Responses of a plethodontid salamander to conspecific and congeneric intruders

After inhabiting their home sites for a few days, both males and females of the salamander Desmognathus monticola directed agonistic behaviour toward intruding salamanders. Resident D. monticola were significantly more aggressive toward D. fuscus intruders than toward conspecific ones, although both conspecific and congeneric intruders were frequently attacked. Responses of D. monticola residents were independent of sex, and no difference was found in the behaviour of residents toward conspecific male and female intruders. Small D. fuscus intruders were attacked and injured more frequently than similar-sized D. monticola intruders and, in general, smaller-sized salamanders were the victims of aggressive attacks more frequently than larger ones. The proportions of bites on the head and tail of intruders were similar, although injuries were much more frequent to the tail than to the head. This species-related and size-related agonistic behaviour may be functional in maintaining the spatial distribution of species in communities of Desmognathus salamanders.     

Effects of resource distribution on activity and territory defence in house mice, Mus domesticus

How much an animal invests in defending a territory depends, in part, on the quality, quantity and distribution of resources, but do animals target their investment in defence within the territory according to the location of different resources? We examined whether wild-caught male and female house mice increased aggression towards intruders of the same or opposite sex when in areas containing their food/water or nest site. Pairs of resident mice were established in enclosures consisting of two areas. In split enclosures, food and water were in one area and a nest site in the other, while in clumped enclosures all resources were in one area with no resources in the other. Residents of both sexes were quicker to attack intruders, and were more aggressive, in areas containing resources than in an area containing no resources. There was no difference in aggression between areas containing food/water, a nest site or both. The effect of resources on territorial defence was due largely to changes in aggression against intruders of the opposite sex. Residents, especially males, attacked intruders of their own sex more than those of the opposite sex. This bias was much stronger when no resources were present, owing to low aggression against opposite-sex intruders in the absence of resources. There were no differences in intruder aggression, and the relative size of the intruder (heavier or lighter than the resident) had no effect on resident aggression. Residents also spent less time out of their nest in clumped enclosures owing to low activity in the nonresource area.     

The social organization and territoriality of short-tailed shrew (Blarina brevicauda) populations in old-field habitats

The social organization of short-tailed shrew (Blarina brevicauda) populations was studied using field and laboratory experiments and observation of a shrew population inside a large enclosure. Short-tailed shrew populations contain resident and nomadic components. Residents occupy small stationary areas at high prey densities and larger areas that are shifted frequently at low prey densities. Areas occupied by residents overlap minimally in winter, non-breeding populations. In summer breeding populations areas occupied by residents of the same sex do not overlap while those of residents of opposite sexes may overlap. Residents defend the area occupied against conspecifics. Scent markings along boundaries appear to maintain the spatial distribution of residents and deter intrusions by nomadic shrews. During encounters vocalizations function as offensive threats, and attacks and chases follow if the intruding shrew does not retreat. Visual communication appears to be less important than chemical and vocal communication in the defence of the area occupied. These data suggest that Blarina is a solitary territorial species.     

Residency Duration and Shelter Quality Influence Vibratory Signalling Displays in A Territorial Caterpillar

Residents are more likely to win territorial disputes than intruders. One explanation for this prior resident advantage is that residents place a higher value on the resource and are therefore more motivated to win. Although value asymmetry models of animal contests often assume that contestants use information about resource value, information on the proximate cues affecting territorial behaviour is often lacking. We use a simple model system – territorial behaviour in the masked birch caterpillar (Drepana arcuata) to identify factors that affect territorial behaviour. Late instar caterpillars occupy solitary silken leaf shelters, which they defend against wandering conspecifics with a vibratory display. We evaluated how a caterpillar identifies itself as the owner and the factors that influence a resident's motivation to signal. To do so, we conducted three experiments between size‐matched residents and intruders to assess how residency duration and shelter quality independently affected territorial displays during the early stages of a contest. Experiment 1 (Time Exp.) demonstrated that resident signalling rates increase with increased duration on the leaf prior to introducing the intruder. Residents also signal more than intruders after residency periods of 1–3 min and longer, demonstrating that residents gather information about resource value shortly after occupying a leaf. Experiment 2 (Squatter Exp.) aimed to disentangle the effects of time on the leaf and silk accumulation. Squatters (individuals in a shelter made by another) placed for 1–3 min on a leaf containing a full silk shelter signalled more to intruders than did caterpillars placed on a fresh leaf for 1–3 min. Experiment 3 (Shelter Removal Exp.) showed that residents whose shelters had been removed signal less than those occupying an intact shelter, despite an equal length of time investing in them. Our experiment is the first to covary both prior residency duration and territory quality, and we find that the motivation of caterpillars to signal is a function of both of these attributes.     

