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PubMed1998

Finding a dominance order most consistent with a linear hierarchy: a new procedure and review.

A procedure for ordering a set of individuals into a linear or near-linear dominance hierarchy is presented. Two criteria are used in a prioritized way in reorganizing the dominance matrix to find an order that is most consistent with a linear hierarchy: first, minimization of the numbers of inconsistencies and, second, minimization of the total strength of the inconsistencies. The linear ordering procedure, which involves an iterative algorithm based on a generalized swapping rule, is feasible for matrices of up to 80 individuals. The procedure can be applied to any dominance matrix, since it does not make any assumptions about the form of the probabilities of winning and losing. The only assumption is the existence of a linear or near-linear hierarchy which can be verified by means of a linearity test. A review of existing ranking methods is presented and these are compared with the proposed method. 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

Beaver response to recurrent alien scents: scent fence or scent match?

By repeatedly presenting an alien scent to territory-owning beavers, Castor canadensis, we tested two competing hypotheses about the function of scent marking: scent fence and scent matching. The scent-fence hypothesis predicts that territory owners should respond increasingly strongly over time towards a recurrent alien scent because of the ineffectiveness of previous responses. The scent-matching hypothesis predicts that the intensity of response should be the same or decrease because, without the presence of the intruding signaller coupled with the chemical signal, the presence of the scent itself does not advertise the ownership of a territory. The response level of resident beaver families was stable to strangers' anal gland secretions (AGSs) and decreased to strangers' castoreum during a period of 6 days. These results support the scent-matching hypothesis but not the scent-fence 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

Future value and patch choice in least chipmunks.

Animals subsisting on non-renewing patches confront a unique valuation problem, in which the objective value of a patch is inversely related to the amount already harvested. We investigated whether the subjective patch valuations of captive least chipmunks, Tamias minimus, reflected this environmental constraint as they foraged for buried patches of seeds. On the day following partial depletion of two patches, chipmunks spontaneously selected the least depleted patch, despite having no direct information about its former or present value. These findings held across experiments in which the order and extent of patch depletion were under the forager's control or experimental control. The animals consistently chose sites from which they had taken the fewest items, despite experiencing no difference in relative capture rate, suggesting that they discounted patch value on the basis of amount harvested or harvest time. Furthermore, the animals refused to return to patches they had completely depleted, and when induced to re-dig depleted patches by placing seeds above them, the animals chose randomly despite a three-fold difference in the number of items previously taken from each, suggesting that they disregarded rewards taken, attending only to the amount remaining. Subsequent experiments showed that chipmunks can take past reward history into account. When we refilled previously depleted patches and induced chipmunks to re-dig and deplete them again, they treated the patches as renewable types and represented their value in terms of the amount removed, not the amount left. Thus, the assessment mechanism of least chipmunks is facultative: they expect that patches will not replenish, but are prepared for exceptions. 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 recognition and mate choice by male western toads, Bufo boreas.

In field-based choice experiments, we examined sex recognition and mate choice in male western toads, Bufo boreas. When given a simultaneous choice between a male and a female of equal size, males did not discriminate between the sexes and attempted to amplex a male or a female with equal frequency. When a test male clasped a stimulus male, the stimulus male uttered a release call that caused the test male to release the stimulus male. Male-male amplexus never lasted more than 3 s, but male-female amplexus was tenacious and prolonged. Furthermore, males discriminated between gravid females that differed in body size, choosing larger gravid females over smaller ones, but they did not discriminate between gravid females or non-gravid females of equal size. In choice tests that excluded chemical cues, males jumped more frequently towards large females than small ones. Given that females are significantly larger than males, selecting larger individuals as potential mates increases the probability that males amplex with a female. 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 referents and acoustic similarity: field playback experiments with rhesus monkeys.

