Abstract: The concept of personality implies individual differences in behavior and physiology that show some degree of repeatability/consistency over time and across contexts. Most studies of animal personality, particularly studies of individuals' variation in physiological mechanisms, have been conducted on selected individuals in controlled conditions. We attempted to detect consistent behaviors as well as physiological patterns in greylag ganders (Anser anser) from a free-roaming flock living in semi-natural conditions. We tested 10 individuals repeatedly, in a handling trial, resembling tests for characterization of “temperaments” in captive animals. We recorded the behavior of the same 10 individuals during four situations in the socially intact flock: (1) a “low density feeding condition”, (2) a “high density feeding condition”, (3) a “low density post-feeding situation” and (4) while the geese rested. We collected fecal samples for determination of excreted immuno-reactive corticosterone (BM) and testosterone metabolites (TM) after handling trials, as well as the “low density feeding” and the “high density feeding” conditions. BM levels were very highly consistent over the repeats of handling trials, and the “low density feeding condition” and tended to be consistent over the first two repeats of the “high density feeding condition”. Also, BM responses tended to be consistent across contexts. Despite seasonal variation, there tended to be inter-test consistency of TM, which pointed to some individual differences in TM as well. Aggressiveness turned out to be a highly repeatable trait, which was consistent across social situations, and tended to correlate with an individual's resistance during handling trials. Also, “proximity to the female partner” and “sociability” – the average number of neighboring geese in a close distance while resting – were consistent. We conclude that aggressiveness, “affiliative tendencies” and levels of excreted corticosterone and testosterone metabolites may be crucial factors of personality in geese.

Abstract: Eavesdropping can be defined as the extraction of information from the interactions between other individuals. It provides a relatively cheap way of gathering relevant information for fitness enhancement. Here, we propose that obligate avian brood parasites, which always lay their eggs in foreign nests of individuals of other species, may eavesdrop on their host sexual signals to locate nests of high quality individuals in which to lay their parasitic eggs. Sexual signal variation can honestly signal parental quality. Thus, by eavesdropping on sexual signals, parasites may select high quality foster parents for their own offspring. Such a use of sexual signals within host populations by brood parasites differs from signal exploitation theory that proposes that parasite only use signals to locate potential host independently from signaller quality. Here, we review the avian literature concerning host choice within a host species by obligate avian brood parasites and find evidence for host selection within individuals of a host species on the basis of cues potentially functioning as sexually selected traits, or at least revealing parental abilities. We have also found support for the existence of benefits linked to host selection by avian brood parasites. Finally, one study reported on the attenuation of a sexual ornament in host populations under strong pressure by brood parasites. Most of these findings have been interpreted as evidence for host selection by avian brood parasites based on the conspicuousness of sexual signals. We suggest, however, that these findings may in fact reveal eavesdropping on host signalling performance by brood parasites which would use the information extracted to choose the better individuals among conspecifics of a given host. This provides a new perspective for the study of host selection in obligate brood parasites, and raises interesting questions for the study of animal cognition that would deserve experimental studies.

Abstract: The effects of the size of the environment on animals' spatial reorientation was investigated. Domestic chicks were trained to find food in a corner of either a small or a large rectangular enclosure. A distinctive panel was located at each of the four corners of the enclosures. After removal of the panels, chicks tested in the small enclosure showed better retention of geometrical information than chicks tested in the large enclosure. In contrast, after changing the enclosure from a rectangular-shaped to a square-shaped one, chicks tested in the large enclosure showed better retention of landmark (panels) information than chicks tested in the small enclosure. No differences in the encoding of the overall arrangement of landmarks were apparent when chicks were tested for generalisation in an enclosure differing from that of training in size together with a transformation (affine transformation) that altered the geometric relations between the target and the shape of the environment. These findings suggest that primacy of geometric or landmark information in reorientation tasks depends on the size of the experimental space, likely reflecting a preferential use of the most reliable source of information available during visual exploration of the environment.

Abstract: The ability in animals to count and represent different numbers of objects has received a great deal of attention in the past few decades. Cumulative evidence from comparative studies on number discriminations report obvious analogies among human babies, non-human primates and birds and are consistent with the hypothesis of two distinct and widespread mechanisms, one for counting small numbers (<4) precisely, and one for quantifying large numbers approximately. We investigated the ability to discriminate among different numerosities, in a distantly related species, the mosquitofish, by using the spontaneous choice of a gravid female to join large groups of females as protection from a sexually harassing male. In one experiment, we found that females were able to discriminate between two shoals with a 1:2 numerosity ratio (2 vs. 4, 4 vs. 8 and 8 vs. 16 fish) but failed to discriminate a 2:3 ratio (8 vs. 12 fish). In the second experiment, we studied the ability to discriminate between shoals that differed by one element; females were able to select the larger shoal when the paired numbers were 2 vs. 3 or 3 vs. 4 but not 4 vs. 5 or 5 vs. 6. Our study indicates that numerical abilities in fish are comparable with those of other non-verbal creatures studied; results are in agreement with the hypothesis of the existence of two distinct systems for quantity discrimination in vertebrates.