Ingo Hahn

Habitat selection and population trends in terrestrial bird species of Robinson Crusoe Island: habitat generalists versus forest specialists

Habitat loss and degradation on oceanic islands are key processes leading to population decline of endemic birds and facilitating the establishment of invasive bird species. In this study, carried out in the Robinson Crusoe Island, we assessed density and habitat selection of terrestrial bird species, including juan fernandez firecrown and juan fernandez tit-tyrant, two endemics, as well as green-backed firecrown and austral thrush, which apparently originate from the mainland. Results show that perturbed habitats contained a low density of the endemic species whereas the mainland species were significantly more abundant in perturbed scrub habitats. Bird species show different habitat selection patterns, with endemics selecting for native forest and mainland species selecting for perturbed habitats, or using them at random. Bird species experienced temporal trends in their overall population sizes, with the endemic tit-tyrant suffering a significant decline in its population size of about 63% between 1994 and 2009. Only mainland species exhibited temporal changes in habitat use, significantly reducing their densities in the preferred scrub habitats, possibly as a response to decreased habitat quality. Thrushes apparently were able to compensate the population decrease in one non native habitat type by using native forests, a habitat giving them the opportunity of preying on nests of endemic species. We conclude that endemic bird species behave as specialists whereas the mainland species must be treated as invasive generalists on Robinson Crusoe Island.

Matrix composition and corridor function for austral thrushes in a fragmented temperate forest

Although it is widely recognized that animal movement may be facilitated by corridors and hindered by the matrix, the influence of matrix composition on the use of corridors still remain poorly understood. We used translocation experiments and state-space models to assess if the movement response of the frugivorous bird, the austral thrush, to riparian forest strips varies depending on matrix composition (open pasture vs. eucalyptus plantation). In agricultural landscapes, the directions displayed by most birds when moving in the open pasture matrix were consistent with an edge-following behavior. Riparian strips also functioned as passive drift fences in agricultural landscapes, with strips being used as conduits for movements once birds entered into a riparian strip. Our results suggest that visual perception of riparian strips by birds is hampered by the complex habitat structure in the eucalyptus matrix and that the use of riparian strips as habitat is conditioned by the surrounding matrix.

The importance of forest patch networks for the conservation of the Thorn-tailed Rayaditos in central Chile

Conservation of forest birds in fragmented landscapes requires not only determining the critical patch characteristics influencing local population persistence but also identifying patch networks providing connectivity and suitable habitat conditions necessary to ensure regional persistence. In this study, we assessed the importance of patch attributes, patch connectivity, and network components (i.e., groups of interconnected patches) in explaining the occupancy pattern of the Thorn-tailed Rayadito (Aphrastura spinicauda), a forest bird species of central Chile. Using a daily movement threshold distance, we identified a total of 16 network components of sclerophyllous forest within the study area. Among those components, patch area and vegetation structure-composition were important predictors of patch occupancy. However, the inclusion of patch connectivity and component size (i.e., the area of a network component) into the models greatly increases the models’ accuracy and parsimony. Using the best-fitted model, a total of 33 patches were predicted to be occupied by rayaditos within the study area, but such occupied patches were distributed in only six network components. These results suggest that persistence of rayaditos in central Chile requires the maintenance of large single patches and patch networks providing habitat and connectivity.

Los castores mejoran la calidad del hábitat para el pájaro carpintero magallánico

SUMMARY The effect of the disturbances caused by the American beaver (Castor canadensis), introduced to the Cape Horn Biosphere Reserve, on species of birds that are forest habitat specialists is poorly understood. Using telemetry data, we determined which attributes of abandoned beaver meadows have a strong impact on habitat selection by the Magellanic woodpecker (Campephilus magellanicus). We detected a positive relationship between the woodpecker habitat use and the fraction of old-growth forest located near these meadows. These results suggest that favorable habitat conditions are generated around small meadows with old-growth forest, because they might increase availability of wood-boring larvae.

Importance of nest attributes in the conservation of endemic birds of the Juan Fernández Archipelago, Chile.

