Hen Harrier Circus cyaneus population trends in relation to wind farms

Capsule: The data presented here demonstrate a considerable spatial overlap between wind farms and the breeding distribution of Hen Harriers in Ireland, but evidence for a negative impact of wind farms on their population is weak. Aims: To assess the extent of the overlap between wind farms and breeding Hen Harriers and to investigate their potential impact on Hen Harrier population trends. Methods: Data on Hen Harrier breeding distribution in 10 km × 10 km survey squares from national surveys were used in conjunction with information on the location of wind farms to examine whether, and to what extent, changes in Hen Harrier distribution and abundance between 2000 and 2010 were related to wind energy development. Results: Of the 69 survey squares holding Hen Harriers during the 2010 breeding season, 28% also overlapped with one or more wind farms. Data from 36 of the squares with breeding Hen Harriers during the 2000 survey revealed a marginally non-significant negative relationship between wind farm presence and change in the number of breeding pairs between 2000 and 2010. Conclusions: A considerable overlap exists between Hen Harrier breeding distribution and the location of wind farms in Ireland, particularly in areas between 200 and 400 m above sea level. The presence of wind farms is negatively related to Hen Harrier population trends in squares surveyed in 2000 and 2010, but this relationship is not statistically significant, and may not be causal. This is the first study to assess the influence of wind energy development on Hen Harriers at such a large geographic and population scale

Density-dependent productivity in a colonial vulture at two spatial scales

. Understanding how density dependence modifies demographic parameters in long-lived vertebrates is a challenge for ecologists. Two alternative hypotheses have been used to explain the mechanisms behind density-dependent effects on breeding output: habitat heterogeneity and individual adjustment (also known as interference competition). A number of studies have highlighted the importance of habitat heterogeneity in density dependence in territorial species, but less information exists on demographic processes in colonial species. For these, we expect density-dependent mechanisms to operate at two spatial scales: colony and breeding unit. In this study, we used long-term data from a recovering population of Cinereous Vultures (Aegypius monachus) in southern Spain. We analyzed a long-term data set with information on 2162 breeding attempts at four colonies over a nine-year period (2002–2010) to evaluate environmental and population parameters influencing breeding output. Our results suggest that breeding productivity is subject to density-dependent processes at the colony and the nest site scale and is best explained by interference competition. Factors intrinsic to each colony, as well as environmental constraints linked to physiography and human presence, also play a role in regulatory processes. We detected the existence of a trade-off between the disadvantages of nesting too close to conspecifics and the benefits of coloniality. These could be mediated by the agonistic interactions between breeding pairs and the benefits derived from social sharing of information by breeding individuals. We propose that this trade-off may play a role in defining colony structure and may hold true for other colonial breeding bird species. Our findings also have important management implications for the conservation of this threatened species.Peer reviewe

Evidencia en video de fratricidio y canibalismo, movimiento de polluelos e interacciones con depredadores en nidos de Circus cyaneus

During a nest-camera study of Hen Harriers (Circus cyaneus), we recorded siblicide, cannibalism, movement of nestlings by adult birds, and interactions with predators. We deployed cameras at 13 nests across three study areas in Ireland between 2008 and 2010. At a nest with two well-developed nestlings (approximately 25–30 d old), the older nestling killed its sibling and fed on it. This was the first documented case of siblicide in this species, to our knowledge. Recordings also revealed three other events of cannibalism in which one of the nestlings in a brood died from unknown causes and was then eaten by its siblings (n = 1), by the adult male (n = 1), or was used by the adult female to feed the remaining nestlings (n = 1). At two nests, recordings showed the adult female picking up and moving nestlings that were outside the nest cup. In addition, cameras recorded two instances of full brood predation by red fox (Vulpes vulpes) and an attack on a nest by a female Eurasian Kestrel (Falco tinnunculus) that had no apparent consequences for the nestlings or the female Hen Harrier. The behaviors reported here, which are difficult to observe directly, may have important consequences for our understanding of productivity and population dynamics of Hen Harriers.Durante un estudio sobre patrones de actividad de individuos reproductores de Circus cyaneus realizado con cámaras para monitoreo de nidos, registramos comportamientos de fratricidio, canibalismo, movimientos de polluelos e interacciones con depredadores. Colocamos cámaras en 13 nidos distribuidos en tres áreas de estudio en Irlanda entre 2008 y 2010. En un nido con dos polluelos en un estado de desarrollo avanzado (c. 25-30 días), el polluelo de mayor edad mató al otro y se alimentó de él. Este es el primer caso documentado de fratricidio en esta especie. Obtuvimos imágenes de otros tres casos de canibalismo en que uno o más polluelos fallecieron por causas desconocidas y sus cadáveres fueron usados como alimento por los otros polluelos (n = 1), por el macho adulto (n = 1) o por la hembra adulta para alimentar a los otros polluelos (n = 1). En dos nidos, las imágenes muestran a la hembra adulta repetidamente recogiendo polluelos que se alejan del nido para intentar llevarlos al nido. Por último, las cámaras captaron dos eventos de depredación de polluelos por parte de Vulpes vulpes y un enfrentamiento entre la hembra adulta de C. cyaneus y una hembra de Falco tinnunculus sin consecuencias para los polluelos o la hembra adulta. Estos comportamientos, difíciles de detectar mediante metodologías de monitoreo tradicionales, pueden tener consecuencias para el éxito reproductivo y la dinámica poblacional de esta especie

