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AIMS : The sub-Antarctic cushion plant, Azorella selago, is usually hemispherical when small but frequently crescent-shaped when larger. Spatial variation in wind speed and in air-borne seed and sediment deposition is examined to determine if wind scouring and deposition patterns could contribute to the development of nonhemispherical shapes in cushion plants. METHODS : Computational fluid dynamic analyses were conducted for hemispherical and crescent-shaped cushion plants parameterizing models with data from A. selago habitats on Marion Island. Numerical data were contextualized with field observations to arrive at a conceptual model for shape development. RESULTS : Airflow modelling showed that both wind scouring and seed deposition of the commonly cooccurring grass Agrostis magellanica are greater on the windward side of the plant. By contrast, heavier sediment particles are predominantly deposited on the leeward side of plants, leading to burial of lee-side A. selago stems. This sediment accumulation may initiate the development of the crescent-shape in hemispherical plants by increasing stem mortality on the plant’s leeward edge. Once developed, the crescent-shape is probably self-reinforcing because it generates greater air recirculation (and lower air velocities) which enhances further deposition and establishment of A. magellanica grasses in the lee of the crescent. The conceptual model consists therefore of three stages namely, (1) negligible air recirculation, (2) sediment deposition and grass establishment, and (3) differential cushion growth. CONCLUSION : This conceptual model of plant shape development may explain the occurrence and orientation of crescent-shaped cushion plants and highlights how predicted changes in wind patterns may affect vegetation patterns.

The use of miniaturized video cameras to study the at-sea behavior of flying seabirds has increased in recent years. These cameras allow researchers to record several behaviors that were not previously possible to observe. However, video recorders produce large amounts of data and videos can often be time-consuming to analyze. We present a new technique using open-source software to extract bank angles from bird-borne video footage. Bank angle is a key facet of dynamic soaring, which allows albatrosses and petrels to efficiendy search vast areas of ocean for food. Miniaturized video cameras were deployed on 28 Wandering Albatrosses (Diomedea exulans) on Marion Island (one of the two Prince Edward Islands) from 2016 to 2018. The OpenCV library for the Python programming language was used to extract the angle of the horizon relative to the bird's body (= bank angle) from footage when the birds were flying using a series of steps focused on edge detection. The extracted angles were not significantly different from angles measured manually by three independent observers, thus being a valid method to measure bank angles. Image quality, high wind speeds, and sunlight all influenced the accuracy of angle estimates, but post-processing eliminated most of these errors. Birds flew most often with cross-winds (58%) and tailwinds (39%), resulting in skewed distributions of bank angles when birds turned into the wind more often. Higher wind speeds resulted in extreme bank angles (maximum observed was 94°). We present a novel method for measuring postural data from seabirds that can be used to describe the fine-scale movements of the dynamic-soaring cycle. Birds appeared to alter their bank angle in response to varying wind conditions to counter wind drift associated with the prevailing westerly winds in the Southern Ocean. These data, in combination with fine-scale positional data, may lead to new insights into dynamic-soaring flight. El uso de cámaras de video en miniatura para estudiar el comportamiento en el mar de las aves marinas durante el vuelo ha aumentado en los últimos años. Estas cámaras permiten a los investigadores registrar varios comportamientos que antes no eran posible de observar. Sin embargo, las grabadoras de video producen grandes cantidades de datos y los videos a menudo pueden llevar mucho tiempo analizarlos. Presentamos una nueva técnica que utiliza software de código abierto para extraer los ángulos de inclinación de imágenes de videos. El ángulo de inclinación es una faceta clave para la dinámica de planeo, que permite a los albatros y petreles buscar alimentos en vastas áreas del océano. Las cámaras de video en miniatura se colocaron en 28 albatros errantes (Diomedea exulans) en la isla Marion (una de las dos islas del Príncipe Eduardo) entre 2016 y 2018. La biblioteca OpenCV para el lenguaje de programación Python se usó para extraer el ángulo del horizonte en relación con el cuerpo del ave (= ángulo de inclinación) del video cuando las aves volaban usando una serie de pasos centrados en la detección de bordes. Los ángulos extraídos no fueron significativamente diferentes de los ángulos medidos manualmente por tres observadores independientes, por lo que es un método válido para medir ángulos de banco. La calidad de la imagen, las altas velocidades del viento y la luz solar influyeron en la precisión de las estimaciones de ángulo, pero el procesamiento posterior eliminó la mayoría de estos errores. Las aves volaron con mayor frecuencia con vientos cruzados (58%) y vientos de cola (39%), lo que resulta en una distribución sesgada de los ángulos de las orillas cuando las aves giraron hacia el viento con más frecuencia. Las velocidades más altas del viento dieron como resultado ángulos extremos de inclinación (el máximo observado fue 94°). Presentamos un método novedoso para medir datos de posturas de aves marinas que se pueden usar para describir los movimientos a escala fina del ciclo dinámico del vuelo de planeo. Las aves parecen alterar su ángulo de inclinación en respuesta a las condiciones variables del viento para contrarrestar la deriva del viento asociada con los vientos predominantes del oeste en el Océano Austral. Estos datos, en combinación con datos posicionales a escala fina, pueden conducir a nuevas ideas sobre el vuelo de planeo dinámico.

