Previous work has shown a positive correlation between relative forebrain size and feeding innovation frequency, corrected for species number, over different taxonomic groups of birds. Several confounding variables could account for this relationship: ornithologists could notice and report innovations more often in certain taxa because of biased expectations, greater research effort, editorial bias in journals or large population sizes of the taxa. The innovationforebrain correlation could also be spuriously caused by phylogeny or juvenile development mode. We examined these possibilities by entering species number per taxon, population size, number of full length papers, expectations (assessed by a questionnaire), journal source and development mode in multiple regressions that also included relative forebrain size. We did this with and without phylogenetic corrections and tested two behavioural categories, feeding and nesting, where flexibility and learning are clearly thought to differ, but confounds should have similar effects. Through an exhaustive survey covering 30 years in 11 journals, a total of 683 innovations was gathered for the northwestern part of Europe, 507 for feeding and 176 for nesting. Species number per taxon was the only significant confound for both feeding and nesting reports; as predicted, forebrain size was a second significant predictor for feeding innovations, but not for nesting. The frequency of feeding innovations in the short notes of ornithology journals thus appears to be a valid and reliable way to operationalise behavioural flexibility in birds.
Tools are traditionally defined as objects that are used as an extension of the body and held directly in the hand or mouth. By these standards, a vulture breaking an egg by hitting it with a stone uses a tool, but a gull dropping an egg on a rock does not. This distinction between true and borderline (or proto-tool) cases has been criticized for its arbitrariness and anthropocentrism. We show here that relative size of the neostriatum and whole brain distinguish the true and borderline categories in birds using tools to obtain food or water. From two sources, the specialized literature on tools and an innovation data base gathered in the short note sections of 68 journals in 7 areas of the world, we collected 39 true (e.g. use of probes, hammers, sponges, scoops) and 86 borderline (e.g. bait fishing, battering and dropping on anvils, holding with wedges and skewers) cases of tool use in 104 species from 15 parvorders. True tool users have a larger mean residual brain size (regressed against body weight) than do users of borderline tools, confirming the distinction in the literature. In multiple regressions, residual brain size and residual size of the neostriatum (one of the areas in the avian telencephalon thought to be equivalent to the mammalian neocortex) are the best predictors of true tool use reports per taxon. Innovation rate is the best predictor of borderline tool use distribution. Despite the strong concentration of true tool use cases in Corvida and Passerida, independent constrasts suggest that common ancestry is not responsible for the association between tool use and size of the neostriatum and whole brain. Our results demonstrate that birds are more frequent tool users than usually thought and that the complex cognitive processes involved in tool use may have repeatedly co-evolved with large brains in several orders of birds.
The present study is an attempt to link principles of organization of grooming sequences to environmental, ontogenetic and phylogenetic factors through a comparative study of five species of North American squirrels (Glaucomys sabrinus, Spermophilus columbianus, Spermophilus lateralis, Spermophilus richardsonii and Tamiasciurus hudsonicus) that occupy a variety of ecological niches and have different degrees of taxonomic relatedness and morphological similarity. Three measures of grooming organization are analysed: bout length distributions, transition structure and anatomical distribution. Grooming bout length distributions in both adult and young sciurids fit with the geometric model. Mean bout length varies between species and is possibly influenced by social and ecological factors such as disturbance by conspecifies and predator surveillance. Transition structure follows a cephalocaudal progression that appears to be characteristic of rodent grooming and could be phylogenetically very old. 'I'he degree of organization of the sequences, as measured by transition structure, seems to be related to average bout length. Postural facilitation can also be invoked to explain some of the transitions. No general rule emerges from the comparative analysis of transition structure. Ecology phylogeny and morphology influence anatomical distribution of grooming activity. The three Spermophilus spp. are similar in pattern. Tail size in T. hudsonicus and the possible use of echolocation in G. sabrinus favour more frequent care of the tail and head regions respectively in these species.
Adaptive views of learning predict that natural selection should lead to differences in specialized learning abilities between animals that face different ecological pressures. Group-living is thought to favour social learning, but previous comparative work suggests that differences between gregarious feral pigeons (Columba livia) and territorial Zenaida doves (Zenaida aurita) exceed the specialized effect on social tasks predicted by the adaptive hypothesis. In this paper, we show that group-foraging Zenaida doves from Barbados learn an individual shaping task more quickly than territorial Zenaida doves from a site 9 km away. These results suggest that the scramble competition associated with group-foraging favours several types of leaming, both social and non-social, and that its effects are more wide-ranging than previously thought. Since genetic isolation between Zenaida dove populations is highly unlikely, the results also suggest that differences in foraging ecology may lead to different learned responses to local reward contingencies as well as natural selection for different genotypes affecting learning. In some cases, the standard comparative prediction of ecologically-correlated learning differences may therefore not distinguish between adaptive specialization and general process theories.
