The Effect of Income and Wealth on Behavioral Strategies, Personality Traits, and Preferences

Individuals living in either harsh or favorable environments display well-documented psychological and behavioral differences. For example, people in favorable environments tend to be more future-oriented, trust strangers more, and have more explorative preferences. To account for such differences, psychologists have turned to evolutionary biology and behavioral ecology, in particular, the literature on life-history theory and pace-of-life syndrome. However, critics have found that the theoretical foundations of these approaches are fragile and that differences in life expectancy cannot explain vast psychological and behavioral differences. In this article, we build on the theory of optimal resource allocation to propose an alternative framework. We hypothesize that the quantity of resources available, such as income, has downstream consequences on psychological traits, leading to the emergence of behavioral syndromes. We show that more resources lead to more long-term orientation, more tolerance of variance, and more investment in low marginal-benefit needs. At the behavioral level, this translates, among others, into more large-scale cooperation, more investment in health, and more exploration. These individual-level differences in behavior, in turn, account for cultural phenomena such as puritanism, authoritarianism, and innovation.

Efficiency traps beyond the climate crisis: exploration-exploitation trade-offs and rebound effects

Higher levels of economic activity are often accompanied by higher energy use and consumption of natural resources. As fossil fuels still account for 80% of the global energy mix, energy consumption remains closely linked to greenhouse gas (GHG) emissions and thus to climate change. Under the assumption of sufficiently elastic demand, this reality of global economic development based on permanent growth of economic activity, brings into play the Jevons Paradox, which hypothesises that increases in the efficiency of resource use leads to increases in resource consumption. Previous research on the rebound effects has limitations, including a lack of studies on the connection between reinforcement learning and environmental consequences. This paper develops a mathematical model and computer simulator to study the effects of micro-level exploration-exploitation strategies on efficiency, consumption and sustainability, considering different levels of direct and indirect rebound effects. Our model shows how optimal exploration-exploitation strategies for increasing efficiency can lead to unsustainable development patterns if they are not accompanied by demand reduction measures, which are essential for mitigating climate change. Moreover, our paper speaks to the broader issue of efficiency traps by highlighting how indirect rebound effects not only affect primary energy (PE) consumption and GHG emissions, but also resource consumption in other domains. By linking these issues together, our study sheds light on the complexities and interdependencies involved in achieving sustainable development goals. This article is part of the theme issue 'Climate change adaptation needs a science of culture'.

Exploratory preferences explain the human fascination for imaginary worlds in fictional stories

Imaginary worlds are present and often central in many of the most culturally successful modern narrative fictions, be it in novels (e.g., Harry Potter), movies (e.g., Star Wars), video games (e.g., The Legend of Zelda), graphic novels (e.g., One Piece) and TV series (e.g., Game of Thrones). We propose that imaginary worlds are popular because they activate exploratory preferences that evolved to help us navigate the real world and find new fitness-relevant information. Therefore, we hypothesize that the attraction to imaginary worlds is intrinsically linked to the desire to explore novel environments and that both are influenced by the same underlying factors. Notably, the inter-individual and cross-cultural variability of the preference for imaginary worlds should follow the inter-individual and cross-cultural variability of exploratory preferences (with the personality trait Openness-to-experience, age, sex, and ecological conditions). We test these predictions with both experimental and computational methods. For experimental tests, we run a pre-registered online experiment about movie preferences (N = 230). For computational tests, we leverage two large cultural datasets, namely the Internet Movie Database (N = 9424 movies) and the Movie Personality Dataset (N = 3.5 million participants), and use machine-learning algorithms (i.e., random forest and topic modeling). In all, consistent with how the human preference for spatial exploration adaptively varies, we provide empirical evidence that imaginary worlds appeal more to more explorative people, people higher in Openness-to-experience, younger individuals, males, and individuals living in more affluent environments. We discuss the implications of these findings for our understanding of the cultural evolution of narrative fiction and, more broadly, the evolution of human exploratory preferences.

