The courtship song of Drosophila is thought to be involved in sexual selection and species recognition. Because of the mating system of flies, however, directly demonstrating that song influences female preference is difficult. The majority of previous studies have used an experimental design that potentially confounds male and female reactions to song. In D. montana, correlational evidence has suggested that males that produce short sound pulses consisting of a high number of sound cycles (i.e. a high carrier frequency) have a higher mating success than other males. In this study, we played synthetic song that varied in pulse length and carrier frequency to individual females in the laboratory, both alone and in the presence of mute males. We scored female preference via an acceptance posture, 'wing spreading', which the females of this species usually display prior to mounting by a male. Females responded to synthetic song in the absence of males. The presence of mute males significantly increased their overall responsiveness, but the relative effectiveness of the songs did not change, eliminating male reaction to song as a possible confounding factor in the results. The interaction between pulse length and carrier frequency determined the discrimination between song types, with females responding most readily to song consisting of short pulses with a high carrier frequency. Thus, direct examination of female preferences supports the previous studies of male mating success, and confirms female song preference as a likely determinant of male mating success. Copyright 1998 The Association for the Study of Animal Behaviour
Seven female and six male zebra finches, Taeniopygia guttata, were reared in acoustic isolation from song and tested for their preference for conspecific song when 28-53 days old by allowing them to select exposure to zebra finch or European starling, Sturnus vulgaris, song. The birds hopped more frequently on a perch that generated zebra finch song than one that produced starling song, and they spent more time listening to zebra finch song. There were no sex differences. The results indicate that during their sensitive period for song learning, and prior to experience with song, zebra finches prefer conspecific song to heterospecific song. Copyright 1999 The Association for the Study of Animal Behaviour.
The mating system of the seaweed fly Coelopa frigida involves a vigorous premating struggle during which females attempt to dislodge mounted males by kicking and shaking from side to side. Additionally females can prevent engagement of genitalia by curling their abdomens downwards. Large males gain a mating advantage. Male size is partially determined by a chromosomal inversion polymorphism which is maintained by strong heterosis. Thus female mate choice on the basis of size will affect offspring fitness. We report the occurrence of premating struggles and mate choice for large males in five additional species of seaweed fly, namely, C. nebularum, C. vanduzeei, C. pilipes, Gluma musgravei and G. nitida. Four of these species appear to lack the inversion system, suggesting that mate choice for large males can be maintained in its absence and also evolved before its establishment. Gluma females had stronger preferences than Coelopa females and showed an additional response to mounting, namely, curling their abdomens upwards into the male. This may allow assessment of male size. Copyright 2000 The Association for the Study of Animal Behaviour.
The effects of removing the mothers of rhesus monkey infants for 13 days were qualitatively similar to those found previously, when the mothers were removed for 6 days. The infants' behaviour changed markedly in the first few days of separation: thereafter there was no clear evidence, from the measures used, of any further changes. After the mothers' return these infants gave more distress calls, and showed a greater depression of locomotor and play behaviour, than did the infants whose mothers had been removed for only 6 days.
Male tiger salamanders, Ambystoma tigrinum tigrinumare slightly larger in body size and have considerably higher and longer tails than females. To determine how these dimorphic traits affected reproductive performance and success, we conducted breeding trials using 12 males and six females per trial and monitored male-female and male-male interactions. Larger males had an advantage in most aspects of mate competition investigated. Males with higher tails had no advantage in either mate competition or mate choice. Males with longer tails also had no advantage in mate competition but were preferred as mates by females. Larger males interrupted courting males more often than smaller males did. The form of male-male interference was conditional on body size and not on either tail dimension. If the intruder was larger than the courting male, it would shove the female away from the courting male and initiate courtship; if the intruder was smaller, it adopted a female mimicry tactic in which it positioned itself between the courting male and female and performed female behaviours to the courting male while simultaneously courting the female. Our trials indicated that the two components of sexual selection may influence the evolution of different male morphological traits in tiger salamanders. Mate competition may favour increased male body length; mate choice may select for greater male tail length.
Cerambycid beetles have exaggerated antennae that are usually sexually size-dimorphic. We investigated the relationship between antenna morphology and sexual selection in the species Stenurella melanura (L.) in which males on average have antennae that are 13% longer than those of females. Males and females aggregate at flowers near oviposition sites for feeding during June-August. We sampled both copulating and single individuals at these sites. Fluctuating asymmetry (a measure of developmental instability) in antennae was considerably larger than in tibia and elytra and males had larger degrees of asymmetry in their antennae than females. Mated individuals did not differ from unmated individuals with respect to any of three size variables, but antennal asymmetry was smaller in mated individuals of both sexes. When two males were released with a female on a flower, males with symmetric antennae more often won the fight over the female than expected by chance. When two females and a male were released on a flower, the male more often preferred the female with more symmetric antennae than expected by chance. These results suggest that antennal symmetry, but not length, is currently under sexual selection.Copyright 1997 The Association for the Study of Animal Behaviour
Male rats sexually inexperienced to 16 months of age and subsequently kept in cohabitation underwent fertility and copulation tests between 16 and 20 months of age. Control males were raised in cohabitation from puberty. At 20 months of age the rats were killed and their accessory reproductive organs were removed and weighed.