Group-living is often thought to be associated with social learning. Comparative tests are useful in evaluating the link between ecological variables and learning specializations, but controls are required to guard against possible confounding variables. In this paper, we test the association between group-living and social learning by comparing two opportunistic, urbanized, Columbids in a set of experiments involving shaping and individual learning controls. In part 1, we provide quantitative field data on foraging group size for the two species, the feral pigeon (Columba livia) studied in central Montréal and the Zenaida dove (Zenaida aurita) studied in coastal Barbados. The data confirm anecdotal reports that contrast the gregarious social organization of C. livia with the territorial organization of coastal Z. aurita. In part 2, we test pigeons and Zenaida doves on two food-finding tasks and show (1) that feral pigeons are better than Zenaida doves at solving all variants of the tasks presented, whether individually or socially learned, and (2) that once general species differences are taken into account, territorial Zenaida doves are not less efficient than gregarious feral pigeons at using food-finding information provided by a conspecific tutor. The results do not support the association between group-living and social learning and show that procedures like shaping and control variants of the task may help interpret interspecific differences in learning.
Foraging innovation, in which an individual eats a novel food or uses a novel foraging technique, has been observed in a wide range of species. If other individuals are nearby, they may adopt the innovation, thus spreading it through the population. Much research has focused on this social transmission of behaviour, but the effect of social context on the emergence of novel behaviour is unclear. Here, we examine the effect of social context on innovative feeding behaviour in the Carib grackle (Quiscalus lugubris), an opportunistic, gregarious bird. We test the effect of the proximity of conspecifics, while eliminating the direct effects of interference, scrounging, or aggression. Using a repeated-measures design, we found that birds took significantly longer to contact novel foraging tasks when in the presence of others vs. alone, and during playbacks of alarm calls vs. a control sound. Further, performance of a food-processing behaviour decreased when birds were with others, and individuals adjusted their behaviour depending on their distance from conspecifics. Our results suggest that feeding in groups may slow down or inhibit innovative foraging behaviour in this species. We discuss the implications of a trade-off between feeding in groups and taking advantage of new feeding opportunities.
In Barbados, Carib grackles (Quiscalus lugubris) forage in opportunistic aggregations that include territorial Zenaida doves (Zenaida aurita) and flocks of conspecifics. In searching for and handling food, grackles use complex beak movements and modulate priority of access with a mixture of postural signals and intra- and interspecific scramble (unaggressive) competition. We show in two experiments that wild-caught grackles learn as readily from a Zenaida dove as they do from a conspecific tutor, whether tutors use similar or different food-finding techniques. Grackles also imitate the technical variant that the hetero- and conspecific tutors were shaped to demonstrate: those who observed a Zenaida dove used the dove's closed beak pecking technique, while those who observed a conspecific used the grackle's open beak pulling, probing or prying. Our findings suggest that imitation, like other forms of social learning, is strongly influenced by a species' foraging ecology. In particular, the ability to imitate novel motor skills should be favored in opportunistic species which exhibit scramble competition and which use complex searching and handling techniques to forage on embedded foods.
Many authors have proposed that behavioural flexibility in the field is associated with learning ability in captivity, relative forebrain size and rate of structural evolution. In birds, the frequency of feeding innovations reported in the short notes sections of ornithology journals may be a good way to operationalize flexibility. In this paper, we examine in the birds of Australia and New Zealand the relationship between forebrain size and innovation frequency found in a previous study covering North America and the British Isles. From a methodological point of view, the two variables are highly reliable: innovation frequency per taxonomic group is similar when different readers judge innovation reports and when different editorial styles govern journals; relative forebrain size yields very similar estimates whether mean residuals from a log-log regression are used or ratios of forebrain to brainstem mass. Innovation frequency per taxon is correlated between the two Australasian zones and between these zones and the more northerly ones studied previously. Innovation frequency is also associated with relative forebrain size in Australia and, to a lesser extent, in New-Zealand; in Australia, parrots show the high frequency of innovations predicted by their large forebrain, but yield no innovations in the New Zealand sample. The forebrain/innovation trend is independent of juvenile development mode, but phylogeny appears to be an important intervening variable in Australasia, as evidenced by non-significant independent contrasts.