states for positive and negative point charges shielded by the response of a two-dimensional homogeneous electron gas. The problem is related to many physical situations and has recently arisen in experiments on impurities on metal surfaces with Shockley surface states. Mathematical theorems ascertain a bound state for two-dimensional circularly symmetric potentials V(r) with ∫∞0drrV(r)⩽0. We find that a shielded potential with ∫∞0drrV(r)>0 may also sustain a bound state. Moreover, on the same footing we study the electron-electron interactions in the two-dimensional electron gas, finding a bound state with an energy minimum for a certain electron gas density.Peer reviewe

Shell and supershell structures of nanowires: A quantum-mechanical analysis

The stability of sodium nanowires is studied by modeling them as infinite uniform jellium cylinders and solving self-consistently for the electronic structure. The total energy per unit length oscillates as a function of the wire radius giving a shell structure. The amplitude of the energy oscillations attenuates regularly, reflecting a supershell structure. We compare our theoretical results with recent experiments [A. I. Yanson et al., Nature 400, 144 (1999); Phys. Rev. Lett. 84, 5832 (2000)] performed by the mechanically controllable break junctions (MCB) technique. The comparison clarifies the origin of the observed shell structure and especially the formation of the quantum beats of the supershell structure and supports the conclusions based on an earlier semiclassical model. The comparison is also a quantitative test for the reliability of the simple stabilized-jellium model as well as for the accuracy of the equation used to relate the conductivity and the area of the narrowest point of the constriction.Peer reviewe

Spontaneous Magnetization of Simple Metal Nanowires

On the basis of self-consistent density-functional calculations, it is predicted that three-dimensional nanowires of simple (nonmagnetic) metals undergo a transition to a spin-polarized magnetic state at critical radii. The magnetic transition also contributes to the elongation force on the nanowire. The force exhibits oscillations due to quantum confinement, in tune with the conductance steps as the wire is pulled.Peer reviewe

Electronic structure of cylindrical simple-metal nanowires in the stabilized jellium model

The ground-state electronic structures of cylindrical quantum wires are studied within the stabilized jellium model and using the spin-dependent density-functional theory. The subband structure is shown to affect the cohesive properties, causing an oscillating structure in the force needed to elongate the wire. Because the steps in the quantized conductance reflect also the subband structure a correlation between the force oscillations and conductance steps is established. The model also predicts magnetic solutions commensurate with the subband structure and consequently additional steps in the conductance.Peer reviewe