acta ethologica最新文献

Eastern gray squirrels (Sciurus carolinensis) exhibit a variety of color morphs, including black. In the USA and UK, a common folk belief is that black squirrels are more aggressive than squirrels of other colors. We tested the biological basis of that belief using data from the 2018 Central Park squirrel census. Contrary to the belief, black squirrels do not chase other squirrels more often than do conspecifics of other colors. Black and non-black squirrels were equally likely to approach people for food and to display indifference to human presence, but black squirrels were more likely than non-black squirrels to flee from people. Although other research has found that aggression among squirrels increases when they live in higher population densities, black squirrels were no more aggressive than non-black squirrels despite the fact that they were sighted in parts of Central Park with higher squirrel population densities than other locations.

Sexual selection predicts evolution of secondary sexual traits favoring mating. Here, we address the within population variation in courtship display behavior among male White-throated Manakins, Corapipo gutturalis, from Central Amazonia. We repeatedly quantified the courtship display elements used by 16 males over multiple days and specifically tested whether male presence and displays at courts could be explained by variation in environmental conditions (forest shade with small sunny gaps, large sunny gaps, and cloudy), male age (juvenile or adult), or yet the social context (other males and female visits) during displays. Our results show that total male presence and time displaying varied with the total number of other males and female visits at the court. In addition, the type of courtship elements used in displays (assessed by principal component analysis) also varied with the presence of both females and other males on the court. Male age, however, did not influence male activity. Overall, the social context at the court was the strongest predictor of within-population variations in male courtship display, whereas light conditions only affected display duration. Variation in display repertoire with female presence might reflect variation in female preferences. In addition, similar displays among males of different age classes suggest a competitive, rather than cooperative lek system of White-throated Manakins in Central Amazonia.

In Southeast Asian forests, there are dramatic supra-annual peaks in fruit availability known as mast fruiting, followed by low-fruit periods. Gibbons are frugivorous small apes. In this study, we investigated how gibbons varied their social and calling behaviors in response to changes in fruit availability. Activity budget, travel distance, sleeping time, and song duration of two wild Northern Gray gibbon (Hylobates funereus) groups were investigated during both mast and non-mast fruiting periods at the Danum Valley Conservation Area, Sabah, Malaysia. Gibbons traveled longer, entered the sleeping tree later, and spent more time engaged in singing, playing, and grooming behaviors during the mast fruiting period. Playing and grooming are intra-group social interactions. Gibbon songs were sung antiphonally within and among groups, indicating that singing is both an intra- and inter-group social interaction. Furthermore, copulatory behaviors that occurred during female pregnancy were observed during the mast fruiting period, suggesting this might be a social interaction behavior rather than a reproductive activity. Our results show that gibbons extended their daily activity schedules during the mast fruiting period and spent this extra time on social interactions. We examined whether male song complexity increased during the mast fruiting period by using the Levenshtein distance method, but we did not find such a trend. In the mast fruiting period, gibbons may consume more energy than in the non-mast fruiting period. Social and calling behaviors are energetically costly. Our results show that there is a link between energy intake and social and calling behaviors.

Water turbidity deteriorates visibility and thereby may change the physiology and behavior of aquatic animals that rely on vision. In the guppy fish (Poecilia reticulata), a key element in the mating behavior and reproductive success of males is female mate choice, which is predominantly based on visual signals. Females choose attractive males based on body coloration, and males court females by displaying their coloration. Here, we demonstrate that guppy males exhibit morphological and behavioral adjustments in response to changes in the visual environment. Males reared in turbid water had more conspicuous coloration than males reared in clear water, with higher intensity of carotenoid-based and ultraviolet colors, but not a larger area of red spots on the body. However, they performed less courtship displays in turbid water than males reared in clear water performed in clear water. Thus, increased coloration in turbid-water males was not accompanied by increased effort to display it. Although our findings demonstrated developmental plasticity in mating-related traits, turbidity-induced alteration in coloration did not match behavior change as could be predicted by favoring male attractiveness.

Animals have evolved a variety of mechanisms to detect and avoid predation. The non-vocal sounds produced by some bird species during takeoff flights have been considered to function as an alarm call, because they may convey information about predation risk. Here, we experimentally investigated the effects of the non-vocal sound (wing trills) produced by the scaled dove (Columbina squammata) on antipredation behaviours of conspecifics. We evaluated the individual response to playbacks of the wing trill stimulus and compared it to the response to other two control stimuli (vocalizations of the scaled dove and the southern house wren). We found that doves’ probability to become vigilant or to display freezing behaviour was higher after a wing trills stimulus in comparison to the other playback stimuli. These results suggest that wing trill production in scaled doves communicate potential risks and are considered by the individuals in the decision-making process, but we cannot rule out the possibility that any takeoff flight sound might also promote antipredator responses.

