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The zoo soundscape has a number of important implications for animal welfare, management, and conservation. However, despite its importance, the zoo soundscape is yet to be examined in depth using multiple measures. Consistent human presence can influence the zoo soundscape. However, it is difficult to determine the specific impact of human presence, as visitors are usually present during the day when animals are active. The COVID-19 lockdown in 2020 provided a unique opportunity to study zoo soundscapes in the absence of visitors. We compared the sound environment during the 2020 closure period to a comparable open period in 2019 across three zoo aviaries, examining broad band frequency measures of sound pressure levels, sound pressure levels in defined frequency bands, and acoustic indices (Acoustic Complexity Index and Normalized Difference Soundscape Index) to describe the zoo soundscape. Acoustic indices have not, to our knowledge, previously been used in the zoo setting, although they may provide a useful metric to assess sound disturbance. Therefore, we also used this natural experiment to explore how successful these measures may be in assessing disturbances in captive environments. We found a significant effect of human presence on the sound environment; aviaries were generally quieter with less low frequency noise and with a greater proportion of biotic sound during the 2020 zoo closure period. We argue that NDSI could be a useful index for determining anthropogenic disturbance in zoos, although further information on how it is influenced by additional factors, such as human speech, would be beneficial. The use of multiple measures to assess the sound environment in zoos can provide additional information beyond ‘loudness’, such as frequencies where sound energy is concentrated and characteristics of the soundscape, which could be used to better target management and mitigation.

The nociceptive network, responsible for transmission of nociceptive signals that generate the pain experience, is not fully developed at birth. Descending serotonergic modulation of spinal nociception, an important part of the pain network, undergoes substantial postnatal maturation and is suggested to be involved in the altered pain response observed in human newborns. This review summarizes preclinical data of the development of descending serotonergic modulation of the spinal nociceptive network across the life span, providing a comprehensive background to understand human newborn pain experience and treatment. Sprouting of descending serotonergic axons, originating from the rostroventral medulla, as well as changes in receptor function and expression take place in the first postnatal weeks of rodents, corresponding to human neonates in early infancy. Descending serotonergic modulation switches from facilitation in early life to bimodal control in adulthood, masking an already functional 5-HT inhibitory system at early ages. Specifically the 5-HT3 and 5-HT7 receptors seem distinctly important for pain facilitation at neonatal and early infancy, while the 5-HT1a, 5-HT1b, and 5-HT2 receptors mediate inhibitory effects at all ages. Analgesic therapy that considers the neurodevelopmental phase is likely to result in a more targeted treatment of neonatal pain and may improve both short- and long-term effects. Impact: The descending serotonergic system undergoes anatomical changes from birth to early infancy, as its sprouts and descending projections increase and the dorsal horn innervation pattern changes.Descending serotonergic modulation from the rostral ventral medulla switches from facilitation in early life via the 5-HT3 and 5-HT7 receptors to bimodal control in adulthood.A functional inhibitory serotonergic system mainly via 5-HT1a, 5-HT1b, and 5-HT2a receptors at the spinal level exists already at the neonatal phase but is masked by descending facilitation.

The influence of neonatal experiences upon later-life affective behavior is increasingly recognized, but the reported effects on anxiety are often contradictory. The observed effect may depend upon the type of anxiety (state or trait) affected. The current study aims to investigate whether neonatal repetitive needle pricking alters anxiety behavior in adulthood, by assessing both state and trait anxiety in rats. Sprague–Dawley rat pups received four unilateral needle pricks per day, while controls received four tactile stimuli or were left completely undisturbed during the first postnatal week. Mechanical sensitivity was assessed in the neonatal phase and throughout the development. State anxiety was assessed in the open field test and trait anxiety in the elevated zero maze. The results show that repetitive needle pricking leads to acute mechanical hypersensitivity, but does not affect baseline mechanical sensitivity throughout development. In adulthood, animals previously exposed to neonatal procedural pain (including repetitive handling and removal from litter) showed lower state anxiety but did not differ in trait anxiety, as compared with the undisturbed controls. These findings indicate that early-life procedural pain decreases state but not trait anxiety behavior in later life in a rodent model of repetitive needle pricking.

