Animals may assess the vocal traits of opponents during resource competition to determine threat, which is a combination of the fighting ability and motivation of the opponent. Most studies have looked at how vocal traits reflect threat in males, but females and groups also vocalize during competition. Here, we examine how the vocal traits of males, females and male-female pairs signal threat in chestnutbacked antbirds, Poliocrania exsul, a tropical species that sings and duets to defend permanent territories. We quantified the threat of all birds in terms of both body size (indicative of fighting ability) and territory quality (indicative of fighting ability or motivation), measured as territory size and vegetation density, then recorded songs to analyse the vocal traits of each bird. We found that males and females communicated information about body size through the rate and fine-scale attributes of their songs and those communication strategies were largely similar between sexes. Furthermore, male-female pairs coordinated their songs into duets and the timing of their singing signalled the level of threat. Our results indicate that fine-scale attributes of vocalizations convey important information about individuals and groups in the context of competition. (c) 2025 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Invasive fruit-eating animals (hereafter frugivores) can form novel mutualisms with fruiting plants and alter seed dispersal. Plant-frugivore interactions are often linked to frugivore preference for certain fruit traits, but for invasive frugivores, it is uncertain if novelty—whether or not a fruit is familiar—impacts foraging decisions. We experimentally tested fruit preferences of the four most abundant and frugivorous bird species on O‘ahu, a Hawaiian Island, all of which are globally invasive songbirds. With captive wild birds, we tested for preference in relation to fruit size, color, nutrients, and bird sex. We also tested how novelty of fruits affected trait-based preferences, with fruits from plant species either established in the wild or novel. Using arrays that offered multiple fruit species, we conducted 252 trials with 111 plant species, 59.5

Rodents are among the most widespread and problematic invasive animals on islands worldwide contributing to declining endemic island biota through predation and disruption of mutualisms. Identifying what rodents eat is critically important to understanding their effects on ecosystems. We used DNA metabarcoding to identify the diets of three invasive rodents in Hawaiian forests: house mouse ( Mus musculus ), black rat ( Rattus rattus ), and Pacific rat ( Rattus exulans ). These rodents primarily eat invertebrates and plants, but previous diet studies have provided only a limited understanding of the diet breadth by relying on morphological identification methods. We opportunistically collected fecal samples from rodents trapped at seven forest sites across Oʻahu, Hawaiʻi for two years. Plant and invertebrate diet items were identified from DNA extracted from fecal samples using rbc L and COI primers, respectively. Intact seeds were identified using a dissecting microscope to quantify potential contributions to seed dispersal. All rodent species ate primarily plants and invertebrates of introduced species. However, some native taxa of conservation importance were identified. Neither the rodent species nor the sites drove patterns of diet composition, suggesting that diet variation may be determined by opportunistic foraging or intraspecific variation. Black rat fecal samples contained intact seeds more frequently than house mouse samples, but surprisingly, when samples contained seeds, black rats and house mice both defecated hundreds of introduced seeds, likely contributing to seed dispersal. Conservation efforts targeting invasive rodent control should specifically include house mice and should monitor introduced prey items to prevent predation release of unwanted introduced species.

In altered communities, novel species' interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the roles of two galliform species as seed dispersers and seed predators in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel's Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O'ahu and Hawai'i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants significantly reduced the probability of seeds germinating, especially for the native plants. Further, larger-seeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of non-native plants, but they also destroy the seeds of some native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species' interactions.

As human-caused extinctions and invasions accumulate across the planet, understanding the processes governing ecological functions mediated by species interactions, and anticipating the effect of species loss on such functions become increasingly urgent. In seed dispersal networks, the mechanisms that influence interaction frequencies may also influence the capacity of a species to switch to alternative partners (rewiring), influencing network robustness. Studying seed dispersal interactions in novel ecosystems on O‘ahu island, Hawai‘i, we test whether the same mechanisms defining interaction frequencies can regulate rewiring and increase network robustness to simulated species extinctions. We found that spatial and temporal overlaps were the primary mechanisms underlying interaction frequencies, and the loss of the more connected species affected networks to a greater extent. Further, rewiring increased network robustness, and morphological matching and spatial and temporal overlaps between partners were more influential on network robustness than species abundances. We argue that to achieve self-sustaining ecosystems, restoration initiatives can consider optimal morphological matching and spatial and temporal overlaps between consumers and resources to maximize chances of native plant dispersal. Specifically, restoration initiatives may benefit from replacing invasive species with native species possessing characteristics that promote frequent interactions and increase the probability of rewiring (such as long fruiting periods, small seeds and broad distributions).

