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PubMed1998

Five primate species follow the visual gaze of conspecifics.

Individuals from five primate species were tested experimentally for their ability to follow the visual gaze of conspecifics to an outside object. Subjects were from captive social groups of chimpanzees, Pan troglodytes, sooty mangabeys, Cercocebus atys torquatus, rhesus macaques, Macaca mulatta, stumptail macaques, M. arctoides, and pigtail macaques, M. nemestrina. Experimental trials consisted of an experimenter inducing one individual to look at food being displayed, and then observing the reaction of another individual (the subject) that was looking at that individual (not the food). Control trials consisted of an experimenter displaying the food in an identical manner when the subject was alone. Individuals from all species reliably followed the gaze of conspecifics, looking to the food about 80% of the time in experimental trials, compared with about 20% of the time in control trials. Results are discussed in terms of both the proximate mechanisms that might be involved and the adaptive functions that might be served by gaze-following. 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

Natal attraction: allomaternal care and mother-infant separations in wild bottlenose dolphins.

To determine whether allomaternal care occurs among bottlenose dolphins, we examined patterns of association and mother-infant separations for eight infants (164.4 focal h) during the first 3 months of life. During the first week of life, three inexperienced females (nullipara and mothers of infants that did not survive the newborn period) attempted to take infants from their mothers 13 times. Mothers responded by rapidly retrieving the infant and threatening the female. By the second week, mothers consistently allowed the same females to escort their infants to tens of metres away from them, suggesting that such separations were no longer risky, possibly because infants had imprinted on their mothers. To determine whether escorts benefited mothers after the first week, we compared maternal behaviour when infants were away from their mothers, but alone (solitary separations), to when infants were away, but with escorts (social separations). Mothers were less likely to forage and were more likely to engage in non-foraging activities (socialize, rest or travel) when infants were with young escorts (other dependent infants) compared with when infants were alone. When infants were with older (juvenile or adult) escorts, maternal activity did not differ significantly compared with when infants were alone. This result suggests that escorts did not benefit mothers by allowing them to forage. Inexperienced females that never raised an infant were more likely to escort newborns than were parous experienced females, supporting the 'learning to parent' hypothesis. 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

What cues do brown-headed cowbirds use to locate red-winged blackbird host nests?

I examined ecological and behavioural variables influencing the susceptibility of red-winged blackbird, Agelaius phoeniceus, nests to brood parasitism by brown-headed cowbirds, Molothrus ater, in a prairie-nesting population of redwings in southern Wisconsin. I compared the following variables between parasitized and unparasitized nests: proximity of nests to trees and other prominent perches; physical characteristics of nests such as nest height and cover; and aspects of host behaviour, including vocal behaviour and aggression directed towards female cowbirds. I used these data to discriminate among four non-exclusive hypotheses for how brood parasites locate host nests: the perch-proximity, nest-exposure, nesting-cue and host-activity hypotheses. Parasitized nests were significantly closer than unparasitized nests to trees in the 2 years of the study. There was no evidence that nest height or nest cover differed significantly between parasitized and unparasitized nests, suggesting that cowbirds do not use nest exposure as a cue for locating redwing nests. The responses of both parasitized and unparasitized redwings towards a female cowbird mount decreased with increasing mount presentation distance from the nest. There were no significant differences in responses towards the mount between parasitized and unparasitized redwings, giving no support for the nesting-cue hypothesis. Female redwings whose nests were subsequently parasitized gave significantly more nest-associated (type I) vocalizations during the egg-laying period than did unparasitized females. These findings suggest that female brown-headed cowbirds in search of potential host nests use trees to search from, and that female redwing vocalizations may serve as a proximate cue for cowbirds to locate redwing nests at appropriate stages for parasitism, giving support for both the perch-proximity and host-activity hypotheses. 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

Behavioural suppression of female pine voles after replacement of the breeding male

