Volume 30, Issue 5, September/October 2019

Animals engage in contests for resources like food, space, and mates. We present a theoretical framework for understanding how individual animals in a population resolve these conflicts based on three information sources: themselves, their opponent, and the contested resource. We propose an updated statistical approach for empiricists, the efficacy of which we demonstrate with simulated data.

As humans learn to talk, many bird species learn their songs and social factors play a key role in the process. First experiments showed that juvenile birds could learn the species’ typical song just by listening to recordings, leading to the notion that interactions with conspecifics were not necessary for avian vocal learning. However, we now know that different types of interactions have important effects on triggering and enhancing song learning, and determining which song types are learned.

Captive breeding is used to prevent extinction of species worldwide, but the importance of mate choice in captivity is only now being realised. The MHC is a family of genes involved with mate choice. We examined whether MHC diversity contributes to breeding success of captive Tasmanian devils compared to a wild population. Despite large sample sizes, we found no association between MHC diversity and breeding success for devils; these results will inform conservation planning.

Experiments with 2 related bird species with slightly divergent songs show that males are able to recognize individuals of their own species. This study shows that the evolution of even minor song differences between species can be effective in specific recognition.

Physiological state predicts the response of chickadees to new foods. After presenting birds with different types of novel food, we show that higher baseline levels of corticosterone are associated with decreased latency to contact these food items as well as a greater probability of consuming them. These results are in line with the known function of baseline corticosterone as a hormone that regulates metabolism and promotes foraging behavior in animals.

Males occasionally employ different reproductive tactics within the species. Our study on a water strider species shows that these within-species differences in reproductive tactics generate different correlations among behaviors. In males using courtship tactics, those more eager to mate tend to leave their refuges more rapidly. In contrast, sneaker males do not show such behavioral patterns. This is because, under different selection regimes, different tactics evolve within a species.

A major benefit of living in a group is the ability to learn from others. We investigated how spider societies learn and respond to important information when that information is held by the majority or by single influential or generic individuals. We found that groups adopted a “better safe than sorry” strategy and exhibited caution when the group or any individual, regardless of their presumed social influence, had been previously exposed to danger.

When conflicts escalate into physical aggression, injuries are likely to occur. Here, we examined how competitive contexts, such as the mating season for males, the period before conception for females, and the time surrounding maturation and dispersal for both sexes, predict the frequency of injury in 2 species of colobine monkeys. With few exceptions (e.g., group size), injuries were more frequent when stronger competition was expected.

Infidelity is common in animals that form breeding pairs. Why this behavior occurs—and varies in frequency between species, populations, and individuals—remains unresolved. We investigate the role of social, demographic, and ecological factors on the occurrence of infidelity in Seychelles warblers. In this species, dominant pairs are often joined by subordinates to form breeding groups. We find that social conditions—group size and pair relatedness—promote female infidelity, but this infidelity almost always occurs with extra-group males.

To achieve reproduction, males of some species can attract females by performing elaborate songs and dances. However, they also may end up attracting predators. We experimentally tested how a tropical bird species solves this problem. We found that males in better condition and with greater chances of future breeding did not modify their attempts to attract females when exposed to a predator cue. Alternatively, males with little expectation of future reproduction increased investment in courtship, attempting to breed while they still could.

Can nutrition shape an individual’s personality throughout life? By performing a long-term manipulative diet experiment in a frog, we show that personality and behavioral plasticity can be shaped by nutritional conditions at different life stages. Low quality nutritional conditions during life increased the amount of variation among and within-individuals in adult exploration behavior. Nutrition is likely to be a widespread yet underappreciated proximate mechanism underpinning individual behavioral variation.

Songbirds sing less and start singing later when faced with an increase in perceived predation risk. Perceived predation risk can have substantial behavioral effects on prey species, but whether or not it affects dawn singing – an important sexual signal - remains unknown. We played back predator calls in a songbird community throughout the breeding season to simulate increased predation risk and found that the majority of species inhibited or delayed their dawn song.

