Sex difference in natal dispersal distances of Golden Eagles Aquila chrysaetos in Scotland

Natal dispersal distance (NDD) is critical in understanding and defining populations and their conservation. It is defined as the linear distance between the natal location and first reproductive (‘effective NDD’) or potential reproductive (‘gross NDD’) location. It is a measure of gene flow and the functional connectivity across generations between individuals breeding in the same or different geographies. NDD is difficult to record in large raptors. GPS-satellite telemetry has facilitated its recording. Previous Scottish studies showed that gross and effective NDD were apparently equivalent, and an algorithm based on telemetric data could identify the territory settlement timing and location of birds originally tagged as nestlings. We analysed natal dispersal data from 39 Golden Eagles GPS-tagged in Scotland to estimate NDD. Raw median estimates were 29.8 km for males (n = 22) and 58.6 km for females (n = 17), 38.1 km averaged across sexes. Males had significantly shorter NDD, as theoretically predicted. Our NDD estimates were shorter but not grossly dissimilar to those from the USA, where sex differences in NDD had not been confirmed. Respective sample sizes may underly the latter contrast in confirmation. We also showed that in the absence of data from sexed birds, NDD estimates can be different. Natal dispersal duration was not related to NDD, suggesting that time to prospect a territory opportunity was not associated with the selected territory's distance from the natal site. The previous status of the subsequent settled territory (occupied or vacant) was also not related to NDD. We conclude that sex differences in NDD are important in application to population demography and conservation. Although we found no support for two other potential drivers of NDD (natal dispersal duration and previous territory status), identifying additional influences on NDD is in its infancy in large raptors and deserves more study.     

Diet specificity is not associated with increased reproductive performance of Golden Eagles Aquila chrysaetos in Western Scotland

Amongst raptor species, individuals with specialized diets are commonly observed to have higher reproductive output than those with general diets. A suggested cause is that foraging efficiency benefits accrue to diet specialists. This diet specificity hypothesis thus predicts that diet breadth and reproductive success should be inversely related within species. We highlight, however, that a prey availability hypothesis also makes the same prediction in some circumstances. Hence, when high diet specificity results from high encounter rates with an abundant, preferred prey, then prey availability may affect reproductive success, with diet specialization as an incidental correlate. Using three insular study areas in western Scotland, we examine diet specificity and reproductive success in Golden Eagles Aquila chrysaetos. Diet breadth and breeding productivity were not negatively related in any of our study areas, even though birds with specific diets did tend to have a higher incidence of preferred prey (grouse and lagomorphs) in the diet. Indeed, in two study areas there was evidence that diet generalists had higher breeding productivity. Our results therefore failed to support the diet specificity hypothesis but were consistent with the prey availability hypothesis. We highlight that although many other studies are superficially consistent with the diet specificity hypothesis, our study is not alone in failing to provide support and that the hypothesis does not provide a generic explanation for all relevant results. Diet specificity in predators can be at least partially a response to prey diversity, availability and distribution, and benefits associated with different prey types, so that being a generalist is not necessarily intrinsically disadvantageous. We suggest that the available evidence is more consistent with variation in prey abundance and availability as a more influential factor explaining spatial and temporal variation in breeding productivity of ‘generalist’ species such as the Golden Eagle. Under this argument, prey abundance and availability are the main drivers of variation in reproductive output. Diet specificity is a consequence of variation in prey availability, rather than a substantial cause of variation in reproductive success.     

Ranging distance of resident Golden Eagles Aquila chrysaetos in western Scotland according to season and breeding status

Capsule Home-range of resident pairs of Golden Eagle was usually smaller during a successful breeding season than during winter and during an unsuccessful breeding season.

Aims To examine how Golden Eagles use space around their nests with respect to season and breeding status, and to compare home-range-use between a high and a low density region.

Methods Nine adults in six mainland Argyll ranges were radiotracked between 1991 and 1996. On the island of Mull visual observations of range-use were obtained for five ranges between 1994 and 1998.

Results Overall, Mull ranges were smaller than the Argyll ranges, reflecting the much higher range density on Mull. In both regions there were significant differences between ranging distances with season and breeding status. In general, ranging distances were smallest during breeding seasons when young were fledged.

Conclusions Studies of range-use in Golden Eagles must be conducted across a 12-month period, as a minimum.     

Population structure and dispersal patterns in Scottish Golden Eagles Aquila chrysaetos revealed by molecular genetic analysis of territorial birds

Conservation management of species distributed across fragmented habitats requires consideration of population genetic structure and relative levels of genetic diversity throughout the relevant geographical range. The Golden Eagle Aquila chrysaetos is monitored within Scotland to ensure its survival in the face of land‐use pressure, persecution and future climate change. In this study we constructed DNA profiles for 271 individual birds using a collection of over 1600 moulted feathers collected from 148 territories, representing 34% of known Scottish territories in the largest population genetic study of Golden Eagles undertaken to date. The results, based on data from 10 nuclear microsatellite loci, revealed previously unreported genetic structure between the islands of the Outer Hebrides and the rest of Scotland (F_ST = 0.03), together with evidence of reduced genetic diversity in the Outer Hebridean population compared with mainland Scotland. Analysis of gene flow supports a hypothesis of limited, predominantly male‐mediated, dispersal from the Outer Hebrides to mainland Scotland. The persistence of this pattern is discussed with respect to variation in population density and persecution pressure across Scotland. A finding of non‐random mating within the Outer Hebrides is interpreted as evidence of natal philopatry that was revealed by more intensive sampling in these islands, and is likely to be accentuated by the apparent degree of isolation of the islands from the rest of Scotland.     