Examination of the mechanism of reproductive suppression includes determining which cues are involved and the context in which they occur. We studied groups of pine voles, Microtus pinetorum, that were disrupted by the replacement of the breeding male and compared them with intact family groups. If reproductive suppression is mediated by chemical cues, then soiled bedding should be sufficient to prevent production of litters by daughters. If reproductive suppression involves a behavioural component, we should observe aggressive behaviours or those indicative of dominance interactions directed from the mother towards the daughter or the replacement male. If replacement of the breeding male leads to conflict between the breeding female and her daughter, then more aggression or dominance interactions would be expected in disrupted than in intact families. The presence of the mother decreased reproduction by daughters, but chemical cues alone were not sufficient to prevent the daughter from mating with the replacement male. Rather, this decrease in reproduction seemed to be mediated by behavioural interactions. We propose that the mother's tugging on the daughter may lead to subordination of the daughter. The mother's presence may also alter the behaviour patterns of the male and daughter, which could delay reproductive activation of the daughter, prevent the formation of pair bonds or inhibit sexual behaviour. These behavioural interactions appear to depend on the presence of an unfamiliar male, because tugging, for example, was less frequent in intact family groups. 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

Early handling increases lamb affinity for humans

Domestic animals that are socialized to humans are often more easily managed and less timid than those that are not. We examined whether increased handling and artificial feeding of domestic sheep, Ovis aries, at an early age would decrease their subsequent timidity towards people. Forty-eight lamb twin sets were divided into four treatment groups for 2 days of treatment at ages 1-3, 3-5, 5-7 or 7-9 days. Treatment lambs were fed milk replacer and were handled four times/day for 5-min periods. Their twins, used as controls, were left with their dams. Two 5-min tests of lamb temperament were conducted at ages 2, 4, 6, 8, 10, 15 and 25 days. Testing consisted of a stationary human encounter, in which lambs' responses to a sitting person were recorded continuously, and a moving human encounter, in which lambs' responses to a person walking at 0.5 m/2 s were recorded by instantaneous scans. Measures included latency to proximity (<2 m) and arm's reach (<1 m) of the person, time spent in proximity and within arm's reach, average distance (m), mean number of human contacts, number of lambs contacting a person and following/approach/avoidance. Treatment lambs showed significantly greater affinity for humans than their twin controls. The 1-3-day treatment group showed the greatest response to treatment, consistently outperforming controls in all of the above measures. These results suggest that 40 min of positive human contact at age 1-3 days reduces lamb timidity to people. Socialization of lambs to humans need not disrupt the primary lamb-dam bond, and it may have positive management as well as welfare implications.\C 1998 The Association for the Study of Animal Behaviour 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

Extra-pair mating effort of male hooded warblers, Wilsonia citrina

Few researchers have been able to quantify the time or effort expended by male birds in seeking extra-pair copulations with neighbouring females. In this study, we radio-tracked male hooded warblers, to determine the frequency and duration of intrusions onto neighbouring territories. Extra-pair fertilizations are common in hooded warblers, with 35% of females producing extra-pair young. Males intruded onto territories where females were nest building more often than expected by chance and approached females during most intrusions (78%), suggesting that these intrusions were extra-pair copulation attempts. Almost all intrusions (96%) were to adjacent territories, and males made an average+/-se of 0.4+/-0.2 forays/h and spent 4.7+/-2.6% of their time off-territory. Males were involved in fights or chases with the resident male in 21% of intrusions, but were apparently undetected during most intrusions. Males with high intrusion effort onto neighbouring territories had the lowest rate of intrusions onto their own territory by other radio-tracked males. Males varied extensively in their intrusion effort, but this was not significantly correlated with male body mass, age or song rate. The percentage of time spent intruding onto other territories was small (0-8%), so males probably do not face strong trade-offs between making extra-pair copulation forays and other activities like mate guarding and feeding offspring. 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

Sex-biased mortality in woodrats occurs in the absence of parental intervention

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. 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 and vocal tradition in Nuttall's white-crowned sparrows.

