How do great bowerbirds construct perspective illusions?

This is the final version of the article. Available from the Royal Society via the DOI in this record.Many animals build structures to provide shelter, avoid predation, attract mates or house offspring, but the behaviour and potential cognitive processes involved during building are poorly understood. Great bowerbird (Ptilinorhynchus nuchalis) males build and maintain display courts by placing tens to hundreds of objects in a positive size-distance gradient. The visual angles created by the gradient create a forced perspective illusion that females can use to choose a mate. Although the quality of illusion is consistent within males it varies among males, which may reflect differences in how individuals reconstruct their courts. We moved all objects off display courts to determine how males reconstructed the visual illusion. We found that all individuals rapidly created the positive size-distance gradient required for forced perspective within the first 10 objects placed. Males began court reconstruction by placing objects in the centre of the court and then placing objects further out, a technique commonly used when humans lay mosaics. The number of objects present after 72 hours was not related to mating success or the quality of the illusion, indicating that male skill at arranging objects rather than absolute number of objects appears to be important. We conclude that differences arise in the quality of forced perspective illusions despite males using the same technique to reconstruct their courts.LAK received funding from the People Programme (Marie Curie Actions) of the 459 European Union’s Seventh Framework Programme (FP7/2007-2013) under REA 460 grant agreement PIIF-GA-2012-327423. This research was partially funded by 461 Editor’s fees from Springer-Verlag and Deakin University to JAE

California scrub-jays reduce visual cues available to potential pilferers by matching food colour to caching substrate

This is the final version. Available from the Royal Society via the DOI in this record. Some animals hide food to consume later; however, these caches are susceptible to theft by conspecifics and heterospecifics. Caching animals can use protective strategies to minimize sensory cues available to potential pilferers, such as caching in shaded areas and in quiet substrate. Background matching (where object patterning matches the visual background) is commonly seen in prey animals to reduce conspicuousness, and caching animals may also use this tactic to hide caches, for example, by hiding coloured food in a similar coloured substrate. We tested whether California scrubjays (Aphelocoma californica) camouflage their food in this way by offering them caching substrates that either matched or did not match the colour of food available for caching. We also determined whether this caching behaviour was sensitive to social context by allowing the birds to cache when a conspecific potential pilferer could be both heard and seen (acoustic and visual cues present), or unseen (acoustic cues only). When caching events could be both heard and seen by a potential pilferer, birds cached randomly in matching and non-matching substrates. However, they preferentially hid food in the substrate that matched the food colour when only acoustic cues were present. This is a novel cache protection strategy that also appears to be sensitive to social context. We conclude that studies of cache protection strategies should consider the perceptual capabilities of the cacher and potential pilferers.European Union’s Seventh Framework Programm

Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2

The Deep Impact spacecraft fly-by of comet 103P/Hartley 2 occurred on 2010 November 4, one week after perihelion with a closest approach (CA) distance of about 700 km. We used narrowband images obtained by the Medium Resolution Imager (MRI) onboard the spacecraft to study the gas and dust in the innermost coma. We derived an overall dust reddening of 15\%/100 nm between 345 and 749 nm and identified a blue enhancement in the dust coma in the sunward direction within 5 km from the nucleus, which we interpret as a localized enrichment in water ice. OH column density maps show an anti-sunward enhancement throughout the encounter except for the highest resolution images, acquired at CA, where a radial jet becomes visible in the innermost coma, extending up to 12 km from the nucleus. The OH distribution in the inner coma is very different from that expected for a fragment species. Instead, it correlates well with the water vapor map derived by the HRI-IR instrument onboard Deep Impact \citep{AHearn2011}. Radial profiles of the OH column density and derived water production rates show an excess of OH emission during CA that cannot be explained with pure fluorescence. We attribute this excess to a prompt emission process where photodissociation of H$_2$O directly produces excited OH*($A^2\it{\Sigma}^+$) radicals. Our observations provide the first direct imaging of Near-UV prompt emission of OH. We therefore suggest the use of a dedicated filter centered at 318.8 nm to directly trace the water in the coma of comets.Comment: 21 page

Herring gulls respond to human gaze direction

This is the final version. Available from The Royal Society via the DOI in this record. Human-wildlife conflict is one of the greatest threats to species populations worldwide. One species facing national declines in the UK is the herring gull (Larus argentatus), despite an increase in numbers in urban areas. Gulls in urban areas are often considered a nuisance owing to behaviours such as food-snatching. Whether urban gull feeding behaviour is influenced by human behavioural cues, such as gaze direction, remains unknown. We therefore measured the approach times of herring gulls to a food source placed in close proximity to an experimenter who either looked directly at the gull or looked away. We found that only 26% of targeted gulls would touch the food, suggesting that food-snatching is likely to be conducted by a minority of individuals. When gulls did touch the food, they took significantly longer to approach when the experimenter's gaze was directed towards them compared with directed away. However, inter-individual behaviour varied greatly, with some gulls approaching similarly quickly in both treatments, while others approached much more slowly when the experimenter was looking at them. These results indicate that reducing human-herring gull conflict may be possible through small changes in human behaviour, but will require consideration of behavioural differences between individual gulls.Royal Society Dorothy Hodgkin Research fellowshi

