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PubMed1998

Path integration in dogs.

We studied path integration in dogs, Canis familiaris, required to return to the starting point of L-shaped outward paths in the absence of landmark information. The analysis of the distributions of errors in the return direction and distance showed that the dogs made both systematic and random errors. They tended to overestimate by about 6 degrees the amount of turning required at the end of the outward path to take the correct return direction. Random angular errors were characterized by a standard deviation of about 9 degrees. The dogs also tended to underestimate the correct return distance by about 6%, and random distance errors were characterized by a standard deviation of about 13% of the correct return distance. While random errors are assumed to stem simply from inaccuracies in kinaesthetic and vestibular systems, systematic errors are likely to be generated because path integration is implemented at the neural level through approximate rather than mathematically exact solutions. A path integration model in which the moving animal is assumed to overestimate slightly the inferred motion parallax of the starting point can roughly account for the dogs' directional bias, but not for systematic errors in distance estimation. 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

Barbary macaques categorize shrill barks into two call types.

In response to disturbances in their surroundings, Barbary macaques, Macaca sylvanus, utter a distinctive call, the 'shrill bark'. Differences within this call type correlate with the stimulus eliciting the calling. I tested whether monkeys categorized calls according to the eliciting stimulus and whether their perception of calls coincided with the classification derived from the acoustic analysis. Different playback designs using the habituation-dishabituation paradigm were created in which calls exhibiting varying degrees of acoustic difference were paired. I conducted experiments in two populations of semi-free ranging Barbary macaques. The results suggest that subjects categorized calls according to the eliciting stimulus. In addition, subjects from the population in which the recordings were made were significantly better than subjects from the other population at discriminating between calls with small acoustic differences. The results suggest that call categorization is influenced by experience, mediated by individual knowledge of the caller or common call characteristics within the population. 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

Soldiers effectively defend aphid colonies against predators in the field

Morphologically specialized soldiers occur in more than 50 aphid species in the families Pemphigidae and Hormaphididae. To study the effectiveness of soldiers of the gall-forming aphid, Pemphigus spyrothecae Pass., in protecting their galls against natural levels of predation, we manipulated the proportions of soldiers and non-soldiers in sets of galls still attached to poplar trees in the field. Galls with 50 soldiers and 50 non-soldiers were approximately 10 times less likely to be attacked by predators than galls that contained 100 non-soldier aphids. There were significantly fewer live aphids, and significantly more dead aphids, in galls without soldiers than in galls protected either by soldiers or by being within a bag. There were no significant differences in the survival of aphids in galls protected by soldiers compared with those protected by bagging. The soldiers did not protect the galls against invasion by the cohabiting aphid Chaitophorus leucomelas Koch. These observations provide the first demonstration that soldiers are effective in defence against natural levels of predation under field conditions. 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

Intraspecific responses to distress calls of the pipistrelle bat, Pipistrellus pipistrellus

Responses of the vespertilionid bat Pipistrellus pipistrellus to five recently caught conspecifics confined to a wire-mesh cage, at distances of 50 and 5 m from their roosts, were recorded on 12 separate evenings at three roosts during pregnancy and lactation. When bats were confined 50 m from their roost, an almost 20-fold increase in the number of bats that passed across an open site around the cage was recorded and the strength of response (number of bat passes) increased with time. When the bats were 5 m from the roost there was an 80-fold increase in bat activity above the cage. Playbacks of recorded distress calls produced by single hand-held bats resulted in a more than three-fold increase in bat passes, but the response waned rapidly. The distress calls of recently caught P. pipistrellus were generally similar to those of individuals from the same colony held for longer in captivity, and differences in distress calls between two of the three colonies studied probably reflect differences in the physiological states of recorded bats, rather than the existence of colony-specific vocalizations. Distress calls probably function in attracting conspecifics which perform mobbing behaviour as an anti-predator response. 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

Effects of temperature on anti-predator behaviour in the guppy, Poecilia reticulata.

Warmer environmental temperatures are likely to increase the frequency of predator-prey interactions in ectothermic animals, and therefore might be expected to influence anti-predator behaviour. In a first experiment, groups of recently fed guppies, placed in a novel environment, schooled significantly more closely at 26 degrees than at 22 degreesC. Changes in two of three measures of schooling tendency over time indicated that aggregation increased during the trial periods, probably as a result of increased familiarity within the experimental groups. In a second experiment, pairs of female guppies were tested at 22 degrees and 26 degreesC, with and without predation threat from a confined cichlid. From multifactor analysis of 18 behaviour types, temperature was shown to affect behavioural time budgets profoundly, particularly in the presence of the predator. At the higher temperature, a shift occurred from inactive anti-predator behaviours and minimal foraging activity towards active predator inspection-related behaviours and a much higher level of feeding. Guppies in the warmer water might have been physically able to school more closely as a result of faster swimming ability, or might have used temperature as a cue indicating higher potential predation risk, and aggregated accordingly. The use of temperature as a source of information about the biotic environment is discussed. 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

Certainty of paternity and paternal investment in eastern bluebirds and tree swallows.

