Familiarity with adults,but not relatedness,affects the growth of juvenile red-backed salamanders (<Emphasis Type="Italic">Plethodon cinereus</Emphasis>)

The relative roles of kinship and familiarity in affecting an individual’s growth and fitness are not easy to disentangle. Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also be related (in terms of kinship) to those nearby conspecifics. While some studies have inferred that kin discrimination affects fitness correlates, other studies found that familiarity alone can reduce aggressive interactions, thus increasing fitness. These studies have all focused on intra-age class pairs or groups. However, many animals interact with conspecifics from different cohorts. In many populations, adults of Plethodon cinereus territorially defend rocks and logs that retain moisture and food resources. We investigated whether juveniles of P. cinereus grew more in the presence of adults that were relatives or familiar. We collected pairs of juveniles and adults found under the same cover objects in the forest (familiar) and pairs of juveniles and adults found under different cover objects, approximately 10 m apart (unfamiliar). We determined parentage and relatedness of the adult–juvenile pairs and then placed these pairs in semi-natural mesocosms for 17 days. We found that juveniles housed with familiar adults had significantly greater increases in mass and snout–vent length than juveniles housed with unfamiliar adults in 2006 but not in 2007. Relatedness had no effect on growth. In addition, juveniles cohabitating with adults were not more likely to be their offspring. At least under certain environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the growth of juvenile salamanders.     

A field test of the effects of familiarity and relatedness on social associations and reproduction in prairie voles

Inbreeding depression is a well-documented phenomenon. In animals, one means of avoiding the costs of inbreeding is through the recognition and avoidance of kin as mates. Prairie voles (Microtus ochrogaster) are short-lived, socially monogamous rodents that demonstrate inbreeding depression in the laboratory. Field data indicate that pair formation in nature is opportunistic but pairing among close relatives seems uncommon. We examined the role of relatedness and familiarity on prairie vole social associations and reproduction by placing adult voles into 0.1-ha enclosures with familiar siblings, unfamiliar siblings, and unrelated, unfamiliar conspecifics. Live-trapping data indicated that indices of social pair bonding were random with respect to relatedness and familiarity. Among females whose litters were sired by a single male, litters were significantly more likely to be sired by unfamiliar than familiar males, but the number of litters sired by males that were unrelated to their partner was not different from the number of litters sired by males that were related to their partner. Additionally, females that produced offspring with familiar siblings were significantly more likely to have litters with multiple paternity than females not producing offspring with familiar siblings. However, multiple paternity was not influenced by relatedness of sires. Finally, older individuals were more likely to produce offspring with each other than with younger individuals. Our findings suggest that prior association is a more important mechanism of inbreeding avoidance than phenotype matching for prairie voles mating under ecologically relevant conditions.     

Discrimination between related and unrelated individuals in the Australian lizard Egernia striolata

We examined evidence for kin-related signal discrimination in the Australian scincid lizard Egernia striolata, using 41 juvenile lizards from 14 litters from a population in the Mount Lofty Ranges, South Australia. We characterised each juvenile at four polymorphic microsatellite DNA loci, determined genetic relatedness among pairs of juveniles, and assigned for each litter one other litter that was genetically closest and one other litter that was genetically most distant. Lizards responded significantly more strongly, with tongue flicks and time in contact, to skin secretion stimuli from more distant than genetically close, unfamiliar conspecific juveniles. When presented with an intruder, juvenile lizards basked for shorter periods when the intruder was more distantly related, and aggressive lizards directed more aggressive acts towards more distantly related than closely related conspecific intruders. We deduce from these results that there is kin recognition in juvenile E. striolata, and that they are able to discriminate related from unrelated individuals among unfamiliar conspecifics.     

Kin recognition by juvenile predatory mites: prior association or phenotype matching?

