High altitude echolocation of insects by bats

Summary The orientation sounds of many bats, almost certainly belonging to the genus Tadarida, were recorded at altitudes of 100 to 300 m above the ground by means of an ultrasonic radio microphone. Both in North Queensland, Australia, and in southern Utah and Nevada, USA, bats were often more numerous at 200 to 300 m than near the ground. Rapid increases in pulse repetition rate often indicated that these bats were actively hunting flying insects. The absence of clutter at high altitudes may significantly facilitate the detection and capture of insect prey.     

Exudation of biologically-active metabolites in the sponge Aplysina fistularis

Specimens of the demosponge Aplysina fistularis forma fulva (Pallas) from the intertidal zone at La Jolla, California, USA, contain two antimicrobial metabolites, aerothionin (1) and homoaerothionin (2). Both metabolites are exuded into seawater. The rates of exudation into artificial seawater were measured under near in situ conditions (7.7x10^-4 g aerothionin min^-1 g^-1 dry weight of sponge) and in an aquarium (8.9x10^-3 g min^-1 g^-1) for undamaged sponges. Sponges responded to a simulated injury by exuding 10 to 100 times as much of these metabolites. The exudation of aerothionin and homoaerothionin may inhibit surface overgrowth by fouling organisms and tissue damage by mobile animals.Please address requests for reprints to Dr. J. E. Thompson     

Intra-specific variability in the temporal organisation of foraging activity in the limpet<Emphasis Type="Italic"> Patella vulgata</Emphasis>

Patella vulgata is one of the most common limpet species on rocky shores throughout the north-eastern Atlantic. Foraging activity of this species has been described during various different diel and tidal phases and several factors have been suggested that might influence the timing of its activity. Among these, inclination of rock surfaces seems to have a clear role, with limpets on horizontal rocks being active during daylight at high water, while limpets on vertical rocks were active during night-time low water. However, by comparing the results of previous investigations it is difficult to separate clearly the effect of any single factor from the effects of their interactions. In the present paper we investigated the simultaneous influence of height on the shore, slope of rock surface and date of sampling (August–September and March–April) on the behaviour of a population of P. vulgata on the Isle of Man (UK). The study was carried out using modern telemetric methods, allowing the activity patterns of limpets to be recorded for long periods of time. The results showed that limpets concentrated their activity during two distinct temporal windows—daytime tide-in and night-time tide-out—while no significant activity was observed during daytime tide-out or night-time tide-in. The observed behaviour appeared to be driven by complex interactions among the three factors examined, and the influence of rock slope alone was not so strong as to override the effect of other factors completely. In addition, a key finding of this study was the conspicuous variability in the individual behaviour of P. vulgata. The greatest level of variability was observed in limpets on vertical surfaces on the upper shore, which showed an extreme switch in behavioural patterns, according to date of sampling (daylight/tide-in foraging during the spring and night-time/tide-out foraging during late summer). In addition, individuals apparently sharing the same set of conditions (inclination, height on the shore and sampling date) differed in their behaviour, and a given behavioural pattern was not always shared by all individuals from a given group. Finally, variability was also observed at the intra-individual level since the same individual could be active during different tidal and diel phases. In conclusion, although the existence of endogenous rhythms has previously been demonstrated in this species, our data clearly show that P. vulgata was able to modulate its behavioural patterns in relation to a variety of exogenous determinants.Communicated by R. Cattaneo-Vietti, Genova     

Functional mechanisms underlying cetacean distribution patterns: hotspots for bottlenose dolphins are linked to foraging

Many studies have shown that the distribution of cetaceans can be closely linked to habitat, but the underlying function of the preferred habitats often remains unclear. Only when behavioural observations are made in relation to habitat types can functional mechanisms behind the habitat use be revealed. Within the range of a bottlenose dolphin (Tursiops truncatus) population off NE Scotland, dolphins show clear preferences for several discrete areas. If the observed patterns of distribution are related to foraging, we predict that behaviour patterns shown by dolphins would reflect this relationship. In this study we identify behaviours of dolphins at the water surface that were related to feeding events, evaluate whether the patterns of distribution were related to foraging and whether they were related the local submarine habitat characteristics. To investigate whether visible surface evidence of foraging behaviour varied spatially, we analysed data collected from 104 regular boat-based surveys made within the Moray Firth, NE Scotland, between 1990 and 2000. To determine whether underlying bathymetry had any influence on the surface behaviour of dolphins, a land-based observation study was carried out in the populations core region of use. The results of this study show that feeding behaviour by dolphins was significantly higher in areas used intensively by dolphins. Furthermore, there were clear relationships between feeding events and the submarine habitat characteristics; certain forms of feeding occur primarily over steep seabed gradients, and in deeper waters during June and July. These results quantitatively support the hypothesis that the distinctive patterns of distribution shown by these dolphins are related to foraging behaviour or opportunities, and that submarine habitat characteristics may be a significant factor in the foraging efficiency of dolphins. Future work should focus on collecting detailed information on the distribution patterns of prey within the study area to allow direct comparisons between predator and prey distributions.Communicated by J.P. Thorpe, Port Erin     

Linking chronic wasting disease to mule deer movement scales: a hierarchical Bayesian approach.