All but one of sixteen inexperienced males fathered litters between 16 and 17 months of age; there was no significant difference in the ability of both groups to impregnate females caged with them. However, in 15 min copulation tests the sexual activity of the previously inexperienced males was significantly inferior to that of the experienced males. At 16 months of age the inexperienced males showed hardly any sexual activity; gradually their activity increased and between 19 and 20 months of age it reached a level not significantly different from that of the control group. At 20 months, of all the accessory reproductive organs, only the mean penis weight of the inexperienced males was significantly smaller than that of the control group.
It is concluded that in male rats aged 16 months or more continuous heterosexual contact is needed to maintain a maximal potential for sexual behaviour.
1.1. The ‘maternal’ behaviour of male and female group companions towards rhesus monkey infants has been analysed according to age of group companions, and in the case of females whether or not they have borne live young and whether or not these were present.2.2. The most conspicuous-differences between categories of females were that those which had had live young showed less behaviour than those which had not, and a lower proportion of them did so. The proportions of the different types of behaviour also differed most between those groups of categories. Females about 2 years old were most likely to show behaviour.3.3. Two-year-old males were more likely to show behaviour than those younger or older.4.4. Females showed more behaviour, and a higher proportion were involved, than males of equivalent age class.5.5. Siblings showed more behaviour towards an infant than an animal of the same category also present in the group.6.6. When the mother was removed from the group the categories tended to stay in the same relation to one another as when she was present, and the amount of cuddles, hits and grooming received by the infant increased.
We tested the discrimination abilities of aardwolves by monitoring their response to scent marks of male or female donors varying in familiarity translocated into their territories. We followed aardwolves in a vehicle and collected grass stalks with single fresh scent marks. The next evening we placed these grass stalks at dens and middens in the territory of another aardwolf, which we subsequently followed for the whole night. During 43 experiments 617 stalks were translocated. Of these, 164 were located by the animal followed. Both males and females overmarked more frequently, changed their dens more often and increased their scent-marking rate more when they found scent marks of same-sex donors than those of the opposite sex, except during the mating season. Along territory borders and at middens, the majority of marks were sniffed for short periods and overmarked. However, aardwolves seldom overmarked marks at dens in use and sniffed them for much longer, often showing flehmen. Flehmen and prolonged sniffing seemed to indicate investigatory behaviours. They were most prevalent towards the first mark of a nonresident found that evening and particularly towards strangers' marks or (in the case of males) those of a female during the mating season. Overmarking seemed to be asserting territorial ownership. After locating a neighbour's scent mark the resident also immediately increased its rate of scent-marking and often went directly to the respective border. The results suggest that scent marks may function in intimidating intruders and to synchronize mating in the aardwolf. (c) 1998 The Association for the Study of Animal Behaviour
The structure of the population of northern elephant seals, Mirounga angustirostris, on San Nicolas Island, California, was studied during the 1970 and 1971 breeding season. At the population peak on 31 January 1971, there were 77 males, 306 females, 315 pups, and 6 yearlings on shore. The breeding population was subdivided into 15 groups, containing from 3 to 75 breeding animals. Fourteen of the groups were considered territories defended by individual males, and one group, the largest, was controlled by three males in a social hierarchy. The relatively small size of the San Nicolas population and the large amount of available beach space allowed the existence of numerous small breeding groups. Female elephant seals, although gregarious, apparently prefer to be in small groups when conditions permit it. It is likely that the same males that were territorial would have formed the nucleus of a social hierarchy if space had been limited enough to cause all of the females in the population to congregate in one large group.
► We address the authors' criticisms of Range et al. (2007, Curr Biol, 17, 1–5). ► We point at unfavourable methodological differences between the two studies. ► Most critical is a substantial difference in the dogs' baseline performance. ► Priming cannot account for the selective imitation effect. ► We are therefore not surprised that the “replication” failed.
Open-field testing of rats and mice did not yield significant behaviour-steroid correlations in experiment 1. In experiment 2 albino and hooded rats maintained under a 12 hr light-dark regimen were observed in a reaction-to-handling situation and an open-field at the peaks and troughs in the previously determined 24 hr rhythm in adrenal cortical activity. Strain differences were observed in the reaction-to-handling test and to a lesser extent in the open-field, and were independent of the time of testing. Hooded animals had heavier adrenal glands than albinos, but neither adrenal weight nor plasma and adrenal corticosterone values were related to emotionality. The plasma corticosterone response to behavioural testing varied as a function of the test and the time at which it occurred.