We investigated song sharing and dispersion of song types in the wild in a colour-marked population of the non-migratory Nuttall's white-crowned sparrow, Zonotrichia leucophrys nuttalli. The songs of fathers, their male progeny (sons), and the neighbours of the sons at recruitment sites were analysed spectrographically and compared qualitatively and quantitatively. To determine whether a son's song more closely matched that of his father or a neighbour at the site settled, we subjected frequency and temporal characteristics of songs within each father-son-neighbour triad to multivariate cluster analysis. The songs of 14 of 16 sons clustered with their neighbours' rather than their fathers' songs, confirming that song matching of neighbours is an integral component of territory settlement by juveniles. Principal components analysis of frequency and temporal measurements of song within a dialectal area show that songs group into neighbourhoods and are non-randomly distributed. Multivariate analysis suggests that sons may entrain on frequency and temporal characteristics of a neighbour's song without matching phrases or complex syllables. Implications for models of instructive versus selective learning are discussed. The timing of closure of the sensitive phase, the length of the silent interval between the sensory phase and plastic song stage, and the time to song crystallization remain open questions in song ontogeny. 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

Body fat and time of year interact to mediate dispersal behaviour in ground squirrels

Behaviour is often influenced by energy availability. Hibernation presents an energetic challenge to Belding's ground squirrels, Spermophilus beldingi, which depend entirely on stored energy for survival during their 8-9 month dormant period each year. Dispersal from the natal area may also place energetic demands on S. beldingi. In this study, we assessed the relationship between dispersal behaviour, body mass and body fat of juvenile male S. beldingi over 3 consecutive years, one of which had a substantially delayed juvenile active season due to heavy spring snowfall. We evaluated body fat using the non-destructive method of measuring electrical conductivity of the body. When the active season began late, acquisition of body mass and body fat were accelerated, and dispersal behaviour was inhibited. These results suggest that the ontogeny of mass and fat gain in juvenile male S. beldingi is influenced by a seasonal time-keeping mechanism. Energy allocation was hierarchical in S. beldingi, with pre-hibernation fattening taking precedence over dispersal. Physiological signals reflecting body fat content appear to interact with an endogenous timing mechanism in this species to regulate the dispersal behaviour of juvenile males.\C 1998 The Association for the Study of Animal Behaviour 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

Sexual selection and the evolution of mechanical sound production in manakins (Aves: Pipridae).

I surveyed and described modulated, non-vocal, mechanical sounds of the lek-breeding Neotropical manakins (Pipridae). Variation among manakin species in mechanical sound production, repertoire size, acoustic structure, associated feather specialization, and mechanical sound production mechanisms were analysed comparatively in the context of a phylogenetic hypothesis for the family. Mechanical sound production has probably evolved five or six times independently and been lost once within the 42 species of manakins. Complex mechanical sound repertoires have also evolved independently several times. Acoustic structure of these sounds indicates that at least four different physical mechanisms of mechanical sound production have evolved: short, broad-frequency spectrum pulses; short, low-frequency pulses; aerodynamic vortices; and harmonic oscillations. All well-known mechanical sounds in manakins are associated with obvious wing movements and sexually dimorphic wing feather specializations. Both primary and secondary wing feather specializations have evolved convergently within the family for the production of short, broad-frequency mechanical sound pulses. Two less well-known manakin clades also have tail feather specializations that may function in mechanical sound production. A concentrated-changes test documented that the dynamic patterns of evolution in mechanical sound production in the polygynous manakins are highly unlikely by chance alone. Intersexual selection for acrobatic display may have created subsequent opportunities for the evolution of novel preferences for incidental non-vocal sounds produced by acrobatic movements. Novel female preferences for these mechanical sounds led to further elaboration of these sounds and to the evolution of complex mechanical sound repertoires in independent lineages of the family. 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

Two cooperatively social populations of the theridiid spider Anelosimus studiosus in a temperate region

Social spiders are typically found only in the tropics. In laboratory tests and field observations, adult female A. studiosus in two populations in Tennessee, U.S.A., a temperate region, showed inter-attraction (grouping behaviour caused by the presence of conspecifics), greater tolerance towards conspecifics, and cooperation during prey capture and brood care. These are the three classical conditions considered typical of social spiders. The populations also had female-biased sex ratios and limited dispersal. Anelosimus studiosus can thus be regarded as a quasi-social or cooperative spider species. These populations of A. studiosus are the first social spiders to be described from typically temperate regions. 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