The value of spatial experience and group size for ant colonies in direct competition

Animals often search for food more efficiently with experience. However, the contribution of experience to foraging success under direct competition has rarely been examined. Here we used colonies of an individually foraging desert ant to investigate the value of spatial experience. First, we trained worker groups of equal numbers to solve either a complex or a simple maze. We then tested pairs of both groups against one another in reaching a food reward. This task required solving the same complex maze that one of the groups had been trained in, to determine which group would exploit better the food reward. The worker groups previously trained in the complex mazes reached the food reward faster and more of these workers fed on the food than those trained in simple mazes, but only in the intermediate size group. To determine the relative importance of group size versus spatial experience in exploiting food patches, we then tested smaller trained worker groups against larger untrained ones. The larger groups outcompeted the smaller ones, despite the latter's advantage of spatial experience. The contribution of spatial experience, as found here, appears to be small, and depends on group size: an advantage of a few workers of the untrained group over the trained group negates its benefits.

Beyond Bio-Inspired Robotics: How Multi-Robot Systems Can Support Research on Collective Animal Behavior

In the study of collective animal behavior, researchers usually rely on gathering empirical data from animals in the wild. While the data gathered can be highly accurate, researchers have limited control over both the test environment and the agents under study. Further aggravating the data gathering problem is the fact that empirical studies of animal groups typically involve a large number of conspecifics. In these groups, collective dynamics may occur over long periods of time interspersed with excessively rapid events such as collective evasive maneuvers following a predator’s attack. All these factors stress the steep challenges faced by biologists seeking to uncover the fundamental mechanisms and functions of social organization in a given taxon. Here, we argue that beyond commonly used simulations, experiments with multi-robot systems offer a powerful toolkit to deepen our understanding of various forms of swarming and other social animal organizations. Indeed, the advances in multi-robot systems and swarm robotics over the past decade pave the way for the development of a new hybrid form of scientific investigation of social organization in biology. We believe that by fostering such interdisciplinary research, a feedback loop can be created where agent behaviors designed and tested in robotico can assist in identifying hypotheses worth being validated through the observation of animal collectives in nature. In turn, these observations can be used as a novel source of inspiration for even more innovative behaviors in engineered systems, thereby perpetuating the feedback loop.

Upper-limit agricultural dietary exposure to streptomycin in the laboratory reduces learning and foraging in bumblebees

In the past decade, the broadcast-spray application of antibiotics in US crops has increased exponentially in response to bacterial crop pathogens, but little is known about the sublethal impacts on beneficial organisms in agroecosystems. This is concerning given the key roles that microbes play in modulating insect fitness. A growing body of evidence suggests that insect gut microbiomes may play a role in learning and behaviour, which are key for the survival of pollinators and for their pollination efficacy, and which in turn could be disrupted by dietary antibiotic exposure. In the laboratory, we tested the effects of an upper-limit dietary exposure to streptomycin (200 ppm)-an antibiotic widely used to treat bacterial pathogens in crops-on bumblebee (Bombus impatiens) associative learning, foraging and stimulus avoidance behaviour. We used two operant conditioning assays: a free movement proboscis extension reflex protocol focused on short-term memory formation, and an automated radio-frequency identification tracking system focused on foraging. We show that upper-limit dietary streptomycin exposure slowed training, decreased foraging choice accuracy, increased avoidance behaviour and was associated with reduced foraging on sucrose-rewarding artificial flowers flowers. This work underscores the need to further study the impacts of antibiotic use on beneficial insects in agricultural systems.

Cognitive flexibility in the wild: Individual differences in reversal learning are explained primarily by proactive interference, not by sampling strategies, in two passerine bird species

Behavioural flexibility allows animals to adjust to changes in their environment. Although the cognitive processes that explain flexibility have been relatively well studied in psychology, this is less true for animals in the wild. Here we use data collected automatically during self-administered discrimination-learning trials for two passerine species, and during four phases (habituation, initial learning, first reversal and second reversal) in order to decompose sources of consistent among-individual differences in reversal learning, a commonly used measure for cognitive flexibility. First, we found that, as expected, proactive interference was significantly repeatable and had a negative effect on reversal learning, confirming that individuals with poor ability to inhibit returning to a previously rewarded feeder were also slower to reversal learn. Second, to our knowledge for the first time in a natural population, we examined how sampling of non-rewarding options post-learning affected reversal-learning performance. Sampling quantity was moderately repeatable in blue tits but not great tits; sampling bias, the variance in the proportion of visits to each non-rewarded feeder, was not repeatable for either species. Sampling behaviour did not predict variation in reversal-learning speed to any significant extent. Finally, the repeatability of reversal learning was explained almost entirely by proactive interference for blue tits; in great tits, the effects of proactive interference and sampling bias on the repeatability of reversal learning were indistinguishable. Our results highlight the value of proactive interference as a more direct measurement of cognitive flexibility and shed light on how animals respond to changes in their environment.