In a straight runway, following or approach behaviour of day-old broiler and leghorn chicks was found to be mainly a linearly decreasing function of stimulus complexity. The patterned stimuli used were checkerboard-like matrices containing, on the average, 4, 36, 100, 400, or 900 bits of information. Preference for simpler stimuli was not found to depend upon experience in the test situation nor upon the degree of complexity of the home pen. When stimulus illuminance was varied, there was a tendency for a plain grey square (zero bits) to be preferred over the pattern containing 4 bits of information, suggesting that approach or following behaviour is energized maximally by some optimal combination of stimulus illuminance and complexity.
Three types of Colobus guereza groups may be distinguished on the bases of size and composition, namely small one-male groups, large, one-male groups and multi-male groups. The social structure of each type of group is described in terms of the distribution of non-agonistic interactions, the frequency and distribution of agonistic behaviour and the organization of the roles of vigilance, territorial defence and leadership. A number of differences are found between the group types which appear to be related to the differences in group size and composition. It is suggested that these group types represent stages in the life-cycle of colobus groups, and that such an interpretation may help to resolve some of the conflicting reports in the literature.
The quality of an individual's odour can allow potential mates to discriminate against individuals of low social class, poor health status or unsuitable genotype. Competitive scent marking provides a further mechanism which could allow mates to discriminate between individuals of apparently high quality. The presence or absence of fresh countermarks from competitors within an owner's territory or area marked by a dominant animal provides a reliable indicator of the owner's ability to defend its territory or dominate competitors. This could be used by potential mates to discriminate between individuals advertising their apparently high competitive ability through their scent-marking behaviour and odour quality. We tested this by manipulating scent marks in the neighbouring territories of wild-caught male house mice, Mus domesticus. As predicted, oestrous females used scent marks to select males apparently able to defend exclusive territories over those unable to exclude intruders. Females were more strongly attracted to the odour of owners of exclusively marked territories and showed more sexually related behaviour when interacting with these males. Furthermore, while females preferred a territory containing a better protected nest site regardless of the owner's apparent competitive ability, they still used the presence or absence of intruder countermarks when selecting a potential mate. This suggests that females use scent marks as a reliable signal of the best-quality mate among neighbouring males independently of their nest location. Since assessment depends on both the territory holder's own marks and those of competitor males, countermarking is likely to be an important mechanism of competition for mates between neighbours. Copyright 1998 The Association for the Study of Animal Behaviour
We tested the risk-sensitive foraging preferences of wild rufous hummingbirds, Selasphorus rufus, with three types of artificial flowers. All three flower types provided the same mean volume of 30 µl of sucrose, but differed in terms of variability of the reward: constant, low variance and high variance. In trinary comparisons, subjects preferred the low-variance reward over the constant reward, and the constant reward over the high-variance reward; a result not predicted by risk-sensitive foraging theory. However, when tested with traditional binary comparisons, hummingbirds showed conventional risk-averse behaviour and selected the constant reward over the low- or high-variance rewards. This reversal of preference represents a context-dependent foraging preference. The utility of selecting intermediate levels of risk and the source of the preference reversal are discussed relative to risk-sensitive foraging theory and the effects of local context on foraging choices. Copyright 1999 The Association for the Study of Animal Behaviour.
Three groups of fifteen male C57BL/6J mice were given 30 days of differential training prior to a test for negative geotaxis on inclines of 20°, 30°, 40°, 50°, 60°, and 70° from the horizontal. One group received no special handling; another group received practice on wide elevated runways; and a third group received practice on narrow elevated runways which required continual bodily adjustments in order to remain on the runways. Twenty-four hours after the last practice period each animal was tested for negative geotaxis on all six inclines. When every orientation up the incline was averaged for each animal, a trend analysis indicated a significant variation for the effects of practice. The group receiving balancing practice on the narrow runways responded at a steeper orientation up the incline than the other two groups. The trend for linearity was highly significant, indicating that as the angle of the incline steepened, the orientation progressed toward the vertical. These same animals were given an additional 10 days of differential experience, as before, and again tested, but this time only at the 20° incline. The results were similar to those of the first test, indicating that balancing experience increases the steepness of the orientation up the incline. This time three different methods of measuring orientation were used. Identical defecation scores on the runways of the first test suggest that the difference displayed due to balancing is not related to an emotional response. Body weight was equal for all groups as were the weights for the cerebrum and cerebellum. Balancing practice was noted to create a phenocopy of genetic differences found in arboreal and non-arboreal species of Peromyscus mice.