House mice (Mus musculus L.) were introduced to sub-Antarctic Marion Island more than two centuries ago, and have been the only introduced mammal on the island since 1991 when feral cats were eradicated. The first mouse-injured wandering albatross (Diomedea exulans L.) chick was found in 2003 and since then attacks have continued at a low level affecting <1% of the population. In 2009, the first ‘scalpings’ were detected; sooty albatross (Phoebetria fusca Hilsenberg) fledglings were found with raw wounds on the nape. In 2015, mice attacked large chicks of all three albatross species that fledge in autumn: grey-headed (Thalassarche chrysostoma Forster) (at least 102 wounded chicks; 4.6% of fledglings), sooty (n=45, 4.3%) and light-mantled albatross (P. palpebrata Forster) (n=1, 4%). Filming at night confirmed that mice were responsible for wounds. Attacks started independently in small pockets all around the island’s 70 km coastline, separated by distances hundreds of times greater than mouse home ranges. The widespread nature of mouse attacks in 2015 on large, well-feathered chicks is alarming and highlights not only Marion Island as a priority island for mouse eradication but also that mice alone may significantly affect threatened seabird species.

We report the breeding success of four species of burrow-nesting petrels at sub-Antarctic Marion Island where house mice Mus musculus are the sole introduced mammal. Feral cats Felis catus were present on Marion for four decades from 1949, killing millions of seabirds and greatly reducing petrel populations. Cats were eradicated by 1991, but petrel populations have shown only marginal recoveries. We hypothesize that mice are suppressing their recovery through depredation of petrel eggs and chicks. Breeding success for winter breeders (grey petrels Procellaria cinerea (34±21%) and great-winged petrels Pterodroma macroptera (52±7%)) were lower than for summer breeders (blue petrels Halobaena caerulea (61±6%) and white-chinned petrels Procellaria aequinoctialis (59±6%)) and among winter breeders most chick fatalities were of small chicks up to 14 days old. We assessed the extent of mouse predation by monitoring the inside of 55 burrow chambers with video surveillance cameras (4024 film days from 2012–16) and recorded fatal attacks on grey (3/18 nests filmed, 17%) and great-winged petrel chicks (1/19, 5%). Our results show that burrow-nesting petrels are at risk from mouse predation, providing further motivation for the eradication of mice from Marion Island.

Motivated by a case study of vegetation patterns, we introduce a mixture model with concomitant variables to examine the association between the orientation of vegetation stripes and wind direction. The proposal relies on a novel copula-based bivariate distribution for mixed axial and circular observations and provides a parsimonious and computationally tractable approach to examine the dependence of two environmental variables observed in a complex manifold. The findings suggest that dominant winds shape the orientation of vegetation stripes through a mechanism of neighbouring plants providing wind shelter to downwind individuals.