Slow-Fast Cognitive Phenotypes and Their Significance for Social Behavior: What Can We Learn From Honeybees?

Cognitive variation is proposed to be the fundamental underlying factor that drives behavioral variation, yet it is still to be fully integrated with the observed variation at other phenotypic levels that has recently been unified under the common pace-of-life framework. This cognitive and the resulting behavioral diversity is especially significant in the context of a social group, the performance of which is a collective outcome of this diversity. In this review, we argue about the utility of classifying cognitive traits along a slow-fast continuum in the larger context of the pace-of-life framework. Using Tinbergen’s explanatory framework for different levels of analyses and drawing from the large body of knowledge about honeybee behavior, we discuss the observed interindividual variation in cognitive traits and slow-fast cognitive phenotypes from an adaptive, evolutionary, mechanistic and developmental perspective. We discuss the challenges in this endeavor and suggest possible next steps in terms of methodological, statistical and theoretical approaches to move the field forward for an integrative understanding of how slow-fast cognitive differences, by influencing collective behavior, impact social evolution.

Responsiveness to inhibitory signals changes as a function of colony size in honeybees (Apis mellifera)

Biological collectives, like honeybee colonies, can make intelligent decisions and robustly adapt to changing conditions via intricate systems of excitatory and inhibitory signals. In this study, we explore the role of behavioural plasticity and its relationship to network size by manipulating honeybee colony exposure to an artificial inhibitory signal. As predicted, inhibition was strongest in large colonies and weakest in small colonies. This is ecologically relevant for honeybees, for which reduced inhibitory effects may increase robustness in small colonies that must maintain a minimum level of foraging and food stores. We discuss evidence for size-dependent plasticity in other types of biological networks.

Spontaneous choices for insect-pollinated flower shapes by wild non-eusocial halictid bees

The majority of angiosperms require animal pollination for reproduction, and insects are the dominant group of animal pollinators. Bees are considered one of the most important and abundant insect pollinators. Research into bee behaviour and foraging decisions has typically centred on managed eusocial bee species, including Apis mellifera and Bombus terrestris. Non-eusocial bees are understudied with respect to foraging strategies and decision making, such as flower preferences. Understanding whether there are fundamental foraging strategies and preferences that are features of insect groups can provide key insights into the evolution of flower-pollinator co-evolution. In the current study, Lasioglossum (Chilalictus) lanarium and Lasioglossum (Parasphecodes) sp., two native Australian generalist halictid bees, were tested for flower shape preferences between native insect-pollinated and bird-pollinated flowers. Each bee was presented with achromatic images of either insect-pollinated or bird-pollinated flowers in a circular arena. Both native bee species demonstrated a significant preference for images of insect-pollinated flowers. These preferences are similar to those found in A. mellifera, suggesting that flower shape preference may be a deep-rooted evolutionary occurrence within bees. With growing interest in the sensory capabilities of non-eusocial bees as alternative pollinators, the current study also provides a valuable framework for further behavioural testing of such species.

Wolbachia manipulate fitness benefits of olfactory associative learning in a parasitoid wasp

Upon encountering a host, a female parasitoid wasp has to decide whether to learn positive or negative cues related to the host. The optimal female decision will depend on the fitness costs and benefits of learned stimuli. Reward quality is positively related to the rate of behavioral acquisition in processes such as associative learning. Wolbachia, an endosymbiotic bacterium, often plays an impressive role in the manipulation of its arthropod host's biology. Here, we studied the responses of two natural Wolbachia infected/uninfected Trichogramma brassicae wasp populations to theoretically high- and low-reward values during a conditioning process and the consequences of their responses in terms of memory duration. According to our results, uninfected wasps showed an attraction response to high-value rewards, but showed aversive learning in response to low-value rewards. The memory span of uninfected wasps after conditioning by low-value rewards was significantly shorter than that for high-value rewards. As our results revealed, responses to high-quality hosts will bring more benefits (bigger size, increased fecundity and enhanced survival) than those to low-quality hosts for uninfected wasps. Infected wasps were attracted to conditioned stimuli with the same memory duration after conditioning by both types of hosts. This was linked to the fact that parasitoids emerging from both types of hosts present the same life-history traits. Therefore, these hosts represent the same quality reward for infected wasps. According to the obtained results, it can be concluded that Wolbachia manipulates the learning ability of its host, resulting in the wasp responding to all reward values similarly.