The role of pictorial cues and contrast for camouflage

This is the final version. Available on open access from Springer via the DOI in this recordData Availability: Supporting data are available in the Supplementary Material (S4 & S5).Code Availability: Supporting code are available in the Supplementary Material (S6).Shadows that are produced across the surface of an object (self-shadows) are potentially an important source of information for visual systems. Animal patterns may exploit this principle for camouflage, using pictorial cues to produce false depth information that manipulates the viewer’s detection/recognition processes. However, pictorial cues could also facilitate camouflage by matching the contrast (e.g. due to shadows) of 3D backgrounds. Aside from studies of countershading (patterning that may conceal depth information), the role of self-shadows in camouflage patterns remains unclear. Here we investigated whether pictorial cues (self-shadows) increase the survival probability of moth-like prey presented to free-living wild bird predators relative to targets without these cues. We manipulated the presence of self-shadows by adjusting the illumination conditions to produce patterned targets under directional lighting (lit from above or from below; self-shadows present) or diffuse lighting (no self-shadows). We used non-patterned targets (uniform colour) as controls. We manipulated the direction of illumination because it has been linked with depth perception in birds; objects lit from above may appear convex while those lit from below can appear concave. As shadows influence contrast, which also determines detectability, we photographed the targets in situ over the observation period, allowing us to evaluate the effect of visual metrics on survival. We found some evidence that patterned targets without self-shadows had a lower probability of survival than patterned targets with self-shadows and targets with uniform colour. Surprisingly, none of the visual metrics explained variation in survival probability. However, predators increased their foraging efficiency over time, suggesting that predator learning may have overridden the benefits afforded by camouflaging coloration.Australian Research Council (ARC)Royal SocietyNatural Environment Research Council (NERC

Spectral properties of the X-ray binary pulsar LMC X-4 during different intensity states

We present spectral variations of the binary X-ray pulsar LMC X-4 observed with the RXTE/PCA during different phases of its 30.5 day long third period. Only out of eclipse data were used for this study. The 3-25 keV spectrum, modeled with high energy cut-off power-law and iron line emission is found to show strong dependence on the intensity state. Correlations between the Fe line emission flux and different parameters of the continuum are presented here.Comment: 4 pages, 4 figure

Quantum tomography of mesoscopic superpositions of radiation states

We show the feasibility of a tomographic reconstruction of Schr\"{o}dinger cat states generated according to the scheme proposed by S. Song, C.M. Caves and B. Yurke [Phys. Rev. A 41, 5261 (1990)]. We present a technique that tolerates realistic values for quantum efficiency at photodetectors. The measurement can be achieved by a standard experimental setup.Comment: Submitted to Phys. Rev. Lett.; 4 pages including 6 ps figure

Sex differences in behavioural and anatomical estimates of visual acuity in the green swordtail Xiphophorus helleri

This is the author accepted manuscript. The final version is available on open access from the Company of Biologists via the DOI in this recordData availability: All data and codes underlying the analyses in this paper have been uploaded to the Dryad data repositoryAmong fishes in the family Poeciliidae, signals such as colour patterns, ornaments, and courtship displays play important roles in mate choice and male-male competition. Despite this, visual capabilities in Poeciliids are understudied, in particular visual acuity, the ability to resolve detail. We used three methods to quantify visual acuity in male and female green swordtails (Xiphophorus helleri), a species in which body size and the length of the male’s extended caudal fin (‘sword’) serve as assessment signals during mate choice and agonistic encounters. Topographic distribution of retinal ganglion cells (RGC) was similar in all individuals and characterized by areas of high cell densities located centro-temporally and nasally, as well as a weak horizontal streak. Based on the peak density of RGC in the centro-temporal area, anatomical acuity was estimated to be approximately 3 cycles/degree (cpd) in both sexes. However, a behavioural optomotor assay found significantly lower mean acuity in males (0.8 cpd) than females (3.0 cpd), which was not explained by differences in eye size between males and females. An additional behavioural assay, in which we trained individuals to discriminate striped gratings from grey stimuli of the same mean luminance, also showed lower acuity in males (1-2 cpd) than females (2-3 cpd). Thus, although retinal anatomy predicts identical acuity in males and females, two behavioural assays found higher acuity in females than males, a sexual dimorphism which is rare outside of invertebrates. Overall, our results have implications for understanding how Poeciliids perceive visual signals during mate choice and agonistic encounters.European Union Horizon 2020Australian Research Council (ARC)Royal Societ