Ethology最新文献

Male Japanese bush warblers (Cettia diphone) produce not only typical songs but also long, conspicuous vocalizations (continuous songs) during the breeding season. In my preliminary observations, male warblers produced continuous songs in response to both the appearance of a predator and the calls of conspecific females. Although predator-elicited vocalizations by males have been studied in some species, there are no known cases in which an acoustically identical vocalization is also triggered in response to conspecific females. Here, I examined whether these continuous songs triggered in response to predators and females were acoustically similar. In field experiments, I presented dummies of a Eurasian sparrowhawk and a female warbler before (April) and after (June) female arrival at the breeding ground. Before female arrival, 11.1% of males responded with continuous songs to each of the hawk and female presentations; after female arrival, the respective values were 27.6% and 48.3%. Thus, more males responded to the model presentations with continuous songs after female arrival. There was no difference in the acoustic characteristics of the continuous songs between the two models. The males approached the female model more intensively than the hawk model. These findings do not support the hypothesis that the song functions as an alarm or predator deterrent. The function of these continuous songs remains unclear, but this study is the first to show an example where males produce the same vocalization in response to both predators and conspecific females. The continuous song contains a trill-like structure, which can be considered a performance-related song trait. Therefore, the continuous song may possibly be an honest signal of male quality for females. Further studies are required to understand the function of this novel vocalization, particularly the effects of female breeding stage on male singing activity and the female response to the songs.

Top marine predators, such as odontocetes, pinnipeds, and seabirds, are known to forage around fishing boats as fishermen aggregate and/or discard their prey. Recently, incidents of humpback whales interacting with fishing boats have been reported. However, whether humpback whales utilise discard fish as a food source and how they forage around fishing boats is unknown. This study reports, for the first time, the foraging behaviour of a humpback whale around fishing boats. Three whales were tagged using a suction-cup tag containing a video camera, and a behavioural data logger in the coastal area of Tromsø, Norway. Video data from one tagged whale showed that the whale remained in close vicinity of fishing boats for 43 min, and revealed the presence of large numbers of dead fish, fish-eating killer whales, fishing boats, and fishing gear. In waters with large numbers of dead fish, the whale raised its upper jaw, a motion associated with engulfing discard fish from fishing boats, and this feeding behaviour differed markedly from lunge-feeding observed in two other whales in the same area. This behaviour was defined as “pick-up feeding”. No lunge feeding was seen on the data logger when the whale foraged around fishing boats. This study highlights a novel humpback whale foraging strategy: low energy gain from scattered prey but also low energy costs as high-energy lunge feeding is not required.

Reciprocal altruism has been proposed to generate evolutionarily stable levels of cooperation, but empirical evidence in non-human animals is contentious. A series of experimental studies on Norway rats revealed that these animals reciprocate received help by using decision rules characterising direct and generalized reciprocity. The direct reciprocity decision rule states that individuals should help someone who previously helped them, whereas the generalized reciprocity decision rule implies that individuals should help anyone after having received help from someone. Here, we present results from meta-analyses assessing if Norway rats generally help partners according to the direct and generalized reciprocity decision rules by giving more help sooner and matching help received either to previously cooperative partners or to anyone after having received help from a conspecific. We also compared the rats' performance when applying the direct or generalized reciprocity decision rules. Results from these meta-analyses clearly show that female and male focal rats help partners according to the direct reciprocity decision rule. Rats did not adjust the amount of help they gave by matching the help they received according to both the direct and generalized reciprocity decision rules; however, they may adjust the duration to the first help they gave by matching the help they received according to the direct reciprocity decision rule. Female, but not male, focal rats help partners according to the generalized reciprocity decision rule. There was no apparent difference in the help given by female rats to partners between the direct and generalized reciprocity decision rules. These results (i) demonstrate, across a wide range of studies, the reciprocal cooperation of Norway rats by use of decision rules denoting direct and generalized reciprocity, and (ii) suggest that rats may frequently apply the cognitively less demanding decision rule of generalized reciprocity, unless they need to distinguish between individuals differing in helpfulness.