Success in territorial defence by male tarantula hawk wasps Hemipepsis ustulata: the role of residency

1. Some male tarantula hawk wasps Hemipepsis ustulata defend landmark shrubs growing on mountain tops, while others only visit a succession of territory sites, generally fleeing from territorial males. To determine whether residency asymmetries contribute to the short duration of most interactions between territorial males and visiting intruders, established residents were held captive for varying periods while other males replaced them at their territories.
2. Replacement males immediately assumed resident status and began to defend the shrubs and trees with success against non-resident intruders, many of which were larger. Interactions between replacements and non-resident intruders rarely escalated into pursuits leading to ascending flights.
3. In contrast, when the original resident was released, its subsequent encounter with the replacement male almost always resulted in one or more ascending flights, even when the replacement had been on territory for less than 10 min. The longer the period of territory occupation by replacements, the longer on average the interaction and the more ascending flights, showing that the duration of time on a territory affects male motivation to defend the site. Despite strong resistance from long-term replacements, however, returning residents almost always regained their territories.
4. The strong residency effect in H. ustulata may be an adaptive proximate control mechanism for male behaviour that arises because established residents typically have high resource holding power, which makes them difficult to displace.     

Hilltopping Behavior of Polistes commanchus navajoe (Hymenoptera: Vespidae)

Males of the paper wasp Polistes commanchus aggregate in large numbers on hilltops in central and southeastern Arizona where individual males defend perch sites on shrubs, trees or rocks. Residents chase intruders away quickly and exhibit strong site fidelity at their perches. Takeovers are rare as are prolonged battles for possession of a site. Males have only weak preferences for peaktop perch sites as opposed to those lower on hillsides, and a similarly weak preference for perches in shrubs as opposed to those on rocks. Receptive females appear occasionally at the male aggregation sites to mate with perch holders. The relatively weak territoriality exhibited by P. commanchus may stem in part from the high density of males at peaktops and the correspondingly high rate of interactions. The evolution of hilltopping in a species whose reproductive females are clumped spatially at nest sites poses a puzzle for the ecological analysis of mating systems.     

Reproductive behavior of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

The reproductive behavior of the dragonfly,Orthetrum japonicum, is described. Behavioral processes of turnover of territorial males, simultaneous guarding of 2 females by a male, and copulation by non-territorial males are described. The males with longer hind wings won the territorial conflicts more frequently. The total duration of territorial residence of a given male was correlated with the number of his matings, but not correlated with the length of his abdomen or hind wings. The territorial site with the lower degree of vegetation cover was occupied by males more consistently. Males in more consistently occupied territorial sites did not have longer abdomen and hind wings than males in less consistently occupied sites. The territorial site where the larger number of copulations was observed was not occupied more consistently. Selection episode analysis using the method of Arnold & Wade (1984a, b) showed that direct selection on the hind wing length favored the short wing and that direct selection on the abdomen length favored the long abdomen during mating.     

Selection of diurnal refuges by the nocturnal squirrelfish, <Emphasis Type="Italic">Holocentrus rufus</Emphasis>