Bird carcass detection from integrated trials at multiple wind farms

It is often necessary to estimate the number of wind turbine collision fatalities to assess impacts to birds following construction of wind farms. Detection of bird carcasses at wind turbines in the field is affected by carcass persistence and searcher detection rate. Integrated detection trials, which integrate carcass persistence and searcher detection trials into the periodic fatality search, have been proposed as an effective method for estimating these parameters. The purpose of our study was to test whether and how environmental factors affect integrated detection trial outcomes at multiple wind farms. We conducted this study at 10 wind farms in various environments of Japan. Binary data on trial outcomes in open versus forested areas served as our response variable in a generalized additive mixed model informed by days into trial, carcass body mass, season, whether snow covered the ground, and precipitation. For both ground cover types, days into trial and body mass were included in all the top models, suggesting that these factors most influenced bird carcass detection probability in integrated trials. The best model in open areas included days into trial, body mass, snow, and precipitation, and the best model in forested areas included days into trial, body mass, snow, precipitation, and season. Values of area under the curve indicated high accuracy of the best model for both ground cover types. The survey design needs to be appropriate to the size of the target species and to the environment in which the impacts will occur, such as the site's seasonality, its ground cover, and whether snow will cover the ground. Frequency of post-construction fatality monitoring should also be set cautiously, especially at wind farms located on small-bird migration routes, at wind farms in open areas, in areas with snow-covered ground in winter, or in forested areas during spring and summer because detection probabilities decline fastest under such conditions.     

Using probability of occurrence to assess potential interaction between wind farms and a residual population of golden eagle Aquila chrysaetos in NW Spain

We evaluate the areas with potential negative impacts in a golden eagle population derived of the development of wind farms. At present, the entire golden eagle Galician population (5–6 pairs) is located within an area of about 2,000 km². Grid squares of 10 × 10 km UTM in the province were scored for current and future wind turbine density and probability of occurrence of golden eagle. This probability was obtained using cartographic models of habitat selection for two different historic periods. Potential risk index (PRI) was calculated for each grid square by multiplying the wind turbine density score by the probability of occurrence score. With the PRIs obtained a cartographic model of potential impact of wind farms on the golden eagle population was constructed. No significant correlation was observed between current wind turbine density and the probability of occurrence of golden eagle. A significant positive correlation was observed between current and future wind turbine density and the probability of occurrence of golden eagle. The areas with highest potential risk are eastern and the central mountains of Ourense where the species breeds. The risk model presented could be applied to future wind farm proposals and monitor potential interactions of golden eagles with wind farms in the Province of Ourense.     

Flight Tunnel Responses of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) to Olfactory and Visual Stimuli

Cohorts of mass-reared, naive Diachasmimorpha longicaudata, parasitoids of tephritid fruit flies, were released in a laminar airflow wind tunnel to study their responses to visual and olfactory stimuli associated with their host habitat. Parasitoids were five times more likely to land on yellow plastic spheres emitting the odor of ripe, guava fruit (Psidium guajava L.) than to spheres emitting clean air. The rate of landing was not modified by the presence of green artificial leaves adjacent to the spheres in the tunnel or by the inclusion of green leaf volatiles emanating with the guava odors. However, hovering activity was twice as frequent around spheres adjacent to artificial leaves than around isolated spheres. Oviposition activity on spheres emitting guava odor was not affected by the presence of artificial leaves nor by green leaf volatiles. This suggests that inexperienced D. longicaudata may be instinctively attracted to foliage and to fruit odor but that landing (arrestment) and oviposition are influenced more by odor than by the appearance of fruit or foliage. D. longicaudata are not instinctively attracted to larvae of Bactrocera dorsalis in the absence of host-habitat stimuli. More wasp activity occurred around oviposition units containing larvae if the odor of ripe/overripe guava was present. Successful wasp reproduction occurred only in units with guava odor.     

Movement of apterous Sitobion avenae (Homoptera: Aphididae) in response to leaf disturbances caused by wind and rain

The effect of wind and rain on initiation of dispersal and subsequent distances moved by apterous Sitobion avenae was quantified in five laboratory experiments. Wind duration and type (steady and gusting), rain duration and intensity, and a combination of wind and rain were investigated. With increased duration of wind there was an increase in the average distance aphids moved. There was less movement when aphids were exposed to gentle gusting, than to steady wind or strong gusting. With increased duration of rain there was an increase in the proportion of aphids lost from plants. Under heavy rain, the proportion of aphids off the release plant, the distance moved by them and the proportion of aphids lost, was greater than for drizzle or light rain. When wind and rain were compared, rain had the greater impact on aphid dispersal. It was concluded that leaf disturbances caused by strong gusts of wind or large rain droplets are of considerable importance in the initiation of aphid dispersal, but that wetness alone is not.     