Extra-pair paternity is common in many socially monogamous passerine birds with biparental care. Thus, males often invest in offspring to which they are not related. Models of optimal parental investment predict that, under certain assumptions, males should lower their investment in response to reduced certainty of paternity. We attempted to reduce certainty of paternity experimentally in two species, the eastern bluebird, Sialia sialis, and the tree swallow, Tachycineta bicolor, by temporarily removing fertile females on two mornings during egg laying. In both species, experimental males usually attempted to copulate with the female immediately after her reappearance, suggesting that they experienced the absence of their mate as a threat to their paternity. Experimental males copulated at a significantly higher rate than control males. However, contrary to the prediction of the model, experimental males did not invest less than control males in their offspring. There was no difference between experimental and control nests in the proportion of male feeds, male and female feeding rates, nestling growth and nestling condition and size at age 14 days. We argue that females might have restored the males' confidence in paternity after the experiment by soliciting or accepting copulations. Alternatively, males may not reduce their effort, because the fitness costs to their own offspring may outweigh the benefits for the males, at least in populations where females cannot fully compensate for reduced male investment. 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

Proximate costs of fighting in male cichlid fish: the role of injuries and energy metabolism.

While much is known about the functional significance of strategic decisions in animal fighting, relatively little is understood about the mechanisms that underlie the making of those decisions. In mechanistic terms, strategic decisions, such as either escalating a fight or giving up, are made in relation to the proximate costs that opponents inflict (or can potentially inflict) upon one another. These costs include physical injury and also the physiological consequences of engaging in an energetically demanding activity. We studied the role of injury and energy metabolism during fights between male cichlid fish, Tilapia zillii. In relation to injuries incurred during fights, scale loss differed depending on whether the winner was smaller or larger than its opponent; smaller winners inflicted significantly more damage on their opponents than they received, whereas this difference was not apparent in those fights won by the larger fish. In relation to energy metabolism, escalated fighting resulted in a significant depletion of total sugar reserves in the muscle and the liver. It appears that the muscle energy reserves are respired anaerobically, as was evident from the accumulation of lactate in the muscle. Losers had significantly higher levels of muscle lactate than winners. Together, the injury data and the metabolic data suggest that escalated fighting is costly for both winners and losers, but especially so for losers. These data are discussed in relation to models of animal decision making and we conclude that the difference between opponents in the proximate costs incurred during fighting is likely to underlie the making of decisions such as continuing, giving up or escalating the fight. 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

Fighting and assessment in male cichlid fish: the effects of asymmetries in gonadal state and body size.

In fights between animals over limited resources, the larger contestant often wins. Game theoretical models of animal fighting predict that relative body size is assessed during the fight and thus determines fight duration and intensity. In addition, if the contestants differ in the value they place on the disputed resource, this can also influence the outcome, duration and intensity of the fight. We studied territorial fighting in a cichlid fish, Tilapia zillii, in relation to relative body size and gonad weight. Relative gonad weight was a much stronger predictor of fight outcome than relative body size, even when body weight asymmetries were as large as 30%. This suggested that males with large gonads were fighting harder to defend their territory, perhaps because the value of a territory correlates with the gonadal state of the individual. A detailed analysis of mouth wrestling observed during fighting suggested that relative body size is assessed. However, contestants smaller than their opponent often continued to fight in spite of their size disadvantage. Weight disadvantaged winners appeared to fight more fiercely as suggested by a negative correlation between weight asymmetry and the proportion of bites inflicted by the winner. During escalated fighting, winners and losers differed consistently with regard to a behaviour termed mouth locking. Although neither biting nor persistence in mouth locking was related to gonad weight, we propose that the fish may have been assessing asymmetries unrelated to relative body size and possibly more related to levels of cost and the motivation to persist. 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-role reversal and the absence of extra-pair fertilization in Wilson's phalaropes.

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.

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PubMed1998

Lifetime mating opportunities and male mating behaviour in sexually cannibalistic praying mantids.