Effects of development of wind energy and associated changes in land use on bird densities in upland areas

Wind energy development is the most recent of many pressures on upland bird communities and their habitats. Studies of birds in relation to wind energy development have focused on effects of direct mortality, but the importance of indirect effects (e.g., displacement, habitat loss) on avian community diversity and stability is increasingly being recognized. We used a control‐impact study in combination with a gradient design to assess the effects of wind farms on upland bird densities and on bird species grouped by habitat association (forest and open‐habitat species). We conducted 506 point count surveys at 12 wind‐farm and 12 control sites in Ireland during 2 breeding seasons (2012 and 2013). Total bird densities were lower at wind farms than at control sites, and the greatest differences occurred close to turbines. Densities of forest species were significantly lower within 100 m of turbines than at greater distances, and this difference was mediated by habitat modifications associated with wind‐farm development. In particular, reductions in forest cover adjacent to turbines was linked to the observed decrease in densities of forest species. Open‐habitat species’ densities were lower at wind farms but were not related to distance from turbines and were negatively related to size of the wind farm. This suggests that, for these species, wind‐farm effects may occur at a landscape scale. Our findings indicate that the scale and intensity of the displacement effects of wind farms on upland birds depends on bird species’ habitat associations and that the observed effects are mediated by changes in land use associated with wind‐farm construction. This highlights the importance of construction effects and siting of turbines, tracks, and other infrastructure in understanding the impacts of wind farms on biodiversity

Responses to global change in a river passerine

Human-induced environmental change is affecting biodiversity across the world. River systems and species associated with these habtitats are particularly vulnerable to the different drivers of global change (e.g. land use, climate change, pollution). Understanding how species respond to these drivers is key for any attempts to address and minimise the effects of global change. In this thesis I focus on a river passerine, the white-throated dipper Cinclus cinclus, as a model to assess the effects of two of the main drivers affecting river ecosystems (land use and climate change) on different ecological traits across multiple scales and life stages. Breeding phenology (Chapter 2) was influenced by climate and land use at different scales, but the interactive effect of climate and land use was significant only at local scales. Lay dates were advanced for nests in areas dominated by farmland and under conditions of increased rainfall and warmer temperatures. Land use also affected stress hormones in developing nestlings (Chapter 3): higher forest cover in the riparian area was linked to lower nestling stress hormone levels but had no apparent effect on morphological traits traditionally associated with nestling development. This land use signal on stress hormones however, was no longer evident in later life (Chapter 4), when stress hormone variation had a strong year component, likely due to weather patterns. Climate also appeared to be associated with long-term morphological change (Chapter 5). Female and male dippers experienced a relative shortening of the wing in relation to body size, reducing dimorphism between the sexes during a period concurrent with increased magnitude and fluctuations in river flow conditions. Overall, these findings suggest that dippers are adjusting their phenology, physiology and morphology in response to global change. However, adjustments in one trait may have adverse consequences for other traits. This thesis highlights the value of using multiple approaches to understand how species respond to global change, and the importance of considering multiple drivers of environmental change

Density-Dependent Productivity in a Colonial Vulture at Two Spatial Scales

. Understanding how density dependence modifies demographic parameters in long-lived vertebrates is a challenge for ecologists. Two alternative hypotheses have been used to explain the mechanisms behind density-dependent effects on breeding output: habitat heterogeneity and individual adjustment (also known as interference competition). A number of studies have highlighted the importance of habitat heterogeneity in density dependence in territorial species, but less information exists on demographic processes in colonial species. For these, we expect density-dependent mechanisms to operate at two spatial scales: colony and breeding unit. In this study, we used long-term data from a recovering population of Cinereous Vultures (Aegypius monachus) in southern Spain. We analyzed a long-term data set with information on 2162 breeding attempts at four colonies over a nine-year period (2002–2010) to evaluate environmental and population parameters influencing breeding output. Our results suggest that breeding productivity is subject to density-dependent processes at the colony and the nest site scale and is best explained by interference competition. Factors intrinsic to each colony, as well as environmental constraints linked to physiography and human presence, also play a role in regulatory processes. We detected the existence of a trade-off between the disadvantages of nesting too close to conspecifics and the benefits of coloniality. These could be mediated by the agonistic interactions between breeding pairs and the benefits derived from social sharing of information by breeding individuals. We propose that this trade-off may play a role in defining colony structure and may hold true for other colonial breeding bird species. Our findings also have important management implications for the conservation of this threatened species.Peer reviewe

Activity patterns of breeding Hen Harriers <i>Circus cyaneus</i> assessed using nest cameras

<p>Nest camera footage from 13 Hen Harrier <i>Circus cyaneus</i> nests was analysed to document patterns of adult attendance, incubation, brooding and prey delivery rates. Nest attendance was high throughout the incubation stage and began to decrease when chicks were five days old. Chick provisioning increased gradually after hatching and peaked when the chicks were five days old. Daily activity rates were highest during the middle of the day, from 08:00 to 19:00 hours.</p