Cryptic eggs are rejected less frequently by a cuckoo host

Abstract

Obligate brood parasitism is associated with huge reproduction costs, forcing hosts to evolve various anti-parasitic strategies against brood parasites, among which egg recognition and rejection is the most effective defense strategy. According to the crypsis hypothesis, non-mimetic yet cryptic eggs in a nest can also deceive their hosts and eventually be accepted. To validate this hypothesis, we conducted field experiments on Oriental reed warblers (Acrocephalus orientalis), a common host for common cuckoos (Cuculus canorus). We firstly tested the egg recognition and rejection abilities of Oriental reed warblers, using black and white model eggs in natural nests. Then we designed a comparison test where the cryptic effects of the two groups of experimental eggs were different. We manipulated the nest lining color and added relatively cryptic and bright model eggs to test warblers’ rejection behaviors against cryptic and bright foreign eggs. The results showed that warblers have strong egg recognition and rejection abilities. There is a significant tendency for warblers to prefer to peck and reject relatively distinguishable foreign eggs, which supports the crypsis hypothesis. These findings indicate that even in the host-parasite system of open nests, parasitic eggs that are cryptic enough are prevented from being discovered and rejected by the host, and thus obtain the possibility of successful parasitism.

A review of the unsolvable task in dog communication and cognition: comparing different methodologies

Abstract

Communication between dogs and humans is a topic of growing interest, and the “unsolvable task” is a common method used to measure human-directed communication. In this task, dogs learn how to solve a problem to obtain a reward. After a fixed number of trials, the reward becomes impossible to access, arguably leading to communicative attempts from the dog. Although useful to observe dogs’ communicative behaviors in a fairly naturalistic situation, the methodology varies among studies regarding apparatus, number of trials, and other factors. The proxies used, for instance, gaze duration or frequency of gaze alternation, also vary, and there are discrepancies and a debate regarding what the task actually measures. Therefore, in this study, we reviewed the usage of the unsolvable task in canids of the genus Canis, searching Web of Science and Scopus for the terms “dog*”, “Canis”, “dingo*”, “wolf” or “wolves” in the title and « unsolvable task » or « impossible task » in the topic. We included thirty-five studies in this review and discussed their different methodologies and proxies, such as different apparatuses, number of solvable trials, and different interpretations of “looking back”, pointing out how they can affect results and hinder comparisons. Lastly, we used current data to propose strategies to homogenize the use of this important paradigm, with an ethogram of possible behaviors and their interpretation and a predefined set of methodological aspects for future research.

Production of regular rhythm induced by external stimuli in rats

Abstract

Rhythmic ability is important for locomotion, communication, and coordination between group members during the daily life of animals. We aimed to examine the rhythm perception and production abilities in rats within the range of a subsecond to a few seconds. We trained rats to respond to audio-visual stimuli presented in regular, isochronous rhythms at six time-intervals (0.5–2 s). Five out of six rats successfully learned to respond to the sequential stimuli. All subjects showed periodic actions. The actions to regular stimuli were faster than randomly presented stimuli in the medium-tempo conditions. In slower and faster tempo conditions, the actions of some subjects were not periodic or phase-matched to the stimuli. The asynchrony regarding the stimulus onset became larger or smaller when the last stimulus of the sequence was presented at deviated timings. Thus, the actions of the rats were tempo matched to the regular rhythm, but not completely anticipative. We also compared the extent of phase-matching and variability of rhythm production among the interval conditions. In interval conditions longer than 1.5 s, variability tended to be larger. In conclusion, rats showed a tempo matching ability to regular rhythms to a certain degree, but maintenance of a constant tempo to slower rhythm conditions was difficult. Our findings suggest that non-vocal learning mammals have the potential to produce flexible rhythms in subsecond timing.

To group or not to group: group size dynamics and intestinal parasites in Indian peafowl populations

Abstract

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.

A kestrel without hooked beak and talons is not a kestrel for the red-backed shrike ( Lanius collurio )

Abstract

Birds are strongly motivated to recognize various predators to secure survival and reproductive success. Thus, predator recognition provides a useful tool for the investigation of the process of discrimination and categorization in non-trained animals. The most important role in this process is usually attributed to the prominent unique features shared by all members within the wider category of predators (sharp teeth or beaks, claws, talons and conspicuous eyes). However, birds are also able to discriminate between particular predator species according to their species-specific features (based mainly on colouration). We manipulated general raptor salient features (hooked beak, talons with claws and eyes with supraorbital ridges) and/or species-specific plumage colouration on the dummy of a Eurasian kestrel (Falco tinnunculus) to investigate their importance in the recognition process of the red-backed shrikes (Lanius collurio) during nest defence. We showed that the presence of general raptor salient features is necessary for the recognition of a predator. The kestrel dummy with natural species-specific colouration with altered raptor salient features was treated by shrikes as a harmless bird. Nevertheless, pronounced changes in colouration also prevented successful recognition of the dummy as a kestrel, even when raptor salient features of a raptor were present.