Kin recognition, the biased treatment of conspecific individuals based on genetic relatedness, is a widespread phenomenon in animals. The most common mechanisms mediating kin recognition are prior association (familiarity) and phenotype matching. Recognition based on prior association allows identifying familiar individuals. Recognition based on phenotype matching is an extension of prior-association-based recognition and allows identifying familiar and unfamiliar individuals due to a shared phenotypic trait. I investigated which of the two mechanisms is used by cannibalistic juvenile predatory mites, Phytoseiulus persimilis. Protonymphs that were associated with either siblings or non-kin discriminated familiar and unfamiliar larvae and preferentially cannibalized the latter irrespective of genetic relatedness. In contrast, despite previous association with either siblings or non-kin, protonymphs did not discriminate unfamiliar sibling and unfamiliar non-kin larvae. Association in the larval stage therefore mediated kin recognition based on familiarity, but not phenotype matching in cannibalistic P. persimilis protonymphs. Furthermore, in the presence of a familiar prey individual, sibling cannibalism occurred significantly sooner than non-kin cannibalism. This quick sibling cannibalism may have been the consequence of preferential association of siblings and/or may indicate the occurrence of an alternative cannibal phenotype. I discuss the adaptive significance of prior-association-based recognition for P. persimilis juveniles and emphasize the ability of P. persimilis to use multiple recognition mechanisms in dependence of the ontogeny and the ecological context.     

Chemical rival recognition decreases aggression levels in male Iberian wall lizards, <Emphasis Type="Italic">Podarcis hispanica</Emphasis>

In an agonistic interaction, the assessment of the probable outcome of future encounters with the same individuals may be the best way of decreasing costs of fighting, but this may only be accomplished if animals are able to recognize individual conspecifics. We staged encounters between male lizards, Podarcis hispanica, to examine whether odoriferous cues are involved in rival recognition during agonistic interactions. We experimentally manipulated the odour of intruding males, creating familiar males with their own odour or bearing odours of unfamiliar males, and unfamiliar males bearing unfamiliar odours or odours of familiar males. The results showed that when familiar males were impregnated with scents from unfamiliar males, they elicited an aggressive response by resident unmanipulated males similar to that observed for a new unfamiliar male with unfamiliar odour. This suggests that resident males were unable to recognize familiar males when their own scents were removed. In contrast, responding males were less aggressive towards familiar males impregnated with their own odour and towards unfamiliar males impregnated with scents of familiar males, suggesting that when two males have already interacted, their scents become familiar for both males, and that the detection in successive encounters of the familiar scent suffices to reduce the aggressive response of territorial males. Therefore, recognition mechanisms based on chemical cues during agonistic encounters may contribute to reducing the intensity and the costs of fighting in P. hispanica and may play an important role in the organization of their social system.     

Differences in olfactory species recognition in the females of two Australian songbird species

Although birds have recently been shown to possess olfactory abilities and to use chemical cues in communication, limited effort has been made to demonstrate the use of odorants in social contexts. Even less is known regarding the use of odorants in species recognition. The ability to recognize conspecifics should be more pronounced in social species. This study investigated the importance of olfactory cues in species recognition in females of two estrildid finch species with different levels of sociality. Combining odor preference tests with chemical analyses, we surveyed whether female zebra finches and diamond firetails are able to distinguish between the species based on volatile traits and whether individuals exhibit species-specific differences in body odorants. Zebra finches are more social than diamond firetails; nevertheless, both species have an overlapping distribution area. Applying an experimental Y-maze paradigm, we showed that zebra finches can use differences in their species odor fingerprints and displayed a significant preference for the odor of conspecifics over that of heterospecifics, whereas diamond firetails did not reveal a preference. Using gas chromatography and mass spectrometry, we demonstrated that body odorants of the two species were significantly different in relative composition. This finding demonstrates the potential importance of olfactory cues in species recognition, at least in social bird species. Even these two closely related species displayed remarkable differences in their responsiveness to similar chemical cues, which might be caused by species-specific differences in ecology, physiology, or evolution.     

Individual specific contact calls of pallid bats (<Emphasis Type="Italic">Antrozous pallidus</Emphasis>) attract conspecifics at roosting sites

Contact calls are utilized by several bird and mammal species to maintain group cohesion and coordinate group movement. From a signal design perspective, contact calls typically exhibit acoustic features that make them easily localizable and encode information about individual or group identity. Pallid bats (Antrozous pallidus) are unusual among vespertilionids in that they often emit a loud, partially audible frequency-modulated social call several times in rapid succession while in flight. This call appears to function as a contact call in that it is frequently given when bats return from foraging and perform circular flights before entering a crevice roost. However, the degree to which pallid bats respond to the calls of conspecifics and what information is provided in the call is unknown. Thus, the goal of this study was to investigate pallid bat calling behavior to determine if calls attract roostmates or elicit responses from them and provide sufficient information for individual recognition. In playback studies, we found that contact calls, elicit calls, and approaches and that free-flying bats respond more to familiar than unfamiliar calls. In addition, analysis of frequency and temporal measurements of calls collected from multiple sites and spectral cross correlation analysis of calls recorded from the same radio-tagged bats on multiple evenings revealed that the frequency pattern of contact calls is highly repeatable over time within individuals but exhibits significant differences among individuals. Thus, contact call structure appears to be unique to individuals and stable through time, which makes these calls well-suited for roostmate recognition.     

