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PubMed1998

Individual variation in male vocal traits and female mating preferences in Bufo americanus.

We investigated the amount of variation in mating behaviour between and within individual male and female American toads, because both sources of trait variation can influence the course of sexual selection. Males varied in all four call parameters investigated (dominant call frequency, pulse rate, call rate and call duration). Individual males lowered the dominant frequency of their call when they interacted vocally with nearby males. Dominant call frequency was more highly correlated with body size in vocally interacting males than in non-interacting males. Pulse rate of calls primarily varied with water temperature. Call rate and call duration showed the most variation of the four call properties, but this variation was unrelated to male morphology or social interactions. Females varied in three aspects of mating behaviour: two measures of pair formation and their preference for dominant frequency of male calls. The body size of paired males varied between females both in pairings initiated by either sex and in pairings initiated only by females. Males chosen by females were usually larger than average, although age and prior breeding experience of females did not affect mate choice. Playback experiments indicated that female preference for calls of low dominant frequency depended on the temporal patterning of alternative calls presented. Each of the four male vocal properties showed significant repeatability, but only one of the three aspects of female mating behaviour was repeatable. We discuss how different degrees of repeatability in sexual traits of males and females may influence the action and detection of sexual selection in this and other species. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

High population density in bank voles stimulates food hoarding after breeding.

The effects of conspecific density (i.e. risk of intraspecific competition) on hoarding behaviour were studied in breeding pairs of bank voles, Clethrionomys glareolus. I simulated high population density by using odours of conspecifics, to exclude the direct effects of exploitation or interference competition for food. The pairs of bank voles hoarded only at the end of their breeding season. Hoarding was not correlated with whether the voles had a litter during the experiment or their litter size, but was more likely at the high population density and for pairs with small females. This may indicate that smaller females especially make caches in the autumn, possibly to ensure better winter survival under high population density. I discuss the hoarding behaviour of bank voles in relation to their territorial behaviour and food resources during the breeding season and predictable population changes during winter. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Functions of mudballing behaviour in the European fiddler crab Uca tangeri.

European fiddler crabs place mudballs around their burrow openings. Both males and females placed mudballs, but there were major differences between the sexes in mudballing behaviour, suggesting that the female's mudballs were a by-product of digging out the burrow whereas the male's may have additional functions. When the male's mudballs were removed experimentally, the number and intensity of male-male agonistic interactions increased significantly. Experimentally visually isolated males spent longer making mudballs and less time waving. In a binary choice test, females were more likely to approach dummy males with mudballs, spent longer near these males and were more likely to enter their burrows than dummy males without mudballs. The same pattern was apparent for males with 30 rather than 20 mudballs. These results are consistent with a dual function for mudballs in U. tangeri: to reduce the number and intensity of aggressive interactions between neighbouring males and to attract females. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

The effect of complete versus incomplete information on odour discrimination in a parasitic wasp.

We studied the function of learning in the parasitoid Leptopilina heterotoma by looking at discrimination of odour stimuli used in foraging for a host. To optimize the rate of encounters with hosts, these parasitoids are expected to assess the extent to which variation in host-substrate odours is reliably associated with variation in the presence of hosts, that is, substrate profitability. Where the association is reliable, parasitoids should attend to variation in odours and discriminate between them; where it is not, they should ignore it. We hypothesized that foraging decisions are based on the completeness of information the animal has about differences in substrate profitabilities. Our laboratory studies showed that discrimination and non-discrimination of odour stimuli are dynamic behavioural decisions that can be related to the degree of substrate variation and to an animal's informational state. In wind-tunnel studies, females learned to discriminate between odours from substrates that were qualitatively different, for example, between odours from apple and pear substrates or between yeast substrates with different C6 compounds added. They did not discriminate when differences were small (e.g. between odours from two apple varieties or between yeast patches with different concentrations of ethyl acetate), unless unrewarding experiences provided evidence of the absence of hosts in one of the substrates. Hence, we suggest that non-discrimination between odour stimuli in L. heterotoma is not a lack of ability to discriminate but a functional decision by the parasitoid. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Experimental evidence for spatial memory in foraging wild capuchin monkeys, Cebus apella.