A growing body of evidence indicates that early-life exposure to selective serotonin reuptake inhibitor has long-term consequences on the offspring's pain in addition to affective disorders like anxiety disorder and major depression. Serotonin, besides its role in regulating pain and emotions, promotes neuronal network formation. The prefrontal cortex and the amygdala are two key brain regions involved in the modulation of pain and its affective comorbidities. Thus, the aim of this review is to understand how early-life selective serotonin reuptake inhibitor exposure alters the developing prefrontal cortex and amygdala and thereby underlies the long-term changes in pain and its affective comorbidities in later life. While there is still limited data on the effects of early-life selective serotonin reuptake inhibitor exposure on pain, there is a substantial body of evidence on its affective comorbidities. From this perspective paper, four conclusions emerged. First, early-life selective serotonin reuptake inhibitor exposure results in long-term nociceptive effects, which needs to be consistently studied to clarify. Second, it results in enhanced depressive-like behaviour and diminished exploratory behaviour in adult rodents. Third, early-life selective serotonin reuptake inhibitor exposure alters serotonergic levels, transcription factors expression, and brain-derived neurotrophic factor levels, resulting in hyperconnectivity within the amygdala and the prefrontal cortex. Finally, it affects antinociceptive inputs of the prefrontal cortex and the amygdala in the spinal cord. We conclude that early-life selective serotonin reuptake inhibitor exposure affects the maturation of prefrontal cortex and amygdala circuits and thereby enhances their antinociceptive inputs in the spinal cord.

The ubiquitous anthropogenic low‐frequency noise impedes communication by masking animal signals. To overcome this communication barrier, animals may increase the frequency, amplitude and delivery rate of their acoustic signals, making them more easily heard. However, a direct impact of intermittent, high‐level aircraft noise on birds’ behaviour living close to a runway has not been studied in detail.We recorded common chiffchaffs Phylloscopus collybita songs near two airports and nearby control areas, and we measured sound levels in their territories at Manchester Airport. The song recordings were made in between aircraft movements, when ambient sound levels were similar between airport and control populations. We also conducted playback experiments at the airport and a control population to test the salience of airport, and control population specific songs.In contrast to the general pattern of increased song frequency in noisy areas, we show that common chiffchaffs at airports show a negative relationship between noise exposure level and song frequency.Experimental data show that chiffchaffs living near airports also respond more aggressively to song playback.Since the decrease in song frequency results in increased overlap with aircraft noise, these findings cannot be explained as an adaptation to improve communication. The increased levels of aggression suggest that chiffchaffs, like humans, might be affected behaviourally by extreme noise pollution. These findings should influence environmental impact assessments for airport expansions globally., This paper shows that birds sing at a lower frequency and are more aggressive, when exposed to aircraft noise. The lower song frequency cannot be explained as an adaptation to the local sound environment. Instead, the data are consistent with the birds suffering from noise‐induced hearing loss.

Vocal repertoires and call structure can provide insights into the behaviour and evolution of species, as well as aid in taxonomic classification. Nocturnal primates have large vocal repertoires. This suggests that acoustic communication plays an important role in their life histories. Little is known about the behavioural context or the intraspecific variation of their vocalisations. We used autonomous recording units and manual recorders to investigate the vocal behaviour and structure of loud calls of the small-eared greater galago (Otolemur garnettii) in Kenya and Tanzania. We describe the vocal repertoire, temporal calling patterns and structure of 2 loud calls of 2 subspecies: O. g. panganiensis and O. g. kikuyuensis. We found considerable intraspecific structural differences in both loud calls. These are congruent with the current subspecies classification. Differences in vocalisations among populations are not consistent with the “acoustic adaptation hypothesis,” rather they are likely a result of geographic variation due to isolation caused by vegetational barriers in southern Kenya.

The Ngorongoro Conservation Area (NCA) is a protected area and UNESCO World Heritage Site and part of the Serengeti‐Ngorongoro Biosphere reserve in northern Tanzania. It is famous for its large volcanic caldera, unique cultural heritage, early hominid fossils and significant wildlife populations. NCA has been managed as a multiple land‐use area since 1959, a designation intended to foster a harmonious coexistence between indigenous residents and wildlife (Goldstein, 2004).

The nociceptive network, responsible for transmission of nociceptive signals that generate the pain experience, is not fully developed at birth. Descending serotonergic modulation of spinal nociception, an important part of the pain network, undergoes substantial postnatal maturation and is suggested to be involved in the altered pain response observed in human newborns. This review summarizes preclinical data of the development of descending serotonergic modulation of the spinal nociceptive network across the life span, providing a comprehensive background to understand human newborn pain experience and treatment. Sprouting of descending serotonergic axons, originating from the rostroventral medulla, as well as changes in receptor function and expression take place in the first postnatal weeks of rodents, corresponding to human neonates in early infancy. Descending serotonergic modulation switches from facilitation in early life to bimodal control in adulthood, masking an already functional 5-HT inhibitory system at early ages. Specifically the 5-HT