Producers, scroungers and the price of a free meal

In social foraging, scroungers take a disproportionately large share of the food found relative to their own food-searching efforts, while producers find more food than they manage to monopolize. We present a model of social foraging acknowledging the finder's advantage and foraging role asymmetries among individuals but incorporating the possibility that producers and scroungers differ in vigilance level and in vulnerability to predators. This allows simultaneous examination of both foraging benefits and anti-predatory aspects of grouping behaviour. Instead of seeking for equal payoff conditions, we first look for groups in which foraging character combinations and anti-predatory properties of producers and scroungers minimize the phenotype-specific predation hazard over food-intake rate, Ri/Ii, that is, fixed phenotype Ri/Ii minima. In the second approach, we allow individuals to change their foraging status to achieve lower Ri/Ii and look for combinations where it no longer pays for either producers or scroungers to change their roles, that is, evolutionarily stable group compositions, ESS. Various character combinations allow the phenotype-specific minima. In most cases, however, producers' and scroungers' minima are achievable only in different group compositions. The ESS combinations of producers and scroungers deviate widely from those combinations yielding phenotype-specific minima of Ri/Ii. If individuals are allowed to be flexible in adopting either a producer or a scrounger role, ESS group compositions will emerge, even though they are more expensive for both producers and scroungers in terms of Ri/Ii than group compositions yielding the phenotype-specific Ri/Ii minima. 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

Teat massage after milk ingestion in domestic piglets: an example of honest begging?

After milk ejection, piglets spend several minutes massaging their own teats on the sow. We examined whether this behaviour could be a mammalian counterpart to begging in young birds, and hence be explained by theories of honest begging. In one experiment, the behaviour of piglets was examined in relation to their previous milk intake. In each of 16 litters, one focal piglet was exposed to three treatments for three consecutive sucklings: 'no milk', where the piglet was withheld from the teat during milk ejection; 'extra milk', where it was fed 10 ml of extra milk directly after milk ejection; and 'control', when it received its normal intake. Average massage duration in the next three sucklings was significantly longer in the 'no milk' than in the control piglets. 'No milk' pigs massaged more intensely (number of massage movements/min), were more persistent in attempting to maintain udder contact and spent less time away from the udder. However, there were no significant differences between 'control' and 'extra milk' treatments. In a second experiment, in which we manually massaged teats for 0, 3 or 10 min, we found no significant effect of massage duration on milk output (measured by weighing piglets before and after milk ejection), although massage tended to increase output. We conclude that post-sucking massage in piglets has a number of aspects similar to honest begging in birds. 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

Functional equivalence in a California sea lion: relevance to animal social and communicative interactions.

Laboratory investigations into equivalence class formation suggest how animals in social and communicative contexts learn to place dissimilar individuals, signals, responses and social reinforcers into the same functional class. Kastak & Schusterman (1994, Anim. Learn. Behav., 22, 427-435) demonstrated that a California sea lion performed generalized identity matching-to-sample; that is, it chose visual stimulus A conditionally upon an identical sample A (AA matching), chose stimulus B conditionally upon sample B (BB matching) and chose stimulus C conditionally upon sample C (CC matching). The sea lion was later trained on 30 problems with similar stimuli to select comparison B conditionally upon sample A (AB matching), and trained on another 30 problems to select comparison C conditionally upon sample B (BC matching). Subsequently, the sea lion demonstrated trial-1 BA and CB matching and trial-1 AC and CA matching (Schusterman & Kastak 1993, Psychol. Rec., 43, 823-839). Matching of these derived relations defines the phenomenon of stimulus equivalence: when one member (A) of an equivalence class (ABC) becomes discriminative for a given behaviour, then B and C should become discriminative for the same behaviour. In the current study, we tested whether the sea lion could transfer the relations it had acquired between equivalence class members from a matching-to-sample paradigm to a simple discrimination paradigm. In 28 of 30 tests, the sea lion immediately transferred the discriminative function acquired by one member of an equivalence class to the remaining members of that class. Substitutability among members of an equivalence class is relevant to an analysis of referential communication, for example, the representational function of alarm 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

Resource distribution, female home range dispersion and male spatial interactions: group structure in a solitary carnivore.

