Abstract Temperatures globally are increasing, resulting in numerous behavioral consequences for wildlife. Mobbing, a collective antipredator response important for many species, is one such behavior affected by high temperatures. Recent research has shown the number of individuals involved in a mobbing event to be an important determinant of whether individuals join in, suggesting a role for numerical abilities in this behavior. However, whether temperature affects an animal's ability to discern the number of conspecifics involved in a mobbing event has not yet been investigated. Temperature-induced cognitive declines may affect the processing and decision making involved in the anti-predator response, potentially leading to maladaptive anti-predator behaviors. We presented wild great tits (Parus major) with playback of the mobbing calls of 1 or 5 conspecifics at different temperatures (from 16 to 35 °C; representing temperatures both within and outside of the thermoneutral zone [15 to 30 °C] of this species), to determine if temperature affected their mobbing response. We found a quadratic relationship between temperature and the number of mobbing calls produced by great tits, with the number of calls produced by individuals decreasing at higher temperatures, regardless of playback treatment. Importantly, while great tits showed a stronger approach response to 5 compared with 1 caller at low temperatures, they failed to do so at higher temperatures, either due to an impaired ability to discern the number of mobbing individuals, or an altered thermoregulation-predation risk trade-off at these high temperatures. Inappropriate anti-predator responses in the heat are likely to have substantial effects on survival, particularly as temperatures continue to rise.

Abstract Climate change is intensifying ocean deoxygenation and warming, compounding stressors that threaten tropical marine ecosystems. On coral reefs, cleaner wrasses sustain fish health and community stability by removing ectoparasites from client species during cooperative interactions. However, the mutualism is inherently unstable, as cleaners prefer to feed on clients’ protective mucus—a behavior considered cheating. To maintain cooperation, clients use partner control strategies, while cleaners employ sophisticated social techniques to manage conflict and maximize food intake. In this study, cleaner wrasses (Labroides dimidiatus) and their clients (Naso elegans) were exposed for at least 33 days to projected climate scenarios of ocean deoxygenation (90% O2 sat), warming (+3 °C), and the combination of both stressors. We assessed the resilience of the mutualistic interaction through a cooperativeness task (feeding against preference test), measuring learning and cooperation, and through cleaning interactions. Deoxygenation and warming significantly reduced the proportion of time spent in cleaning interactions and led to the breakdown of behavioral strategies, including tactile stimulation and clients’ retaliation. Notably, dishonesty persisted at similar levels during natural interactions, likely due to altered client responses rather than maintained self-control. Clients under stress were more tolerant to dishonesty, allowing cheating to go unpunished. This is supported by the cooperativeness test, in which cleaners exposed to deoxygenation exhibited reduced cooperation and diminished ability to suppress preferred but non-cooperative behavior, suggesting impaired cognitive control. Our results reveal that climate stressors impair cognitive and behavioral mechanisms underpinning cleaning mutualisms, potentially destabilizing key trophic interactions on coral reefs under future ocean conditions.

Contests over resources are widespread in nature. To optimize outcomes, animals assess fighting abilities, deciding to escalate conflicts based on their own strength (self-assessment) or comparing their own strength with that of their rival (mutual assessment). While most research focuses on one-on-one (dyadic) contests, the assessment strategies employed by groups remain poorly understood, even though animal groups from ants to humans engage in intergroup conflict. Mutual assessment is frequently assumed, as more information is thought to improve decision-making; however, this assumption has rarely been tested. Here we used a dataset spanning 21 years and 633 intergroup contests in a banded mongoose (Mungos mungo) population in Queen Elizabeth National Park, Uganda. Our results support a model of self-assessment: groups with many males tend to escalate conflicts regardless of the rival group's strength, thus contrasting the commonly held assumption that decisions during intergroup contests are made by mutual assessment. We suggest that assessing rival group strength during conflict could be disproportionately costly, compared with assessing own group strength, which can be done over longer time periods and is easier to obtain. Greater understanding of these dynamics can shed light on the drivers and escalation patterns of intergroup conflict across social species, including humans.

Environmental conditions and experiences during development can have long-term fitness consequences, including a reduction of adulthood survival and reproduction. These long-term fitness consequences may play an important role in shaping the evolution of life history. We tested two hypotheses on the long-term fitness effects of the developmental environment—the silver spoon hypothesis and the internal predictive adaptive response (PAR) hypothesis. We compared the change in annual survival and annual reproductive output with age for adult birds hatched and/or reared in poor––impacted by anthropogenic noise, and/or high sibling competition––and good––not impacted by anthropogenic noise, and/or low sibling competition––environments. We used a 23-year longitudinal dataset from a wild house sparrow (Passer domesticus) population inhabiting an isolated island, which enabled near-complete monitoring and unusually accurate lifetime fitness estimates. We used a cross-fostering setup to disentangle environmental effects experienced postnatally from those experienced prenatally. We found that adults that, as chicks experienced more within-brood competition had a stronger increase in early-life annual survival, but also a stronger decrease in late-life annual survival. Females that hatched in a noisy environment produced fewer genetic recruits annually, supporting a sex-specific silver spoon hypothesis. Males reared in a noisy environment had accelerated reproductive schedules, supporting a sex-specific internal PAR hypothesis. Our results highlight that anthropogenic noise (∼68 dB from power generators) can have long-term fitness consequences in wild animals, altering their life-history strategies, and that effects may be sex-specific.