Ecosystems with a mix of native and introduced species are increasing globally as extinction and introduction rates rise, resulting in novel species interactions. While species interactions are highly vulnerable to disturbance, little is known about the roles that introduced species play in novel interaction networks and what processes underlie such roles. Studying one of the most extreme cases of human-modified ecosystems, the island of O'ahu, Hawaii, we show that introduced species there shape the structure of seed dispersal networks to a greater extent than native species. Although both neutral and niche-based processes influenced network structure, niche-based processes played a larger role, despite theory predicting neutral processes to be predominantly important for islands. In fact, ecological correlates of species' roles (morphology, behavior, abundance) were largely similar to those in native-dominated networks. However, the most important ecological correlates varied with spatial scale and trophic level, highlighting the importance of examining these factors separately to unravel processes determining species contributions to network structure. Although introduced species integrate into interaction networks more deeply than previously thought, by examining the mechanistic basis of species' roles we can use traits to identify species that can be removed from (or added to) a system to improve crucial ecosystem functions, such as seed dispersal.

Increasing rates of human-caused species invasions and extinctions may reshape communities and modify the structure, dynamics, and stability of species interactions. To investigate how such changes affect communities, we performed multiscale analyses of seed dispersal networks on O. ahu, Hawai'i. Networks consisted exclusively of novel interactions, were largely dominated by introduced species, and exhibited specialized and modular structure at local and regional scales, despite high interaction dissimilarity across communities. Furthermore, the structure and stability of the novel networks were similar to native-dominated communities worldwide. Our findings suggest that shared evolutionary history is not a necessary process for the emergence of complex network structure, and interaction patterns may be highly conserved, regardless of species identity and environment. Introduced species can quickly become well integrated into novel networks, making restoration of native ecosystems more challenging than previously thought.

El Nino Southern Oscillation events (ENSO) and the subsequent opposite weather patterns in the following months and years (La Nina) have major climatic impacts, especially on oceanic habitats, affecting breeding success of both land and sea birds. We assessed corticosterone concentrations from blood samples during standardized protocols of capture, handling and restraint to simulate acute stress from 12 species of Galapagos Island birds during the ENSO year of 1998 and a La Nina year of 1999. Plasma levels of corticosterone were measured in samples collected at capture (to represent non-stressed baseline) and subsequently up to 1 h post-capture to give maximum corticosterone following acute stress, and total amount of corticosterone that the individual was exposed to during the test period (integrated corticosterone). Seabird species that feed largely offshore conformed to the brood value hypothesis whereas inshore feeding species showed less significant changes. Land birds mostly revealed no differences in the adrenocortical responses to acute stress from year to year with the exception of two small species (<18 g) that had an increase in baseline and stress responses in the ENSO year - contrary to predictions. We suggest that a number of additional variables, including body size and breeding stage may have to be considered as explanations for why patterns in some species deviated from our predictions. Nevertheless, comparative studies like ours are important for improving our understanding of the hormonal and reproductive responses of vertebrates to large scale weather patterns and global climate change in general. (C) 2018 Elsevier Inc. All rights reserved.