Nesting ecology does not explain slow-fast cognitive differences among honeybee species

Slow-fast behavioral and life history differences have been tied to slow-fast variation in cognition that is part of the general speed-accuracy tradeoff. While there is growing evidence for such cognitive variation and its association with behavior and life history at the intraspecific level, it is unknown if a similar relationship extends to the interspecific level. Since interspecific differences in cognition have been shown to be a function of ecology and life history, such differences should be reflected in multiple traits that comprise the slow-fast cognitive axis. In this study, by measuring multiple cognitive traits in individuals, we tested for differences in the cognitive phenotype among four honeybee species, which differ in their behavior and life history in a manner that is associated with differences in their nesting ecology. Our results indicate that a set of cognitive traits consistently covary within each species, resulting in slow and fast cognitive phenotypes that largely meet the predictions of the speed-accuracy tradeoff. We also find that the four species group into two distinct clusters on a slow-fast cognitive axis, although their positions do not align with the known differences in their life history and nesting ecology. We instead find that cognitive differences among the four species are correlated with their brain size. We discuss the possible implications of these results for the role of ecology on slow-fast cognitive differences and the evolution of cognition.

Spatial allocation without spatial recruitment in bumblebees

Any foraging animal is expected to allocate its efforts among resource patches that vary in quality across time and space. For social insects, this problem is shifted to the colony level: the task of allocating foraging workers to the best patches currently available. To deal with this task, honeybees rely upon differential recruitment via the dance language, while some ants use differential recruitment on odor trails. Bumblebees, close relatives of honeybees, should also benefit from optimizing spatial allocation but lack any targeted recruitment system. How bumblebees solve this problem is thus of immense interest to evolutionary biologists studying collective behavior. It has been thought that bumblebees could solve the spatial allocation problem by relying on the summed individual decisions of foragers, who occasionally sample and shift to alternative resources. We use field experiments to test the hypothesis that bumblebees augment individual exploration with social information. Specifically, we provide behavioral evidence that, when higher-concentration sucrose arrives at the nest, employed foragers abandon their patches to begin searching for the better option; they are more likely to accept novel resources if they match the quality of the sucrose solution experienced in the nest. We explored this strategy further by building an agent-based model of bumblebee foraging. This model supports the hypothesis that using social information to inform search decisions is advantageous over individual search alone. Our results show that bumblebees use a collective foraging strategy built on social modulation of individual decisions, providing further insight into the evolution of collective behavior.

BiteOscope, an open platform to study mosquito biting behavior

Female mosquitoes need a blood meal to reproduce, and in obtaining this essential nutrient they transmit deadly pathogens. Although crucial for the spread of mosquito-borne diseases, blood feeding remains poorly understood due to technological limitations. Indeed, studies often expose human subjects to assess biting behavior. Here, we present the biteOscope, a device that attracts mosquitoes to a host mimic which they bite to obtain an artificial blood meal. The host mimic is transparent, allowing high-resolution imaging of the feeding mosquito. Using machine learning, we extract detailed behavioral statistics describing the locomotion, pose, biting, and feeding dynamics of Aedes aegypti, Aedes albopictus, Anopheles stephensi, and Anopheles coluzzii. In addition to characterizing behavioral patterns, we discover that the common insect repellent DEET repels Anopheles coluzzii upon contact with their legs. The biteOscope provides a new perspective on mosquito blood feeding, enabling the high-throughput quantitative characterization of this lethal behavior.

Modification of reproductive schedule in response to pathogen exposure in a wild insect: Support for the terminal investment hypothesis

Trade-offs in the time and energy allocated to different functions, such as reproductive activities, can be driven by alterations in condition which reduce resources, often in response to extrinsic factors such as pathogens or parasites. When individuals are challenged by a pathogen, they may either reduce reproduction as a cost of increasing defence mechanisms or, alternatively, modify reproductive activities so as to increase fecundity thereby minimizing the fitness costs of earlier death, a behaviour consistent with the terminal investment hypothesis (TIH). The TIH predicts that individuals with decreased likelihood of future reproduction will maximize current reproductive effort, which may include shifts in reproductive timing. We examined how wild, adult female click beetles (Agriotes obscurus) responded after exposure to the fungal pathogen Metarhizium brunneum. Field-collected beetles exposed to a high concentration of M. brunneum died earlier and in greater numbers than those exposed to a low concentration. Using a multivariate approach, we examined the impact of pathogen challenge on lifespan and a suite of reproductive traits. Stepdown regression analysis showed that only female lifespan differed among the fungal treatments. Fungal-induced reductions in lifespan drove changes in the reproductive schedule, characterized by a decrease in preoviposition period. Moving the start of egg laying forward allowed the females to offset the costs of a shortened lifespan. These changes suggest that there is a threshold for terminal investment, which is dependent on strength of the survival threat. From an applied perspective, our findings imply that exposing adult click beetles to M. brunneum to reduce their population density might not succeed and is an approach that needs further investigation.

