Why are Male Columbian Ground Squirrels Territorial?

Male territorial defence is a component of many vertebrate mating systems and is often regarded as a tactic for acquiring mates. Traditionally considered within the context of overt site‐specific defence, territoriality actually may have several components which encompass a variety of behavioural tactics (e.g. post‐copulatory mate‐guarding, defence of resources that females need, defence of area around females) that underlie a mating system. The purpose of our study was to evaluate such influences on the territorial behaviour of male Columbian ground squirrels in southwestern Alberta, Canada. Males were dominant and territorial if they defended a minimum convex polygon activity range by chasing other males more within the activity range than they were chased. Subordinate males had no territory and were chased throughout their ranges, but they competed for mates by increasing chases in their activity range when nearby females were oestrous. Dominant males exhibited conditional breeding tactics, tending to chase other dominant males from their territory when nearby females were oestrous, but travelling outside their activity ranges to chase subordinate males when females were not oestrous. Although females mated first with a dominant male on whose territory they resided (and in order from oldest to youngest if several territories overlapped), mating pairs were not exclusive, as females usually mated with additional males. Males also guarded females after copulation and defended females directly just before oestrus, rather than defending territory per se during those times. Thus, males possess a repertoire of behaviours that complement site‐specific territoriality, and territory ownership serves to facilitate a first mating with females that live on the territory.     

Social organization in the pheasant (Phasianus colchicus): harem formation, mate selection and the role of mate guarding

Harem formation and mate selection were studied in the pheasant in order to determine the advantages of territorial harem defence polygyny to the two sexes. We investigated the factors affecting harem size and the advantage to a female in remaining with one territorial male during breeding.
Female group size declined during late March and early April as females moved from large overlapping ranges into smaller, more widely dispersed breeding ranges. The proportion of female groups accompanied by males increased during this period.
Some males had a disproportionate share of females. Settled females were monogamous but, because a female's nest was generally outside the male's territory, her home range was larger than his territory.
Harem members were usually from the same winter group. Harem size was not related to territory quality in terms of food supply or nesting cover. Females were loyal to one male in more than one year even if his territory position changed. Older, territory-owning males had more females, both adult and immature, than males with newly-established territories. Harem size was not correlated with territory size.
We conclude that the mating system of the pheasant is based on mate guarding which protects females not only from the risk of predation or injury, but also from excessive energy expenditure incurred through being chased by other males. When escorted by a territorial male, females spent three times as much time feeding, one-fifth as much time running, and one-tenth as much time alert, as they did when not guarded.     

Territory acquisition during winter by juvenile Willow Tits Parus montanus

Willow Tits Parus montanus live within exclusive territories in non-kin winter flocks with a dominance hierarchy in which males dominate females and adults dominate juveniles. Because they live in habitats that are saturated with dominant territory owners, the options of subordinate juveniles surviving the winter are: (1) to become a dominant owner of a vacated territory, (2) to stay in an occupied territory and hope for ownership or (3) to leave the area and hope for territory acquisition elsewhere. Removal experiments during December to February revealed that particularly the most dominant of the juvenile pairs left their own flock territory and replaced birds experimentally removed from a neighbouring flock, if by doing so they increased their own dominance position. It is suggested that juvenile Willow Tits updated their information about the composition and dominance structure of adjacent winter flocks by regularly visiting these territories and attempted to become dominant owners during winter, thereby increasing their chances of breeding.     

Pairing strategies and mate choice in female robins Erithacus rubecula

Female European robins (Erithacus rubecula) adopted three different pairing strategies. These were, in order of frequency: moving on to a male's territory; fusing her territory with that of a neighbouring male; and being joined by a male on her territory. Although females were not free to choose between strategies during a particular season, individuals frequently changed strategy between different years. Their behaviour suggested that they were exercising mate choice, although the scope for such choice was limited by a strong tendency for a female to pair in areas where she had lived previously (her ‘Familiar Areas’). Males with large territories were more likely to pair and tended to pair earlier than those defending small territories. Female pairing strategy was also correlated with the area of their own territory. Although it is considered likely that some unidentified confounding variable was responsible for at least part of these relationships, possible causal explanations involving territory size are discussed. These include mate choice and a random settlement model. However the simplest explanation for the advantage enjoyed by males on large territories is that their territories were more likely to overlap with females' Familiar Areas.     