Temperature affects ectotherms in a variety of ways. These effects can be especially complex in sexual behaviors, as different sexes may be affected differently by temperature. We examined this in the jumping spider, Habronattus clypeatus. In this species, males court females using visual and vibratory signals. We tested whether key intersexual behaviors would change with temperature in similar, predictable ways across males and females. We first measured temperature and apparent activity of individuals across the day. We found that H. clypeatus are active across a wide range of temperatures (11–56 °C) and are most active at times of day when temperature ranges from 13 to 46 °C. Next, we performed mating experiments across behaviorally relevant temperatures. Females were more likely to allow males to progress to later stages of courtship and had higher mating rates at higher temperatures. Male visual and vibratory courtship behaviors generally became faster, higher-pitched, and lower in amplitude at higher temperatures. This relationship between temperature and signal aspects attained a roughly curvilinear shape, with an asymptote around 40 °C. Intriguingly, mating rates in the lab were highest at temperatures potentially above those during peak spider activity in the field. Our results suggest that temperature’s effects on behavior are complex and can affect males and females differently. This work emphasizes that understanding temperature effects on mating is critical to understanding sexual selection patterns particularly in species which use complex signals.

Animals eavesdrop on other species to obtain information about their environments. Heterospecific eavesdropping can yield tangible fitness benefits by providing valuable information about food resources and predator presence. The ability to eavesdrop may therefore be under strong selection, although extensive research on alarm-calling in avian mixed-species flocks has found only limited evidence that close association with another species could select for innate signal recognition. Nevertheless, very little is known about the evolution of eavesdropping behaviour and the mechanism of heterospecific signal recognition, particularly in other ecological contexts, such as foraging. To understand whether heterospecific eavesdropping was an innate or learned behaviour in a foraging context, we studied heterospecific signal recognition in ant-following birds of the Neotropics, which eavesdrop on vocalizations of obligate ant-following species to locate and recruit to swarms of the army ant Eciton burchellii, a profitable food resource. We used a playback experiment to compare recruitment of ant-following birds to vocalizations of two obligate species at a mainland site (where both species are present) and a nearby island site (where one species remains whereas the other went extinct approx. 40 years ago). We found that ant-following birds recruited strongly to playbacks of the obligate species present at both island and mainland sites, but the island birds did not recruit to playbacks of the absent obligate species. Our results strongly suggest that (i) ant-following birds learn to recognize heterospecific vocalizations from ecological experience and (ii) island birds no longer recognize the locally extinct obligate species after eight generations of absence from the island. Although learning appears to be the mechanism of heterospecific signal recognition in ant-following birds, more experimental tests are needed to fully understand the evolution of eavesdropping behaviour.

Animals frequently make decisions based on social information obtained from other animals, which can influence interspecific interactions and affect individual fitness. For example, animals eavesdrop on other animals to find profitable food resources, yet the types of cues they use and how these cues influence decisions to approach a resource remain poorly understood. In tropical systems, arthropods inadvertently flushed by army ant, Eciton burchellii, swarms are an important food resource for many bird species, which form mixed-species foraging aggregations at swarms. Competition at swarms is intense and birds vocalize to defend foraging areas, inadvertently producing acoustic social information about the swarm's location. Eavesdropping birds may use these acoustic cues, which provide information about the bird aggregation (i.e. species participating in the aggregation, the size of the aggregation and/or diversity of the aggregation) to assess potential benefits (food resources) and costs (competition for food) of joining an aggregation. To test this hypothesis, we used an acoustic playback experiment to simulate aggregations of birds foraging at ant swarms and we measured community-wide and guild-specific responses of forest birds to playbacks. We included three types of acoustic social information in playbacks that potentially interact to affect an eavesdropping bird's probability of attraction to a swarm: (1) aggregation size, (2) aggregation species richness and (3) degree of specialization on ant swarms for food of birds vocalizing in the aggregation (hereafter 'dependency'). Using Bayesian generalized linear mixed models, we found that playbacks of obligate ant-following species elicited greater community-wide responses (i.e. attracted more individuals and species) to simulated aggregations compared to playbacks of other, less dependent guilds. We also found that interactions between dependency, species richness and aggregation size influenced the overall community response to playbacks and that species from one guild generally responded to the guild above them (i.e. from less to more specialized). Our results suggest that species evaluate multiple types of acoustic cues representing the costs and benefits of foraging in a mixed-species aggregation at a swarm. We hypothesize that species change from information receivers to information producers upon joining a swarm, ultimately producing an information cascade that further affects the dynamics of feeding aggregations at swarms. (C) 2017 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Insects of many species depend on the chemical cues in sex pheromones to identify potential reproductive partners. Previous studies have shown that odd beetle, Thylodrias contractus utilize sex pheromones at the onset of reproductive physiology that leads to mating behavior. This is a study to make strides to identify the sex pheromone(s) for the odd beetle, T. contractus. In this study, efforts to isolate the sex pheromone of this pest insect began with observations of the mating behavior of this insect. This was followed by dissections of adult virgin females in an attempt to reveal which parts of the anatomy were producing the pheromone. In addition, several sampling methods were used to help identify this pheromone on a Gas Chromatograph. These methods included blowing filtered-air across live beetles onto an absorbent column, solvent washes of adult beetles and a sampling technique using solid phase microextraction (SPME) on live insects. Finally, an analysis of the headspace above live adult virgin females using a Gas Chromatograph/ Mass Spectrometer (GC-MS) was made. Comparison of the Gas Chromatograph results and the results of the GC-MS has narrowed the possibilities of what compounds may be included in the female attractant pheromone.