Behavioural decisions require the appropriate use of relevant information about the environment. However, individuals may have imperfect information, imposing a constraint on adaptive behaviour. We explored how information use influences the sex allocation behaviour of the parasitoid wasp Nasonia vitripennis in response to local mate competition. Optimal sex ratios under local mate competition require females to estimate the number of other females that contribute eggs to a patch. Females rapidly changed their sex allocation in response to changes in the number of females in the environment, suggesting that they are not constrained by how quickly they can respond to new information. Furthermore, females also showed some response to olfactory cues that indicated oviposition by other females, suggesting that such indirect cues may be part of their information repertoire. Both the absolute and the relative size of the patch were important for sex ratio decisions, with sex ratios declining on larger patches in a way that suggests that large patches in effect become more than one patch, with females on larger patches allocating sex increasingly independently of other females. We conclude by highlighting variation among species in whether particular cues are used for sex allocation.
Sixteen male rats raised in social isolation from weaning exhibited disorientation and inability to achieve intromission in 2 or 3 copulation tests with receptive females. Four other males raised under presumably similar conditions, but tested at a slightly older age in a smaller arena, exhibited normal sexual behaviour. The only controlled factor to which aberrant sexual behaviour could be attributed was social isolation. Although social isolation is apparently necessary to produce aberrant sexual behaviour in the male rat, other unidentified experimental factors are also necessary to bring it about.
The behaviour of a wild population of tassel-eared squirrels was investigated from September 1969 to January 1971. Squirrels were live captured and marked for individual recognition. Adult squirrels were generally non-gregarious throughout the non-mating season. During the mating season (April and May) periodic bouts of sexual activity occurred involving interactions between an oestrous female and a group of socially ranked males. The most dominant male in each mating bout was first to copulate with the female. Aggressive behaviour in males was also positively correlated with the frequency of copulation. Male dominance hierarchies were characterized by non-linear arrangements and were relatively unstable over bouts. Certain males tended to be dominant in their own home areas with females from the same areas.
The role of the forebrain in learning in the teleost fish, Tilapia h. macrocephala, was studied by comparing their ability to make a conditioned avoidance response before and after forebrain ablation. The fish were trained in massed or spaced sessions to avoid intermittent electric shock by swimming from one compartment to another of a specially constructed shuttle-box in response to a light signal. When the fish consistently avoided the shock, the forebrain (experimental subjects) or the olfactory bulbs (controls) were ablated and testing was resumed.Ablation of the olfactory bulbs, which controlled for loss of olfaction and operative trauma, had no effect on performance of the conditioned response. In all cases, forebrain ablation resulted in an increase in latency and in variability of response. The number of avoidance responses decreased while the number of ‘no crossings’ increased sharply. With continued testing the performance of some forebrain-ablated subjects improved but in no case was the highly consistent pre-operative level attained.When the forebrain was removed prior to training, two subjects never learned to avoid. A third subject eventually learned the avoidance response after a long training period, but his performance remained more variable than that of fish trained before forebrain ablation.Subjects trained on a spaced-trial schedule learned faster than did those trained on a massedtrial schedule, but the effects of olfactory bulb and forebrain ablations were similar in both instances.This study thus provides evidence for the hypothesis that the teleost forebrain is concerned with facilitating the acquisition and performance of conditioned responses by contributing to the general arousal level of the organism.
Eight pregnant Soay ewes were made anosmic by ablation of the olfactory bulbs before their lambs were born. They were observed during parturition and in the following few days. Four out of five ewes seen during parturition did not show pre-natal lip licking which is normally seen in Soays. Four ewes did not lick their lambs properly after birth, and in six there was a lack of specific response to their own lambs, so that strange lambs were often fed. Post-mortem examination showed that olfactory tracts were absent in all except one of the ewes examined. It is suggested that the importance of olfaction in maternal care is concerned with identification of the lamb at close quarters and in forming the ewe-lamb relationship.
The majority of heron species (Aves, Ardeidae) forage on aquatic prey in shallow water. Prey detection, aiming and the beginning of the capture strikes are performed while the heron's eyes are above water. For most angles, as a result of air/water light refraction, the apparent image available to a heron is vertically displaced from the prey's real position. Herons must therefore correct for refraction. We tested the hypothesis that species that forage in aquatic habitats should be more able to correct for image disparity than those of terrestrial habitats. The ability of hand-reared herons of four species to capture stationary prey (fish) underwater (submerged) or in air (aerial) was tested. Three species (little egret Egretta garzetta, squacco heron Ardeola ralloides, and night heron Nycticorax nycticorax) normally forage in aquatic habitats while the fourth (cattle egret Bubulcus ibis) forages in terrestrial habitats. No individuals missed aerial prey. Success rates of little egrets and of squacco herons with submerged prey were high, while night herons became less successful with increased prey depth and/or distance. In cattle egrets, success rate was low and negatively correlated with prey depth. The observed interspecific differences may thus be related to (1) differential ability to correct for air/water light refraction and (2) the species' foraging behaviour. We suggest that cattle egrets are in the process of losing their ability to cope with submerged prey. Copyright 1999 The Association for the Study of Animal Behaviour.