We examined the diurnal refuges occupied by the nocturnal squirrelfish, Holocentrus rufus, to describe refuges and the behavior associated with their use and to determine which, if any, refuge characteristics were selected. We tagged 21 H. rufus on two sites on a fringing reef in Barbados, West Indies, identified the refuges they used (n = 57), measured ten characteristics of each refuge and the surrounding microhabitat, and monitored their refuge use for 4 weeks. To evaluate refuge selection, we measured the same characteristics on a comparable number of unused potential refuges (n = 67) on the same reefs and used classification tree models to determine which characteristics separated used from unused refuges. Each fish used 1–9 refuges, which did not overlap among individuals and were defended against intrusion by conspecifics and some heterospecifics. Fish with more than one refuge frequently moved among them. There was strong site fidelity with no immigration of untagged fish or emigration of tagged fish on either reef during the study period and no additional refuges being occupied over the 4-week period. Refuges were primarily holes, open at one or two ends, which varied in size, distance from the reef edge, entrance orientation, and vertical relief at the entrance. Holes used as refuges differed significantly from unused holes mainly in characteristics related to the vertical position of their entrance, but the classification tree models differed for the two sites. This study provides the first detailed information on characteristics of daytime refuges used by a nocturnally active reef fish and the first evidence of selectivity of refuges. It suggests that the abundance and characteristics of holes on reefs could influence the density of H. rufus on natural reefs.     

Effects of information asymmetries in contests between net spinning caddis larvae (Plectrocnemia conspersa)

Summary During five days prior to the introduction of potential intruder larvae, residents were treated in four different ways. In one treatment the residents were unfed and their nets were taken away at daily intervals. Nets were not taken away in the other treatments, and residents were unfed, fed 2 or 4 items per day, respectively. Small intruders were equally successful as large ones in taking over low energy demanding nets of unfed, disturbed residents whose nets were taken away daily. Take overs of high ranked nets of larvae fed four prey items per day were mainly performed by large intruders. Low investment nets of unfed, disturbed resident larvae were often taken over during the first day upon the implantation of intruder larvae. On the contrary, unfed undisturbed larvae defending a five times as energy demanding net only suffered a slight net loss. Nets of unfed, undisturbed larvae were taken over somewhat more often than those from residents fed two prey per day. The results indicate prior treatment to inform these three resident categories of their resource values. Owners of high ranked nets fed two prey per day were most keen on defence during the first day upon introduction of potential intruders. Residents fed four prey per day suffered from a significantly higher number of take overs during the first day compared with larvae only fed two prey per day. The residents fed four prey per day stored some of the food in their nets making this resource more valuable also to intruders. After five days the number of take overs was about the same irrespective of previous treatment.     

Structural complexity of territories: preference, use of space and defence in commensal house mice, Mus domesticus

Previous studies suggest the physical structure of a habitat has profound effects on intraspecific competition and spacing behaviour among small mammals. We compared habitat preferences and the exploratory behaviour and aggressive territorial defence of male house mice in three types of enclosure differing only in their degree of structural complexity. Each enclosure contained a nestbox placed in one corner, a central food hopper and 10 house bricks. The bricks were either placed around the outer walls (open enclosures), lined up across the middle (wall enclosures) or scattered separately across the floor (complex enclosures). In pairwise choice tests, mice showed a strong preference for wall or complex enclosures over open enclosures but no preference between wall and complex enclosures. They were more active throughout the enclosure with complex structuring and stayed near the side walls in open enclosures. Residents in open enclosures initially showed a lower rate of attack and duration of pursuit when faced with an intruder but not when faced with a second intruder. In complex enclosures, nearly all encounters ended because the residents continued pursuit but lost track of the intruder. This occurred in only half of intruder pursuits in open and wall enclosures. Our results suggest that mice prefer areas containing physical structure because this provides a degree of protection from predators but territories with complex physical structuring appear to be much more difficult to defend. Complex areas may thus support a higher density of mice than open areas or those with more simply aligned physical structuring. Copyright 2000 The Association for the Study of Animal Behaviour.     

Differential effects of moving versus stationary territorial intruders on territory defence in a songbird

1.  In territorial contests, not only acoustic or other signals, but also the movements of a territorial intruder are likely to influence the response of a resident.
2.  We tested this movement hypothesis by simulating moving vs. stationary intruders into the territories of winter wrens Troglodytes troglodytes , using the same non-interactive song playbacks in both treatments.
3.  Male winter wrens showed a different long-term singing reaction in response to a moving than to a stationary intruder.
4.  One day after experiencing an intruder that was switching between three locations, residents started to sing earlier before sunrise, and they sang more and longer songs at dawn than before the intrusion.
5.  Residents receiving the same playback from one location only reacted by starting to sing later relative to sunrise, and by singing fewer and shorter songs than before the intrusion.
6.  We could not discriminate between the treatments when examining the short-term singing reactions during and immediately after the playbacks. However, our results clearly demonstrate an effect of the spatial behaviour of territorial intruders on the long-term territory defence of residents at dawn, about 24 h after an intrusion.
7.  We argue that spatial behaviour of territorial intruders should be an integral part of the study of animal territory defence behaviour. Investigating long-term changes in territory defence at dawn is a sensitive tool for discriminating between different types of intruders.     