In recent years, temperatures have increased globally, and nestlings of many bird species are likely regularly exposed to increased temperatures both pre- and post-natally. Even small increases in nest temperature during incubation affect offspring growth and survival in a variety of species, one cause of which is thought to be increased production of pro-oxidants in embryos and nestlings. Defences marshalled in response to this oxidative stress could, in turn, result in trade-offs that lead to reduced survival or growth. If so, any downstream negative effects on nestlings of increased ambient temperatures during incubation could be counteracted by increasing their antioxidant intake. We predicted, therefore, that dietary supplements of an antioxidant would reduce or eliminate any detrimental effects on nestling growth and survival of experimentally increased nest temperature during the incubation period. We employed a split-brood design in which we increased the nest temperature of entire clutches and, after hatching, provided dietary supplements of the antioxidant vitamin E to half of the nestlings within broods. We also recorded female incubation and provisioning behaviour to control for the possibility that heating nests might also influence maternal behaviour. There was a significant interaction between nestbox heating treatment and vitamin E treatment in their effect on nestling mass, a trait that is positively correlated with survival and future reproductive success in the study population. Vitamin E supplementation promoted increased nestling mass in heated nests, whereas it had the opposite effect in control nests but these effects were weak. Heating significantly affected female incubation behaviour, with females in heated nestboxes investing less in incubation than those in unheated boxes. These results suggest that within at least some range of expected increased ambient temperatures during the 21st century, effects of climate change on nestling bird development can be mitigated by adjustments in female incubation behaviour.

Prosocial behaviour (i.e. benefitting others without receiving a direct gain) has long been perceived as an evolutionary puzzle but is nevertheless relatively common among non-human animals. Prosocial food provisioning has recently been documented in several large-brained bird species, such as corvids and parrots. Yet, to date, little is known about which factors influence food provisioning in these species. Here, we investigated whether kinship, reciprocity and dominance affected food provisioning in the group service paradigm in three corvid species, namely azure-winged magpies (Cyanopica cyana), carrion crows (Corvus corone) and common ravens (C. corax). In this paradigm, the subjects are tested in their regular social groups and can choose to make food available to their group members by landing on a simple seesaw apparatus. We found no evidence for an effect of kinship or reciprocity on food provisioning. Contrary to our predictions, the subjects' dominance was not positively correlated with their rate of food provisioning in any species. Among ravens, dominance was instead positively correlated with receiving food. We conclude that preferential provisioning for kin and direct reciprocity might have been impeded by the provider's inability to control who receives the food in the group service paradigm, but that our findings provide another piece of evidence that dominance is a highly important factor in the social interactions of common ravens.

Sexually monomorphic species have been historically overlooked in the sexual/social selection literature, but there is growing evidence that mutual ornamentation can be driven by selective forces such as mutual sexual selection or selection for individual recognition. Examining the properties of a trait may elucidate which forces most likely play a role, especially when comparing the characteristics of quality and identity traits. Atlantic puffins (Fratercula arctica) are an example of a mutually ornamented monomorphic species, where both males and females display a bright orange-red bill and orange gape rosette during the breeding season and are ornamented to similar degrees. In this study, we investigate whether the properties of the colorful bill and rosette, specifically lability across the breeding season and condition-dependence, more closely align with signals of quality or identity. Our findings support prior work that the bill is sexually monochromatic from an avian visual perspective. We also determined that the bill changes in a discriminable way within individuals across the breeding season and is especially dynamic in the fleshy rosette. However, no metric of color on any region of the bill or rosette was significantly related to current body condition. Ultimately, we argue that bill color could potentially function as a quality signal, although further study is needed to determine which aspect of quality coloration signals, if not condition. These results provide a basis for experimentally evaluating the signal value of the colorful bill in Atlantic puffins (e.g., color manipulation experiments), and more broadly, a framework for investigating the properties of mutual ornamentation in avian species.