The effect of food preference, landmarks, and maze shift on maze-solving time in desert ants

We studied how food type and available landmarks affect spatial learning in the ant Cataglyphis niger while searching for food in a maze. We expected the ants to solve the maze faster with consecutive runs, when the preferred food type is offered, and in the presence of landmarks. Ants should also solve the maze more slowly following a mirror-route switch in the maze. As expected, maze-solving improved when searching for a preferred food type than a less preferred one, as determined in a separate food preference experiment. In contrast, adding landmarks to the maze had only little effect on maze-solving and the number of searching workers. Switching the route to a mirror-imaged route in the maze delayed maze-solving and required more workers to search for food. Our findings extend the knowledge on the ants’ learning abilities and demonstrate how foragers detect food faster when offered a high-ranking food item.

Behavioral responses to colony-level properties affect disturbance resistance of red harvester ant colonies

Self-organizing biological systems, such as colonies of social insects, are characterized by their decentralized control and flexible responses to changing environments, often likened to swarm intelligence. Although decentralized control is well known to be a product of local interactions among agents, without the need for a bird's-eye view, indirect knowledge of properties that indicate the current states of the entire system also helps each agent to respond to changes, thereby leading to a more adaptive system. In this study, we analyze the rules that govern workers' behavioral responses to colony-level properties and assess whether they contribute to adaptive flexibility in social insect colonies. We focus on task allocation among red harvester ants (Pogonomyrmex barbatus) as a model system and develop an ordinary differential equation model to describe the system of task allocation among workers. We simulate 12 scenarios specifying how workers respond to changes in the colony-level properties of colony size and nutritional state. We found that when workers decrease their contact rates in response to increasing colony size, they enable achievement of a larger colony size, similar to that of P. barbatus colonies in nature, and when workers increase their foraging levels in response to decreasing colony-wide nutritional levels, they increase resilience to environmental disturbances. These negative feedback rules governing the response to colony-level properties are consistent with previous reports on ants and honeybees.

Hunger increases delay discounting of food and non-food rewards

How do our valuation systems change to homeostatically correct undesirable psychological or physiological states, such as those caused by hunger? There is evidence that hunger increases discounting for food rewards, biasing choices towards smaller but sooner food reward over larger but later reward. However, it is not understood how hunger modulates delay discounting for non-food items. We outline and quantitatively evaluate six possible models of how our valuation systems modulate discounting of various commodities in the face of the undesirable state of being hungry. With a repeated-measures design, an experimental hunger manipulation, and quantitative modeling, we find strong evidence that hunger causes large increases in delay discounting for food, with an approximately 25% spillover effect to non-food commodities. The results provide evidence that in the face of hunger, our valuation systems increase discounting for commodities, which cannot achieve a desired state change as well as for those commodities that can. Given that strong delay discounting can cause negative outcomes in many non-food (consumer, investment, medical, or inter-personal) domains, the present findings suggest caution may be necessary when making decisions involving non-food outcomes while hungry.

Spare to share? How does interindividual variation in metabolic rate influence food sharing in the honeybee?

A central benefit of group living is the cooperative acquisition and sharing of resources but the costs associated with these processes can set up a potential conflict between individual and group level fitness. Within a honeybee colony, the task of resource acquisition is relegated to the foragers and any interindividual differences in their metabolic rate and the consequent carbohydrate demand may pose a constraint on the amount of resources they can contribute to the colony. We investigated whether the carbohydrate demand of a forager is a function of her metabolic rate and if this impacts the amount of food she shares with the nestmates. Our results show that the sucrose consumption rates of foragers with high metabolic rates did not meet their carbohydrate demand, placing them at an energy deficit while those with lower metabolic rates had an energy surplus. Our food sharing experiments showed a trend but did not detect a significant difference among individuals with different consumption rates in terms of the amount of food they shared with their nestmates. These results suggest that honeybee foragers with different metabolic rates are likely to differ in terms of whether they have an energy surplus or deficit, but more long-term datasets may be required to detect how this may influence food sharing.