Non-defendable resources affect peafowl lek organization: a male removal experiment

A lekking mating system is typically thought to be non-resource based with male providing nothing to females but genes. However, males are thought to clump their display sites on areas where they are more likely to encounter females, which may depend on non-defendable resource location. We tested this hypothesis on a feral population of peacocks. In agreement, we found that, within the lek, display site proximity to food resources had an effect on female visitation rate and male mating success. The attractiveness of display sites to male intruders was explained by the distance to the feeding place and by the female visitation rate. We randomly removed 29 territorial males from their display sites. Display sites that were more attractive to male intruders before removal remained highly attractive after removal and display sites closer to the feeding area attracted the attention of intruders significantly more after removal. Similarly, display sites that were more visited by females before removal remained more visited after removal, suggesting again that the likelihood of encountering females is determined by the display site location. Overall, these results are in agreement with non-defendable resources affecting lek spatial organization in the peafowl.     

The influence of human and goshawk Accipiter gentilis activity on wood-pigeons Columba palumbus at brassica feeding sites

Humans caused more than half the disturbance of wood-pigeons, Columba palumbus, from roadside brassica feeding sites. The birds always flew away from pedestrians, cyclists and horsemen, but often remained feeding when closed vehicles passed. The pigeons resettled immediately on the same feeding site after 23% of goshawk, Accipiter gentilis, attacks, and birds were feeding there later the same day after nearly half the attacks. They resettled immediately after a similar proportion (19%) of the times they were approached by humans on foot, and rarely fed in fields where people were working. The shorter the time pigeons had spent feeding before an interruption, the sooner they returned after it. This probably reflected the level of their crop food reserves. This behaviour should minimise the effect of short duration disturbance, as caused by goshawk attacks, on wood-pigeons feeding at brassica sites. Goshawk attacks did not cause a reduction in pigeon pecking-rate. Pigeons feeding in roadside fields tended to avoid the side nearest to the road, but not parts of fields adjoining walls and hedges which could have provided cover for predatory attacks. It is concluded that scaring techniques based on man himself are more promising than use of the goshawk in protecting crops against wood-pigeons.     

Owl Monkeys (Aotus nigriceps and A. infulatus) Follow Routes Instead of Food-Related Cues during Foraging in Captivity

Foraging at night imposes different challenges from those faced during daylight, including the reliability of sensory cues. Owl monkeys (Aotus spp.) are ideal models among anthropoids to study the information used during foraging at low light levels because they are unique by having a nocturnal lifestyle. Six Aotus nigriceps and four A. infulatus individuals distributed into five enclosures were studied for testing their ability to rely on olfactory, visual, auditory, or spatial and quantitative information for locating food rewards and for evaluating the use of routes to navigate among five visually similar artificial feeding boxes mounted in each enclosure. During most experiments only a single box was baited with a food reward in each session. The baited box changed randomly throughout the experiment. In the spatial and quantitative information experiment there were two baited boxes varying in the amount of food provided. These baited boxes remained the same throughout the experiment. A total of 45 sessions (three sessions per night during 15 consecutive nights) per enclosure was conducted in each experiment. Only one female showed a performance suggestive of learning of the usefulness of sight to locate the food reward in the visual information experiment. Subjects showed a chance performance in the remaining experiments. All owl monkeys showed a preference for one box or a subset of boxes to inspect upon the beginning of each experimental session and consistently followed individual routes among feeding boxes.     