Behavioral imprinting is a learning phenomenon by which animals acquire preferences for stimuli through perceptual exposure during critical periods, without substantial external reinforcement. Since being acknowledged in 1516 by Sir Thomas More in artificially incubated domestic chickens, imprinting has been reported in diverse species, across various sensory modalities, and during different life-history stages. Due to this diversity, imprinting research uses highly varied methodologies, with distinctive differences between the methods employed for different types of imprinting. We systematically review relevant literature, identifying and describing the range of methodologies used to study imprinting across taxa and modalities. After compiling a representative dataset of 192 behavioral imprinting-focused experiments, we categorize studies by imprinting sensory modality, focal species, ontogenetic stage addressed, and methods applied for both exposure and testing. The majority of studies in the sample focus on filial imprinting in precocial birds but nonfilial types, such as sexual or home range imprinting in altricial and non-avian species, are also present, albeit at far lower proportions. Filial imprinting is studied across different sensory modalities, mostly through applying artificial stimuli, but nonfilial imprinting studies mainly use live animals as stimuli, without isolating the relevant sensory modalities. Most studies of filial imprinting measure preference by spatial proximity, following response, or the suppression of a fear response, whereas most studies of sexual imprinting employ the attempt frequency of sexual behaviors. Finally, we analyze the relative frequencies of methodological approaches in each imprinting category, to highlight potential biases due to uneven research effort rather than intrinsic biology. The patterns and biases in imprinting methodologies that we uncover hamper attempts to establish whether different forms of imprinting share mechanistic foundations, including whether imprinting constitutes a biologically meaningful learning category.

The behavioral plasticity among and within cetacean species can be driven by their prey sources, local adaptations to environmental features, and/or interactions with human activities. One of the tactics displayed by cetaceans is the barrier feeding, in which individuals or groups herd fish schools against natural and non-natural barriers to restrict movements of their prey. Coastal odontocetes, for example, are known for using shorelines and underwater slopes to trap their prey. Here, we documented two distinct populations of Guiana dolphin using the mangrove margins as a natural barrier to herd and capture fish. The observations took place in the Cananéia estuary, São Paulo State, southeastern Brazil, and in the Paranaguá estuary, Paraná State, southern Brazil. A total of 63 dolphins over eight encounters were observed performing six different events using mangroves as a natural barrier, summing both study areas. These findings not only expand our understanding of the behavior plasticity of the species but also call attention to the importance of the mangrove ecosystem directly to Guiana dolphins and indirectly to the components of their food web.

Adolescence is a sensitive phase when cues from the social environment can shape consistent individual differences in behavioral and hormonal profiles, but the effect of the social partner on these phenotypes is not well-understood, especially for females. We therefore aimed to investigate whether the age class and sex of the housing partner affect social behavior and cortisol concentrations in female guinea pigs during adolescence and estimate the repeatability of cortisol concentrations in this life stage. Female guinea pigs were housed upon weaning for 4 weeks with either an adult female, adolescent female, or adolescent male. Social behavior was observed in the home enclosure and a preference test and social interaction test were carried out at the end of the experiment. Cortisol concentrations (baseline and response to a challenge) were measured prior to the start of the experiment and 2 and 4 weeks after pair formation. We hypothesized that the social partner would affect behavior and cortisol concentrations. We found that females housed with an adult female were less aggressive and more consistently displaced by their housing partner than females housed with an adolescent female. Sex of the housing partner did not affect focal female behavior. Regarding hormones, baseline cortisol concentration was neither significantly repeatable nor significantly affected by the housing partner. However, cortisol responsiveness was highly repeatable both 1 h and 2 h after the onset of a challenge. The age class of the housing partner affected cortisol responsiveness, with higher cortisol concentrations measured at 1 h in females housed with an adult female. These results indicate that adolescent female guinea pigs exhibit consistent individual differences in cortisol responsiveness while retaining plasticity to adjust to cues from the social environment. Taken together, we show in a female rodent that the social environment can significantly shape behavioral and endocrine parameters during adolescence.

Competition over resources often leads to intra- and interspecific interactions, which can be detrimental to the individuals involved. Thus, natural selection should favor communication systems that reliably convey information regarding the relative competitive abilities of an individual, reducing the need for physically damaging confrontation. Body size, sex, age, relatedness, and ornamentation are important factors determining dominance across diverse taxa in intraspecific interactions. These traits, when perceptible, may serve as signals across species in guilds that have frequent interspecific interactions. Hummingbirds provide a tractable system to study such community dynamics due to their high frequency of interactions, variable ornamentation, diverse body sizes, fast metabolism, and large overlap in resource utilization. Even in this system, potential interactions between morphology and coloration are rarely accounted for together when analyzing dominance between species. We take a novel approach to understanding interspecific dominance by assessing behavior, morphology, and coloration across different types of behavioral interactions. Across 11 tropical montane hummingbird species, we find that dominance is predicted by wing size and some metrics of plumage coloration. However, the biological significance of these factors varies between the different dominance behaviors performed. These results inform our understanding of interspecific signaling and its role in the evolution of intraguild communication and resource competition.