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.
Animals commonly approach (i.e. 'inspect') potential predators. Glowlight tetras, Hemigrammus erythrozonus, have previously been shown to inspect the combined chemical and visual cues originating from novel predators and to modify their inspection (approach) behaviour depending upon the predator's diet. We conducted two experiments to determine whether tetras would inspect the chemical cues of injured prey or the dietary cues of a novel predator in the absence of any visual cues. Shoals of glowlight tetras were exposed to either distilled water (control) or the skin extract of swordtail (lacking ostariophysan alarm pheromones) or the skin extract of tetra (with alarm pheromones). There was no significant difference in the frequency of predator inspection behaviour towards swordtail or tetra skin extract compared to the distilled water controls. In the second experiment, we exposed shoals of tetras to either distilled water or the odour of Jack Dempsey cichlids, Cichlasoma octofasciatum, which had been food deprived, or fed a diet of swordtails or tetras. There was no significant difference in the frequency of predator inspection behaviour towards the odour of the starved cichlids and the odour of the fed cichlids in either of the two diet treatments. However, when tetras were exposed to the odour of cichlids fed tetras, they took significantly longer to initiate an inspection visit, remained further from the source of the chemical cues and inspected in smaller groups, compared with the odour of a starved cichlid or a cichlid fed swordtails. These data strongly suggest that tetras will inspect chemical cues alone, but only if the cue contains information about the predator. Copyright 2000 The Association for the Study of Animal Behaviour.
Parasitic wasps are commonly found to learn olfactory and visual cues that are associated with successful host location. For many parasitoids the cues that are associated with hosts vary in space and time, and are therefore unpredictable. An ability to learn allows the wasp to concentrate on those cues that will lead it to new hosts most effectively in a particular area. In contrast, parasitoids that forage in a predictable homogeneous environment and/or make only a few foraging decisions do not need to learn and should rely on innate responses to specific cues. The role of learning in host foraging was studied in Cotesia flavipes (Hymenoptera: Braconidae), a parasitoid of stemborer larvae with an ecology where learning is expected to be of low adaptive value. There was no evidence that C. flavipes uses odour learning in host-micro-habitat location. There was no significant effect of the development and emergence environment on the response level or preference towards the odour of infested plants. Neither was there evidence that experience with a particular plant-host complex during foraging influences subsequent foraging decisions in C. flavipes females. The absence of learning in C. flavipeswhich seems an exception among the parasitoids studied, is discussed in relation to its ecology.
Absolute and masked auditory thresholds (critical masking ratios) were determined behaviourally in the great tit, Parus major, using a GO/NOGO-procedure. Absolute sensitivity was measured between 0.25 and 10 kHz. In the absence of noise, great tits were most sensitive to frequencies between 2 and 4 kHz. In background noise, however, the sensitivity was only a function of the noise level and was independent of frequency. Critical masking ratios determined for signals between 0.25 and 8 kHz were almost constant (median values varied between 23.8 and 25.9 dB) irrespective of signal frequency. Therefore, in contrast to the majority of bird species, great tits have unusually low critical masking ratios at high frequencies. This means that great tits can use high-frequency vocalizations to communicate efficiently in noisy (i.e. natural) environments. Copyright 1998 The Association for the Study of Animal Behaviour.
Extra-pair fertilizations are common in birds, which has led to great interest in how this phenomenon is regulated at a proximate level and how extra-pair fertilizations, and extra-pair fertilization avoidance, shape avian social systems. In Wilson's phalaropes, Phalaropus tricolor, incubation and brood-rearing is performed exclusively by males. Males are able to rear only a single brood of four during a breeding season. This suggests that males have a high level of paternity in clutches and broods under their care and, thus, that extra-pair fertilizations are infrequent. In contrast, female social dominance, lack of territoriality and frequent interactions among breeding adults suggest that both males and females have the opportunity to engage in extra-pair copulations. Using DNA fingerprint band-sharing between putative parents and offspring, we found no evidence of extra-pair fertilizations among 51 offspring from 17 families of phalaropes. Copulation disruption by non-copulatory adults, ability of females to reject copulation attempts and potential fitness benefits to females by avoiding extra-pair fertilizations were sufficient to explain the absence of extra-pair fertilizations in Wilson's phalaropes. We propose that sex-role reversal affects the relative costs and benefits to females of seeking extra-pair fertilizations. At the time of clutch completion, females have invested particularly heavily in their clutches due to intense competition among females to gain and keep a mate during the pre-laying and laying periods. After clutch completion, nest success requires significant male parental care. Benefits to females in gaining extra-pair fertilizations may be offset by the risk of losing male parental care. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.