Kin recognition in rainbowfish (Melanotaenia eachamensis): sex, sibs and shoaling

Living with relatives can be beneficial to individuals via the evolution of kin-directed altruism, but this is tempered by the increased risk of inbreeding. Therefore, in social species, the ability to recognise relatives can be highly advantageous. This study focuses on kin discrimination in the Lake Eacham rainbowfish, Melanotaenia eachamensis, an endangered freshwater species from north-east Queensland, Australia. First, I examined kin recognition abilities when a combination of both chemical and visual recognition cues was available. When given a choice of shoaling with same-sex groups, females spent significantly longer with full-sibs rather than half-sibs, full-sibs rather than non-relatives and half-sibs rather than non-relatives. Males spent significantly longer shoaling with full-brothers versus half-brothers, but showed no other shoalmate preferences. Second, in the presence of only chemical cues, females did not discriminate among groups of different levels of relatedness, but males showed a non-significant tendency to associate with full-sibs rather than non-relatives. Male shoaling behaviour seemed to be more influenced by factors other than relatedness, e.g. intra-sexual competition. Finally, I found that the shoaling preferences of females changed when exposed to groups of males. Females preferred to associate with non-relatives rather than half-brothers and non-relatives rather than full-brothers. There was no significant difference in the time spent with half-brothers versus full-brothers. Taken together, my results suggest that females have very good kin recognition abilities. They prefer to shoal with female relatives but avoid male relatives, and so are able to balance the benefits of nepotism and the costs of incest. Received: 2 May 2000 / Revised: 26 July 2000 / Accepted: 30 July 2000     

Boldness and body size of male Spanish terrapins affect their responses to chemical cues of familiar and unfamiliar males

Recognition and avoidance of conspecifics based on chemical cues could reduce the risk of aggressive interactions between males. Success in agonistics encounters with unfamiliar males should be lower than with previously known familiar males. Then, males should avoid the chemicals from unfamiliar males with respect to those from familiar males. However, boldness and size could affect the outcome of encounters between males and, consequently, the response to chemical cues of conspecific males. We compared the time spent by male turtles Mauremys leprosa in water pools with chemical stimuli from unfamiliar or familiar males or with their own chemical stimuli. We also performed a behavioral test to estimate boldness of turtles in an antipredatory situation. Turtles avoided the chemicals from unfamiliar males respect to familiar ones and their own odors, but their responses depended on boldness and size of the tested turtle. Bold turtles avoided water with chemicals of unfamiliar males, but not with chemicals of familiar males, whereas shy turtles avoided chemicals of both familiar and unfamiliar males. On the other hand, large males avoided the odor from unfamiliar males, but small males did not avoid water with the odor from other males. Results suggest that male M. leprosa can detect chemicals released to water from conspecific males and discriminate between familiar and unfamiliar males. However, responses to these chemicals depended on boldness and body size of the responding turtle because these factors may affect intrasexual competition.     

Kin recognition in the common lizard

The ability to recognize parents has never been reported in species in which parents do not provide care to their young; in such species, only sibling recognition has been found. However, there may be several advantages of parent recognition, even in the absence of parental care. We investigated the ability of neonates to recognize olfactory cues from both their mother and siblings in the common lizard, Lacerta vivipara, a species without parental care. Juveniles from 264 gravid females were reared for 2 days either with their mother, with another female, or separated from all other adults. Juveniles from some families were split into two or three groups so that each juvenile was unfamiliar with a subset of its siblings. After 2 days, we offered the juveniles a choice of two nocturnal shelters: one containing a lizard odor and the other without odor. The response to the odor of an unrelated and unfamiliar adult was influenced by both the sex of the adult and the sex of the juvenile. Juveniles of both sexes recognized the odor of their mother whether they were familiar with her or not (pre-natal determinism). Juveniles recognized familiar but not unfamiliar siblings (post-natal determinism). In the wild, spatial association with kin declines shortly after birth. Thus, recognition of the mother is likely to have biological relevance. Recognition of the mother may reduce competition and/or enhance juvenile establishment. Received: 15 May 1997 / Accepted after revision: 29 December 1997     