Calling as an ownership convention on pied wagtail territories

Winter feeding territories were more profitable to owners than intruders. Even when intruders landed on a territory undetected they failed to achieve a profitable feeding rate because they fed in areas recently depleted by the owner. For intruders therefore, ownership was a sign of unprofitability. Intruder scalled ‘chis-ick’, apparently to find out if a territory was occupied. Owners replied ‘chee-wee’ and this was usually sufficient to cause the intruder to retreat. Only owners called ‘chee-wee’. Owners reacted more aggressively to tape-recorded broadcasts of the ‘chee-wee’ call played on their territory than to broadcasts of ‘chis-ick’.     

FOOD RESOURCES, TERRITORY DENSITY AND REPRODUCTIVE SUCCESS OF AN ISLAND SILVEREYE POPULATION ZOSTEROPS LATERALIS

We examined the relationships between food resources, territory density and some breeding parameters (individual reproductive success and parental age) of a Capricorn Silvereye population during two years' detailed study on Heron Island, Great Barrier Reef. The territorial behaviour of the Silvereyes included dawn song. aggression and distinctive vocalizations. During both years, about 85% of pairs occupied territories although the population sizes differed. The dispersion pattern of territories was not regular and was correlated with the density of figs and human food scraps. Nestlings were fed more figs as they grew, and the parents foraged in fig trees outside their territories. However, only about 60%, of territorial pairs fledged young. Pairs which fledged most young were older, fed more insects to their nestlings, and nested in areas containing more fruiting fig trees per territory. We conclude that food resources were in short supply, and that access to fig trees provided breeding birds with a quick energy source while they searched for insect protein for the young. The data are consistent with the predictions of the ‘sufficient resource‘ hypothesis of the adaptive significance of territoriality but not with its assumption that the principal benefit is the food within the territory.     

The day after: effects of vocal interactions on territory defence in nightingales

1. Models on territory acquisition and tenure predict that territorial animals benefit by adjusting territorial defence behaviour to previous challenges they had experienced within the socially complex environment of communication networks. 2. Here, we addressed such issues of social cognition by investigating persisting effects of vocal contests on territory defence behaviour in nightingales Luscinia megarhynchos (Brehm). 3. Using interactive playback during nocturnal song of subjects, a rival was simulated to countersing either aggressively (by song overlapping) or moderately (by song alternating) from outside the subjects' territory. Thereby, the time-specific singing strategy provided an experimentally controlled source of information on the motivation of an unfamiliar rival. 4. Expecting that nightingales integrate information with time, the same rival was simulated to return as a moderately singing intruder on the following morning. 5. The results show that the vigour with which male nightingales responded to the simulated intrusion of an opponent during the day depended on the nature of the nocturnal vocal interaction experienced several hours before. 6. Males that had received the song overlapping playback the preceding night approached the simulated intruder more quickly and closer and sang more songs near the loudspeaker than did males that had received a song alternating playback. 7. This adjustment of territory defence strategies depending on information from prior signalling experience suggests that integrating information with time plays an important part in territory defence by affecting a male's decision making in a communication network.     

Non-territorial nightingales prospect territories during the dawn chorus

Male songbirds usually sing when they have occupied a territory, but the territory prospecting of non-territorial males is more elusive and has been rarely studied. Here, we simulated newly arriving, non-territorial males by translocating unmated male nightingales (Luscinia megarhynchos) to our study site. We show that territory prospecting of translocated males was largely confined to the hour before sunrise. The radio-tagged males made extensive excursions visiting several singing males at dawn, but after dawn they remained stationary outside occupied territories. As in many other songbird species, dawn was also the time when resident males sang the most. These results suggest that nonterritorial male nightingales use the dawn chorus to assess singing residents or territory occupancy. For resident males, dawn singing may be important to announce territory occupancy to prospecting males and may thus play a role in territory maintenance.     