Abstract Animals adjust behavior to changes in perceived predation risk, even when risk is non-consumptive, as is the case for human recreation. However, individuals within populations can differ greatly in their plasticity toward perceived risk, especially when antipredator responses incur fitness costs via lost foraging opportunities. Therefore, risk-benefit trade-offs are usually made at the individual level. We test whether red deer (Cervus elaphus) inhabiting the Bavarian Forest National Park show individual variation in behavioral plasticity toward human disturbance. We measured human disturbance as the number of recreationists on the closest trail on a given day and used random regression to dissolve movement responses, measured as hourly step-length, of 63 GPS-collared red deer females to fine scale spatio-temporal variation in disturbance. We quantified behavioral state-specific between-individual variation along the disturbance gradient. At the population level, red deer responded to recreational disturbance during the middle of the day only, and reduced movement in response to recreation. However, population patterns masked strong between-individual variation in plasticity to recreational disturbance during the morning, midday, and evening, such that some deer reacted with increased or decreased movement rates while others responded little. Behavioral responses were mediated by vegetation cover with stronger responses in more open habitat. Flight responses are costly due to lost foraging opportunities. A shift in risk-benefit tradeoffs when risk is non-lethal, as is the case for recreation in many national parks, may favor more human-tolerant individuals over time.

To maximize their reproductive fitness, females of many polyandrous species should display mating status-dependent choice, where they mate relatively indiscriminately once to ensure reproductive output, and then become choosy and mate preferentially with higher-quality males. Despite this potential contrast in choosiness, most mate choice experiments use virgin females. Here, using a panel of 20 isofemale strains that originated from wild-caught flies, we allowed virgin and non-virgin Drosophila melanogaster females to choose among males from the same panel of strains. We used single-male latency trials and a series of male competition trials to help disentangle female “choices” from male-male competitive effects. Most virgin females mated within 2 h of males being introduced, compared with fewer than half of non-virgin females mating over the same period. However, despite mating more rapidly, virgin females did not mate indiscriminately, and their “choices” strongly aligned with those of previously mated females across both the single-male latency and male-male competition trials. Our results challenge the idea that virgin females mate relatively indiscriminately and show that female choice may be more stable than is generally appreciated.

Alternative reproductive phenotypes involve polymorphic behaviors and forms within sexes. Testing whether behavioral variants such as alternative tactics (eg sneaking or satellite behavior) are initially co-expressed or decoupled from morphological polymorphisms (eg weapon size or color pattern) can provide insight into the origins of reproductive diversity. In Hawaiian field crickets (Teleogryllus oceanicus), an eavesdropping parasitoid fly selected for rapid, parallel evolution of male wing mutations that reduce acoustic signals. Two of these, “flatwing” and “curly-wing”, co-occur in populations alongside ancestral “normal-wing” males that can sing. These convergent alternative morphs may both rely on satellite tactics in which nonsinging males position themselves near calling males to intercept females, rather than attracting mates directly by producing a conspicuous song. Here, we test whether flatwing and curly-wing vary in their tendencies to express satellite behavior using playback experiments with virgin, unmanipulated males simulating natural conditions. Surprisingly, flatwing males were significantly less likely to behave as satellites than normal-wing or curly-wing males. Normal-wing males with poorer body condition were more likely to behave as satellites, consistent with theory and previous findings, but the reduced-sound morphs showed no such condition dependence. Our findings suggest that morph-specific variation in the tendency to adopt satellite behavior may contribute to the maintenance of convergent male reproductive morphs; future work would benefit from testing whether such variation is driven by acoustic self-assessment. A decoupled relationship between behavioral reproductive tactics and morphological reproductive strategies may promote diversification of alternative mating morphs in nature.

Abstract While female mate choice is well established, mutual choice may play a larger role in mate selection than currently recognized. Assortative mating is a common form of nonrandom mating in animals that can result from mutual choice. However, few studies address assortative patterns beyond the social pair, potentially overlooking assortativity in the mating pair and in the social environment that shapes reproductive decisions. We asked whether North American barn swallows (Hirundo rustica erythrogaster) breeding in a large colony form pairs, mate (through both within-pair and extra-pair fertilizations), and interact assortatively by ventral plumage color, wing length, and age. Social interactions were tracked using proximity loggers, which recorded close contact between tagged individuals when birds were mating and laying eggs. Barn swallows paired and mated assortatively by their ventral plumage color; however, the assortative patterns in mating pairs were not as strong as they were in social pairs. Barn swallows also interacted assortatively, associating more often with individuals of both sexes who had similar phenotypes relative to the other birds in the colony. Finally, older males and females with darker ventral plumage achieved the highest reproductive success. Investigation of assortative behavior beyond the level of the social pair provides a more complete understanding of mate choice and suggests a mechanism that may maintain the large variation in ventral plumage color in North American barn swallows.

Abstract Reproductive senescence may affect mating decisions if older individuals produce fewer and lower-quality offspring, but the effect of reproductive senescence on mate choice decisions remains poorly understood. Mountain chickadees (Poecile gambeli) do not exhibit clear reproductive senescence within their natural lifespans and therefore offer a unique opportunity to test whether the absence or delay of reproductive senescence affects social mate choice for mates of certain ages. Given the lack of obvious reproductive senescence in this species, we predicted that older individuals would be preferred as social mates because pairing with an experienced mate is often associated with direct and indirect benefits. In apparent support of our predictions, we observed positive assortment for age within breeding pairs and older individuals were more likely to be paired with one another than expected by chance. However, assortative pairing also occurred within most younger age classes, and when we restricted our analyses to consider only new pairings, rates of assortative pairing within age classes were similar to those expected by chance. Thus, the observed pattern of age-related assortative mating in this system likely occurs due to longevity of some pair bonds rather than active assortment for age among individuals forming new pair bonds. Combined, our results suggest that choice of a social mate based on age may be constrained in socially monogamous mating systems when many individuals maintain long-term pair bonds.