Estimación de los componentes de la varianza en los parámetros demográficos del cárabo común, Strix aluco

Survival rates of Tawny Owls (Strix aluco) were estimated using recapture and recovery data from approximately 20,000 nestling and adult owls ringed between 1980 and 1999 in southern Finland. Survival rates averaged 33% in the first year of life, 64% in the second, and 73% in subsequent years, but varied dramatically among years. Approximately 50% of annual variation in survival could be explained by stage of the vole cycle and severity of winter weather. Capture probabilities, an index of breeding propensity, varied dramatically among years, and could almost entirely be explained by the vole cycle, superimposed on a long–term increase in capture effort. Matrix models based on mean values in each year of the vole cycle, predict that in 2 out of 3 years, the population would decline by 13%–15% per year, offset by a large increase in the 3rd year. Numbers of nesting pairs are predicted to be low in one of three years, with no long–term trend, consistent with observed estimates of active nests.Se calcularon las tasas de supervivencia del cárabo común (Strix aluco) utilizando datos de recaptura y recuperación correspondientes a unos 20.000 cárabos comunes —entre polluelos y adultos—, anillados entre 1980 y 1999 en el sur de Finlandia. Las tasas de supervivencia alcanzaron un promedio del 33% en el primer año de vida, del 64% en el segundo y del 73% en los años subsiguientes, variando de forma espectacular entre los distintos años. Alrededor del 50% de la variación anual en la supervivencia pudo ser explicada por el estadio en que se encontraba el ciclo poblacional de los micrótidos y el rigor del clima invernal. Las probabilidades de captura —que representan un índice de la propensión a la reproducción—variaron considerablemente entre los distintos años, pudiendo explicarse en su práctica totalidad por el ciclo de los micrótidos, superpuesto a un aumento a largo plazo del esfuerzo de captura. Según los modelos matriciales basados en los valores promedio correspondientes a cada año del ciclo de los micrótidos, predicen que en dos de cada tres años la población disminuirá entre un 13% y un 15% anual, aunque ello se verá compensado por un considerable aumento durante el tercer año; asimismo, se calcula que el número de parejas nidificantes será bajo uno de cada tres años, sin ninguna tendencia a largo plazo, lo que concuerda con las estimaciones observadas acerca de los nidos activos

Estudio comparativo de la adecuación temporal y de las rutas migratorias mediante el empleo de hallazgos de anillas y métodos de randomización

A method for comparing two migration routes is introduced. In the method are needed approximations of the average daily positions which are computed based on averages of dates and of positions in a window sliding through the encounters ordered in ascending order by date. The method contains two tests. The first, global, test statistic compares the entire migration routes and is the average of the distances between the daily positions of the two routes to be compared. The second test is used to identify sections during migration where the routes may deviate and is based on consecutive averages of the distances of short time periods between the daily positions of the two routes. A randomization test is used to assess the statistical significance of the test statistics in both components. The methods are applied to artificial and real data. Examples of the use of the method are computed with data sets of ring recoveries of Common terns (Sterna hirundo) and Ospreys (Pandion haliaetus) ringed in Finland in 1930–2002.El trabajo presenta un método para comparar rutas migratorias. El método utiliza aproximaciones para el cálculo de las localizaciones medias diarias basadas en las fechas y localizaciones promedio, en una ventana que se va desplazando a lo largo de las distintas observaciones ordenadas en orden ascendente según fecha. El método incluye dos pruebas estadísticas. La primera compara de forma global todas las rutas migratorias, y lo que se compara es la media de las distancias entre las distintas posiciones diarias de las dos rutas. La segunda prueba permite identificar tramos durante la migración en los que las rutas se pueden desviar, y se basa en promedios consecutivos de las distancias de breves períodos de tiempo entre las posiciones diarias de las dos rutas. Se utiliza una prueba de randomización para evaluar la relevancia estadística de las pruebas en ambos componentes. Los métodos se aplican a datos artificiales y reales. Los ejemplos del empleo del método se calculan con conjuntos de datos de recuperaciones de anillas de charranes comunes (Sterna hirundo) y de águilas pescadoras (Pandion haliaetus) anillados en Finlandia entre 1930 y 2002

Estimating components of variance in demographic parameters of Tawny Owls, Strix aluco

Survival rates of Tawny Owls (Strix aluco) were estimated using recapture and recovery data from approximately 20,000 nestling and adult owls ringed between 1980 and 1999 in southern Finland. Survival rates averaged 33% in the first year of life, 64% in the second, and 73% in subsequent years, but varied dramatically among years. Approximately 50% of annual variation in survival could be explained by stage of the vole cycle and severity of winter weather. Capture probabilities, an index of breeding propensity, varied dramatically among years, and could almost entirely be explained by the vole cycle, superimposed on a long-term increase in capture effort. Matrix models based on mean values in each year of the vole cycle, predict that in 2 out of 3 years, the population would decline by 13%-15% per year, offset by a large increase in the 3rd year. Numbers of nesting pairs are predicted to be low in one of three years, with no long-term trend, consistent with observed estimates of active nests

Long-term trends in survival of a declining population: the case of the little owl (Athene noctua) in the Netherlands