Early comers occupy popular territories in a lycaenid butterfly,Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae)

Territorial activities of a lycaenid butterfly, Chrysozephyrus smaragdinus, were observed throughout its adult season to investigate the territorial dynamics. The territories occupied earlier in the season were abandoned later than later‐occupied territories, indicating that the site preference of male C. smaragdinus was largely maintained during the adult season. Three indexes of territory quality based on animal preference, occupation duration (OD), initial occupation date (IOD) and the number of contests (NOC), were highly correlated. Therefore, these preference‐based indexes are consistent and reliable, although they are indirect estimates of benefits obtained from territories. Males arriving at territory sites early in the season were more likely to hold territories of better quality when NOC was used as the index of territory quality. The positive relationship between territory quality and male arrival date is congruent with the result of a previous study showing that early comers tend to hold a territory whereas late comers do not. However, male arrival date was not related to territory quality when OD or IOD was used as an index of territory quality. One possible reason for this apparent discrepancy is that the coefficient of variation of NOC is larger than those of OD and IOD, and therefore NOC could evaluate territory quality more quantitatively than the other two indexes. To date, studies of territoriality in butterflies have not considered the quality of territories. More studies considering the quality of territories will provide new insights into butterfly territoriality.     

Winter territory prospecting is associated with life‐history stage but not activity in a passerine

Finding a high quality territory is essential for many animals to reproduce successfully. Despite its importance for fitness, we know little about the process of territory prospecting in wild birds, and whether individual traits and behaviours, such as personality, co‐vary with territory prospecting. Here, we use long‐term data from a wild, insular house sparrow Passer domesticus population to test three hypotheses about territory fidelity and prospecting: 1) house sparrows show high territory fidelity between years and also during winter. 2) Individuals will prospect for a breeding territory during their first winter whereas older, more experienced individuals will keep a territory from previous years and will, therefore, show no or reduced winter territory prospecting. 3) More active behavioural types will prospect more than less active behavioural types. We use data from four winters from automatically, daily recorded nest‐box visits of 188 birds of known age. The number of nest‐boxes that each individual visited within each winter was used as a proxy of winter territory prospecting. We show that house sparrows visit multiple nest‐boxes during their first winter, whereas older individuals keep territories year‐round and, potentially because of this, indeed show reduced winter territory prospecting. Activity was not associated with the number of nest‐boxes visited. Further research is needed to investigate whether time of territory and mate acquisition differs among individuals and the possible effect on lifetime fitness.     

Pair formation in the Mongolian gerbil

This report describes the initial phase of social organization in Mongolian gerbils, Meriones unguiculatus, in large outdoor enclosures. These conditions offer a comparatively free choice for the establishment of bonds and social structure. In five replicate 20-day studies, the only social unit that formed was the male-female pair. The order of events was related to four sequential 5-day periods: (I) males established territories by male-male competition (1st to 2nd period); (II) females visited more than one male initially (1st and 2nd period), but developed a preference for one male or territory (3rd to 4th period); (III) as the females developed a preference, they also challenged other females having a preference for the same male or territory (approximately the 3rd period); (IV) as one female became locally dominant, some territorial males started chasing all but the dominant female. Males remained more active in territorial defence throughout the study. The defence became more intense as the females became strongly attached to one male and/or territory only. However females, after having established themselves in one particular male territory, spent significantly less time in the preferred area during the day of oestrus compared with the days before and after. Copulatory behaviour patterns, where observed, did not occur exclusively in interactions between territorial mates.     

What factors contribute to an ownership advantage?

In most taxa, owners win fights when defending a territory against intruders. We calculated effect sizes for four factors that potentially contribute to an 'owner advantage'. We studied male fiddler crabs Uca mjoebergi, where owners won 92% of natural fights. Owners were not more successful because they were inherently better fighters (r=0.02). There was a small effect (r=0.18) of the owner's knowledge of territory quality (food availability) and a medium effect (r=0.29) of his having established relations with neighbours (duration of active tenure), but neither was statistically significant. There was, however, a significant effect due to the mechanical advantage the owner gained through access to the burrow during fights (r=0.48, p<0.005).     