Territorial behaviour reflects sexual status in groups of false clown anemonefish (Amphiprion ocellaris) under laboratory conditions

Anemonefishes (genus Amphiprion) are well known as protandrous sex-changing fish. They live symbiotically with sea anemones and form a social unit that consists of a breeding pair and several sexually immature individuals with ambisexual gonads. In general, the hierarchy of the social rank is strictly maintained in a group, and this hierarchy is considered to be one of the critical factors that induce sex change or sex differentiation in anemonefishes. Field observations have shown that behavioural characteristics of anemonefishes vary depending on the environment. In this study we examined the differences in territorial aggression directed at conspecific intruders according to sexual status in the false clown anemonefish, Amphiprion ocellaris, under laboratory conditions. Resident–intruder tests were conducted on groups consisting of three anemonefish: a dominant female, a second-ranked male and a subordinate ambisexual individual. Females and males showed more aggressive behaviour than did ambisexual individuals, and behaviours were specifically directed at intruders of the same sexual status, not at those of the opposite sex. Notably, the female residents displayed fierce aggressive behaviours particularly toward female intruders, whereas male residents engaged more often in side-by-side swimming with male intruders than with female or ambisexual intruders. Ambisexual intruders were threatened by all residents, rarely attacked. We observed only few aggressive acts towards tank mates. These results suggest that sexually mature resident anemonefish in a confined space, such as under laboratory conditions, perceive intruders of the same sexual status as competitors for reproductive status and thus, dominant social rank.     

When to Come Out from a Refuge: Balancing Predation Risk and Foraging Opportunities in an Alpine Lizard

Prey often respond to predator presence by increasing their use of refuges, but because this strategy may be costly, the decision regarding when to come out from a refuge should be optimized. The loss of foraging opportunities may be one of the main costs when safer microhabitats (i.e. refuges) are also the poorest in terms of their foraging profitability. We present the results of an experimental field study to test whether emergence times from a refuge of the Iberian rock lizard, Lacerta monticola, vary as a function of expected foraging opportunities and level of satiation of the lizard. As predicted, short‐term fluctuations in availability of food influenced emergence times; when a lizard had just detected some food in the recent past, emergence times decreased greatly, because the loss of opportunities for foraging increased costs of refuge use. Furthermore, the characteristics and success of the encounter with food, nutritional state of lizards, and the added possibility of capturing new food items influenced the duration of hiding times. Therefore, foraging requirements and avoidance of predators may be conflicting demands that L. monticola lizards balance by modifying the duration of time spent in refuges.     

Intra- and interspecific aggression do not modulate androgen levels in dusky gregories,yet male aggression is reduced by an androgen blocker

Discussions about social behavior are generally limited to fitness effects of interactions occurring between conspecifics. However, many fitness relevant interactions take place between individuals belonging to different species. Our detailed knowledge about the role of hormones in intraspecific interactions provides a starting point to investigate how far interspecific interactions are governed by the same physiological mechanisms. Here, we carried out standardized resident–intruder (sRI) tests in the laboratory to investigate the relationship between androgens and both intra- and interspecific aggression in a year-round territorial coral reef fish, the dusky gregory, Stegastes nigricans. This damselfish species fiercely defend cultivated algal crops, used as a food source, against a broad array of species, mainly food competitors, and thus represent an ideal model system for comparisons of intra-and interspecific territorial aggression. In a first experiment, resident S. nigricans showed elevated territorial aggression against intra- and interspecific intruders, yet neither elicited a significant increase in androgen levels. However, in a second experiment where we treated residents with flutamide, an androgen receptor blocker, males but not females showed decreased aggression, both towards intra- and interspecific intruders. Thus androgens appear to affect aggression in a broader territorial context where species identity of the intruder appears to play no role. This supports the idea that the same hormonal mechanism may be relevant in intra- and interspecific interactions. We further propose that in such a case, where physiological mechanisms of behavioral responses are found to be context dependent, interspecific territorial aggression should be considered a social behavior.     