Changes in sexual signals have the potential to promote rapid divergence and reproductive isolation among populations of animals. Thus, identifying processes contributing to variation in signals is key to understanding the drivers of speciation. However, it is difficult to identify the processes initiating changes in signals in empirical systems because (1) the demographic history of populations under study is usually unclear, and (2) there is no unified hypothesis-testing framework for evaluating the simultaneous contribution of multiple processes. A unique system for study in the Hawaiian Islands, the planthopper species Nesosydne chambersi, offers a clear demographic context to disentangle these factors. By measuring variation in male vibratory sexual signals across different genetic populations on the island of Hawaii, we found that that multiple signal traits varied significantly between populations. We developed a mixed modelling framework to simultaneously test competing hypotheses about which processes contribute to changes in signal traits: genetic drift, sensory drive or reproductive character displacement. Our findings suggest that signal divergence proceeds along different axes for different signal traits under the influence of both neutral and selective processes. They are the first, to our knowledge, to document the relative importance of multiple processes on divergence in sexual signals.

Complex displays play an important role in female mate choice and male–male interactions for many species. Displays used in both inter- and intrasexual interactions offer an opportunity to examine how the ordering and structure of complex displays may vary with context. To understand how social context can influence the performance of complex displays, we investigated the predictability of display elements across displays in the presence and absence of females. The lance-tailed manakin, Chiroxiphia lanceolata, is a small lekking bird that performs complex, acrobatic displays. Pairs of alpha and beta males cooperatively display for females, but they also perform very similar displays in the absence of females. We quantified the performance of individual alpha and beta males within the dual-male display and the joint performance of the two males using Shannon's information entropy, and compared these values to understand how male display predictability varies with social context. Differences were assessed using generalized linear mixed models to account for repeated measures of male pairs. Predictability of individual performance within the dual-male interaction did not differ with female presence; however, entropy metrics describing the interaction of the alpha and beta male indicated that displays for females were more predictable and coordinated. This study provides a quantitative assessment of display element performance across different social contexts of female presence and absence, and suggests that the dual-male phenotype may be an important factor in female mate choice for cooperatively displaying species.

Understanding the interactions of an organism and its environment is essential for us to integrate ultimate and proximate causation on a global scale. Organism–environment interaction includes all organisms including animals, plants, and non-eukaryotes, etc. because all of them are responsive to environmental change including those that are human-induced. A mechanistic approach is important for us to understand why some organisms can cope with change and others cannot. Here, we present three examples of environments ("the three poles") that are changing rapidly and how avian species typical of these ecosystems are responding. These examples include apparently adaptive responses to change in climate (i.e. the predictable environment) in one species in which a lengthened breeding season now allows multiple breeding attempts. Why other species are unable to respond in a similar way remains unclear. A second example describes how changing weather (i.e. the unpredictable) may have disastrous results for breeding success in a species adapted to an extreme cold environment. Implications for climate change in which weather extremes will become more common again suggest a mechanistic approach will be important to understand how organisms may respond. The third example outlines a scenario in which multiple human-induced rapid changes (a combination of predictable and unpredictable such as development, habitat change, introduction of invasive species and climate change) may influence indigenous species in different ways. Organism–environment interaction is a fundamental concept that may unify ultimate and proximate causation and point the way for future investigations striving to understand coping mechanisms in a world where both predictable and unpredictable components of the environment are changing.