Bespoke microsatellite marker panels are increasingly affordable and tractable to researchers and conservationists. The rate of microsatellite discovery is very high within a shotgun genomic data set, but extensive laboratory testing of markers is required for confirmation of amplification and polymorphism. By incorporating shotgun next‐generation sequencing data sets from multiple individuals of the same species, we have developed a new method for the optimal design of microsatellite markers. This new tool allows us to increase the rate at which suitable candidate markers are selected by 58% in direct comparisons and facilitate an estimated 16% reduction in costs associated with producing a novel microsatellite panel. Our method enables the visualisation of each microsatellite locus in a multiple sequence alignment allowing several important quality checks to be made. Polymorphic loci can be identified and prioritised. Loci containing fragment‐length‐altering mutations in the flanking regions, which may invalidate assumptions regarding the model of evolution underlying variation at the microsatellite, can be avoided. Priming regions containing point mutations can be detected and avoided, helping to reduce sample‐site‐marker specificity arising from genetic isolation, and the likelihood of null alleles occurring. We demonstrate the utility of this new approach in two species: an echinoderm and a bird. Our method makes a valuable contribution towards minimising genotyping errors and reducing costs associated with developing a novel marker panel. The Python script to perform our method of multi‐individual microsatellite identification (MiMi) is freely available from GitHub (https://github.com/graemefox/mimi).

© 2019 The Authors. African Journal of Ecology Published by John Wiley & Sons Ltd. Afromontane forests, like those in the Aberdare National Park (ANP) in Kenya, sustain unique avifaunal assemblages. There is a growing need for biodiversity inventories for Afromontane forests, especially through the utilisation of unskilled observers. Acoustic surveys are a potential aid to this, but more comparisons of this technique with that of traditional point counts are needed. We conducted a systematic survey of the ANP avifauna, assessing whether acoustic and traditional surveys resulted in different species richness scores, and whether this varied with habitat and species characteristics. We also investigated the role of habitat and elevation in driving variation in species richness. The ANP provides habitat types including scrub, moorland, montane, hagenia and bamboo forests. Overall, the surveys yielded 101 identified species. The acoustic method resulted in higher species richness scores compared to the traditional method across all habitats, and the relative performance of the two methods did not vary with habitat type or visibility. The methods detected different species, suggesting that they should be used together to maximise the range of species recorded. We found that habitat type was the primary driver of variation in species richness, with scrub and montane forest having higher species richness scores than other habitats.

Social dynamics are of fundamental importance in animal societies. Studies on nonhuman animal social systems often aggregate social interaction event data into a single network within a particular time frame. Analysis of the resulting network can provide a useful insight into the overall extent of interaction. However, through aggregation, information is lost about the order in which interactions occurred, and hence the sequences of actions over time. Many research hypotheses relate directly to the sequence of actions, such as the recency or rate of action, rather than to their overall volume or presence. Here, we demonstrate how the temporal structure of social interaction sequences can be quantified from disaggregated event data using the relational event model (REM). We first outline the REM, explaining why it is different from other models for longitudinal data, and how it can be used to model sequences of events unfolding in a network. We then discuss a case study on the European jackdaw, Corvus monedula, in which temporal patterns of persistence and reciprocity of action are of interest, and present and discuss the results of a REM analysis of these data. One of the strengths of a REM analysis is its ability to take into account different ways in which data are collected. Having explained how to take into account the way in which the data were collected for the jackdaw study, we briefly discuss the application of the model to other studies. We provide details of how the models may be fitted in the R statistical software environment and outline some recent extensions to the REM framework.

Bird song is a sexually selected signal that serves two main functions, attracting a mate and deterring rivals. Different signal parameters may be important in advertising to females compared to advertising to rival males. Species solve the problem of this dual function in a variety of ways, one of which may be to have separate parts of song directed at male and female receivers. The blackcap song has two distinct parts, a complex warble, assumed to be directed at female receivers, followed by a louder and more stereotyped whistle putatively directed at males. We simulated territorial intrusions by broadcasting blackcap song in territories. Comparing songs sung prior, with those produced in response to playback, showed that the proportion of the whistle component of songs increased, but not the warble. This study thus provides empirical evidence that the whistle component of the blackcap song plays a prominent role in male–male competition. The warble component of the blackcap song may be directed at females, but this requires further testing.

Responding to allospecific territorial signals may result in the unnecessary expenditure of energy and time and is therefore, in general, not adaptive. The signals of closely related species are often similar owing to common ancestry, especially when species evolve in allopatry. However, selection for species recognition in sympatry tends to result in distinct territorial signals. The endangered pink pigeon, Nesoenas mayeri, endemic to Mauritius, occurs in sympatry with the invasive Madagascan turtle dove, Nesoenas picturata, and their perch-coos are remarkably similar. We conducted playback experiments to test whether pink pigeons respond to coos from Madagascan turtle doves. Pink pigeons responded similarly to playback of conspecific and Madagascan turtle dove coos but not to those of the more distantly related and sympatric Stigmatopelia chinensis. This study stresses the need to identify the impact of N. picturata on the breeding success and conservation of N. mayeri.