Male-biased mortality in young animals is often viewed as adaptive discrimination against male offspring by parents unable to raise reproductively competitive sons. Unequivocal evidence of the presence or absence of parental discrimination against males is lacking, however, and the adaptive interpretation of male-biased mortality is confounded by an alternative explanation that it reflects differential energetic requirements between the sexes (due to sexual selection for large size in mature males) independent of parental manipulation. To determine whether maternal discrimination against offspring explains postnatal mortality in a sexually dimorphic rodent, we examined patterns of growth and mortality in offspring of food-restricted and food-enriched lactating bushy-tailed woodrats,Neotoma cinerea. We also monitored mothers and their litters daily throughout lactation for evidence of maternal discrimination against offspring. Offspring of food-restricted mothers showed depressed growth, and mortality of offspring born to both food-restricted and food-enriched mothers was male-biased, but in the absence of maternal discrimination. Offspring that died were no less likely to be attached to their mother's teats in the 10 days prior to death than were offspring that successfully weaned. Similarly, offspring of food-restricted mothers were attached as often as were offspring of food-enriched mothers. In a series of behavioural arena trials in the first 10 days after birth, restricted mothers were no less attentive toward their sons than they were to their daughters, nor did mothers treat their offspring that did not survive to weaning differently from those that survived. Our findings provide empirical evidence that postnatal, sex-biased mortality in offspring is not necessarily due to parental intervention, and they call into question the adaptive interpretations of previous examples of sex-biased offspring mortality.
To study whether absolute (m/s) or relative (body lengths/s) speed should be used to compare the vulnerability of differently sized animals, we developed a simple computer simulation. Human 'predators' were asked to 'catch' (mouse-click) prey of different sizes, moving at different speeds across a computer screen. Using the simulation, a prey's chances of escaping predation depended on its speed (faster prey were more difficult to catch than slower prey of the same body size), but also on its size (larger prey were easier to catch than smaller prey at the same speed). Catching time, the time needed to catch a prey, also depended on both prey speed and prey size. Relative prey speed (body lengths/s or body surface/s) was a better predictor of catching time than was absolute prey speed (m/s). Our experiment demonstrates that, in contrast to earlier assertions, per unit body length speed of prey may be more 'ecologically relevant' than absolute speed. Copyright 1998 The Association for the Study of Animal Behaviour.
Maternal abuse of offspring in group-living monkeys was investigated to assess whether abuse of infants can be interpreted as an adaptive reduction of parental expenditure or as a behavioural pathology. I compared the parenting styles of 10 abusive and 10 non-abusive rhesus macaque, Macaca mulatta, mothers living in three large captive groups over the first 12 weeks of infant life. I also analysed the social interactions between mothers and infants and other individuals. Abusive females scored higher than controls on several measures of maternal protectiveness and rejection, indicating that they were highly controlling mothers. They also received fewer contacts and approaches from other individuals, and tended to be more aggressive and more interested in other females' infants compared to non-abusive mothers. Infant abuse was accompanied by similar or higher parental expenditure in the offspring rather than by a reduction in expenditure, as predicted by the adaptive hypothesis. Therefore, the results of this study support the hypothesis that infant abuse is a form of behavioural pathology. Infant abuse in rhesus macaques shows parallels with that in other primate species, but some of its characteristics could be a by-product of species-specific behavioural adaptations of rhesus macaques. Copyright 1998 The Association for the Study of Animal Behaviour.
Both sensory and motor mechanisms can constrain behavioral performance. Sensory mechanisms may be especially important for constraining behaviors that depend on experience, such as learned birdsongs. Swamp sparrows learn to sing by imitating the song of a tutor, but sparrows fail to accurately imitate artificial tutor songs with abnormally accelerated trills, instead singing brief and rapid trills interrupted by silent gaps. This "broken syntax" has been proposed to arise from vocal-motor limitations. Here we consider whether sensory limitations exist that could also contribute to broken syntax. We tested this idea by recording auditory-evoked activity of sensorimotor neurons in the swamp sparrow's brain that are known to be important for the learning, performance and perception of song. In freely behaving adult sparrows that sang songs with normal syntax, neurons were detected that exhibited precisely time-locked activity to each repetition of the syllable in a trill when presented at a natural rate. Those cells failed to faithfully follow syllables presented at an accelerated rate, however, and their failure to respond to consecutive syllables increased as a function of trill rate. This "flickering" auditory representation in animals performing normal syntax reveals a central constraint on the sensory processing of rapid trills. Furthermore, because these neurons are implicated in both song learning and perception, and because auditory flickering began to occur at accelerated trill rates previously associated with the emergence of broken song syntax, these sensory constraints may contribute to the emergence of broken syntax.