I examined the number of lifetime mating opportunities and mating behaviour of males in two sexually cannibalistic species, the Mediterranean, Iris oratoria, and bordered, Stagmomantis limbata, praying mantids (Mantodea: Mantidae). Two approaches estimated the number of lifetime mating opportunities: direct observations of intersexual encounters in the field, and an encounter model. I collected behavioural observations, together with ecological data for use in the model, over three field seasons. The ecological data included an assessment of the feeding condition of S. limbata females in nature; the females fed at a level comparable to females maintained on an abundant diet in the laboratory. As for the number of mating opportunities, individual males of both species encountered two or more females, as predicted by the model. I observed no male, however, in more than one copulation. This result could reflect individual variation in the times and places of sexual activity or an actual low number of mating opportunities in the field. Furthermore, a higher percentage of I. oratoria males encountered two or more females than S. limbata males, as the model indicates. Fewer mating opportunities could lead to greater selection upon S. limbata males to ensure paternity at each mating, which can explain the longer copulation times observed for S. limbata males. I considered two hypotheses about male behaviour in light of the number of lifetime encounters with females: male suicide and male reduction of the risk of cannibalism. Behavioural observations do not strongly support male suicide in either species. Certain male behaviours, such as the nature of copulatory position and, in captivity, mounting females from the rear, are consistent with the idea that males behave so as to reduce the probability that they are cannibalized during intersexual encounters. Moreover, male I. oratoria preferentially mount well-fed, fecund females in captivity. Taken together, these results suggest that the prospect of multiple mating opportunities has influenced male mating behaviour over evolutionary time. 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

Determinants of the longevity of socially learned food preferences of Norway rats.

We conducted three experiments to examine variables that might influence the longevity of socially induced food preferences in Norway rats. The duration of social influence on the food choices of 42-day-old rats (1) increased with both increasing numbers of demonstrators and increasing numbers of demonstrations by a single demonstrator, (2) varied with the temporal distribution of demonstrations, but (3) did not vary with the age of demonstrators. The results suggest that a single episode of social learning produces short-term, but not long-term, effects on a Norway rat's food choices. 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

Context determines the sex appeal of male zebra finch song.

We explored the conditions under which playbacks of male zebra finch, Taeniopygia guttata, song induced reproduction in females. In a laboratory study, a rise in faecal oestrogen levels predicted egg laying. Song playbacks by themselves induced a decrease in oestrogen levels. There was an increase in oestrogen levels, followed by egg laying, when the song was broadcast from inside a male model positioned away from the nest. However, this effect occurred only when a second, silent male model was perched on the rim of the nest. If song was broadcast from inside the model perched on the nest, there was no increase in oestrogen levels. We conclude that tests of song efficacy in female songbirds must respect some contextual rules, which are likely to vary between species. Only then does it become possible to ascertain which sounds are most effective in inducing physiological changes leading to reproduction. 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

Evolution of mate-choice copying: a dynamic model.

Mate-choice copying has recently been demonstrated in several species. Two, not mutually exclusive, explanations for copying have been proposed: it reduces sampling costs and/or error of mate choice. In guppies, Poecilia reticulata, and black grouse, Tetrao tetrix, young females seem most likely to copy. Therefore, copying may teach inexperienced females what attractive males look like. I developed a 2-year dynamic model, to investigate under which conditions a mate-copying strategy might first evolve. An original population of pure choosers was assumed, which was invaded by a mutant female, able to copy during her first mating season, thereby instantly improving her ability to assess male quality. Alternatively, she could either wait and learn by observing males, just as non-copiers may do, but incurring some time costs, or choose, relying on her own abilities. The degree to which copying occurred among these mutant, young, inexperienced females increased with an increasing proportion of old, experienced females in the population, and with decreasing time left until the end of the season. The model demonstrates that mate-choice copying may evolve, when young females are poor at discrimination and need to learn what high-quality males look like. Male quality proved to be unimportant for copying to evolve, as long as there are sufficient differences in quality for mate choice to be meaningful. As with previous models, time constraints are an important assumption for copying to be advantageous over non-copying. 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

Differences in begging behaviour between barn swallow, Hirundo rustica, nestlings.

Recent models of parent-offspring communication suggest that nestling begging reliably reflects food requirements, and therefore should increase with nestling need. Need may be affected by short-term variations in hunger, as well as by long-term factors such as relative size, growth rate and body condition. In the present study, the brood sizes of barn swallows were manipulated to create differences in nestling growth rate and body condition. The extent to which begging behaviour reflects these differences was tested. I measured begging behaviour by removing nestlings from the nest for three laboratory tests in which temporal variations in hunger were controlled, and four target nestlings (small and large, from small and large broods) were tested simultaneously. Small nestlings and nestlings from large broods had lower growth rates and poorer body condition than large nestlings and nestlings from small broods, respectively. Begging was positively correlated with both short- and long-term determinants of need. However, when nestlings grew older (second test), the trend was mixed, mainly because begging levels dropped in the neediest nestling category (small nestlings from large broods). After nestlings had been exchanged between broods for 24 h, small nestlings from large broods improved their growth rate and body condition, but still begged less than expected from their long-term need. The results suggest that nestling begging strategies vary with brood size and with nestling rank. However, these variations may reflect not only long-term need, but also nestling response to past experience or to variations in the cost and effectiveness of their begging efforts. 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

Position of operant costs affects visits to resources by laboratory mice, Mus musculus.