Obtaining convincing evidence for spatial memory of natural food sources in wild animals is hard because the observer rarely knows as much about the available food as does the animal, and the ability of the animal to detect novel food sources is usually not measured. In this study, I took advantage of the scarcity of natural fruit sources in the subtropical winter to present a wild group of brown capuchin monkeys with a large-scale array of 15 feeding platforms spaced ca 200 m apart. With this array, I could control the location, productivity and renewal schedule of the major fruit sources used by these animals. Combining an independent measurement of their detection field for these platforms with the known locations of the platforms, I calculated the expected patterns of movement among platform sites by the group under various models of 'random' foraging. These expected patterns were compared to the actual spatial movements of the group. The capuchin group moved significantly more often toward closer platforms and in straighter lines than expected by any random search model using their observed detection field of 82 m, although their behaviour did agree with such models for unrealistically large search fields of 225-350 m. I infer that the movements of this study group are likely to be guided by spatial memory. However, straight-line movement and a preference for closer platforms are in general not convincing evidence for spatial memory unless the detection field of the forager for the resources is known. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Mate switching as a function of mate quality in convict cichlids, Cichlasoma nigrofasciatum.

We examined mate switching between mated pairs of monogamous convict cichlids as a function of mate quality (size). A mated pair was established in each half of a 284-litre aquarium, an opaque partition separating the two pairs. When the partition was removed, mis-assorted pairs (large males with small females competing with small males with large females) re-sorted themselves such that the larger male and the larger female paired with each other 46% of the time. In contrast, when we exposed initially assorted pairs to each other, large pairs remained intact most of the time and dominated smaller pairs. The pair containing the large male, whether re-sorted or intact, dominated over the other pair and was the only one seen to spawn. Re-sortment resulted both from a preference of males for larger females and of females for larger males, and from the ability of larger individuals to displace their smaller consexual. Small females, however, when paired with a large male, often dominated large females and prevented the large female from mating with the large male. Re-sortment was also influenced by the compatibility of large individuals in their initial pairing situation. Large individuals that had been more compatible with their initial mates were less likely to switch mates. Our results support both the better-option and the incompatibility hypotheses of mate-switching. The availability of more than one breeding site in the aquarium had no effect on the frequency of re-sortment. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Habitat-contingent reproductive behaviour in radio-implanted salamanders: a model and test.

All tiger salamanders, Ambystoma tigrinum, entering a small pond in New York state were given radio-implants and tracked throughout breeding to determine whether reproductive behaviour in nature differs from that described in laboratory studies. I formed an extended model of adult reproductive behaviour that included male and female strategies and differential use of habitat components in the breeding pond, and then tested four key predictions regarding adult movement using the sequence of positions of all salamanders between pond entry and exit. An unexpected, female-biased sex ratio during most courtship activity led to departures from the predicted behaviour, but in all other respects the behaviour of the males and females followed from the predictions. Apparent mate scanning in clear water, and weather assessment in pond-edge shallows just prior to emergence, are new indications for caudate amphibians. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Redstarts, Phoenicurus phoenicurus, can orient in a true-zero magnetic field.

I tested the migratory orientation of redstarts in a true-zero magnetic field to elucidate the importance to this species of access to either magnetic or celestial cues. I also tested the validity of the assumption on which all funnel experiments are based: that what we observe in an orientation funnel reflects what the bird would do if actually migrating. In a set of funnel experiments, I tested 47 night-migrating redstarts caught during their first autumn migration. Each bird was tested once under each of four experimental conditions in a semi-randomized block-design. Upon completion of the final funnel tests the birds were fitted with light indicators and released. The results showed that redstarts can find the migratory direction on the basis of access to either celestial or magnetic cues. Thus, when celestial cues were available they could orient in a true-zero magnetic field. In addition, a starry sky facilitated high migratory activity as well as a clearly directed orientation. The release experiments showed that the vanishing bearings on nights with no wind were in good agreement with the direction of the funnel activity, but that the vanishing bearings were strongly influenced even by light wind. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Stabilizing and directional preferences of female Hyla ebraccata for calls differing in static properties.

