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How camouflage works
For camouflage to succeed, an individual has to pass undetected, unrecognized or untargeted, and hence it is the processing of visual information that needs to be deceived. Camouflage is therefore an adaptation to the perception and cognitive mechanisms of another animal. Although this has been acknowledged for a long time, there has been no unitary account of the link between visual perception and camouflage. Viewing camouflage as a suite of adaptations to reduce the signal-to-noise ratio provides the necessary common framework. We review the main processes in visual perception and how animal camouflage exploits these. We connect the function of established camouflage mechanisms to the analysis of primitive features, edges, surfaces, characteristic features and objects (a standard hierarchy of processing in vision science). Compared to the commonly used research approach based on established camouflage mechanisms, we argue that our approach based on perceptual processes targeted by camouflage has several important benefits: specifically, it enables the formulation of more precise hypotheses and addresses questions that cannot even be identified when investigating camouflage only through the classic approach based on the patterns themselves. It also promotes a shift from the appearance to the mechanistic function of animal coloration.
This article is part of the themed issue ‘Animal coloration: production, perception, function and application’.
Journal Article
Fort Worth then : the art of Samuel P. Ziegler
\"Rare images of Fort Worth, Texas in the 1920s and 1930s abound in the art of Samuel P. Ziegler (1882-1967). Standing apart from his local contemporaries, Ziegler regarded Fort Worth's rapid urban development as an indispensable source of ideas. He expressed these ideas in paintings, drawings, etchings and lithographs of significant buildings, street scenes, demolition sites, construction sites, the Texas Christian University campus, where he taught music and art, and the Trinity River. In the late 1920s, his artistic output grew to include depictions of oil production efforts in counties west of Fort Worth. In this publication, many representative examples of Ziegler's work from this period are presented for the first time. Taken as a whole, these little-known works of art capture a sense of the metamorphosis that the City of Fort Worth experienced in the first half of the twentieth century, as seen through the eyes of a Texas Christian University art professor who never had to look far to find inspiration. Because of his ability to absorb the sights of the city and the oil boom spectacle unfolding on Fort Worth's doorstep, and turn these sights into art, Samuel P. Ziegler embodied the mindset of all Texas artists living in the Depression era who believed in and pursued the regionalist ideal\"-- Provided by publisher.
Book
Geologic controls on supercritical geothermal resources above magmatic intrusions
A new and economically attractive type of geothermal resource was recently discovered in the Krafla volcanic system, Iceland, consisting of supercritical water at 450 °C immediately above a 2-km deep magma body. Although utilizing such supercritical resources could multiply power production from geothermal wells, the abundance, location and size of similar resources are undefined. Here we present the first numerical simulations of supercritical geothermal resource formation, showing that they are an integral part of magma-driven geothermal systems. Potentially exploitable resources form in rocks with a brittle–ductile transition temperature higher than 450 °C, such as basalt. Water temperatures and enthalpies can exceed 400 °C and 3 MJ kg
−1
, depending on host rock permeability. Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water. Our models reproduce the measured thermal conditions of the resource discovered at Krafla. Similar resources may be widespread below conventional high-enthalpy geothermal systems.
Utilizing supercritical geothermal water could multiply energy production, but the abundance, location and size of such resources is unclear. Here, the authors present numerical simulations and suggest that supercritical water may play a key role in removing heat from all magmatic intrusions.
Journal Article
Amphibious shipping shortfalls : risks and opportunities to bridge the gap
In this report, the CSIS Harold Brown Chair in Defense Policy Studies analyzes the types of capabilities necessary across the range of military operations, and compares that with the characteristics of amphibious ships, as well as those in the Combat Logistics Fleet, Maritime Prepositioning Force, and others. Resulting shortfalls in key capability areas suggest some degree of risk. The study then describes how amenable those risks may be to mitigation and some of the associated implications. This report provides a framework for policymakers to understand those areas in which alternative platforms might be most useful, where risks associated with their employment are most significant, and how readily broadening platforms beyond the uses for which they were designed might be accomplished. -- Amazon.
Book
The Camouflage Machine
Evolutionary biologists frequently wish to measure the fitness of alternative phenotypes using behavioral experiments. However, many phenotypes are complex. One example is coloration: camouflage aims to make detection harder, while conspicuous signals (e.g., for warning or mate attraction) require the opposite. Identifying the hardest and easiest to find patterns is essential for understanding the evolutionary forces that shape protective coloration, but the parameter space of potential patterns (colored visual textures) is vast, limiting previous empirical studies to a narrow range of phenotypes. Here, we demonstrate how deep learning combined with genetic algorithms can be used to augment behavioral experiments, identifying both the best camouflage and the most conspicuous signal(s) from an arbitrarily vast array of patterns. To show the generality of our approach, we do so for both trichromatic (e.g., human) and dichromatic (e.g., typical mammalian) visual systems, in two different habitats. The patterns identified were validated using human participants; those identified as the best for camouflage were significantly harder to find than a tried-and-tested military design, while those identified as most conspicuous were significantly easier to find than other patterns. More generally, our method, dubbed the “Camouflage Machine,” will be a useful tool for identifying the optimal phenotype in high dimensional state spaces.