Similar is not the same: Social calls of conspecifics are more effective in attracting wild bats to day roosts than those of other bat species

Many bat species regularly need to find new day roosts as they require numerous shelters each breeding season. It has been shown that bats exchange information about roosts among colony members, and use echolocation and social calls of conspecifics in order to find roosts. However, it is unclear if wild bats discriminate between social calls of conspecifics and other bat species while searching for roosts. Furthermore, the extent that bats are attracted to potential roosts by each of these two call types is unknown. We present a field experiment showing that social calls of conspecifics and other bat species both attract bats to roosts. During two summers, we played back social calls of Bechstein’s bats (Myotis bechsteinii) and Natterer’s bats (Myotis nattereri) from different bat boxes that can serve as roosts for these species. All experimental bat boxes were monitored with infrared video to identify the approaching bat species. Three species (M. bechsteinii, M. nattereri, and Plecotus auritus) approached the boxes significantly more often during nights when bat calls were played compared to nights without playbacks. Bechstein’s bats and Natterer’s bats were both more attracted to social calls of conspecifics than of the other species, whereas P. auritus did not discriminate between calls of either Myotis species. Only Bechstein’s bats entered experimental boxes and only at times when calls from conspecifics were played. Our findings show that wild bats discriminate between social calls of conspecifics and other bat species although they respond to both call types when searching for new roosts.     

Kin and population recognition in sympatric Lake Constance perch (Perca fluviatilis L.): can assortative shoaling drive population divergence?

Prior studies have shown that perch (Perca fluviatilis L.) of Lake Constance belong to two genetically different but sympatric populations and that local aggregations of juveniles and adults contain closely related kin. In this study, we analysed the genetic structure of pelagic perch larvae to investigate if kin-structured shoals already exist during early ontogenetic development or might be the result of homing to natal sites. Analysis of the gene frequencies at five microsatellite loci revealed that three out of five pelagic aggregations of larvae showed significant accumulation of kin. To investigate possible mechanisms of shoal formation, we tested if perch use olfactory cues to recognize their kin. Choice tests in a fluviarium showed preference for odours of unfamiliar kin vs unfamiliar non-kin. Additionally, we showed that perch could differentiate between the odours of the two sympatric populations and significantly preferred unfamiliar and unrelated conspecifics of their own over the foreign population. Our results present a behavioural mechanism that can lead to the observed formation of kin-structured shoals in perch. We further discuss if the ability to discriminate between their own and a foreign population can result in assortative mating within populations and thus form the basis of “socially mediated speciation” in perch.     

Binary individual recognition in hermit crabs

One mechanism that permits the maintenance of dominance hierarchies is individual recognition, defined as the ability of an animal to recognize a conspecific on the basis of one or more identifying cues, and to associate it with experiences of victories or defeats that the animal has gained from preceding encounters with that particular individual. We examined whether the long-clawed hermit crab, Pagurus longicarpus, could differentiate between unfamiliar and familiar opponents. The experimental protocol was designed to control in pairs of interacting individuals several factors together, such as status and relative size of the opponent, as well as species, quality, and fit of the inhabited shell. The hermit crabs were more reactive and their agonistic level was higher in unfamiliar than in familiar pairs; in addition, betas were more prone to initiate an interaction with unfamiliar than with familiar alphas. The alternative explanation—that the ability to discriminate between familiar and novel shells can explain our results per se— was tested following, in part, Jackson and Elwoods (1989) protocol for Pagurus bernhardus and was, at least for this species, rejected. This study did not determine whether a true individual recognition occurs, but demonstrated that P. longicarpus categorizes the individuals into two heterogeneous subgroups, thus being capable of a binary discrimination among opponents.Communicated by T. Czeschlik     

Do yellow-bellied marmots respond to predator vocalizations?