Female frogs of many species show preferences for calls with particular properties. This study focuses on female preferences in Hyla ebraccata for computer-synthesized calls that differ in pulse-repetition rate or dominant frequency. Both of these call properties are static acoustic properties of advertisement calls of H. ebraccata (within-male coefficient of variation <5%). Females exerted directional selection on dominant frequency, preferring low-frequency calls (2960 Hz) to calls with the dominant frequency of the population mean (3240 Hz). Because size is negatively correlated with dominant frequency, female choice could explain size-biased mating success observed in natural populations. Females also exerted stabilizing selection on pulse-repetition rate, preferring calls with a pulse-repetition rate of the population mean (99 Hz) to calls with a pulse-repetition rate that was twice as fast (200 Hz). The results of this study show that female choice creates either directional or stabilizing selection on static properties of calls. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Geographical variation in agonistic behaviour in a ring species of salamander, Ensatina eschscholtzii.

Ensatina eschscholtzii is a plethodontid salamander with several geographical races distributed in a ring-like series throughout the coastal mountains and inland Sierra Nevada mountains of California. Populations of these salamanders show genetic and morphological divergence, and in this study, we examined divergence in overt aggressive, passive aggressive/exploratory, avoidance and sensory behaviours in four populations. Two of the populations represent a zone of secondary contact between coastal and inland lineages of Ensatina. We recorded behaviour of resident salamanders paired with same-sex intruders during the non-courtship season. The residents' behaviour was affected independently by the population of the resident and the population of the intruder but not by the interaction between the resident population and the intruder population. Levels of agonistic and sensory behaviour showed a high degree of constraint among the populations. These behaviours also showed divergence among coastal and inland populations, and the geographical variation in behaviour is consistent with the phylogenetic history of Ensatina. Convergent evolution of behaviour appears to have occurred at the zone of secondary contact between the coastal and inland lineages. Variation in agonistic and sensory behaviour among the populations observed and between the sexes suggests that there may be geographical and sexual variation in territoriality or competition. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1999 The Association for the Study of Animal Behaviour.

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PubMed1998

An abrupt transition in colony founding behaviour in the ant Messor pergandei.

Transitions in behaviour across a continuous distribution of organisms can provide valuable information on how variation in behaviour is maintained. We used analyses developed for interspecific hybrid zones to examine geographic variation in colony founding strategy in the desert seed-harvester ant, Messor pergandei. Newly mated females initiate new colonies either alone (haplometrosis) or cooperatively with other foundresses (pleometrosis). The incidence of these founding strategies were surveyed across the species' range and found to occur in geographically distinct regions joined by a narrow transition zone. Foundresses collected from haplometrotic sites were more likely to display aggression and found solitary nests than foundresses from pleometrotic sites, suggesting that geographical variation in metrosis is due to genotypic divergence. Foundresses from transitional sites were generally not aggressive and tended to co-found nests in the laboratory, yet rarely formed associations in the field. Such an abrupt shift in behaviour indicates that variation in colony founding strategy is maintained by selection rather than the result of secondary contact of neutral characters. Level of aggression displays a wider cline than founding strategy and is likely under selection only when accompanied by active strategy preference. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

How mothers influence the development of litter-mate preferences in Belding's ground squirrels.

We performed three experiments to examine the role of mothers in the development of litter-mate preferences in captive juvenile Belding's ground squirrels, Spermophilus beldingi. First, when observed in the absence of mothers, juveniles did not play preferentially with litter-mates, which suggests that mothers somehow influence the ontogeny of litter-mate preferences. Second, when mothers were present but unable to intervene in social interactions, juveniles displayed litter-mate preferences, which suggests that mothers do not influence their offsprings' social development by directly intervening in social interactions. In another group, mothers were removed daily, a few hours before nocturnal immergence, and returned the following morning. Juveniles in this group did not display litter-mate preferences and at night they occupied burrows with many more non-litter-mates than litter-mates. These results suggest that associating with non-litter-mates can compromise the development of litter-mate preferences, and implies that mothers indirectly influence social development by affecting the identities of sleeping partners. Third, newly emergent juveniles that interacted only with litter-mates for 3 days in the absence of mothers subsequently preferred litter-mates over non-litter-mates as play partners. This result demonstrates that once litter-mate preferences are instilled, due in part to social experiences during juveniles' initial days above-ground, the preferences are expressed even in the absence of mothers. Collectively, the results demonstrate that the presence of S. beldingi mothers is important to juvenile social development, but that mothers do not actively direct the ontogeny of their offsprings' social relationships. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Song learning in brood-parasitic indigobirds Vidua chalybeata: song mimicry of the host species.