Rhesus monkeys, Macaca mulatta, on the island of Cayo Santiago, Puerto Rico produce one or more of five acoustically distinctive calls when they find food. Three of these calls ('warbles', 'harmonic arches' and 'chirps') are produced by individuals finding high-quality, rare food items, whereas the other two calls ('coos' and 'grunts') are produced upon encountering lower-quality, common food items, and in non-food contexts as well. To determine how rhesus classify such acoustic variation, I conducted habituation experiments using a subset of the five call types. I designed experiments to reveal whether classification is based primarily on acoustic features or on the basis of a call's functional referent; caller identity was held constant within sessions. Habituation to 'warbles' transferred to 'harmonic arches', and vice versa. Thus, although these two calls are acoustically distinctive, they appeared to be perceptually clustered into one category based on referential similarities. In contrast, habituation to 'grunts' was followed by dishabituation to 'warbles' or 'harmonic arches', and habituation to 'warbles' or 'harmonic arches' was followed by dishabituation to 'grunts'. Dishabituation could be due to acoustic or referential differences. Significantly, the magnitude of the dishabituating response was asymmetric and depended upon the call type used in the habituation series. Thus, when subjects were habituated to 'grunts', they responded significantly more to tests of 'warbles' or 'harmonic arches' than when the sequence was reversed. These results suggest that for rhesus monkey food-associated calls, referential differences carry more weight during perceptual classification than do acoustical differences. 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

Prey availability and selective foraging in shorebirds.

Accurate measurements of prey availability are vital to our understanding of foraging behaviour, particularly prey selectivity. In the present study, observations of shorebirds foraging for fiddler crabs on intertidal mudflats demonstrate that prey availability depends both on the temporal variation in crab activity and on the crabs' responses to the presence of foraging shorebirds. Our results suggest that measurements of prey availability that do not specifically account for prey activity patterns and their responses to predators are neccessarily inaccurate. Furthermore, our results also show that tests for foraging selectivity are extremely sensitive to the way in which prey availability is measured and can even indicate active prey selectivity when more accurate measures of prey availability show predators to be non-selective. Because inaccurate measures of food resources greatly reduce our ability to detect food preferences, greater care must be taken to account for prey activity patterns and their responses to predators in measurements of prey availability. 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

Dominance between booby nestlings involves winner and loser effects.

Two-chick broods of the blue-footed booby, Sula nebouxii, ordinarily exhibit stable dominance-subordinance, with the senior (first-hatched) chick habitually aggressive and the junior one habitually submissive (Nelson 1978, The Sulidae: Gannets and Boobies. London: Oxford University Press). But are both the subordinate and the dominant chick affected in their agonistic tendencies by early social experience? To answer this, we permanently paired subordinate and dominant chicks, 2-3 weeks old, with singletons (chicks lacking experience with a nestmate) by cross-fostering. During the first 4 h after pairing, subordinate chicks were seven times less aggressive than singletons and twice as likely to be submissive; dominant chicks were six times as aggressive as singletons. Although most subordinates consistently lost agonistic encounters during the first 10 days after pairing, the proportion of dominants that won decreased progressively until, by day 6, only about half of dominant chicks were winning. Early social experience has a strong but reversable training effect on both subordinates and dominants. Training as a subordinate showed more persistent effects than training as a dominant, possibly in part because our testing situation perpetuated subordinate training and counteracted dominant training. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

The effect of quality and availability of foraging materials on feather pecking in laying hen chicks.

Feather pecking resulting in feather damage, injuries and mortality causes severe welfare problems in laying hens. In the present study, we tested whether there is an inverse relationship between feather pecking and foraging behaviour (exploratory and manipulative behaviour away from the feeder). Forty-eight groups of 30 or 31 chicks, Gallus gallus domesticus, were reared in pens and provided with different types of foraging material. Feather pecking and foraging behaviour were quantified when the chicks were 4 and 5 weeks of age. In experiment 1, chicks with access to long-cut straw showed more foraging behaviour and less feather pecking than chicks that were provided with the same straw but in shredded form. On the other hand, there was no difference in foraging behaviour and feather pecking between chicks reared with access to long-cut straw and polystyrene blocks. In experiment 2, the importance of the form of the foraging material was confirmed. Chicks provided with polystyrene blocks performed more foraging behaviour and less feather pecking than chicks with access to polystyrene beads. The provision of an area with a layer of wood-shavings to promote scratching behaviour had no significant effect, however, on the incidence of feather pecking. In experiment 3, polystyrene blocks and beads were offered during the whole day or only in the morning. Both the quality and the availability of the foraging materials had a significant effect on foraging behaviour and a significant but opposite effect on feather pecking. Focal animal observations showed that the chicks performed different types of foraging behaviour at polystyrene blocks and beads. This suggests that not only the quantity but also the quality of foraging behaviour elicited by a given material may be important to prevent the development of feather pecking. Feather pecking should thus be considered as redirected foraging 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

Mate guarding and risk assessment by male mountain baboons during inter-troop encounters.