Geographic isolation in rainforest refugia and local adaptation to ecological gradients may both be important drivers of evolutionary diversification. However, their relative importance and the underlying mechanisms of these processes remain poorly understood because few empirical studies address both putative processes in a single system. A key question is to what extent is divergence in signals that are important in mate and species recognition driven by isolation in rainforest refugia or by divergent selection across ecological gradients? We studied the little greenbul, Andropadus virens, an African songbird, in Cameroon and Uganda, to determine whether refugial isolation or ecological gradients better explain existing song variation. We then tested whether song variation attributable to refugial or ecological divergence was biologically meaningful using reciprocal playback experiments to territorial males. We found that much of the existing song variation can be explained by both geographic isolation and ecological gradients, but that divergence across the gradient, and not geographic isolation, affects male response levels. These data suggest that ecologically divergent traits, independent of historical isolation during glacial cycles, can promote reproductive isolation. Our study provides further support for the importance of ecology in explaining patterns of evolutionary diversification in ecologically diverse regions of the planet.

Many species of socially monogamous birds engage in extra-pair copulations, but the extent of extra-pair paternity varies considerably by species. The ecological conditions contributing to interspecific variation in rates of extra-pair paternity remain unclear. We used a combination of single-nucleotide polymorphisms and microsatellites to document extra-pair paternity in the Banded Wren (Thryothorus pleurostictus), a socially monogamous neotropical passerine that lives in a highly seasonal environment. The rate of extra-pair paternity was relatively low, with extra-pair males siring 4% of offspring in 10% of nests. This low rate is consistent with current hypotheses predicting low rates of extra-pair paternity in nonmigratory species in which survivorship of adults is high, and it is contrary to the pattern predicted by hypotheses linking synchronous breeding with high rates of extra-pair paternity. Extra-pair males sang better and were more genetically similar to females than the males they cu...

Little is known about the role of maternal nutrition in the development of hypospadias, which is the most common urogenital congenital anomaly. This study investigated the relationship between maternal nutrition and the risk of hypospadias, particularly focusing on maternal food patterns. We compared 471 hypospadias cases with 490 controls in the United Kingdom. A questionnaire including information on life style, occupation, usual maternal diet and dietary supplements was administered using telephone interviews. Cases and controls were compared for individual food item intake and food patterns derived by cluster analysis. Multivariable logistic regression analysis adjusted for income, maternal age, low birthweight, smoking and folic acid supplement use was used to assess the relationship between maternal nutrition and hypospadias. Three food patterns were created with the labels 'health conscious', 'mixed' and 'non-health conscious'. 'Non-health conscious' subjects (low frequency of consumption of yoghurt, cheese, eggs, fruit and vegetables, fish, beans and pulses, olive oil and organic food) had a higher risk of hypospadias (odds ratio 1.54; 95% confidence interval 1.06, 2.26) compared with 'health conscious' subjects (high frequency of consumption of fresh fruit and vegetables, dried fruit, fresh or frozen fish, beans, pulses, soya products, olive oil and organic food), after adjustment for potential confounders. Intakes of individual foods were not strongly associated with hypospadias. We could not exclude the possibility of residual confounding, and this needs to be further investigated. We found an association between food pattern and hypospadias, with those with less health conscious food patterns having a higher risk. Further study is needed to confirm this association.

Older males tend to have a competitive advantage over younger males in sexual selection. Therefore, it is expected that signals used in sexual selection change with age. Although song repertoire size in songbirds is often mentioned as an age-related trait, many species, including the banded wren ( Thryothorus pleurostictus ), do not increase their repertoires after the first year. Here, we show that banded wrens reproduce the trill notes in their songs with less variability between them (i.e. more consistently) when they grow older. In a playback experiment, we also show that banded wrens discriminate between younger and older birds based on structural aspects of their song. In a second experiment, banded wrens also respond differentially to natural songs versus songs with artificially enhanced consistency. We argue that consistency in trill note reproduction may be achieved through practice. Sexual selection in the form of male–male competition may therefore operate on a phenotypic trait, the expression of which is enhanced by practice.

Migratory birds are assumed to be under stronger sexual selection pressure than sedentary populations, and the fact that their song is more complex has been taken as confirmation of this fact. However, this assumes that sexual selection pressure due to both male competition and female choice increase together. A further issue is that, in many species, songs become less complex during competitive encounters; in contrast, female choice selects for more complex song, so the two selection pressures may drive song evolution in different directions. We analysed song in two sedentary and two migratory populations of blackcaps ( Sylvia atricapilla ), a species in which different song parts are directed to males and females. We found that migratory populations produce longer, female-directed warbles, indicating sexual selection through female choice is the strongest in these populations. However, the part of the song directed towards males is shorter and more repetitive (as observed in individual competitive encounters between males) in non-migratory populations, indicating sedentary populations, are under stronger selection due to male competition. We show for the first time that the intensity of selection pressure from male competition and female choice varies independently between populations with different migratory behaviours. Rapid alterations in the migration patterns of species are thus likely to lead to unexpected consequences for the costs and benefits of sexual signals.