Previous research has indicated that virgin rats (Rattus norvegicus) behave maternally (sensitize) more rapidly in close proximity with pups. Since both parturient rats and a large percentage of virgin rats avidly consume placenta, we tested whether placenta and amnionic fluid, pups and therefore hasten the onset of maternal behaviour. The results indicated that the procedure indeed shortened the maternal sensitization latency. Furthermore, this effect was not due to the wetness of the pups, to the presence of placenta in the cage, or to the adults having previously ingested placenta. Other attractive ingestibles applied to the pups' skin produced an intermediate, but not significant, shortening of the maternal sensitization latency.
In twenty-two clutches of Japanese quail and twenty clutches of bobwhites, a single egg was stimulated either by sound, or by vibration, at the rate of three per second, from approximately 48 hr before hatching. The remaining eggs in the clutch were hatched at distances of approximately 4 in. from each other. In the great majority of clutches the stimulated egg hatched first, and it is concluded that the development of the embryo had been accelerated by the stimulation provided.
I studied the timing and frequency of male copulatory behaviour in alpine accentors, Prunella collaris, in Japan, with respect to dominance status, age and development of the cloacal protuberance. Males used one of three mating tactics depending on their dominance status. Alpha males guarded several females in succession, but only during the females' fertile period, while gamma males copulated rarely and only with unguarded females. The tactics of beta males were flexible: with unguarded females they usually adopted a frequent-copulation tactic, but when two females had synchronous egg-laying periods, beta males associated closely with whichever female the alpha male left unguarded. When alpha males closely guarded a female, beta males guarded this same female for short periods before and after the guarding period of the alpha male. Subordinate rank restricted a male's opportunities for mating but males of all dominance ranks were sexually active and had fully developed cloacal protuberances. Frequent copulation plus part-time mate guarding (as found in beta males) and opportunistic copulation (as found in gamma males) appears to be a conditional strategy whereby young, subordinate males are 'making the best of a bad job'. A long-term study over 10 years showed that males moved up in social rank with increasing age but 78.9% of males remained subordinate because alpha males occupied the top rank for much of their lifetime. Copyright 1998 The Association for the Study of Animal Behaviour.
The reproductive strategy of female alpine accentors, Prunella collaris, was studied on the summit of Mt Norikura in Japan. Alpine accentors formed polygynandrous groups consisting of three to six males and three to five females; however, each female laid eggs in her own nest. Within each group, females were organized in stable, linear hierarchies based on age. All females were sexually active but high-ranking females copulated more frequently with several males from the group. In contrast, the degree of multiple mating and frequency of copulations of low-ranking females was lower because their sexual activity was interrupted by more dominant females. All copulations were preceded by female solicitation. When the young hatched, males helped to feed the chicks of several females with whom they had copulated. The main factor influencing reproductive success was the amount of parental care that was available for feeding the chicks. High-ranking females had paternal help from two or more males and secured a high provisioning rate for the brood, which increased fledging success and nestling weight. The reproductive success of low-ranking females was lower because the brood did not receive sufficient paternal investment and so often starved to death early in the nestling period. These results suggest that the greatest potential benefit females might obtain from multiple mating is the subsequent assistance of several males in caring for the offspring. I discuss the implications of these observations with the idea that competition among females for males brings about multiple mating as a female reproductive strategy. Copyright 1998 The Association for the Study of Animal Behaviour.
In primates, social context is one of the factors that increases the acceptance of novel foods. Previous experiments showed that tufted capuchins, Cebus apella, eat significantly more of novel foods when in the presence of group members eating the same novel foods. Several processes may have led to these results. The mere presence of group members may reduce the individual's stress of being alone, or its neophobic response and, consequently, may increase its food consumption. The individual may be influenced by what group members do, and local/stimulus enhancement and/or social facilitation may occur. To investigate the above processes, we assessed whether an individual capuchin monkey's consumption of novel foods is lower when (1) the individual is alone with nobody in the nearby cage than when (2) group members are present in the nearby cage with no food or when (3) they are present and eating a familiar food. We tested 15 subjects with three novel foods, each presented in one condition. In both social conditions, the more group members there were by the food box the more the experimental subject ate. In addition, when group members were present and eating food, there was a significant increase in the acceptance of the three foods, regardless of what group members were eating. We argue that social facilitation of eating is a quicker way to overcome neophobia and only social facilitation of eating what the others are eating can be considered a safe way to learn about a safe diet. Copyright 2000 The Association for the Study of Animal Behaviour.
In two experiments the effects of intrajugular tranquilizer (Trilafon with 25 mg perphenazine per ml) injections on the acceptance of orphan lambs by Hampshire ewes were investigated. With a 2-ml injection, five of six ewes raised orphan lambs to weaning compared with only one of six non-injected controls. None of three control ewes receiving a 1-ml dose, one of three receiving two 1-ml injections and two of three given one 2-ml injection raised their orphans. While, the tranquilizer was effective in inducing ewes to permit nursing of orphans data are insufficient to ascertain the most effective dosage levels, or the reasons for continual acceptance after tranquilizer effects diminish.