Intraspecific variation exceeds interspecific variation in the movement distances of a river fish community. Using radio telemetry, we track individuals from 5 large bodied ecologically diverse river fish species over long periods. We show that individual behavioral patterns account for a greater proportion of movement variation than species- specific patterns and a similar proportion of variation as species-specific seasonal patterns.

When females mate multiply, they can potentially use the fluid that surrounds the eggs, the ovarian fluid, to select sperm of the preferred male. Using a controlled experimental design, we demonstrated that the ovarian fluid of certain females selectively increases sperm performance of certain males in zebrafish. Though this effect, females can potentially bias the fertilization success of competing ejaculates and hence the paternity outcome in this species.

Brood parasites exploit the parental investments of others to rear their own offspring. We found that the traits that predict egg discrimination varied with social structure in wasps. In the species that founds nests in coalitions, bold individuals and those that were unresponsive to olfactory cues were better at discriminating against foreign eggs. In the solitary nesting species, individuals with greater olfactory responsiveness were better at removing foreign eggs.

Can common mynas, one of the World's most invasive birds and target of much control effort, learn to avoid trapping? After watching mynas being captured by a person who had previously fed them, observer mynas alarm called specifically to that person. They also learned the place where trapping occurred and showed generalized changes in risk-awareness. Mynas show a remarkable capacity to learn socially, which explains why they are becoming more risk-averse in areas where they are trapped.

Apex predators change the time of day when smaller predators, or “mesopredators” are active in landscapes dominated by people. When coexisting with wolves, mesopredator activity overlapped more with humans and with each other as they attempted to avoid times when wolves were most active. These results suggest mesopredators perceive wolves as more dangerous than humans, and human encounters with mesopredators may increase when they coexist with apex predators.

In species with biparental care, males should reduce parental care if their paternity is threatened; personality traits may further influence this response. Here, we show that males exposed to a paternity threat were less likely to feed their young than control males. Of those males that did provision, however, there was no effect of aggressiveness. Thus, differences in paternal care are mediated by perceived paternity loss but not personality.

Male frogs sing to attract mates, and males must make themselves heard over all other males vying for attention. Indeed, competition among males often drives changes in male songs so any given male can stand out in the crowd. Males differ in how they do this, but it is not clear why. We found that changes in males’ songs might depend on their song structure. This finding lends insight into song diversity and mate choice.

Damage-inducing reactive oxygen species (ROS) are a by-product of oxygen-based energy production that are quenched by energetically expensive antioxidants. Male sexual coloration requires investment of energy and resources, which may constrain allocation to other functions like antioxidant production or spermatogenesis. Here, we explored whether the body condition of colorful male lizards reflected their investment in antioxidants and reduction of ROS, which may influence sperm performance. We found that drab males in better condition had more antioxidants. Colorful males had lower levels of antioxidants and their sperm performed poorly at higher ROS levels. These results suggest a trade-off between color maintenance and sperm performance.

Tropical bird acoustic communities exhibit stable acoustic niches in spite of seasonal change in species composition. Here, I present evidence that winter migrants occupy similar acoustic niches to resident breeding birds in the tropics. Their arrival coincides with species turnover and decreased overall singing activity, but each species still occupies a distinct acoustic niche from others.

Red junglefowl chicks generalize learned preferences differently depending on their behavioral type (aka personality). When an individual generalizes, previous experiences are used when responding to novel situations or objects. Variation in generalization can thus affect decision making and the action taken when responding to novel situations. Here, we show that more cognitively flexible chicks react more strongly to a novel stimulus in a generalization task than less flexible chicks do.

We found that resistance to parasitic mites is highly heritable in male dung beetles, and that males with higher parasite resistance mate for longer, even if they have no parasites at the time of mating. If female dung beetles control copula duration, this means that females chose males on the basis of their parasite resistance, but we still do not know how females evaluate this trait of males.