Animals can form groups for various reasons including safety from predators, access to potential mates and benefits of allo-parental care. However, there are costs associated with living in a group such as competition for food and/or mates with other members of the group, higher chances of disease transmission, etc. Group size dynamics can change with the biotic and abiotic environment around individuals. In the current study, we explored the links between group size dynamics and intestinal parasites of Indian peafowl (Pavo cristatus) in the context of seasons and food provisioning. Data for group size was collected across three seasons (pre-monsoon, monsoon and post-monsoon) at three field sites (Morachi Chincholi, Nashik and Rajasthan). Individual and group sightings of peafowl were noted down along with group size and composition (no. of males, females, adults, juveniles and sub-adults). Faecal samples were collected from food provision and non-provision areas across the same three seasons at same field sites. Parasite load in the samples was quantified using microscopic examination. Group size was significantly higher in pre-monsoon season as compared with monsoon and post-monsoon seasons. Monsoon and post-monsoon seasons had higher intestinal parasite prevalence and load as compared with pre-monsoon season. Thus, group size and intestinal parasites of Indian peafowl have an inverse relationship across seasons. Parasite load was significantly greater at food provision sites as compared with non-provision sites while parasite prevalence was comparable. Aggregation of individuals at the food provision sites may influence the parasite transmission and group-size dynamics in Indian peafowl. In conclusion, Indian peafowl are behaviourally plastic and fission-fusion of social groups may allow them to tackle ecological pressures such as predation and parasite transmission in different seasons.

We described the spatial segregation of two species of cetaceans, the common dolphin and the bottlenose dolphin. We also document the first direct observation of interspecific killing of a common dolphin by bottlenose dolphins and of interspecific necrophilia in cetaceans. The study was conducted from 2014 to 2019 in the Ría de Arousa (Northwest Spain). This study highlights that both species use this area as a foraging ground, although they show different patterns of occurrence (bottlenose dolphins were always observed in the ria and common dolphins were mostly observed outside). During the study period, bottlenose dolphins and common dolphins were only observed on five occasions at the same time and in the same area, including three occasions which led to the displacement of the common dolphin(s), and one lethal interaction. In this event, several bottlenose dolphins, including adults and calves, and males and females, aggressively herded, chased, and assaulted a common dolphin. After approximatively 10 min, the common dolphin corpse appeared floating at the surface, and several adult male bottlenose dolphins repeatedly pushed the body underneath the water surface and an (attempted) copulation was witnessed. We suggest that the common dolphin could have been killed for competition for food resources or practice for infanticide, and sexual arousal might have been triggered by expression of dominance. Further information about the occurrence of such behaviors, and the outcomes through specific studies on fitness would be crucial to further understand the implication of such events.

We report an observation at Jhalana Leopard Reserve (JLR), Jaipur, India. On 16 March 2019, we saw a female walking up the mountain while calling her two, 4-month-old, male and female cubs. This allowed several safari jeeps to park in the shade of nearby Acacia trees. Two Striped Hyenas (Hyaena hyaena) approached and sniffed at the base of one of the trees near the parked jeeps. Upon seeing the Hyaenas, the female ran down the mountain, passed between the jeeps, and climbed into the tree. That is when we noticed the body of the female cub at a height of approximately 4.5 m. The female licked the body of the cub for several minutes and then picked it up in her mouth, climbed down from the tree, passed again between the jeeps, and walked up the mountain towards a dense stand of Thor (Euphorbia caducifolia), a thorny cactus. Our observations display how a mother leopard that has lost a cub refuses to abandon the carcass, cached it in a tree, and when discovered by scavengers removed it to a thicket of cacti. We consider the behavior towards her dead cub, and subsequent caching when discovered by other animals, to be the first evidence for thanatological expression in leopards.

Providing artificial eggs is a commonly used technique to understand brood parasitism, mainly by the common cuckoo (Cuculus canorus). However, the presence of a cuckoo egg in the host nest would also require an earlier physical presence of the common cuckoo within the host territory. During our study of the red-backed shrike (Lanius collurio), we tested two experimental approaches: (1) providing an artificial “cuckoo” egg in shrike nests and (2) additionally placing a stuffed common cuckoo with a male call close to the shrike nest. We expected that the shrikes subject to the additional common cuckoo call stimuli would be more sensitive to brood parasitism and demonstrate a higher egg rejection rate. In the years 2017–2018,  in two locations in Poland, a total of 130 red-backed shrike nests were divided into two categories: in 66 we added only an artificial egg, and in the remaining 64 we added not only the egg, but also presented a stuffed, calling common cuckoo. Shrikes reacted more strongly if the stuffed common cuckoo was present. However, only 13 incidences of egg acceptance were noted, with no significant differences between the locations, experimental treatments or their interaction. Analysis of breeding success revealed significant differences between the locations, between experimental treatments and their interaction, which suggests a strong location effect. The red-backed shrike is an efficient rejector of foreign eggs. It would be interesting to see how similar tests affect hosts that have much higher rates of brood parasitism and egg acceptance.