Brood-parasitic village indigobirds, Vidua chalybeata, were bred in captivity and foster-reared by their normal host, red-billed firefinch, Lagonosticta senegala, or by an experimental foster species, Bengalese finch, Lonchura striata. Male indigobirds reared by Bengalese finches developed the songs of Bengalese finches, and males reared by firefinches developed songs of firefinches. Males copied their foster father only when they had lived with him long after independence (45 days post-fledging), while males separated normally at independence (22-24 days post-fledging) copied songs of other individuals and not songs of their foster father. Males reared by Bengalese finches showed no preference to learn firefinch song over songs of the experimental foster species or other control finch species even when they had lived with firefinches as companions from the time of fledging to independence. Males copied several song themes, acquired the same number of mimicry songs, and acquired their songs at the same age, whether reared by Bengalese finches or by firefinches. When they lived with other indigobirds, the male indigobirds copied mimicry songs of male indigobirds that mimicked the same foster species. We predicted mimicry-song specificity and repertoire size in experimental indigobirds from a hypothesis of an early developmental period when young indigobirds focus their attention on their foster parents, and a later period when they direct their attention to other birds with similar songs. The predictions, based on field observations of wild birds, were that (1) males reared by a novel foster species other than the normal host would learn the song of that foster species, and (2) males that left their foster parents at the normal time of independence would copy the songs of other individuals, including other adult indigobirds that mimicked the same foster species. Begging calls of young indigobirds did not mimic the calls of young firefinches. Indigobirds reared alone, or with young of the normal host or of the experimental foster species, all developed begging calls in adult song that resembled their own begging as nestlings and fledglings, and only males that heard other adult indigobirds with firefinch-mimicry begging developed firefinch begging in their song. The incorporation of the innate begging calls as well as the learned begging calls into adult song, and the modification of the song themes of their individual song models, suggest that song development involves processes in addition to copying the songs of their own foster species and of older adult male indigobirds with songs like their own foster parents. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Predator discrimination error and the benefits of Müllerian mimicry.

Müllerian mimicry has traditionally been thought to benefit both unpalatable mimic and model species but recently its existence has been questioned. Even if both mimic and model species are unpalatable, they are unlikely to be equally unpalatable. It has been argued that the more unpalatable species will suffer a cost of increased predation because the presence of the more palatable mimic will increase its perceived palatability (by the predator), similar to that experienced by a model in Batesian mimicry. Yet, previous models of Müllerian mimicry have assumed that a predator can discriminate perfectly between available prey. We argue that this is not the case and that discrimination error is an important factor in determining the nature of mimetic relationships. Using computer simulations we show that the nature of a mimetic relationship will depend on the trade-off between the cost of an increase in perceived palatability and the benefits of a reduction in predator discrimination error. We show that mimicry can be unequivocally Müllerian, with both species benefiting, and propose that palatability should no longer be used as the sole defining characteristic of a mimetic relationship. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Sedentary snakes and gullible geckos: predator-prey coevolution in nocturnal rock-dwelling reptiles.

We investigated (1) the importance of chemical cues for predator detection by the nocturnal, rock-dwelling velvet gecko, Oedura lesueurii, and (2) how the lizards' responses to snake odour may have exerted selection on the foraging behaviours of a nocturnal elapid snake. This snake species (broadheaded snake, Hoplocephalus bungaroides) feeds primarily on velvet geckos, and does so by means of a distinctive foraging behaviour: the snakes remain sedentary in rock crevices for days or weeks, waiting to ambush geckos. Behavioural assays showed that geckos that are sympatric with this sedentary 'ambush' predator can detect and respond to the scent of the snake. Retreat-site selection experiments showed that geckos are less likely to enter crevices if the snake's scent is distributed over the entire rock surface, rather than localized to a central portion. Together, these data support the notion that the 'ambush' predator benefits by remaining sedentary within a retreat-site for long periods, because it thereby minimizes the extent to which it spreads its scent over the rocks forming the crevice. Geckos from a population sympatric with the 'ambush' predator responded strongly to the snake scent, but those from an allopatric population did not. Additionally, geckos from sympatric populations were able to detect the scent of a nocturnal snake that does not eat geckos (small-eyed snake, Rhinoplocephalus nigrescens), but did not modify their retreat-site selection or locomotory behaviours in response to this cue. Lizards from allopatric populations apparently did not detect the scent of small-eyed snakes. Collectively, our findings support an interpretation of predator-prey coevolution in the present system, and emphasize the importance of chemosensory cues to these rock-dwelling reptiles. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Heat, safety or solitude? Using habitat selection experiments to identify a lizard's priorities.