The little owl (Athene noctua) has declined significantly in many parts of Europe, including the Netherlands. To understand the demographic mechanisms underlying their decline, we analysed all available Dutch little owl ringing data. The data set spanned 35 years, and included more than 24,000 ringed owls, allowing detailed estimation of survival rates through multi-state capture–recapture modelling taking dispersal into account. We investigated geographical and temporal variation in age-specific survival rates and linked annual survival estimates to population growth rate in corresponding years, as well as to environmental covariates. The best model for estimating survival assumed time effects on both juvenile and adult survival rates, with average annual survival estimated at 0.258 (SE = 0.047) and 0.753 (SE = 0.019), respectively. Juvenile survival rates decreased with time whereas adult survival rates fluctuated regularly among years, low survival occurring about every 4 years. Years when the population declined were associated with low juvenile survival. More than 60% of the variation in juvenile survival was explained by the increase in road traffic intensity or in average temperature in spring, but these correlations rather reflect a gradual decrease in juvenile survival coinciding with long-term global change than direct causal effects. Surprisingly, vole dynamics did not explain the cyclic dynamics of adult survival rate. Instead, dry and cold years led to low adult survival rates. Low juvenile survival rates, that limit recruitment of first-year breeders, and the regular occurrence of years with poor adult survival, were the most important determinants of the population decline of the little owl

Long-term trends in survival of a declining population: the case of the little owl (Athene noctua) in the Netherlands

The little owl (Athene noctua) has declined significantly in many parts of Europe, including the Netherlands. To understand the demographic mechanisms underlying their decline, we analysed all available Dutch little owl ringing data. The data set spanned 35 years, and included more than 24,000 ringed owls, allowing detailed estimation of survival rates through multi-state capture–recapture modelling taking dispersal into account. We investigated geographical and temporal variation in age-specific survival rates and linked annual survival estimates to population growth rate in corresponding years, as well as to environmental covariates. The best model for estimating survival assumed time effects on both juvenile and adult survival rates, with average annual survival estimated at 0.258 (SE = 0.047) and 0.753 (SE = 0.019), respectively. Juvenile survival rates decreased with time whereas adult survival rates fluctuated regularly among years, low survival occurring about every 4 years. Years when the population declined were associated with low juvenile survival. More than 60% of the variation in juvenile survival was explained by the increase in road traffic intensity or in average temperature in spring, but these correlations rather reflect a gradual decrease in juvenile survival coinciding with long-term global change than direct causal effects. Surprisingly, vole dynamics did not explain the cyclic dynamics of adult survival rate. Instead, dry and cold years led to low adult survival rates. Low juvenile survival rates, that limit recruitment of first-year breeders, and the regular occurrence of years with poor adult survival, were the most important determinants of the population decline of the little owl

Modelling the impact of toxic and disturbance stress on white-tailed eagle (Haliaeetus albicilla) populations

Several studies have related breeding success and survival of sea eagles to toxic or non-toxic stress separately. In the present investigation, we analysed single and combined impacts of both toxic and disturbance stress on populations of white-tailed eagle (Haliaeetus albicilla), using an analytical single-species model. Chemical and eco(toxico)logical data reported from laboratory and field studies were used to parameterise and validate the model. The model was applied to assess the impact of ∑PCB, DDE and disturbance stress on the white-tailed eagle population in The Netherlands. Disturbance stress was incorporated through a 1.6% reduction in survival and a 10–50% reduction in reproduction. ∑PCB contamination from 1950 up to 1987 was found to be too high to allow the return of white-tailed eagle as a breeding species in that period. ∑PCB and population trends simulated for 2006–2050 suggest that future population growth is still reduced. Disturbance stress resulted in a reduced population development. The combination of both toxic and disturbance stress varied from a slower population development to a catastrophical reduction in population size, where the main cause was attributed to the reduction in reproduction of 50%. Application of the model was restricted by the current lack of quantitative dose–response relationships between non-toxic stress and survival and reproduction. Nevertheless, the model provides a first step towards integrating and quantifying the impacts of multiple stressors on white-tailed eagle populations

Landscape homogenization due to agricultural intensification disrupts the relationship between reproductive success and main prey abundance in an avian predator

Selecting high-quality habitat and the optimal time to reproduce can increase individual fitness and is a strong evolutionary factor shaping animal populations. However, few studies have investigated the interplay between land cover heterogeneity, limitation in food resources, individual quality and spatial variation in fitness parameters. Here, we explore how individuals of different quality respond to possible mismatches between a cue for prey availability (land cover heterogeneity) and the actual fluctuating prey abundance.Peer reviewe

Habitat effects on the breeding performance of three forest-dwelling hawks

PLoS ONE 10(9): e0137877Habitat loss causes population declines, but the mechanisms are rarely known. In the European Boreal Zone, loss of old forest due to intensive forestry is suspected to cause declines in forest-dwelling raptors by reducing their breeding performance. We studied the boreal breeding habitat and habitat-associated breeding performance of the northern goshawk (Accipiter gentilis), common buzzard (Buteo buteo) and European honey buzzard (Pernis apivorus). We combined long-term Finnish bird-of-prey data with multi-source national forest inventory data at various distances (100–4000 m) around the hawk nests. We found that breeding success of the goshawk was best explained by the habitat within a 2000-m radius around the nests; breeding was more successful with increasing proportions of old spruce forest and water, and decreasing proportions of young thinning forest. None of the habitat variables affected significantly the breeding success of the common buzzard or the honey buzzard, or the brood size of any of the species. The amount of old spruce forest decreased both around goshawk and common buzzard nests and throughout southern Finland in 1992–2010. In contrast, the area of young forest increased in southern Finland but not around hawk nests. We emphasize the importance of studying habitats at several spatial and temporal scales to determine the relevant species-specific scale and to detect environmental changes. Further effort is needed to reconcile the socioeconomic and ecological functions of forests and habitat requirements of old forest specialists.Peer reviewe