We conducted four experiments to determine whether yellow-bellied marmots, Marmota flaviventris, discriminate among predator vocalizations, and if so, whether the recognition mechanism is learned or experience-independent. First, we broadcast to marmots the social sounds of coyotes, Canis latrans, wolves, Canis lupus, and golden eagles, Aquila chrysaetos, as well as conspecific alarm calls. Coyotes and eagles are extant predators at our study site, while wolves have been absent since the mid-1930s. In three follow-up experiments, we reversed the eagle call and presented marmots with forward and reverse calls to control for response to general properties of call structure rather than those specifically associated with eagles, we tested for novelty by comparing responses to familiar and unfamiliar birds, and we tested for the duration of predator sounds by comparing a wolf howl (that was much longer than the coyote in the first experiment) with a long coyote howl of equal duration to the original wolf. Marmots suppressed foraging and increased looking most after presentation of the conspecific alarm call and least after that of the coyote in the first experiment, with moderate responses to wolf and eagle calls. Marmots responded more to the forward eagle call than the reverse call, a finding consistent with a recognition template. Marmots did not differentiate vocalizations from the novel and familiar birds, suggesting that novelty itself did not explain our results. Furthermore, marmots did not differentiate between a wolf howl and a coyote howl of equal duration, suggesting that the duration of the vocalizations played a role in the marmots’ response. Our results show that marmots may respond to predators based solely on acoustic stimuli. The response to currently novel wolf calls suggests that they have an experience-independent ability to identify certain predators acoustically. Marmots’ response to predator vocalizations is not unexpected because 25 of 30 species in which acoustic predator discrimination has been studied have a demonstrated ability to respond selectively to cues from their predators.     

Food sharing by sibling vs nonsibling spiny mice (Acomys cahirinus)

Summary In comparison to paired unfamiliar unrelated age-mates, pairs of familiar littermate (sibling) spiny mice (Acomys cahirinus) were more active in exploring a novel environment containing limited food resources and engaged in a greater degree of cooperative feeding or food sharing. When animals born in successive litters were tested, however, familiar siblings did not differ from unfamiliar nonsiblings on measures of food sharing even though subsequent data indicate that such siblings could recognize one another. Young animals were found to feed for longer periods of time than their older cagemate regardless of whether the latter animal was a familiar sibling or an unfamiliar nonsibling.     

Heart rate changes reveal that little blue penguin chicks (Eudyptula minor) can use vocal signatures to discriminate familiar from unfamiliar chicks

Researchers investigating social recognition typically measure only behavioural responses during discrimination tests - physiological changes have been largely ignored. We examined whether little blue penguin chicks (Eudyptula minor) could distinguish siblings from other chicks using auditory cues, by measuring behavioural and heart rate changes during playback experiments. Chicks were exposed to five treatments: the begging calls of siblings, neighbouring chicks and unfamiliar chicks, and two controls (heterospecific begging calls and music). We also determined if chicks developed distinctive begging calls, by using F-ratios to quantify inter- versus intra-individual variability in a range of acoustic parameters, and applying a discriminant-function analysis. Inter-individual variation was greater for pitch than for temporal or amplitude parameters, suggesting that call pitch may be important for individual recognition. The discriminant-function analysis showed each chick's calls were distinctive and could act as a vocal signature. Treatments did not instigate different behavioural responses. However, chick heart rates during playback of sibling calls were significantly higher than those recorded during stranger, but not neighbour, playback. A simple recognition system based on familiarity may allow this plesiomorphic and loosely colonial penguin to gain at least some of the benefits associated with more advanced sibling recognition systems (some highly colonial seabirds discriminate siblings from neighbouring chicks). Heart rate could be a useful measure of social recognition abilities, particularly in species where changes in behaviour are not always evident or are difficult to observe.     

The effects of mating on infanticide and pup discrimination in white-footed mice

Summary A laboratory study was conducted with white-footed mice (Peromyscus leucopus) to determine (1) if cohabitation and/or successful mating inhibits infanticide, and if so for how long, and (2) if males and females can discriminate between their own (familiar) and strange (unfamiliar) pups. Infanticidal males and females that were paired for 15 days and did not reproduce were not inhibited from killing pups, whereas infanticidal males and females that were paired until they reproduced were inhibited from committing infanticide at 4 days postpartum. Neither males nor females discriminated between familiar and unfamiliar pups with regard to engaging in infanticide. Approximately 50% of wild-caught males and females killed pups in the laboratory. Infanticidal pairs bred significantly sooner than did noninfanticidal pairs. The results are consistent with the promiscuous nature of P. leucopus males and territoriality of P. leucopus females. Offprint requests to: Donna M. Cicirello, Kellogg Biological Station, 3700 E. Gull Lake Drive, Hickory Corners, MI 49060, USA     

