Early development of gaze following into distant space in juvenile Greylag geese (Anser anser)

Visual co-orientation with another's gaze direction (gaze following) may provide important information about the location of food, social interactions or predators. Gaze following has been shown in a variety of mammals, but only in few bird species, and has not been tested in precocial birds at all. It has been suggested that gaze following is an anti-predator behaviour, and in Common ravens (Corvus corax) and rooks (C. frugilegus), it emerges shortly after fledging, at a time when young birds leave the predator-safe nest. However, if gaze following is adaptive, the developmental pattern should differ between altricial and precocial birds. Greylag geese (Anser anser) are highly social birds with a precocial development. Goslings move and feed independently within 24 h post-hatching, and they are highly vulnerable to aerial predators. We therefore predicted that greylag geese are capable of gaze following and that they develop this skill already pre-fledging. We experimentally tested 19 hand-raised greylag goslings for their ability to follow a conspecific's gaze when they were between 10 days and 6 weeks old. In line with our predictions, first responses were already detectable in 10-day-old goslings. Our results therefore not only demonstrate that greylag geese follow the gaze of conspecifics into distant space, but that they also develop this ability much earlier than altricial birds.     

What you see is what you get--reloaded: can jackdaws (Corvus monedula) find hidden food through exclusion?

Choice by exclusion, that is, the ability to base the choice of a target on the rejection of potential alternatives, is becoming increasingly interesting for comparative cognition research. Recently, ravens have been shown to solve an exclusion task and it had been suggested that this ability might benefit ravens in a food-caching context. To investigate this possibility, the raven study was replicated with a closely related, but noncaching, species, the jackdaw (Corvus monedula). In the first test, the birds had to find food hidden in one of two differently shaped tubes. The results suggest that the jackdaws found the food through intensive search behavior, with little evidence for exclusion abilities. In a follow-up experiment, the tubes were replaced by cups, and before the birds made a choice, one of the cups was lifted to inform them about its content. In a final task, this procedure was modified to control for the influence of local enhancement. In both experiments, the jackdaws were successful only if they had seen the food before. These findings are in contrast to the previous results on ravens and support the idea that exclusion abilities may have evolved as specific adaptations to food caching.     

Understanding of and reasoning about object–object relationships in long-tailed macaques?

Diagnostic reasoning, defined as the ability to infer unobserved causes based on the observation of their effects, is a central cognitive competency of humans. Yet, little is known about diagnostic reasoning in non-human primates, and what we know is largely restricted to the Great Apes. To track the evolutionary history of these skills within primates, we investigated long-tailed macaques’ understanding of the significance of inclinations of covers of hidden food as diagnostic indicators for the presence of an object located underneath. Subjects were confronted with choices between different objects that might cover food items. Based on their physical characteristics, the shape and orientation of the covers did or did not reveal the location of a hidden reward. For instance, hiding the reward under a solid board led to its inclination, whereas a hollow cup remained unaltered. Thus, the type of cover and the occurrence or absence of a change in their appearance could potentially be used to reason diagnostically about the location of the reward. In several experiments, the macaques were confronted with a varying number of covers and their performance was dependent on the level of complexity and on the type of change of the covers’ orientation. The macaques could use a board’s inclination to detect the reward, but failed to do so if the lack of inclination was indicative of an alternative hiding place. We suggest that the monkeys’ performance is based on a rudimentary understanding of causality, but find no good evidence for sophisticated diagnostic reasoning in this particular domain.     

Do common ravens (<Emphasis Type="Italic">Corvus corax</Emphasis>) rely on human or conspecific gaze cues to detect hidden food?

The ability of non-human animals to use experimenter-given cues in object-choice tasks has recently gained interest. In such experiments, the location of hidden food is indicated by an experimenter, e.g. by gazing, pointing or touching. Whereas dogs apparently outperform all other species so far tested, apes and monkeys have problems in using such cues. Since only mammalian species have been tested, information is lacking about the evolutionary origin of these abilities. We here present the first data on object-choice tasks conducted with an avian species, the common raven. Ravens are highly competitive scavengers, possessing sophisticated cognitive skills in protecting their food caches and pilfering others’ caches. We conducted three experiments, exploring (i) which kind of cues ravens use for choosing a certain object, (ii) whether ravens use humans’ gaze for detecting hidden food and (iii) whether ravens would find hidden food in the presence of an informed conspecific who potentially provides gaze cues. Our results indicate that ravens reliably respond to humans’ touching of an object, but they hardly use point and gaze cues for their choices. Likewise, they do not perform above chance level in the presence of an informed conspecific. These findings mirror those obtained for primates and suggest that, although ravens may be aware of the gaze direction of humans and conspecifics, they apparently do not rely on this information to detect hidden food.     

Is caching the key to exclusion in corvids? The case of carrion crows (Corvus corone corone)

Recently, two corvid species, food-caching ravens and non-caching jackdaws, have been tested in an exclusion performance (EP) task. While the ravens chose by exclusion, the jackdaws did not. Thus, foraging behaviour may affect EP abilities. To investigate this possibility, another food-caching corvid species, the carrion crow (Corvus corone corone), was tested in the same exclusion task. We hid food under one of two cups and subsequently lifted either both cups, or the baited or the un-baited cup. The crows were significantly above chance when both cups were lifted or when only the baited cup was lifted. When the empty cup was lifted, we found considerable inter-individual variation, with some birds having a significant preference for the un-baited but manipulated cup. In a follow-up task, we always provided the birds with the full information about the food location, but manipulated in which order they saw the hiding or the removal of food. Interestingly, they strongly preferred the cup which was manipulated last, even if it did not contain any food. Therefore, we repeated the first experiment but controlled for the movement of the cups. In this case, more crows found the food reliably in the un-baited condition. We conclude that carrion crows are able to choose by exclusion, but local enhancement has a strong influence on their performance and may overshadow potential inferential abilities. However, these findings support the hypothesis that caching might be a key to exclusion in corvids.