Habitat geometry rather than visual acuity limits the visibility of a ground-nesting bird's clutch to terrestrial predators

The nests of ground-nesting birds rely heavily on camouflage for their survival, and predation risk, often linked to ecological changes from human activity, is a major source of mortality. Numerous ground-nesting bird populations are in decline, so understanding the effects of camouflage on their nesting behavior is relevant to their conservation concerns. Habitat three-dimensional (3D) geometry, together with predator visual abilities, viewing distance, and viewing angle, determine whether a nest is either visible, occluded, or too far away to detect. While this link is intuitive, few studies have investigated how fine-scale geometry is likely to help defend nests from different predator guilds. We quantified nest visibility based on 3D occlusion, camouflage, and predator visual modeling in northern lapwings, Vanellus vanellus, on different land management regimes. Lapwings selected local backgrounds that had a higher 3D complexity at a spatial scale greater than their entire clutches compared to local control sites. Importantly, our findings show that habitat geometry-rather than predator visual acuity-restricts nest visibility for terrestrial predators and that their field habitats, perceived by humans as open, are functionally closed with respect to a terrestrial predator searching for nests on the ground. Taken together with lapwings' careful nest site selection, our findings highlight the importance of considering habitat geometry for understanding the evolutionary ecology and management of conservation sites for ground-nesting birds.

MGL: Mutual Graph Learning for Camouflaged Object Detection

Camouflaged object detection, which aims to detect/segment the object(s) that blend in with their surrounding, remains challenging for deep models due to the intrinsic similarities between foreground objects and background surroundings. Ideally, an effective model should be capable of finding valuable clues from the given scene and integrating them into a joint learning framework to co-enhance the representation. Inspired by this observation, we propose a novel Mutual Graph Learning (MGL) model by shifting the conventional perspective of mutual learning from regular grids to graph domain. Specifically, an image is decoupled by MGL into two task-specific feature maps - one for finding the rough location of the target and the other for capturing its accurate boundary details. Then, the mutual benefits can be fully exploited by reasoning their high-order relations through graphs recurrently. It should be noted that our method is different from most mutual learning models that model all between-task interactions with the use of a shared function. To increase information interactions, MGL is built with typed functions for dealing with different complementary relations. To overcome the accuracy loss caused by interpolation to higher resolution and the computational redundancy resulting from recurrent learning, the S-MGL is equipped with a multi-source attention contextual recovery module, called R-MGL_v2, which uses the pixel feature information iteratively. Experiments on challenging datasets, including CHAMELEON, CAMO, COD10K, and NC4K demonstrate the effectiveness of our MGL with superior performance to existing state-of-the-art methods. The code can be found at https://github.com/fanyang587/MGL.

Sexually dimorphic dorsal coloration in a jumping spider: testing a potential case of sex-specific mimicry

To avoid predation, many animals mimic behaviours and/or coloration of dangerous prey. Here we examine potential sex-specific mimicry in the jumping spider Habronattus pyrrithrix. Previous work proposed that males' conspicuous dorsal coloration paired with characteristic leg-waving (i.e. false antennation) imperfectly mimics hymenopteran insects (e.g. wasps and bees), affording protection to males during mate-searching and courtship. By contrast, less active females are cryptic and display less leg-waving. Here we test the hypothesis that sexually dimorphic dorsal colour patterns in H. pyrrithrix are most effective when paired with sex-specific behaviours. We manipulated spider dorsal coloration with makeup to model the opposite sex and exposed them to a larger salticid predator (Phidippus californicus). We predicted that males painted like females should suffer higher predation rates than sham-control males. Likewise, females painted like males should suffer higher predation rates than sham-control females. Contrary to expectations, spiders with male-like coloration were attacked more than those with female-like coloration, regardless of their actual sex. Moreover, males were more likely to be captured, and were captured sooner, than females (regardless of colour pattern). With these unexpected negative results, we discuss alternative functional hypotheses for H. pyrrithrix colours, as well as the evolution of defensive coloration generally.

Variation in activity rates may explain sex-specific dorsal color patterns in Habronattus jumping spiders

In many animals, color pattern and behavior interact to deceive predators. For mimics, such deception can range from precise (near-perfect mimicry) to only subtle resemblance (imperfect mimicry) and such strategies often differ by sex because of differing ecological selection pressures. In this field study, we examine variation in behavior and ecology that may be linked with sex differences in dorsal color pattern in three sympatric species of Habronattus jumping spiders (H. clypeatus, H. hallani, H. pyrrithrix). Males of these species have conspicuous dorsal patterning that is subtly reminiscent of the general color patterns of wasps and bees, while females are cryptic. We show that, compared with females, these conspicuous males exhibited increased leg-waving behavior outside of the context of courtship; such behavior is common in jumping spiders that mimic wasps and bees presumably because a mimic’s waving legs resemble antennae. Males of a fourth sympatric species (H. hirsutus) without conspicuous dorsal patterning did not exhibit increased leg-waving. These results are consistent with and offer preliminary support for the idea that male color and behavior may work together to deceive predators. We also examined whether higher movement rates of males (who must wander to find females) and/or different use of the microhabitat by the sexes could explain sexual dichromatism. We found that microhabitat use was similar for males and females, but males of all three conspicuously-colored species spent more time actively moving than females. To our knowledge, this is the first study to speculate that conspicuous male dorsal coloration in Habronattus may have a deceptive function, and to explore why dorsal coloration differs between the sexes.

Camouflage strategies interfere differently with observer search images

Numerous animals rely on camouflage for defence. Substantial past work has identified the presence of multiple strategies for concealment, and tested the mechanisms underpinning how they work. These include background matching, D-RUP coloration to destroy target edges, and distractive markings that may divert attention from key target features. Despite considerable progress, work has focused on how camouflage types prevent initial detection by naive observers. However, predators will often encounter multiple targets over time, providing the opportunity to learn or focus attention through search images. At present, we know almost nothing about how camouflage types facilitate or hinder predator performance over repeated encounters. Here, we use experiments with human subjects searching for targets on touch screens with different camouflage strategies, and control the experience that subjects have with target types. We show that different camouflage strategies affect how subjects improve in detecting targets with repeated encounters, and how performance in detection of one camouflage type depends on experience of other strategies. In particular, disruptive coloration is effective at preventing improvements in camouflage breaking during search image formation, and experience with one camouflage type (distraction) can decrease the ability of subjects to switch to and from search images for new camouflage types (disruption). Our study is, to our knowledge, the first to show how the success of camouflage strategies depends on how they prevent initial and successive detection, and on predator experience of other strategies. This has implications for the evolution of prey phenotypes, how we assess the efficacy of defences, and predator-prey dynamics.