Aggressive herding of females is a frequent but not invariant response by male savannah baboons, Papio cynocephalus, to encounters with other troops. While males in some troops are consistently more likely to herd than those in others, not all inter-troop encounters result in herding, even within particular troops. This suggests that males assess the risk of male invasion posed by each encounter and respond accordingly. We used data from baboon troops in the Drakensberg mountains to determine the rules males follow in deciding whether to herd. Consistent differences between troops were explained only by the adult sex ratio. Males were more likely to herd if the sex ratio of their own troop was female biased, a finding that is concordant with the observation that males are more likely to immigrate into troops where the sex ratio is more female biased than the population average. Differences within troops were a consequence only of encounter distance, with herding being more likely at closer distances. We found a negative correlation between the angle of approach to the other troop and the subsequent angle of deflection. We interpret this to mean that herding functions to increase the distance between the interacting troops, thereby curtailing opportunities for strange males to inspect the troop and determine its sex ratio. In this way, possibly unlike those in other populations, the decision rules of these male baboons are geared to protecting longer-term reproductive prospects. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1997 The Association for the Study of Animal Behaviour.

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PubMed1998

Behavioural and hormonal responses of the pied flycatcher to environmental stressors.

I investigated the effects of high plasma levels of corticosterone in male pied flycatchers, Ficedula hypoleuca, during the period of territorial establishment and the nestling period. In a second experiment males were exposed to a territorial intruder, a great spotted woodpecker model and a weasel model during the nest-building and nestling periods and their behavioural and hormonal reactions studied. Males were also exposed to handling stress (hormonal study) during these periods. During the period of territorial establishment, corticosterone-treated males, as well as control males, abandoned the territory in which they were captured; however, males in both groups very soon established new territories. During the nestling period, corticosterone-treated males, but not control males, abandoned their nests. During the nest-building period, intact males frequently attacked the territorial intruder but corticosterone-treated males never did; the woodpecker was only rarely attacked by intact males, and the weasel never. During the nestling period, the weasel was not attacked and territorial intruders only rarely; but woodpeckers were frequently attacked. With the progress of the breeding season, male flycatchers significantly reduced their sensitivity, in terms of the adrenocortical response, to all stressors tested. During the nest-building period, corticosterone levels were significantly higher in males exposed to handling, a weasel and a territorial intruder than in unmanipulated males; corticosterone levels in males exposed to a woodpecker did not differ from those in unmanipulated males; and testosterone levels were significantly elevated in males exposed to a woodpecker and to an intruder, but were reduced in males exposed to a weasel. Handling did not affect the testosterone level. During the nestling period, all groups showed low testosterone levels, and only exposure to a weasel and to handling increased corticosterone levels significantly. The results indicate that environmentally induced changes in testosterone and corticosterone secretion can be affected independently from one another, and that there are ecological bases for the differentiated hormonal responses to stress. 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

Direct homing behaviour in the ant Tetramorium caespitum (Formicidae, Myrmicinae).

Direct homing refers to the behaviour whereby an ant with food runs in an almost straight line to the nest. We determined whether non-polarized light acts as a directional cue in the direct homing behaviour of the grass ant, Tetramorium caespitum. We carried out tests (1) under a blue sky or in total overcast conditions in the field, and (2) with a view of the sun or with a non-polarized light within a box in the laboratory. The ants' paths were recorded, and then analysed by means of circular and linear statistics. Ant workers with food were able to home directly under a blue sky, under totally overcast skies, and even under non-polarized lighting. In a fifth test we displaced the ants at the beginning of the homing trip; they returned to the presumed nest location along a path that ran parallel to the true homing vector, as if they had not been displaced. The results suggest that the ants home by dead reckoning, that is, they can measure directional changes and distances travelled during the outward trip, and integrate them into a mean home vector for direct homing depending on an external light-based reference system, that is, either the polarized skylight pattern or non-polarized lighting. 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 energetic cost of begging behaviour in nestling house wrens.