Observed spatial patterns in natural systems may result from processes acting across multiple spatial and temporal scales. Although spatially explicit data on processes that generate ecological patterns, such as the distribution of disease over a landscape, are frequently unavailable, information about the scales over which processes operate can be used to understand the link between pattern and process. Our goal was to identify scales of mule deer (Odocoileus hemionus) movement and mixing that exerted the greatest influence on the spatial pattern of chronic wasting disease (CWD) in northcentral Colorado, USA. We hypothesized that three scales of mixing (individual, winter subpopulation, or summer subpopulation) might control spatial variation in disease prevalence. We developed a fully Bayesian hierarchical model to compare the strength of evidence for each mixing scale. We found strong evidence that the finest mixing scale corresponded best to the spatial distribution of CWD infection. There was also evidence that land ownership and habitat use play a role in exacerbating the disease, along with the known effects of sex and age. Our analysis demonstrates how information on the scales of spatial processes that generate observed patterns can be used to gain insight when process data are sparse or unavailable.     

The chemical form of mercury stored in South Atlantic seabirds

Concentrations of total mercury and organic (methyl) mercury were measured in the liver tissue of adults of 12 seabird species collected at colonies on Gough Island, South Atlantic Ocean. Total mercury levels showed both great intra- and interspecies variation, ranging from a mean of 1343.0 microg g(-1) dry weight in wandering albatrosses to a mean of 0.8 microg g(-1) dry weight in broad-billed prions. Organic mercury levels were less variable both between, but especially within, species. Organic mercury levels, expressed as a percentage of total mercury levels, ranged from a mean of 2.6% in wandering albatrosses up to a mean of 92.6% in littee shearwaters. Within each species, individuals with the highest total mercury levels tended to have the lowest percentage organic mercury, this trend being statistically significant in several species. Two species exhibited a significant positive correlation between organic mercury levels, in absolute terms, and total mercury levels. When all 12 species were considered, a highly significant negative correlation between mean percentage organic mercury and mean total mercury was found (rs = -0.888, P < 0.001). These results provide evidence to suggest that some seabirds may be capable of demethylating organic mercury in a species-dependent and that eliminatory pathways for the excretion of dietary mercury may influence the mode of response of a particular species.     

Euro Chlor Risk Assessment for the Marine Environment Osparcom Region: North Sea - Trichloroethylene

This risk assessment on trichloroethylene (TRI) was carried out specifically for the marine environment, according to the methodology laid down in the EU risk assessment Regulation (1488/94) and the Guidance Document of the EU New and Existing Substances Regulation (TGD, 1997). The study consists of the collection and evaluation of data on effects and environmental concentrations from analytical monitoring programs in large rivers and estuaries in the North Sea area. The risk is indicated by the ratio of the "predicted environmental concentrations" (PEC) and the "predicted no effect concentrations" (PNEC) for the marine aquatic environment. In total, 19 studies for fish, 30 studies for invertebrates and 14 studies for algae have been evaluated. Both acute and chronic toxicity studies have been taken into account and the appropriate assessment factors have been used to define a PNEC value of 150 µg/l. Most of the available monitoring data apply to rivers and estuaries and were used to calculate PECs. The most recent data (1991-1995) support a typical PEC of 0.1 µg TRI/l water and a worst case PEC of 3.5 µg TRI/l water. The calculated PEC/PNEC ratios give a safety margin of 40 to 1,500 between the predicted no effect concentration and the exposure concentration. Additional evaluation of environmental fate and bioaccumulation characteristics showed that no concern for food chain accumulation is expected.     

Relationship between the Aerodynamic Roughness Length and the Roughness Density in Cases of Low Roughness Density*

This paper presents measurements of roughness length performed in a wind tunnel for low roughness density. The experiments were performed with both compact and porous obstacles (clusters), in order to simulate the behavior of sparsely vegetated surfaces. The experimental results have been used to investigate the relationship between the ratio z₀/h and the roughness density, and the influence of an obstacle's porosity on this relationship. The experiments performed for four configurations of compact obstacles provide measurements of roughness length z₀ for roughness densities between 10^–3 and 10^–2 which are in good agreement with the only data set available until now for this range of low roughness densities. The results obtained with artificial porous obstacles suggests that the aerodynamic behavior of such roughness elements can be represented by the relationship established for compact obstacles, provided a porosity index has been used to determine the efficient roughness density (the fraction of the silhouette area actually sheltered by solid elements) rather than counting the porous object as solid. However, the experiments have been performed with relatively low porosity indices (maximum =25%) for which the porosity has a negligible influence. In this range of porosity index, representing the aerodynamic behavior of porous obstacles using the relationship established for compact obstacles, should not lead to a significant error. However, the influence of the porosity may be important for porosity indices larger than 30%.     

Diving deep in a foraging hotspot: acoustic insights into bottlenose dolphin dive depths and feeding behaviour

To exploit resources in their environment, odontocete cetaceans have evolved sophisticated diving abilities to allow effective foraging. However, data on the diving behaviour and underwater foraging behaviour remains limited. This study made use of echolocation clicks and other calls to study the diving behaviour of bottlenose dolphins. Dolphins used the full water column and consistently dived to depths of around 50 m, close to the seabed. However, the majority of their time appeared to be spent within the surface layers of the water column. In addition, by localising calls that have been associated with prey capture events (Janik, Proc R Soc Lond Ser B 267:923–927, 2000a), it appeared that certain forms of feeding behaviour occurred primarily at depths of between 20 and 30 m. Furthermore, data on the depth of clicks made before and after these feeding calls suggested that during the minute before the calls, dolphins were consistently diving from the surface to depths close to the seabed, and were subsequently returning to the surface after the calls. This passive acoustic technique proved an accurate method for studying the depth distribution of dolphin vocalisations. By exploiting the natural sounds made by these wild odontocetes, this investigation provided a previously unavailable perspective on the the 3D nature of bottlenose dolphins foraging behaviour. It confirmed that while the dolphins spent the majority of time close to the surface, the full water column was exploited during foraging events.