We monitored 74 (41 male, 33 female) radiocollared raccoons (Procyon lotor) from February 1990 to July 1992 on the Welder Wildlife Refuge, Texas, to relate male and female space use to each other and to the spatial distribution of water, a critical resource for raccoons. Female home ranges were spatially aggregated early in the study, when standing water occurred in only a few, widely separated patches on the study site, but were randomly distributed during seasons when water was more widely distributed. Adult females generally foraged and rested independently of other adults. Most adult males were arranged in spatial groups whose home ranges overlapped little with those of adjacent groups. These groups were usually composed of three to four individuals; Doncaster's (1990, J. theor. Biol., 143, 431-443) test for dynamic interaction and visual observations showed that group members tended to associate positively during resting and foraging activities in all seasons. Among raccoons, as among many other mammals, female spatial patterns are apparently determined primarily by resource distribution, whereas male patterns are influenced by the distribution of 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 relative cost of children's physical play.

There has been a long-standing debate regarding the functions of play during childhood. An important, but neglected, first step in this debate entails documenting the costs associated with play. In this study we analysed energetic costs (expressed in terms of caloric expenditure) associated with physical play in four field experiments of play in primary school children. Experiment 1 established the concurrent validity of an observational check list to estimate caloric expenditure of children's physical play. Experiment 2 compared caloric expenditure of the play (defined as all behaviour exhibited during play time) for two age groups of children during playtime outdoors and during indoor sedentary activity; caloric expenditure of outdoor activity was greater and was significantly correlated with ambient temperature. In experiment 3, children were observed during indoor play to control for the influence of ambient temperature. Outdoor physical play was more energetically costly than indoor physical play. In experiment 4, children's behaviour was observed outdoors and caloric expenditure for play, games and other activities was compared. Physical play was more costly than other forms of behaviour and games. Estimates of total energetic costs of play ranged from 6 to 15%. Results are discussed in terms of the relatively low caloric costs of play. 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

Cooperative breeding and monogamy in prairie voles: influence of the sire and geographical variation.

Mammalian monogamy is characterized by pair bonding and a relative absence of sexual dimorphism in body size. Alloparental behaviour is a characteristic of mammalian cooperative breeding systems. Studies of prairie voles, Microtus ochrogaster, from stock captured in a resource-abundant habitat in Illinois have supported the assumption that this species is a monogamous, cooperative breeder, while other studies of prairie voles from a more arid habitat in Kansas have called this assumption into question. We hypothesized that reported differences between these populations represented true intraspecific variation. Patterns of sexual dimorphism in body size, partner preferences and parental contact behaviour were compared in prairie voles from stocks originating in Illinois or Kansas. Both Illinois and Kansas voles showed a strong preference for a familiar partner, which is suggestive of monogamy. Sexual dimorphism in body size was observed in Kansas, but not Illinois voles. Illinois voles displayed significantly higher levels of parental contact behaviour than did voles from Kansas. When animals from Illinois and Kansas were crossed, the expression of parental contact behaviour of the 'hybrid' offspring followed the pattern seen in the population of origin of the sire. Removal of the sire prior to the birth of the litter increased alloparenting in Kansas voles, but removal of the sire was associated with lower levels of alloparenting in Illinois voles. Thus, some traits associated with the social system may show intraspecific variation and can be influenced by the presence or absence of the sire during rearing. 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

Parasites and flower choice of bumblebees.

In a field experiment, we tested whether workers of bumblebees, Bombus pascuorum and B. humilis, parasitized by larvae of conopid flies, Physocephala rufipes and Sicus ferrugineus, differ in their flower choice from unparasitized ones. We collected workers at random in the field and immediately tested them in experimental arenas that offered the choice of a reference plant (red clover, Trifolium pratense) versus a test plant (from five species). The choices of 396 workers were analysed with logistic regression models (logit analysis). We performed all tests in the same field and at the same time where the workers were foraging naturally. On average, the parasitized bees were less likely to visit the reference plant. In addition, they were more likely to switch plant species even after the first visit in the experimental sequence. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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