This study presents data relevant to the hypothesis that the energy expenditure associated with begging influences the signalling of need by nestling birds. We used open-circuit respirometry to measure the energy costs of resting, begging and non-begging activities in nestling house wrens, Troglodytes aedon, ranging in age from 1 to 11 days post-hatching. Across all ages, begging caused a 27% increase in metabolism above resting rates. The metabolic rate during begging was not related to begging vigour. However, more vigorous begs were longer and so required a greater total energy expenditure. We analysed videotapes of broods for nestling behavioural time budgets which were combined with the metabolic data and data on growth at different ages to generate daily energy budgets. Over a 24-h period, the cumulative energy allocated to begging was slight, ranging from 0.02% of the energy budget in younger nestlings (3 days old) to 0.22% in older ones (10 days old). In contrast, non-begging movements accounted for 2 and 9% of the daily energy budget of younger and older nestlings, respectively. Relative to daily growth, the energy allocated to begging was equivalent to 0.05% (younger nestlings) and 2.3% (older nestlings) of the energy sequestered in new tissue, whereas the values for non-begging activities were 5.1 and 96.8%, respectively. These results suggest that the energetic cost of begging is not likely to have a substantial role in influencing communication of need by nestlings. 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 influence of tail autotomy on agonistic behaviour in a territorial salamander.

Assessment of potentially asymmetrical characters (such as fighting ability and resident advantage) is often important in determining the outcome of agonistic interactions. Loss of body parts, a predator defence mechanism used by many animals, may lead to a reduction in fighting ability and may be easily assessed by competitors. We investigated the influence of tail loss on the expression of agonistic behaviour in the territorial red-backed salamander, Plethodon cinereus. Residents and intruders were matched for body size, and pairs were tested in all combinations of tailed or tailless residents with tailed or tailless intruders. Neither residents nor intruders altered their behaviour based on their own tail condition, but they did alter their behaviour based on the tail condition of their opponents. Intruders showed more aggression or less submission towards tailless residents than towards tailed residents. When contests were between residents and intruders of the same tail condition (both tailed or tailless), intruders were more aggressive towards residents when both were tailless than when both were tailed, indicating that tail loss does not directly hamper aggressive displays. In contests where the asymmetry between residents and intruders was small (based on tail condition and residency status), intruders showed more aggression and less submission than in contests where the asymmetry was large. Residents did not differ in their behaviour for most comparisons. Thus, for intruders, the tail condition of residents is an important determinant of agonistic behaviour displayed in territorial contests. For residents, factors other than tail condition (such as resource value) may be more likely to influence their 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

Greater spear-nosed bats discriminate group mates by vocalizations.

Individuals often benefit from identifying their prospective social partners. Some species that live in stable social groups discriminate between their group mates and others, basing this distinction on calls that differ among individuals. Vocalizations that differ between social groups are much less common, and few studies have demonstrated that animals use group-distinctive calls to identify group mates. Female greater spear-nosed bats, Phyllostomus hastatus, live in stable groups of unrelated bats and give audible frequency, broadband calls termed screech calls when departing from the roost and at foraging sites. Previous field observations suggested that bats give screech calls to coordinate movements among group members. Prior acoustic analyses of 12 acoustic variables found group differences but not individual differences. Here, we use the same acoustic variables to compare calls from three cave colonies, and find that calls differ between caves. We also report results from field and laboratory playback experiments designed to test whether bats use acoustic differences to discriminate calls from different colonies, groups or individuals. Results from field playbacks indicate that response depends on the cave of origin, indicating that bats can discriminate among calls from different caves. This discrimination ability may be based, in part, on whether calls are familiar or unfamiliar to the listening bats. Laboratory playbacks demonstrate that bats discriminate calls given by their group mates from calls given by other bats from the same cave irrespective of familiarity. However, these experiments provide no evidence that bats discriminate among individuals. Previous field work indicates that females that forage with social group mates may benefit from shared information about food or mutual defence of feeding sites. Indicating group membership is essential, since these benefits appear to be restricted to group mates. 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

Estimating ancestral states of a communicative display: a comparative study of Cyclura rock iguanas.