Secondary contact between closely related species can lead to hybridization. The fitness of hybrid individuals within and outside the hybrid zone determines whether the hybrid zone expands into the ranges of the 2 parental species or remains a stable, geographically narrow area in between the allopatric ranges of the parental species. In birds, vocalizations play an important role in male‐male competition and female mate choice and are often affected by hybridization. One of the factors that will influence male hybrid fitness is the ability to defend a territory against competitors by vocalizing. We tested the efficacy of territorial signals of hybrids of 2 dove species, Streptopelia vinacea and Streptopelia capicola, compared with the vocalizations of the parental species. With playback experiments, we assessed the response to hybrid and the 2 parental species vocalizations in the hybrid zone and adjacent allopatric populations of each species. In the hybrid zone, males did not respond differently to the 3 vocalization types. In both allopatric populations, however, males responded more to conspecific than to heterospecific signals and the response strength to hybrid signals was intermediate. Therefore, in the allopatric populations, hybrid males may have a reduced success in defending territories. In male‐male interactions in the hybrid zone, hybrids may not have a disadvantage compared with males of the parental species. The ability to defend a territory against competitors may thus help maintain a stable hybrid zone in the area of overlap. Key words: acoustic signals, hybrid zone, playback, song, Streptopelia doves, territorial interactions. [Behav Ecol]

Food sharing in birds occurs largely in the context of parental care and courtship. Previous studies found that juvenile jackdaws demonstrate high levels of active giving outside these contexts in the 3 months following nest dispersal. The function of this behaviour is not understood, although it seemed compatible with hypotheses of mutualism (both participants benefit), reciprocity and harassment avoidance. We propose a new functional explanation for active giving in this species, namely facilitating the formation of social bonds. Captive juvenile jackdaws actively gave 2.5% of temporarily available food items and objects to peers, irrespective of sex and kinship. Active giving accounted for 43.7% of all food transfers. Donors advertised food and objects through a distinctive display and initiated active giving more than recipients. The direction of giving was initially unfocused, but became selective until each donor predominantly gave to one recipient and affiliative relationships were formed. We conclude that food-sharing may be an integral part of jackdaw ontogeny which allows juveniles to explore their social environment and facilitates the formation of affiliative relationships when family bonds dissolve. We also suggest that the ritualised food offer display may signal the 'collaborative intent' of the donor and serve to attract potential partners/mates.

Food sharing is common in birds between mated pairs during courtship and by helpers at the nest in cooperatively breeding species. In contrast to primates, however, food sharing between peers in birds has received little attention. We explored the extent and pattern of food sharing in a group of juvenile jackdaws. The birds shared food with a number of individuals, regardless of sex and kinship. The frequency of food sharing and the number of recipients per donor decreased over time. Active food sharing, where the initiative for the transfer lies with the donor, appeared to be much more common in jackdaws than in any primate species studied so far. In addition, jackdaws shared more of a preferred food than of a less preferred food. Three functional explanations for food sharing between peers were tested: reciprocity, harassment avoidance and food sharing as a signal of social status. The results were consistent with reciprocity and harassment avoidance.

Food caching has been linked to better performance on spatial memory tasks and enlarged hippocampal volume in both birds and mammals. Within food-caching birds, it has also been predicted that species less reliant on stored food should have inferior spatial memory and a smaller hippocampus compared to species that depend heavily on food caches. Several comparisons suggest that North American corvids have a significantly smaller hippocampus and overall brain volume compared to the Eurasian corvid species and that western scrub-jays (Aphelocoma californica) have a smaller hippocampus compared to the more specialized Clark’s nutcracker. Here we present the largest data set of scrub-jay brains and, in contrast to previous reports, show that relative to body mass western scrub-jays have a brain size similar to the largest brain size of Eurasian corvids. The relative hippocampal volume of scrub-jays is also among the largest of all investigated corvids. These findings may not be surprising considering that scrub-jays have been reported to have remarkable cognitive capacities such as episodic-like memory and experience projection. Our data suggest that many previously made assumptions about western scrub-jays as less specialized food hoarders might be an oversimplification and that simple categorization of species into specialized and non-specialized hoarders might not provide useful insights into the evolution of memory and the hippocampus.

A new noise-figure measurement method, which combines the simplicity of the "classical" Y-factor method with the accuracy of the widely used "cold noise-source" method, is reported. Implemented in our fully automated wide-band 1-18-GHz on-wafer noise-parameter measurement system, accurate results are obtained using a small set of precharacterized source impedances. We illustrate our method and its accuracy with data taken on a low-noise GaAs pseudomorphic high electron-mobility transistor device, and quantify the impact of the instrumental uncertainties on the extracted noise parameters.