Journal Article
Intergenerational nutrition benefits of India’s national school feeding program
India has the world’s highest number of undernourished children and the largest school feeding program, the Mid-Day Meal (MDM) scheme. As school feeding programs target children outside the highest-return “first 1000-days” window, they have not been included in the global agenda to address stunting. School meals benefit education and nutrition in participants, but no studies have examined whether benefits carry over to their children. Using nationally representative data on mothers and their children spanning 1993 to 2016, we assess whether MDM supports intergenerational improvements in child linear growth. Here we report that height-for-age z-score (HAZ) among children born to mothers with full MDM exposure was greater (+0.40 SD) than that in children born to non-exposed mothers. Associations were stronger in low socioeconomic strata and likely work through women’s education, fertility, and health service utilization. MDM was associated with 13–32% of the HAZ improvement in India from 2006 to 2016.
India’s national school feeding program is the largest of its kind in the world, but the long-term program benefits on nutrition are unknown. Here, the authors show intergenerational program benefits, in that women who received free meals in primary school have children with improved linear growth.
Journal Article
Optimal background matching camouflage
Background matching is the most familiar and widespread camouflage strategy: avoiding detection by having a similar colour and pattern to the background. Optimizing background matching is straightforward in a homogeneous environment, or when the habitat has very distinct sub-types and there is divergent selection leading to polymorphism. However, most backgrounds have continuous variation in colour and texture, so what is the best solution? Not all samples of the background are likely to be equally inconspicuous, and laboratory experiments on birds and humans support this view. Theory suggests that the most probable background sample (in the statistical sense), at the size of the prey, would, on average, be the most cryptic. We present an analysis, based on realistic assumptions about low-level vision, that estimates the distribution of background colours and visual textures, and predicts the best camouflage. We present data from a field experiment that tests and supports our predictions, using artificial moth-like targets under bird predation. Additionally, we present analogous data for humans, under tightly controlled viewing conditions, searching for targets on a computer screen. These data show that, in the absence of predator learning, the best single camouflage pattern for heterogeneous backgrounds is the most probable sample.
Journal Article
Dazzle Camouflage Affects Speed Perception
Movement is the enemy of camouflage: most attempts at concealment are disrupted by motion of the target. Faced with this problem, navies in both World Wars in the twentieth century painted their warships with high contrast geometric patterns: so-called \"dazzle camouflage\". Rather than attempting to hide individual units, it was claimed that this patterning would disrupt the perception of their range, heading, size, shape and speed, and hence reduce losses from, in particular, torpedo attacks by submarines. Similar arguments had been advanced earlier for biological camouflage. Whilst there are good reasons to believe that most of these perceptual distortions may have occurred, there is no evidence for the last claim: changing perceived speed. Here we show that dazzle patterns can distort speed perception, and that this effect is greatest at high speeds. The effect should obtain in predators launching ballistic attacks against rapidly moving prey, or modern, low-tech battlefields where handheld weapons are fired from short ranges against moving vehicles. In the latter case, we demonstrate that in a typical situation involving an RPG7 attack on a Land Rover the reduction in perceived speed is sufficient to make the grenade miss where it was aimed by about a metre, which could be the difference between survival or not for the occupants of the vehicle.
Journal Article
Distance-dependent defensive coloration in the poison frog Dendrobates tinctorius, Dendrobatidae
Poison dart frogs provide classic examples of warning signals: potent toxins signaled by distinctive, conspicuous coloration. We show that, counterintuitively, the bright yellow and blue-black color of Dendrobates tinctorius (Dendrobatidae) also provides camouflage. Through computational modeling of predator vision, and a screen-based detection experiment presenting frogs at different spatial resolutions, we demonstrate that at close range the frog is highly detectable, but from a distance the colors blend together, forming effective camouflage. This result was corroborated with an in situ experiment, which found survival to be background-dependent, a feature more associated with camouflage than aposematism. Our results suggest that in D. tinctorius the distribution of pattern elements, and the particular colors expressed, act as a highly salient close range aposematic signal, while simultaneously minimizing detectability to distant observers.
Journal Article