Animals vary greatly in how much they play. Why? Some species do not appear to exhibit play at all. Some exhibit only simple, often solitary, play behavior when juvenile, while others engage in complex, often social, play behavior that extends into adulthood. We discuss the evolutionary benefits and costs of play, review interspecies variation, and discuss how that variation relates to the evolutionary tradeoffs during life history. We structure our discussion around a simple mathematical model.

We examined the relationship between habitat use and song structure in the wolf spider Schizocosa floridana. We found the spiders restricted their habitat use to oak litter, which transmitted their songs best, even though their environment contained many substrate types. We also found that the pure tone “chirp” unique to this spider’s song was more strongly degraded by nonoak substrates than other song components, suggesting that substrate specialization may have been key to its evolution.

Animals are often observed biasing their social associations toward kin. In species that exhibit parental care, it is difficult to ascertain whether these associations may be, at least partly, socially transmitted, rather than formed on the basis of relatedness. Kin associations may also be driven merely by spatial proximity. By accounting for spatial patterns, we show that eastern water dragons, which lack parental care, bias their social associations toward kin most likely on the basis of relatedness.

Upon receiving a novel mechanical disturbance, minnow shoals exposed to elevated levels of background risk resume predisturbance shoaling cohesion quicker than low-risk control shoals. This finding is consistent with risk allocation but contrasts generalized neophobia, whereby fish are expected to show elevated responses to all novel cues when risk increases.

Threats from rival groups can lead to changes in within-group behavior. Using call playbacks and fecal presentations to simulate the presence of rivals, we show that wild dwarf mongooses groom groupmates for longer, forage closer together, and more regularly act as sentinels (raised guards) after encountering indicators of an out-group threat. These behavioral changes likely arise from greater anxiety and, in the case of sentinel behavior, the need to seek additional information about the threat.

Performance in winter sports predicts attractiveness in men, but not in women. We examined the relationship between career-best performance metrics and attractiveness ratings for men and women who compete annually in the biathlon World Cup, a multidisciplinary sport that combines target shooting and cross-country skiing. Male biathletes who had achieved a higher peak performance in their career were rated as more attractive by the opposite sex, whereas there was no such relationship for female biathletes.

In burying beetles, larvae survive better in the presence of a caring female at 15 °C, while they survive as well in the presence or absence of a female at 20 and 25 °C. Our results show that the presence of a caring female parent can protect offspring against the otherwise damaging effects of variable ambient temperatures.

The quality of parental care provided by one parent can affect the reproductive success of both parents and therefore, choosing a good parent can be crucial during mate choice. In the broad-nosed pipefish, large males brood embryos at lower densities, that become larger but have relatively lower survival during brooding than those of small males. As females prefer large mates, our work suggests that offspring size post-birth is more important than number to female fitness.

Males of a gift-giving spider do not modify their allocation to reproduction when mating opportunities vary. Due to their costly courtship via provision of food gifts to females, with high female availability males should reduce their reproductive investment per partner to avoid exhausting their energetic budget too early. Our findings suggest instead that males may be able to enlarge their total reproductive budget, possibly drawing resources from their food gifts by partially feeding on them.

Humans routinely overestimate their ability to compete, but no one knows whether other animals engage in this type of self-deception. We used a mathematical model to predict the behavior of crayfish engaging in self-deception. Consistent with our model, weak crayfish behaved as aggressively as strong crayfish, suggesting that they fail to recognize their own strength. Individuals that overestimate their strength can scare away stronger opponents without a fight.

Starved burying beetle mothers delayed egg laying and provided less care. Yet, their offspring survived and grew just as well as offspring of control mothers. Burying beetles breed on carcasses that serve as food for both parents and offspring. Starved mothers spend more time feeding for themselves, which boosts their condition and opens the carcass, allowing offspring to self-feed. We show that the mother’s nutritional state can affect reproduction without costs to offspring.

Jumping spiders use acute vision to solve complex 3-dimensional tasks, including the use of detours to reach a specific goal. We show that they can assess differences between routes enabling escape from a stressful situation, discriminating routes by length and by riskiness. Differential spatial abilities between closely related species, possibly through selection based on the characteristics of the environment in which each species lives, may explain our results.