Queen acceptance and the complexity of nestmate discrimination in the Argentine ant

In most social insect species, individuals recognize and behave aggressively towards non-nestmate conspecifics to maintain colony integrity. However, introduced populations of the invasive Argentine ant, Linepithema humile, exhibit pronounced variation in intraspecific aggression denoting diversity in nestmate recognition behavior, which possibly shapes their social structure and the varying levels of unicoloniality observed among these populations. One approach to better understand differential aggression behaviors towards conspecifics and recognition cue perception and response in L. humile is to examine variation in nestmate discrimination capability among genetically distinct colonies under different social contexts. Consequently, we investigated the dynamics of queen and worker recognition in southeastern US L. humile queenless and queenright colonies by measuring rates of non-nestmate worker and queen adoption and intercolony genetic similarity. Aggression levels between colony pairs differed and were associated with non-nestmate worker, but not queen adoption. Adoption of queens and workers was a function of host colony origin, while colony queen number affected adoption of queens, but not workers, with queens more readily accepted by queenless hosts. Fecundity of adopted non-nestmate queens was comparable to that of rejected non-nestmate and host colony queens, suggesting that queen fecundity did not affect adoption decisions. Genetic similarity between colonies ranged from 30 to 77% alleles shared, with more genetically similar colonies showing lower levels of intraspecific aggression. Non-nestmate queens and workers that were more genetically similar to host colony workers were more likely to be adopted. We provide the first evidence for the role of L. humile colony queen number on queen discrimination and suggest an effect of resident queens on worker conspecific acceptance thresholds. Our findings indicate a role for genetically based cues in L. humile nestmate recognition. However, subtle discrimination capability seems to be influenced by the social context, as demonstrated by more frequent recognition errors in queenless colonies.     

Asexuals looking for sex: conflict between species and mate-quality recognition in sailfin mollies (Poecilia latipinna)

When two closely related species are sympatric the process of species recognition (identifying conspecifics) and mate-quality recognition (increased fitness benefits) can yield a conflict when heterospecifics resemble high-quality conspecifics. Conflict in species versus mate-quality recognition may serve as a possible mechanism for the persistence of unisexual, gynogenetic Amazon mollies (Poecilia formosa). Amazon mollies require sperm from closely related species (e.g., sailfin mollies, P. latipinna) to start embryogenesis but inheritance is strictly maternal. When choosing mates, male sailfin mollies from populations sympatric with Amazon mollies may rely on traits indicating species identity rather than those indicating mate quality. Conversely, males from allopatric populations may rely more on traits indicating mate quality. Previous work has found that male sailfin mollies in sympatry exhibit a significantly greater mating preference for female sailfin mollies over Amazon mollies compared to males in allopatry. In addition, male sailfin mollies prefer to associate with and produce more sperm in the presence of larger conspecific females, which are more fecund. We hypothesized that male sailfin mollies experience a conflict in species recognition and mate-quality recognition in the presence of Amazon mollies that are relatively larger than female sailfin mollies. To test this hypothesis, we paired males from sympatric and allopatric populations with a larger Amazon molly and a smaller female sailfin molly. We scored the number of mating attempts that males directed to conspecific and heterospecific females. Males in most sympatric and allopatric populations demonstrate no clear preference for conspecifics. In addition, we found some evidence for a difference in mating preference between allopatric and sympatric populations with males from allopatry showing a greater heterospecific mate preference. These results indicate a conflict between species and mate-quality recognition. In sympatry this conflict may contribute to the persistence of gynogenetic Amazon mollies.     

Further experiments on olfactory navigation and non-olfactory pilotage by homing pigeons

Summary Supplementary to a previous investigation (Wallraff and Neumann 1989), further experiments were conducted with homing pigeons that were either familiar of unfamiliar with the release area, and that had or lacked olfactory access to environmental odours. All four possible pairwise combinations of these factors were tested. The previous results were confirmed, showing that in an unfamiliar area olfactory inputs are necessary for home-related orientation, while in a familiar area both olfactory and non-olfactory information can be utilized and each is more or less redundant as long as the other kind of information is also available. The degree of redundancy of olfactory inputs varies, obviously depending on the pattern of individual local experience. Correspondence to: H.G. Wallraff