Episodic-like memory, the retrospective component of cognitive time travel in animals, needs to fulfil three criteria to meet the behavioral properties of episodic memory as defined for humans. Here, we review results obtained with the cache-recovery paradigm with western scrub-jays and conclude that they fulfil these three criteria. The jays remember the what-when-where components of a caching episode (content), these components are integrated (structure), and can be updated and generalized over situations (flexibility). The interpretation of the temporal aspect of the jays’ episodic memory remains contentious however. For the memory to be episodic-like, the when component needs to result from time being encoded explicitly in memory as opposed to being a by-product of a decaying memory trace. We present new data in favor of explicit encoding of temporal information in the memory of scrub-jays. Finally, we discuss episodic-like memory in scrub-jays in relation to results obtained with other species.

Behavioural ecology assumes that cognitive traits and their underlying neural substrates are shaped by natural selection in much the same way as morphological traits are, resulting in adaptation to the natural environment of the species concerned. Recently, however, the 'neuroecology' approach of attempting to gain insight into brain structure and function by testing predictions about variation in brain structure based on knowledge of the lifestyle of the animal has been criticized on the grounds that such an adaptationist view cannot provide insight into the underlying mechanisms. Furthermore, the criticism has focussed on attempts to use variation in demand for spatial memory and in hippocampal size as a basis for predicting variation in cognitive abilities. Here, we revisit this critique against the field of so-called 'neuroecology' and argue that using knowledge of the natural history of animals has lead to a better understanding of the interspecific variation in spatial abilities and hippocampal size, and to the generation of novel hypotheses and predictions.

This paper presents a new method, developed for the capacitance–voltage (C–V) characterization of leaky dielectrics. The method comprises measurements in the gigahertz range on specially designed RF test structures. The method is verified against high-frequency C–V measurements on NMOS and PMOS structures. It yields reliable results even when the gate leakage is in excess of 100 A/cm2.

Most bird species produce different acoustic signals in different behavioural contexts. This intraspecific variation in signal types is thought to be the result of selection for optimal communication in each context. Doves in the genus Streptopelia have three distinct behavioural contexts in which they produce coo vocalizations. Some Streptopelia species have three acoustically similar coo vocalizations associated with the three contexts, but in others the coo vocalizations differ in acoustic structure. Using a well-resolved phylogeny, we examined whether acoustic differentiation between coo types was the ancestral state. Unexpectedly, the results showed that the common ancestor of Streptopelia had differentiated coos rather than a single coo type. This result implies that context-specific acoustic signals disappeared from the vocal repertoire independently at least two times. We further tested whether different context-dependent signal types follow different evolutionary pathways and whether they differ in rate of evolutionary change. We found that the long-range signal (perch-coo) evolves at a higher rate than the short-range signal (bow-coo). These results are discussed in relation to selection for species recognition and transmission requirements.

Sympatric occurrence of two closely related species is expected to lead to diverging or converging shifts in signal characteristics of one or both species. We examined signal characteristics in the vinaceous dove Streptopelia vinacea and the ring-necked dove S. capicola, two sister species that are mainly allopatric but occur in sympatry in northwestern Uganda. Vocal characteristics of the birds in sympatry were compared with those of an adjacent and a distant allopatric population of each species. The sympatric population showed intermediate values between the allopatric populations from Uganda. However, within each species there is little geographic variation between distant allopatric populations. Since vocal differences between dove species have a genetic base, the convergence in vocal characteristics is most likely explained by hybridization. Probably, the two species came into secondary contact relatively recently. Climatic changes during the last several thousand years and recent habitat changes caused by the growing human population, may have allowed Streptopelia capicola to extend its range in the northern direction.

Two closely related dove species, Streptopelia vinacea and S. capicola, show clear interspecific divergence in one acoustic signal (perch-coo), but much less so in another (bow-coo). Both signals play a role in territorial defense and mate attraction and may thus convey information used for species recognition. In Uganda, there is a small zone of overlap where the two species most probably hybridize. With playback experiments in allopatric populations of each species we tested the potential of the two signal types for species isolation. Allopatric populations showed a stronger response to conspecific than to heterospecific perch-coos, but an equal response to bow-coos of either species. However, S. vinacea responded relatively stronger to S. capicola perch-coos than vice versa. The hybrid population showed an equal response to bow-coos of either species, but a marginally stronger response to perch-coos of S. capicola compared to perch-coos of S. vinacea. Hybrids have a variable and intermediate vocal structure compared to both parental species, which allowed for testing of behavioral coupling between production and perception of these signals. Hybrids showed no relationship between their coo structure and that of the species to which they respond most strongly, indicating a lack of behavioral coupling. Although perch-coos may differ sufficiently to allow species isolation, the similarity in bow-coos may allow interspecific interactions. We suggest that the similarity in bow-coos and the higher salience of S. capicola perch-coos may have allowed S. capicola to extend its range into that of S. vinacea, resulting in hybridization.