Laboratory experiments with a rock-dwelling nocturnal gecko, Oedura lesueurii, showed that retreat-site selection (and other behaviours) are affected by the interplay between thermal benefits, social advantages and avoidance of predators. Velvet geckos were highly selective in habitat choice: they preferred artificial retreat-sites that mimic the thermal properties of natural rocks in full sun rather than those that mimic rocks in full shade; mature male geckos rarely shared retreat-sites with other adult males; and these lizards strongly avoided retreat-sites covered with the scent of a natural predator (the broadheaded snake, Hoplocephalus bungaroides). After documenting these preferences, we carried out additional trials in which two or more of these factors co-occurred, as is often the case in nature. Social dominance interacted with thermal benefits in determining retreat-site selection, with smaller (subordinate) males forced to use cooler retreat-sites when larger (dominant) males were present. Avoidance of predators was a higher priority than thermoregulation: the lizards would forego a warmer retreat-site with predator scent in favour of a cooler, unscented one. There was also an interplay between social dominance and predator scent: smaller males were forced to use either predator-scented retreat-sites or no retreat-site when larger males were present. General activity levels, and the frequencies of specific behavioural acts, also shifted in response to social and predator-scent cues. Our study emphasizes the complexity of habitat-selection behaviour in these lizards, and clarifies the criteria used in retreat-site selection when (as is commonly the case) the animal must choose between conflicting priorities. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Yellowhammers get fatter in the presence of a predator.

According to predictions from theoretical models, body mass and the daily foraging pattern of small birds in winter should be sensitive to predation risk. With increased risk of predation birds are expected to lower their body mass and shift their foraging to the afternoons. I studied the effect of predator presence on daily mass gain in captive yellowhammers, Emberiza citrinella. The birds were tested in unisex pairs, one bird being dominant over the other. In the first treatment the amount of food was restricted, and the daily pattern of mass gain was recorded. The second treatment was identical to the first, but, in addition, a stuffed sparrowhawk, Accipiter nisus, was displayed to the birds in the morning. Contrary to predictions from some theoretical models and other studies, the birds gained weight on days when the hawk was shown. Furthermore, the increased foraging happened mainly in the first half of the day, which also contradicts predictions from models. These results could be explained as a response to interrupted foraging, decreasing the probability of the birds acquiring the critical evening body mass. Alternatively, the birds increased their body reserves in preparation to leave a dangerous situation. Both dominance classes showed a similar response. The results suggest that the effects of predators on foraging interruptions should be included in models of daily routines of reserve accumulation. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Individual variability in state-dependent feeding behaviour in three-spined sticklebacks.

We studied state-dependent feeding behaviour of three-spined sticklebacks, Gasterosteus aculeatus, during several trials of sequential encounters with 6-mm and 8-mm Asellus aquaticus prey. We used stomach fullness (the number of prey eaten previously) as an indicator for state, which we assumed to affect motivation for feeding. Dummy variable regression was used to study how the per trial energy consumption, the number of events experienced, feeding efficiency and the average time spent on each accepted prey depended on trial number, day and fish. A clear individual variability was found. Feeding behaviour was strongly related to the individual's recent feeding history (within a day). Logit regression models showed that the decision to accept or reject a prey encountered depended on the size of the fish as well as its state (stomach fullness). Although limited, our results demonstrate pronounced heterogeneity in feeding behaviour among individual fish. We discuss this phenomenon in the broader context of population regulatory mechanisms. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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