Movement coordination and signalling in ravens (Corvus corax): an experimental field study

Vagrant non-breeding ravens frequently attract conspecifics to rich ephemeral food sources. There, grouping may allow them to overcome the defence of territorial breeders. Here, we focus on ravens making use of regular food supplies in a game park, where they divert food from the provision of park animals. We investigated if ravens foraging in the Cumberland game park (Grünau, Austria) are attentive towards one another when they experience some unpredictability in food provisioning. We confronted a group of 30–50 ravens with two different treatments. Ten minutes ahead of the feeding of either wolves or wild boars we showed buckets containing pieces of meat to the ravens flying overhead. In the reliable cue treatment (RCT), the meat was placed next to one of the two enclosures, whereas in the unreliable cue treatment (UCT), the buckets were placed simultaneously in front of both enclosures though only in one of the enclosures were the animals fed 10 min later. Thus, during RCT but not during UCT, ravens could predict where food would become available. Only during UCT, ravens moved in large groups between the two feeding sites. Many ravens moving at the same time in the same direction may indicate some co-ordination in space and time, which is most likely achieved by social attraction among individuals. Furthermore, the number of ravens approaching and leaving, respectively, a feeding site cross-correlated with a temporary increase in the rate of a food-associated call, the yell. This suggests that in addition to watching each other, calling may have contributed to group formation. Possible benefits of group formation during food inspection are discussed. Received: 9 February 2000 / Received in revised form: 30 May 2000 / Accepted: 1 June 2000     

Foraging patterns of voles at heterogeneous avian and uniform mustelid predation risk

Temporal variation of antipredatory behavior and a uniform distribution of predation risk over refuges and foraging sites may create foraging patterns different from those anticipated from risk in heterogenous habitats. We studied the temporal variation in foraging behavior of voles exposed to uniform mustelid predation risk and heterogeneous avian predation risk of different levels induced by vegetation types in eight outdoor enclosures (0.25 ha). We manipulated mustelid predation risk with weasel presence or absence and avian predation risk by reducing or providing local cover at experimental food patches. Foraging at food patches was monitored by collecting giving-up densities at artificial food patches, overall activity was automatically monitored, and mortality of voles was monitored by live-trapping and radiotracking. Voles depleted the food to lower levels in the sheltered patches than in the exposed ones. In enclosures with higher avian predation risk caused by lower vegetation height, trays were depleted to lower levels. Unexpectedly, voles foraged in more trays and depleted trays to lower levels in the presence of weasels than in the absence. Weasels match their prey's body size and locomotive abilities and therefore increase predation risk uniformly over both foraging sites and refuge sites that can both be entered by the predator. This reduces the costs of missing opportunities other than foraging. Voles changed their foraging strategy accordingly by specializing on the experimental food patches with predictable returns and probably reduced their foraging in the matrix of natural food source with unpredictable returns and high risk to encounter the weasel. Moreover, after 1 day of weasel presence, voles shifted their main foraging activities to avoid the diurnal weasel. This behavior facilitated bird predation, probably by nocturnal owls, and more voles were killed by birds than by weasels. Food patch use of voles in weasel enclosures increased with time. Voles had to balance the previously missed feeding opportunities by progressively concentrating on artificial food patches.     

Nest intrusions, infanticide, and parental care in the burying beetle, Nicrophorus orbicollis (Coleoptera: Silphidae)

Duration of paternal care in the burying beetle Nicrophorus orbicollis Say is highly variable. Both parents bury and defend mouse-sized vertebrate carcasses as food resources for their offspring, but males abandon their broods several days before females. Nests defended by single female parents were taken over by aggressive conspecifics in live of nine cases, whereas only six of 16 nests defended by both parents were taken over. In the event of a takeover, the intruding beetle replaced the resident beetle of the same sex, destroyed any eggs that were present, and paired with the remaining resident to produce a new clutch. Broods raised by usurpers following takeovers were less successful than broods raised by initial residents on unused carcasses. The majority of takeovers occurred 35 days after carcass burial. The occurrence of nest intrusions by conspecifics did not significantly influence duration of male parental care; when conspecific intruders were excluded from nests males remained with their broods (± S.E.) 11·2 ± 0·8 days ( n = 15), and when intruders were added to nests males remained with their broods 12·2 ± 0·6 days ( n = 8). Conflict for carcasses intensified in response to larger brood mass, but duration of male care was unaffected by brood mass. Overall. brood mass and the presence or absence of intruders explained only 5% of the variance associated with brood abandonment by males.