Summary 1 Sentinel behaviour involves a unique cooperative system of dedicated look-outs which protect members of their social group from attack by predators. Using detailed observations from groups of Arabian babblers, Turdoides squamiceps, we tested the original theoretical suggestion that cooperative sentinel systems are simply the result of individually selfish state-dependent patterns of behaviour. 2 Sentinel effort and the number of sentinel bouts per individual per hour were greater for males than females, and both increased with individual dominance status within the group. 3 Sentinel behaviour was unaffected by group social structure, in terms of patterns of relatedness and the number of potential breeders. 4 Total group sentinel effort increased with group size, while the effort per individual decreased irrespective of sex and dominance rank. Simultaneous sentinel behaviour by two or more birds was very rare, but increased with group size. 5 Sentinel effort followed seasonal fluctuations in food availability, but not peaks of raptor migration through the study site. 6 Body mass was greater for males than females and was positively related to dominance rank. Overall, body mass explained much of the variation in individual sentinel effort both within and between birds. However, data on individual foraging performance could not be related to changes in body mass and thus to differences in sentinel effort. 7 Sentinel behaviour in groups of Arabian babblers therefore confirms many of the predictions arising from state-dependent models of cooperative, yet individually selfish, sentinel behaviour.

Cooperative sentinel behaviour in Arabian babblers, Turdoides squamiceps, appears generally consistent with state-dependent models of individually selfish antipredator behaviour. We examined further detailed aspects of this cooperative behaviour, including the suggestion that by engaging in this behaviour sentinels advertise their status and gain social prestige. Chosen sentinel locations were higher, but no more exposed, than the best alternative locations within 25 m. Sentinels started off closer to the centre of the foraging group than when sentinel bouts were terminated. Change-overs between sentinels were nearly always due to previous sentinels terminating their own bout. On the rare occasions when bouts were interrupted by upcoming sentinels, physical contact or aggression was extremely rare. Dominant males tended to terminate sentinel bouts of other birds, interrupting especially the dominant females. Other than this, there was no effect of an individual's sex or dominance rank on any aspect of sentinel change-overs or location choice when acting as a sentinel. There were also no differences in any sentinel activity between simple family groups, and those more complex nonfamily groups within which individuals compete for reproduction. Rates of alarm calling did not differ between group members, although dominant males did make more territorial calls to neighbouring groups while acting as a sentinel. Therefore, we found relatively little evidence that individuals compete for the chance to act as a sentinel as a means of showing off within groups of Arabian babblers. Instead, our study confirms the primary function of sentinels as a system of cooperative vigilance.

Using fracture of Cr single crystals at liquid helium temperature, we were able to obtain atomically clean and flat Cr(0 0 1) surfaces. The cleaved surfaces have been characterized by means of low-temperature scanning tunneling microscopy and spectroscopy techniques. Atomically resolved images taken at different locations on the cleaved surfaces show clearly the atomically resolved Cr(0 0 1) lattice with fourfold symmetry. The impurity concentrations did not exceed the bulk concentration, e.g., the brittle fracture process does not appear to cause segregation of impurities to the surface. Larger scans revealed that the cleaved surface consists of clean terraces separated by monoatomic steps with widths from a few to several hundred nanometers belonging to the (0 0 1) cleavage plane. We also found that the Cr(0 0 1) cleavage plane yields [1 0 0] and [1 1 0] steps. High-resolution spectroscopic investigations showed that the surface electronic structure has a very narrow and strong peak located at 26 meV above the Fermi level and allowed us to resolve its intrinsic width and shape. We also found that the peak is strongly reduced above the terrace edges.

A low-temperature scanning tunneling microscope has been used to study the (110)-cleavage surface of indium phosphide (InP) at 4.2 K. InP is a III-V compound semiconductor, and we studied the behavior of doping atoms at different bias voltages in both n- and p-type InP. In neither the n- nor the p-type InP did we observe Friedel oscillations, but the p-type InP with a Zn-dopant concentration of 2.7 x 10 18 cm -3 showed an interesting behavior at positive sample voltages: upon moving the tip Fermi level to the bottom of the conduction band, we observed that depressions in the surface topography caused by the influence of the Zn doping atoms changed into elevations with a triangular shape. This has previously been observed on p-type GaAs(110), and an explanation for these triangular features is not yet available.

Some of the 16 dove species in the genus Streptopelia are very similar with respect to plumage pattern, but all seem to produce species-specific perch-coo vocalizations. Here, we describe variation in perch-coo recordings of all 16 species. All individuals could be correctly classified by species in a discriminant function analysis, which means that the overlap in inter- and intraspecific variation was limited for the total set of acoustic parameters. Interspecific similarity in acoustic parameters was compared with taxonomic classification, based upon qualitative morphological characteristics and geographic distribution (Goodwin 1983). The clustering of species using the acoustic data set showed little congruence with taxonomic clustering. This indicates that differentiation in plumage pattern does not necessarily coincide with differentiation in acoustic characteristics. However, our analysis did not Completely contradict the subdivision into four taxonomic groups based on morphology and distribution. Two of the four putative groups differed significantly from the other groups in one of the components of a principal components analysis. Vocal differentiation in Streptopelia doves was strongest in temporal components, which is in line with expectations based on the evolutionarily conservative syringeal constraints.