Song learning in white-crowned sparrows, Zonotrichia leucophrys, involves three steps: memorization of external models, song practice and selection of a song from the practiced repertoire for crystallization. These three events occur in a sequential and predictable order during the first year of life in captive sparrows. To study the external regulation of these events, we raised nestling sparrows under conditions in which photoperiod and tutor exposure were manipulated. We measured plasma testosterone concentration twice a month to study its role in the mediation of vocal learning. We conclude that the timing of song memorization is relatively impervious to photoperiodic manipulation. Song practice and crystallization, however, were readily influenced by both photoperiod and tutor exposure. We suggest that low testosterone concentrations permit acquisition at an older age than would normally occur, and confirm that testosterone propels the transition to production of crystallized song, but is not required for the onset of song practice. Copyright 1998 The Association for the Study of Animal Behaviour.
Sperm competition in sex-role reversed, polyandrous jacanas is intense because females copulate with multiple male mates before laying each clutch. These males may be unable to attempt to maximize their share of copulations by mate guarding or forcing copulations. Instead, males in polyandrous harems may compete for sexual access to the female by giving a call, termed the 'yell', to attract her. Male bronze-winged jacanas, Metopidius indicus, yelled at higher rates in larger harems, and when the female was further from the yeller or on a comate's territory. Half of all yells were given at mating platforms where all copulations occurred. Males that received the clutch yelled at lower rates during the incubation and chick care periods. Yells attracted the female when she was far from the yeller or with a comate. When the yell of a polyandrous male was broadcast from his territory, the female was more likely to fly to his territory during playback than during control periods. Within polyandrous harems the males that yelled at the highest rates received the most copulations, and three out of four females gave clutches to the male that gave the longest and most frequent yells, so females may have used yells to assess male quality. Intrusions by females, but not males, increased during yell playbacks, and tended to be more frequent on the territories of males with high yell rates. Females may therefore respond to their mates' yells because yells may attract female intruders which may attempt to take over the territory. Copyright 1999 The Association for the Study of Animal Behaviour.
By making female birds pair successively with different males, and analysing the paternity of the eggs laid, it is possible to examine how a male's success in obtaining fertilizations is determined by the timing of his copulatory access to the female. Such an experiment is reported here with pied flycatchers, Ficedula hypoleucaMate switching was induced at different stages within the female's fertile period by removing the resident male. The paternity of the clutch was analysed by microsatellite DNA typing. Removed males had full paternity in the clutch if they were removed as late as after the second egg was laid (day 1), and they lost all paternity if they were removed more than 1 day before the first egg was fertilized (less than day -2). Male switching during the period day -2 to day 1 always resulted in mixed paternity in the clutch. Males that were paired to the female for only a few (1-3) days during this period achieved on average more than one fertilization per access day, with a peak on day -1. Thus, assuming that the timing of observed pair bonds reflects the timing of each male's copulatory access to the female, the first eggs in the laying sequence were fertilized by inseminations occurring shortly before the time of fertilization, whereas the last eggs were fertilized by inseminations taking place several days prior to their fertilization. Our documentation of the most important period for copulatory access has some important implications for understanding sexual behaviour in this species.
The bridled nailtail wallaby, Onychogalea fraenata, is a relatively small, solitary and sexually size dimorphic macropod. We studied the mating system of free-ranging wallabies over 3 years, using microsatellite analysis of paternity, radiotelemetry and behavioural observations. Both sexes were promiscuous, and general reproductive behaviour was similar to that of larger, better-known macropods. Home range size influenced the number of associations with oestrous females, and was a significant component of male reproductive success. Female population density varied within the site, but males with home ranges that overlapped more females did not sire more offspring. Aggression between males occurred only around oestrous females and males did not establish a predetermined dominance hierarchy. Male body weight strongly influenced priority of access to oestrous females, and was related to age. The number of times that males were seen closest to an oestrous female when other males were present (priority of access) was the most important predictor of variation in the number of offspring sired. Females mated with several males within and between oestrous cycles, and may have influenced male-male competition by prolonging advertisement of approaching oestrus, expanding their home ranges at oestrus and engaging in mate chases that attracted groups of up to six males. Despite overall similarities in the mating system of this species and that of other macropods, male mating success may be less skewed in bridled nailtail wallabies than in other species, although paternity analysis of free-ranging populations of other species is required to confirm this conclusion. Copyright 1999 The Association for the Study of Animal Behaviour.
The relationship between accessability of feed, inter-member peck frequencies and disruptions occurring in the pecking order of 3 stable flocks of cockerels was examined. In all flocks intermember peck frequencies increased as accessability to feed became restricted. In 2 of the flocks the order remained linear upon the introduction of feed until the limiting condition, a point source, was reached. At that point in all flocks dramatic, but temporary, disruptions occurred. The relationship between induced high density and accessability of feed is also discussed and further research is indicated.