Genetic similarity in long-eared owl communal winter roosts: a DNA fingerprinting study

The long-eared owl is a nocturnal predator which winters communally and breeds in the same areas in loose colonies during the spring. We tested the hypothesis that roosts, particularly stable roosts, are formed by close relatives, a condition under which group-related behaviours such as information sharing or helping at nest are more likely to be developed. DNA fingerprinting analysis was used to examine genetic similarity within and between two long-eared owl populations, one wintering in a traditional roost and the other in an unstable roost, and both breeding around their roosting sites. Although genetic similarity within roosts was higher than that between roosts, the difference was not significant. Observed genetic similarity within roosts was smaller than that reported in the bird species whose roosts work as information centres. On the other hand, the presence of some closely related individuals in the roost and behavioural observations suggest that co-operation between kin might have occurred, at least in one of the two study sites.     

Climate change and perishable food hoards of an avian predator: Is the freezer still working?

Changing climate can modify predator–prey interactions and induce declines or local extinctions of species due to reductions in food availability. Species hoarding perishable food for overwinter survival, like predators, are predicted to be particularly susceptible to increasing temperatures. We analysed the influence of autumn and winter weather, and abundance of main prey (voles), on the food‐hoarding behaviour of a generalist predator, the Eurasian pygmy owl (Glaucidium passerinum), across 16 years in Finland. Fewer freeze–thaw events in early autumn delayed the initiation of food hoarding. Pygmy owls consumed more hoarded food with more frequent freeze–thaw events and deeper snow cover in autumn and in winter, and lower precipitation in winter. In autumn, the rotting of food hoards increased with precipitation. Hoards already present in early autumn were much more likely to rot than the ones initiated in late autumn. Rotten food hoards were used more in years of low food abundance than in years of high food abundance. Having rotten food hoards in autumn resulted in a lower future recapture probability of female owls. These results indicate that pygmy owls might be partly able to adapt to climate change by delaying food hoarding, but changes in the snow cover, precipitation and frequency of freeze–thaw events might impair their foraging and ultimately decrease local overwinter survival. Long‐term trends and future predictions, therefore, suggest that impacts of climate change on wintering food‐hoarding species could be substantial, because their ‘freezers’ may no longer work properly. Altered usability and poorer quality of hoarded food may further modify the foraging needs of food‐hoarding predators and thus their overall predation pressure on prey species. This raises concerns about the impacts of climate change on boreal food webs, in which ecological interactions have evolved under cold winter conditions.     

Optimal barn characteristics for high-yielding Holstein cows as derived by a new heat-stress model

Meticulous planning is required to minimize heat-stress conditions in barns. The objective of this study was to determine optimum barn characteristics for high-yielding dairy cows under Israeli (Mediterranean) summer ambient conditions, by using a new stress model that takes ambient temperature, relative humidity and wind velocity into account. During the summers of 2004 and 2005, three meteorological stations were alternately installed in 39 barns: two stations inside the barn at the prevailing downwind direction, and a third station outside the upwind end of the barn. Ambient temperature, relative humidity, wind speed and direction were measured and recorded every 10 min for 3 to 5 consecutive days at each barn in turn. The data were collected at different geographical and climatic conditions. Therefore, the data collected by an outside station were used as covariates. A heat-stress model was used to determine the threshold temperature (THRT) at which a cow begins to increase its respiratory rate; THRT was the response variable in the statistical model. The THRT model takes in account assumed values of a cow's physiological characteristics: daily milk yield of 45 kg, containing 3.5% fat, and 3 mm fur depth. The independent variables were: orientation, barn type, roof slope, roof ridge, marginal height, roof type (fixed or sliding) and barn width. Results showed that the optimal barn for high-yielding cows is the loose-housing type, oriented with its long axis perpendicular to the prevailing wind direction. Advantageous to the design would be an open ridge or pagoda with marginal height of over 4.7 m for north-south orientation and over 5 m for east-west orientation, roof slope over 11%, and barn width between 43 and 51 m for north-south orientation but lower than 42 m for east-west orientation. A sliding roof was also found to be an excellent solution when outside yards are banned by environmental regulations.     

Feather steroid hormone concentrations in relation to age,sex, and molting time in a long‐distance migratory passerine