A recently recognized problem in consumer demand studies has been whether subjects should be allowed free exit from a resource cage that they have paid to enter. If decisions related to switches in behaviour are affected by the position of operant costs, then demand studies that offer free return routes from resources may result in different behavioural organization from those that split the same payment between entry to and exit from resources. We aimed to assess the extent of any such differences by comparing results from four operant treatments. The closed economy treatments differed in the position of the operant costs required to allow a mouse to enter a food cage and then return to the home cage. Three of the treatments carried the same overall cost: a full cost to enter the food cage; a full cost to leave the food cage; or with the cost split equally between entering and leaving the food cage. The fourth treatment imposed a half cost to enter the food cage but allowed free exit. The mice spent longer in whichever cage carried an exit cost. The most even distribution of their time was with the split cost. The number of visits undertaken depended on the magnitude of the cost, and on the resource cage for which the mice were paying. Significantly more visits were made when payment was required to enter the home cage. The mice responded to the immediate costs of entry to the cages, rather than the overall costs of a round trip. The lower number of visits made under higher costs was compensated for by the greater duration of those visits. 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 changing trade-off between food finding and food stealing in juvenile oystercatchers

When juvenile oystercatchers, Haematopus ostralegus, first arrived on the wintering grounds in August and September, they regularly stole mussels, Mytilus edulis, from other, mainly older, oystercatchers. By October, however, juveniles stole far fewer mussels and found almost all their mussels independently for themselves on the mussel bed. Although stealing a mussel was always less profitable than taking a mussel from the mussel bed, a simple rate-maximizing optimality model showed that, in August and September, juveniles increased both their net and gross rates of energy intake by stealing because they were rather inefficient at foraging for themselves. By October, their greater efficiency at finding good quality mussels, combined with the increased resistance of potential victims to kleptoparasitic attacks, resulted in higher intake rates if juveniles stopped stealing mussels and took mussels only from the mussel bed. 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

Non-genetic benefits of mate choice: fecundity enhancement and sexy sons.

I compared reproductive success (lifetime number of fertilized eggs) as a function of mate choice among females of the stink bug, Nezara viridula L. (Hemiptera: Pentatomidae). 'Choosing' (C) females were placed with one of two males on alternate days. CI females chose between inexperienced males while CR females chose between males previously rejected by CI females. 'Non-choosing' (N) females were placed with the same male every day. Non-choosing NI, NR and NA females encountered, respectively, inexperienced males, previously rejected males, or previously accepted and mated males. Reproductive success was highest for CI females, showing direct selection on mate preferences. Reproductive success did not differ between CR and NR females, indicating that male quality, not the act of choosing a mate, affects fitness. CI females preferred males with longer antennae and their fecundity (lifetime number of eggs) was correlated with male antenna length, consistent with antenna length as an indicator of male ability to transfer nutritive sperm produced in paired harlequin lobes of the testes. Harlequin lobes were smaller in rejected than chosen males. In second-generation mate choice trials, sons of NR females competed well against sons of NA females but not against sons of CI females. This suggests that non-genetic paternal contributions that decline with prior mating account for the attractiveness of sons because sons of CI and NA females shared the same fathers. Sons experiencing mating success came from larger eggs and egg size was greatest for CI females, perhaps as a consequence of paternal nutritional contributions. 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 choice and mate competition influence male body size in Japanese medaka.

A sexual size dimorphism usually occurs when size-dependent reproductive advantages exist in only one sex. Studies on Japanese medaka, Oryzias latipes, have demonstrated reproductive size advantages in females but not in males, even though males and females are similar in body size. We conducted mate-choice and mate-copying tests in which a female could first associate with, then mate with, either a large (>/=1 sd+X standard length) or a small male (</=1 sd-X standard length). Large males obtained a mating advantage in both tests, and both mate choice and mate competition influenced their mating success. In the majority of trials, females associated with large males. Association preferences of females corresponded to their mating preferences when mate competition between males was weak; however, when mate competition was strong, large males obtained almost every mating regardless of female association preference. Preference for large males may provide females with a reproductive advantage if males mate multiply because small males become sperm-depleted sooner than large males. We found no indication that females copied the mating decisions of other females. Repeatability of female mating preference was low, not because females mated at random with respect to male size, but because most females consistently preferred large males. We also conducted mating tests at four density levels and found that large males maintained their mating advantage relative to small males at all densities. Thus, male and female medaka may be similar in body size because large size provides a fecundity advantage for females, as demonstrated in previous studies, and large size provides a mating advantage for males, as demonstrated in our study. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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