Summary Understanding the particular nesting ecology of island endemic species represents the first step in identifying suitable micro-habitats and establishing efficient management programmes. This could become even more important when island bird assemblages are prone to invasion by ecologically similar species that may eventually cause niche compression or the extirpation of species already present on the island. In this study we describe the nesting ecology of both native and introduced landbird species of the Juan Fernandez Islands and determine the extent to which native species could be negatively affected by alien competitors. A total of 119 nests belonging to the 11 resident landbird species were analysed. Landbirds exhibited a wide range of nesting habitat preferences on the different islands, covering different vegetation types, altitudes and ecosystems. By means of a cluster analysis we determined that competition between alien and endemic species apparently does not represent an important factor affecting resource use by endemic birds. Endemic landbirds preferred sites comparatively higher above the ground, with a greater slope and a larger level of shelter, than alien species. The introduced hummingbird, the Green-backed Firecrown Sephanoides sephaniodes, had different nesting preferences to the endemic Juan Fernandez Firecrown S. fernandensis, whereas the House Sparrow Passer domesticus selected nest sites located in populated areas, suggesting that both alien species may not be competing with endemic passerines for nest sites. However, urgent measures are necessary to reduce the potential predation risk on Juan Fernandez Firecrown nests by the alien Austral Thrush Turdus falcklandii.

VOCALISATIONS OF THE MÁSAFUERA RAYADITO APHRASTURA MASAFUERAE ON ISLA ALEJANDRO SELKIRK, CHILE

ABSTRACT Three vocalisation types of the másafuera rayadito Aphrastura masafuerae are described using sonograms: common call, alarm call, and song. They are analysed according to their structure, kHz-frequency, duration and time of day. The common call can be uttered singly or in a series with regular pauses. This intensive call is heard even through fog and wind and seems to be used for contacting the partner as well as signalling the home range to neighbours. The alarm call is a continuous series of similar syllables without pauses. The song is given exclusively in the morning before sunrise by only one individual of the pair. It has one type of phrase only, which is repeated. Phrases are interrupted by regular pauses. These vocalisation types are clearly different from each other, but also have features in common: the monotonous structure, repetition of units and temporal frequency of elements.

Primera descripción del patrón de selección de micro-hábitat del Cachudito de Juan Fernández

Para las aves que son endemicas de islas oceanicas el nivel de especializacion en el uso del habitat puede ser un factor importante de considerar en el incremento del riesgo de extincion de estas especies. En este estudio, usamos datos de redes de niebla y radiotelemetria para determinar el patron de uso de micro-habitat por el Cachudito de Juan Fernandez (Anairetes fernandezianus), una especie de ave endemica del archipielago de Juan Fernandez (Chile). El individuo seguido por radiotelemetria establecio su ambito de hogar exclusivamente en areas centrales del bosque nativo residual. Los modelos regresivos de abundancia y las Funciones de Utilizacion de Recursos mostraron fuertes preferencias de micro-habitat por los cachuditos. Los valores de abundancia y utilizacion de recurso por los cachuditos decrecieron con la distancia al matorral exotico y aumentaron con la distancia a los claros hechos por humanos dentro bosque. La heterogeneidad natural en las condiciones del micro-habitat tambien afectan el patron de seleccion de micro-habitat, con probabilidades de uso y abundancia aumentando en las proximidades de lugares humedos dominados por Gunnera peltata. Estos hallazgos demuestran que los cachuditos no usan el bosque nativo al azar. Por lo tanto, la conservacion de esta poblacion de cachuditos, que ha experimentado una fuerte declinacion en las ultimas decadas, puede ser mejorada incorporando estas preferencias de micro-habitat en los programas de manejo.

First description of nesting ecology of the endemic Grey-flanked Cinclodes Cinclodes oustaleti baeckstroemii from the Juan Fernández Islands, Chile

Abstract. The habitat and nest sites of an island-endemic, the Másafuera Grey-flanked Cinclodes, are described for the first time. The species breeds only in natural cavities in steep rock-walls and rocky slopes or ridges. The nest entrance diameter ranges from 5.5 to 20 cm, the nest chamber being placed within the rock so as to be invisible from the outside. The nest sites found — solely on Alejandro Selkirk Island — were located from a little above the sea-level to the summit region, the preferred habitats being barren canyon bottoms with small streams, and humid alpine plateaus. Nesting extends from early December to late January, indicating a core breeding season from November to January. Fledgling numbers per clutch average about two.