Task allocation and site fidelity jointly influence foraging regulation in honeybee colonies

Variation in behaviour among group members often impacts collective outcomes. Individuals may vary both in the task that they perform and in the persistence with which they perform each task. Although both the distribution of individuals among tasks and differences among individuals in behavioural persistence can each impact collective behaviour, we do not know if and how they jointly affect collective outcomes. Here, we use a detailed computational model to examine the joint impact of colony-level distribution among tasks and behavioural persistence of individuals, specifically their fidelity to particular resource sites, on the collective trade-off between exploring for new resources and exploiting familiar ones. We developed an agent-based model of foraging honeybees, parametrized by data from five colonies, in which we simulated scouts, who search the environment for new resources, and individuals who are recruited by the scouts to the newly found resources, i.e. recruits. We varied the persistence of returning to a particular food source of both scouts and recruits and found that, for each value of persistence, there is a different optimal ratio of scouts to recruits that maximizes resource collection by the colony. Furthermore, changes to the persistence of scouts induced opposite effects from changes to the persistence of recruits on the collective foraging of the colony. The proportion of scouts that resulted in the most resources collected by the colony decreased as the persistence of recruits increased. However, this optimal proportion of scouts increased as the persistence of scouts increased. Thus, behavioural persistence and task participation can interact to impact a colony's collective behaviour in orthogonal directions. Our work provides new insights and generates new hypotheses into how variations in behaviour at both the individual and colony levels jointly impact the trade-off between exploring for new resources and exploiting familiar ones.

Sampling and tracking a changing environment: persistence and reward in the foraging decisions of bumblebees

The question of when to collect new information and how to apply that information is central to much of behaviour. Theory suggests that the value of collecting information, or sampling, depends on environmental persistence and on the relative costs of making wrong decisions. However, empirical tests of how these variables interact are lacking. We tested whether bumblebee foraging decisions are indeed influenced by these two factors. We gave bees repeated choices between a resource providing a steady, mediocre reward and a resource fluctuating between a low reward and a high reward. In this paradigm, we manipulated environmental persistence by changing how long the quality of a fluctuating resource remained stable at one reward level. We manipulated the costs of decision errors by changing the relative values of the available rewards. Bees sampled the fluctuating resource more frequently when it changed quality more frequently, indicating that they measured environmental persistence and reacted to it as predicted by theory. Bees showed surprisingly suboptimal tracking, not reliably choosing the currently best resource except when the fluctuating resource was very persistent and the potential rewards high. While bees modify their choices in response to different levels of change and potential rewards, they do not always do so according to optimality predictions.

Energy state affects exploratory behavior of tree sparrows in a group context under differential food-patch distributions

BACKGROUND

When facing a novel situation, animals can retreat or leave to avoid risks, but will miss potential resources and opportunities. Alternatively they may reduce environmental uncertainty by exploration, while risking no energy rewards and exposure to hazards, and use the information retrieved for subsequent decision making. When exploring, however, animals may adopt different tactics according to individual states.

RESULTS

We tested that energy states will affect exploratory behavior by experimenting with wild-caught untrained Eurasian tree sparrows (Passer montanus) in fasted or fed states exploring in a novel space with hidden food supply in different patch distribution patterns. Our data revealed that fasted sparrows risked being earlier explorers more often, initiated more exploratory bouts before patches were found, and stayed longer on the ground under both patch patterns. Fasted sparrows discovered more patches and consumed more food than fed sparrows in dispersed, but not necessary so in clumped, patch patterns; whereas fed birds also increased patch finding to a certain level in dispersed patterns. Sparrows of both energy states, however, did not differ in feeding rates in either patch pattern.

CONCLUSIONS

Exploratory behavior of tree sparrows is state-dependent, which supports our prediction that birds with an energy shortage will be risk-prone and explore more readily. Our study also indicates a game nature of tree sparrow exploratory behavior in a group context when explorers are in different energy states and are exposed to different patch distributions. Birds of lower energy state adopting an active exploring tactic may be favored by obtaining higher energy gains in dispersed patch patterns with lower patch richness. More satiated birds, however, achieved a similar feeding rate by lowered exposure time.