In this study we describe the signature headbob displays of seven of the eight extant species of Cyclura iguanas using data collected from the field and from captive animals. We used phylogenetic comparative methods to estimate the ancestral states of several measures of the headbob displays, including number of headbobs and the duration of headbobs and inter-bob pauses. Divergence in the headbob display among species has been substantial, with some major changes occurring within only a few (about six) generations. Otherwise, results are consistent with those obtained previously for other lizards which suggest that there is an evolutionary limit on the total duration of headbob displays. Differences in the results obtained using different phylogenetic methods suggest that although estimates of ancestral states are reasonably robust to violations of evolutionary assumptions, we cannot determine the standard errors of those ancestral phenotypes accurately without more detailed information about the types of forces (e.g. selection, drift) underlying evolutionary change in these traits. In particular, within-species variation had a substantial impact on the standard errors of estimated ancestral states, and should be included in such estimations whenever possible. Finally, our results emphasize the importance of conserving behavioural as well as genetic diversity in trying to preserve endangered species for possible reintroduction into the wild. 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

Temporal manipulation of ejaculate components by newly fertilized Drosophila melanogaster females.

Observations of newly mated Drosophila melanogaster females suggest that females control the times at which components of the ejaculate cause behavioural and physiological changes characteristic of fertilized females. Females that were assayed immediately after they mated elicited as much courtship as they did when they were virgins, but were unreceptive to copulation. Within a few minutes of when they disengaged from copulation, most females performed ovipositor extrusion, which has been classified as a rejection behaviour, in response to courting males or males that had previously performed courtship. Most females that were assayed immediately after mating had already ovulated. The females, however, do not begin to lay eggs until 4-6 h after mating, at which time they elicit very little courtship (Scott & Richmond 1985, Anim. Behav., 33, 817-824). Our observations suggest that neither ovipositor extrusion nor male-synthesized pheromones that are transferred to females' cuticles during copulation inhibit males' courtship of newly fertilized females. Thus, males cannot determine that newly fertilized females are unreceptive to copulation. These observations also indicate that the failure of newly fertilized females to mate with males is not a consequence of the females' inability to elicit vigorous courtship. 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

Moult speed predicts pairing success in male harlequin ducks.

The bright plumage of male ducks in sexually dichromatic species is thought to have evolved through intense sexual selection. This study examined the relationship between the timing and speed of moult into this bright plumage and subsequent mating success of male harlequin ducks, Histrionicus histrionicus. Males that moulted relatively slowly had a lower chance of establishing a pair bond than others. The timing of moult was unrelated to whether a male obtained a mate. Moult speed and timing were not correlated within individual males, but were significantly repeatable in individual males over 2 years. Moult speed probably reflects the condition of males, whereas timing of moult is more likely to be related to the distance to an individual's breeding area, which determines the timing of arrival to the moulting grounds. In waterfowl species that have been studied, males usually form dominance hierarchies before pairing and females tend to choose dominant males. We suggest that male harlequin ducks that moult slowly are poor-quality individuals, which are relegated to subordinate status and are unlikely to attract a mate the following autumn. 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

Feeding interruptions, diurnal mass changes and daily routines of behaviour in the zebra finch

We investigated daily changes in body mass, fat reserves and crop contents, and diurnal organization of behaviour, in the zebra finch, Taeniopygia guttata, in relation to experimental manipulations of food availability. Diurnal mass change and the organization of foraging behaviour during the day were in general agreement with recent theoretical predictions. Foraging intensity, and hence rate of mass gain, was most rapid immediately after dawn and before dusk. The experimental birds did not alter either mean body mass or their diurnal mass trajectory after a period of 2 weeks when food was made unavailable for 2 h a day at unpredictable times. Instead, they changed their allocation of time to different activities during the day, decreasing the mean amount of time spent locomoting and increasing the mean amount of time spent inactive over the day. Thus, contrary to a number of recent studies on different species, zebra finches appear to respond to unpredictable interruptions in food supply by reducing energetically expensive activities rather than adjusting their levels of energy reserves. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

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