Acoustic displays with difficult-to-execute sounds are often subject to strong sexual selection because performance levels are related to the sender’s condition or genetic quality. Performance may also vary with age, breeding stage, and motivation related to social context. We focused on within-male variation in four components of trill performance in banded wren (Thryophilus pleurostictus) songs: note consistency, frequency bandwidth, note rate, and vocal deviation. The latter is a composite measure reflecting deviation from the performance limit on simultaneously maximizing both frequency bandwidth and note rate. We compared the changes in these song parameters at three time scales: over the course of years, across the breeding season, and at different times of the day with contrasting agonistic contexts. Vocal deviation decreased and note consistency increased between years, suggesting that experience may improve individual proficiency at singing trills. Consistency also increased across the season, confirming that practice is important for this parameter. Although there was no significant seasonal change in vocal deviation, one of its components, note rate, increased during the season. Neither vocal deviation nor consistency varied with agonistic context. However, note rate increased during playback experiments simulating territorial intrusions compared to dawn chorus singing. The magnitude of a male’s increase in note rate was positively correlated with his aggressive behavior during the playback experiment. Thus consistency, bandwidth, and vocal deviation indicate age, whereas trill rate flexibly indicates the singer’s aggressive motivation. We also found evidence of a within-male trade-off between vocal deviation and consistency.

In general, it has been found that birds respond to exposure of anthropogenic noise by singing at a higher frequency range. This is presumably the result of an attempt by the birds to reduce the masking effect of the low rumble of urban noise. In sharp contrast, we report that chiffchaffs reduce song frequency at airports where noise levels are intermittent rather than constant, but at a much higher amplitude level. In addition, we show experimentally that airport birds respond more aggressively to playback of airport songs than the control songs, while a nearby control population does not discriminate between airport and control songs. Potential explanations for these results will be discussed.

We present a MOS Capacitance-Voltage measurement methodology that, contrary to present methods, is highly robust against gate leakage current densities up to 1000 A/cm/sup 2/. The methodology features specially designed RF test structures and RF measurement frequencies. It allows MOS parameter extraction in the full range of accumulation, depletion, and inversion.

Geographic isolation in rainforest refugia and local adaptation to ecological gradients may both be important drivers of evolutionary diversification. However, their relative importance and the underlying mechanisms of these processes remain poorly understood because few empirical studies address both putative processes in a single system. A key question is to what extent is divergence in signals that are important in mate and species recognition driven by isolation in rainforest refugia or by divergent selection across ecological gradients? We studied the little greenbul, Andropadus virens, an African songbird, in Cameroon and Uganda, to determine whether refugial isolation or ecological gradients better explain existing song variation. We then tested whether song variation attributable to refugial or ecological divergence was biologically meaningful using reciprocal playback experiments to territorial males. We found that much of the existing song variation can be explained by both geographic isolation and ecological gradients, but that divergence across the gradient, and not geographic isolation, affects male response levels. These data suggest that ecologically divergent traits, independent of historical isolation during glacial cycles, can promote reproductive isolation. Our study provides further support for the importance of ecology in explaining patterns of evolutionary diversification in ecologically diverse regions of the planet.

Little is known about the role of maternal nutrition in the development of hypospadias, which is the most common urogenital congenital anomaly. This study investigated the relationship between maternal nutrition and the risk of hypospadias, particularly focusing on maternal food patterns. We compared 471 hypospadias cases with 490 controls in the United Kingdom. A questionnaire including information on life style, occupation, usual maternal diet and dietary supplements was administered using telephone interviews. Cases and controls were compared for individual food item intake and food patterns derived by cluster analysis. Multivariable logistic regression analysis adjusted for income, maternal age, low birthweight, smoking and folic acid supplement use was used to assess the relationship between maternal nutrition and hypospadias. Three food patterns were created with the labels 'health conscious', 'mixed' and 'non-health conscious'. 'Non-health conscious' subjects (low frequency of consumption of yoghurt, cheese, eggs, fruit and vegetables, fish, beans and pulses, olive oil and organic food) had a higher risk of hypospadias (odds ratio 1.54; 95% confidence interval 1.06, 2.26) compared with 'health conscious' subjects (high frequency of consumption of fresh fruit and vegetables, dried fruit, fresh or frozen fish, beans, pulses, soya products, olive oil and organic food), after adjustment for potential confounders. Intakes of individual foods were not strongly associated with hypospadias. We could not exclude the possibility of residual confounding, and this needs to be further investigated. We found an association between food pattern and hypospadias, with those with less health conscious food patterns having a higher risk. Further study is needed to confirm this association.