In birds, concentrations of testosterone (T) and corticosterone (Cort) are closely connected with many morphological, behavioral, and other physiological traits, including reproduction, metabolism, immunity, and fitness. The direction of the effect of these hormones on above‐mentioned traits, and the potential feedback between hormones are in general unclear; in addition, knowledge on how age and sex can affect T and Cort concentrations is still inconsistent. Our study used a novel method to analyze testosterone and corticosterone in feathers (T_f, Cort_f) based on the precolumn chemical derivatization of hormones before liquid chromatography–tandem mass spectrometry (LC‐MS/MS) analysis. Unlike previously used methods (RIA, EIA), our analytical procedure allows simultaneous analysis of both hormones from small amounts of feathers (4–25 mg) and, thus, overcomes the problem of insufficient detection limits. We applied this method to reveal associations between T_f and Cort_f hormone concentrations and feather growth, age, and sex in feathers grown during the postbreeding (flanks) and prebreeding (tails) periods in barn swallows (Hirundo rustica). There was neither a correlation between prebreeding and postbreeding T_f, nor between prebreeding and postbreeding Cort_f. Tail Cort_f concentrations were negatively associated with tail feather growth rates. Feather hormone concentrations were correlated in the prebreeding period, negatively in males but positively in females. Both Cort_f and T_f were higher in young birds compared to older ones, indicating either an age‐related decrease in hormone concentrations within individuals, or the selective disappearance of individuals with high steroid concentrations. Males and females did not differ in Cort_f, but T_f concentrations were higher in males than females, particularly during the prebreeding period. In this study, we provide an effective method for analyzing hormones in feathers in an ecological context, especially in situations when the total amount of feathers available for the analysis is limited.     

Bird predation by tawny owls (Strix aluco L.) and its effect on the reproductive performance of tits

The density of great tit Parus major L. and blue tit Parus caeruleus L. was artificially increased by placing nest-box colonies for these species in the vicinity of the nests of breeding tawny owls during 1993–1997. Bird prey composition in the owl nests, the proportion of parents disappearing from the breeding tit populations and the reproductive performance of the widowed parents were analysed. The frequency of predation on tits by tawny owls was greater in areas where tit density had been artificially increased. Owls preyed more on tits during the feeding period of owlets than during the incubation period and more in years when snow covered the ground during the incubation period than when it did not. Mortality due to predation was male biased and more females lost their mates in populations breeding near tawny owl nests. Reproductive performance of the widowed parents was lower and their body weights were lighter at the end of the nestling period than those found in birds rearing youngs with their mates. Predation by owls increased the between-year turnover in the breeding tit population: widowed parents did not return to the nesting site for the next breeding season.     

Sources of variability in spotted owl population growth rate: testing predictions using long-term mark–recapture data

For long-lived iteroparous vertebrates that annually produce few young, life history theory predicts that reproductive output (R) and juvenile survival should influence temporal variation in population growth rate (λ) more than adult survival does. We examined this general prediction using 15 years of mark–recapture data from a population of California spotted owls (Strix occidentalis occidentalis). We found that survival of individuals ≥1 year old (ϕ) exhibited much less temporal variability , where CV is coefficient of variation, than R and that R was strongly influenced by environmental stochasticity. Although λ was most sensitive ( ; log-transformed sensitivity) to ϕ and much less sensitive to either R or juvenile survival (survival rate of owls from fledging to 1 year old; ), we estimated that R contributed as much as ϕ to the observed annual variability in λ. The contribution of juvenile survival to variability in λ was proportional to its These results are consistent with the hypothesis that natural selection may have favored the evolution of longevity in spotted owls as a strategy to increase the probability of experiencing favorable years for reproduction. Our finding that annual weather patterns that most affected R (temperature and precipitation during incubation) and ϕ (conditions during winter related to the Southern Oscillation Index) were equally good at explaining temporal variability in λ supports the conclusion that R and ϕ were equally responsible for variability in λ. Although currently accepted conservation measures for spotted owl populations attempt to enhance survival, our results indicated that conservation measures that target R may be as successful, as long as actions do not reduce ϕ.     

Burrowing Owl Mortality in the Altamont Pass Wind Resource Area

Abstract: We estimated wind turbines in the Altamont Pass Wind Resource Area (APWRA), California, USA, kill >100 burrowing owls (Athene cunicularia hypugaea) annually, or about the same number likely nesting in the APWRA. Turbine-caused mortality was up to 12 times greater in areas of rodent control, where flights close to the rotor plane were disproportionately more common and fatalities twice as frequent as expected. Mortality was highest during January through March. Burrowing owls flew within 50 m of turbines about 10 times longer than expected, and they flew close to wind turbines disproportionately longer within the sparsest turbine fields, by turbines on tubular towers, at the edges of gaps in the turbine row, in canyons, and at lower elevations. They perched, flew close to operating turbine blades, and collided disproportionately more often at turbines with the most cattle dung within 20 m, with the highest densities of ground squirrel (Spermophilus beecheyi) burrow systems within 15 m, and with burrowing owl burrows located within 90 m of turbines. A model of relative collision threat predicted 29% of the 4,074 turbines in our sample to be more dangerous, and these killed 71% of the burrowing owls in our sample. This model can help select the most dangerous turbines for shutdown or relocation. All turbines in the APWRA could be shut down and blades locked during winter, when 35% of the burrowing owls were killed but only 14% of the annual electricity was generated. Terminating rodent control and installing flight diverters at the ends of turbine rows might also reduce burrowing owl mortality, as might replacing turbines with new-generation turbines mounted on taller towers.