Extensive sampling of polar bears (Ursus maritimus) in the Northwest Passage (Canadian Arctic Archipelago) reveals population differentiation across multiple spatial and temporal scales

As global warming accelerates the melting of Arctic sea ice, polar bears (Ursus maritimus) must adapt to a rapidly changing landscape. This process will necessarily alter the species distribution together with population dynamics and structure. Detailed knowledge of these changes is crucial to delineating conservation priorities. Here, we sampled 361 polar bears from across the center of the Canadian Arctic Archipelago spanning the Gulf of Boothia (GB) and M'Clintock Channel (MC). We use DNA microsatellites and mitochondrial control region sequences to quantify genetic differentiation, estimate gene flow, and infer population history. Two populations, roughly coincident with GB and MC, are significantly differentiated at both nuclear (F_ST = 0.01) and mitochondrial (Φ_ST = 0.47; F_ST = 0.29) loci, allowing Bayesian clustering analyses to assign individuals to either group. Our data imply that the causes of the mitochondrial and nuclear genetic patterns differ. Analysis of mtDNA reveals the matrilineal structure dates at least to the Holocene, and is common to individuals throughout the species’ range. These mtDNA differences probably reflect both genetic drift and historical colonization dynamics. In contrast, the differentiation inferred from microsatellites is only on the scale of hundreds of years, possibly reflecting contemporary impediments to gene flow. Taken together, our data suggest that gene flow is insufficient to homogenize the GB and MC populations and support the designation of GB and MC as separate polar bear conservation units. Our study also provide a striking example of how nuclear DNA and mtDNA capture different aspects of a species demographic history.     

Effects of the Serotonin1A Agonist, 8-Hydroxy-2-(Di-n-Propylamino)tetralin on Neurochemical Responses to Stress

Abstract: The effects of intracerebroventricular administration of the 5-hydroxytryptamine (5-HT)_1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.1 pmol) on adrenocortical and neurochemical responses to stress were examined in conscious male rats. The following stress paradigms were used: acoustic stimulation (105 dB for 2 min); footshock (0.2 mA, five shocks over 5 min); conditioned fear (animals placed in a footshock chamber for 5 min, 24 h after footshock); restraint (5 min); intraperitoneal (i.p.) injection of recombinant human interleukin-1α (rHu-IL-1α, 20 µg/kg); and injection of cocaine hydrochloride (20 mg/kg, i.p.). As previously shown, 8-OH-DPAT was able to attenuate the adrenocortical response to acoustic stress, conditioned fear, rHu-IL-1α, and cocaine administration. Cocaine decreased 5-hydroxyindoleacetic acid (5-HIAA)/5-HT and dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratios and norepinephrine (NE) concentration in the prefrontal cortex, hypothalamus, and brainstem in all experiments, and 8-OH-DPAT reversed the changes in DOPAC/DA ratio without affecting 5-HIAA/5-HT ratios or NE content. 8-OH-DPAT alone had no effect on these parameters, although it decreased NE content in the prefrontal cortex in several experiments, and in the brainstem in one experiment. Significant decreases in NE content were observed in some brain regions following some of the stressors, but these changes were not generally affected by 8-OH-DPAT. Increases in the 5-HIAA/5-HT and DOPAC/DA ratios were also observed in some brain sites following some stressors, but these changes were not affected by 8-OH-DPAT except in the case of the increased 5-HIAA/5-HT ratio in the prefrontal cortex following the conditioned fear response. These results indicate that although 8-OH-DPAT is able to decrease plasma corticosterone responses following acoustic stress, conditioned fear, rHu-IL-1α, and cocaine administration, these effects do not appear to be related to an action of the 5-HT_1A agonist on biogenic amine metabolism. This observation indicates that the predominant effect of 8-OH-DPAT on adrenocortical responses is mediated at postsynaptic sites not involved in the regulation of cerebral biogenic amine metabolism.     

An investigation inot the use of multiple site characteristics to predict the presence and infestation level of wireworms (Agriotes sup., Coleoptera: Elateridae) in individual grass fields

Sixty-two grass fields were sampled in England and Wales over a three year period to assess the level of wireworm population present. Data on site-specific variables including soil physical characteristics, grass duration, grass genera diversity and other abiotic factors such as field aspect, altitude, and meteorological parameters were abiotic factors such as field aspect, altitude, and meteorological parameters were collected at each site. Only grass duration and soil bulk density showed any association with wireworm infestation stauts when considered as single variates. Data from a sub-set of 41 fields were used to develop a series of multi-variate discriminant rules to predit wireworm presence/absece in individual fields. These were vaildated using data from the remaining 21 fields. In general, the rules tended to over-estimate the number of wireworm-infested fields by misclassifying uninfested fields as infestes. Multivariate models to predict wireworm populaiton levels in infested fields were also developed using multiple and generalised linear regression. The predictive accuracy of these was poor. Neither the population prediciton models nor the presence/absence rulses accounted fully for the large inte-field variation in wireworm infestation status.