Severe environmental conditions affect organisms in two major ways. The environment may be predictably severe such as in deserts, polar and alpine regions, or individuals may be exposed to temporarily extreme conditions through weather, presence of predators, lack of food, social status etc. Existence in an extreme environment may be possible, but then to breed or molt in addition can present major bottlenecks that have resulted in the evolution of hormone-behavior adaptations to cope with unpredictable events. Examples of hormone-behavior adaptations in extreme conditions include attenuated testosterone secretion because territoriality and excess courtship may be too costly when there is one opportunity to reproduce. The individual may even become insensitive to testosterone when target areas of the brain regulating reproductive behavior no longer respond to the hormone. A second example is reduced sensitivity to glucocorticoids following acute stress during the breeding season or molt that allows successful reproduction and/or a vital renewal of the integument to endure extreme conditions during the rest of the year. Reduced sensitivity could involve: (a) modulated response of the hypothalamo-pituitary-adrenal axis, (b) reduced sensitivity to high glucocorticoid levels, or (c) a combination of (a) and (b). Moreover, corticosteroid binding proteins (CBP) buffer responses to stress by reducing the movement of glucocorticoids into target cells. Finally, intracellular enzymes (11 beta-hydroxysteroid dehydrogenase and variants) can deactivate glucocorticoids entering cells thus reducing interaction with receptors. These mechanisms have important implications for climate change and increasing extremes of weather [Current Zoology 57 (3): 363-374, 2011].

Birds in the lowland tropical rain forest are expected to have low energy turnover. Here, we used heart rate telemetry to estimate nighttime resting metabolic rate (RMR), daily energy expenditure (DEE), and locomotor activity of a small, long‐lived tropical rain forest–understory bird, the spotted antbird (Hylophylax naevioides). Heart rate was linearly related to oxygen consumption in respirometry measurements that encompassed 96% of heart rates measured in wild birds. Heart rates in the wild ranged from 260 beats/min at night to 824 beats/min during the day, with a mean of 492 beats/min. Compared with temperate‐forest birds of similar body mass, wild spotted antbirds had a low DEE, only 51% of the expected value. Such low metabolism was achieved mainly by being locomotively inactive for 35% of the daytime (i.e., 0 hops or flights/min). On average, spotted antbirds exhibited 1.6 hops or short flights/min during the daytime. In addition, they decreased nighttime RMR in the wild (at ambient temperatures below their thermoneutral zone [TNZ]) to levels equivalent to nighttime RMR in the laboratory at temperatures within their TNZ. This suggests that wild birds reduce their body temperature every night. Our data confirm and extend previous studies showing that tropical passerines have low metabolic rates.

Interactions among parents, offspring and the environment are a critical aspect of parental care. Begging by offspring usually results in increased parental provisioning. Yet, parents also vary their behaviours to reduce offspring predation. Both begging sounds and provisioning activity can increase risk of nest predation. We predicted in a high nest-predation environment, parents would satiate young and reduce begging by increasing food load but maintaining the same provisioning rates. We also assessed whether increased begging was beneficial to offspring and whether parents changed the allocation of food to particular nestlings. We increased whole-brood begging via playbacks at nests of a tropical passerine bird, the western slaty antshrike, Thamnophilus atrinucha. We observed that parents increased provisioning rates and reduced food load in response to elevated begging. Selection may therefore favour feeding hungry nestlings even when predation risk is elevated, or begging sounds may place offspring at a higher risk than increased activity. Parents reduced the time between arrival to the nest and feeding of nestlings, potentially to reduce begging sounds. Exaggerated begging did not appear to be beneficial to offspring since parents did not deliver more food. Parents switched to preferentially feed the closest offspring during the begging treatment. This suggests that, under elevated begging, parents either allowed sibling competition to influence feeding decisions, or fed the closer nestling to reduce the time between arrival to the nest and feeding. Studying species in different environments provides insight into how ecological factors such as nest predation influence parental behaviour. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.