A Mismatch between the Perceived Fighting Signal and Fighting Ability Reveals Survival and Physiological Costs for Bearers

Signals of fighting indicate an animal''s intention to attack and so they serve to prevent costly aggressive encounters. However, according to theory, a signal that is different in design (i.e. a novel signal) but that fails to inform fighting intentions will result in negative fitness consequences for the bearer. In the present study we used males of the territorial damselfly Hetaerina americana, which have a red wing spot during territory defense that has evolved as a signal of fighting ability. By producing a novel signal (covering the red spot with blue ink) in territory owners, we investigated: a) the behavioral responses by conspecific males; b) survival cost and c) three physiological mediators of impaired survival: muscular fat reserves, muscle mass and immune ability. We predicted that males with the novel signal would be attacked more often by conspecifics as the former would fail to convey fighting ability and intentions adequately. This will result in lower survival and physiological condition for the novel signal bearers. We found that, compared to control males (males whose red spot was not changed), experimental males had reduced survival, were less able to hold a territory, and had a reduced muscle mass. It seems that spot modified males were not able to effectively communicate their territory tenancy, which may explain why they lost their defended sites. Our results provide support for theoretical models that a novel signal that fails to informing fighting ability may lead to a fitness cost for bearers.     

Patterns of territory settlement and consequences for breeding success in the Northern Wheatear Oenanthe oenanthe

We examined the pattern of territory settlement and its consequences for breeding success in the Northern Wheatear Oenanthe oenanthe on Bardsey Island, Wales, during the breeding seasons of 1991-93. Males returned earlier than females, and older males returned earlier than first-year breeders. Although their boundaries shifted between years, the general location of territories was consistent during the three-year study. There was a high degree of fidelity to area and territory between years for both sexes. The order of territory settlement, from which a territory rank was calculated, was highly consistent for males between years irrespective of individual settlement patterns and territory fidelity. Patterns of territory settlement were less predictable for females, although there was a significant correlation between the mean territory ranks of paired males and females. There was a male-biased sex ratio in each year, and between 5% and 26% of males remained unpaired throughout the breeding season. Male mating status and breeding success were dependent on arrival date, territory rank and breeding density. Early-arriving, usually older, males were able to settle on territories first and were more likely to pair, while later-arriving individuals were more likely to remain unmated. These effects were consistent between years, and consequently territories could be classified as either preferred (accounting for proportionately more breeding attempts) or non-preferred. Territory quality as opposed to individual quality appeared to explain much of the variation in breeding success, and both sexes benefited by breeding on preferred territories through enhanced breeding success and an increased probability that their offspring would be recruited to the population.     

Territorial behavior of a green hairstreak Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae): site tenacity and wars of attrition

Males of Chrysozephyrus smaragdinus were active from late morning to late afternoon, during which they showed territorial behavior, perhaps for mating. The territorial male stayed in a particular area and occasionally flew around it, referred to hereafter as the inspection area. When other male intruded into this area, the territorial male rushed to him. Then, they engaged in a circling flight regarded as a "war of attrition". During this flight, the two males sometimes strayed far away from the territory. After the circling flight, the resident returned to his territory in almost all cases (98%). Despite such intrusions, many residents defended their territory for several successive days. This suggests strongly the "effect of prior residence". We recorded the circling flights with a high-speed video camera, and confirmed that the male that ceased the circling flight first was the loser. This finding gave some validity to consider circling flight as wars of attrition. In a few cases, the territorial male mated with a female that came to the territory. These once mated males held the territory no longer, suggesting that mating experience should restrict the next mating opportunity in this species.     

Effects of Exogenous Androgen and Antiandrogen on Territorial and Nonterritorial Red-winged Blackbirds (Aves: Icterinae)

We investigated the role of testosterone (T) in territory establishment and maintenance in male red-winged blackbirds (Agelaius phoeniceus) by implanting exogenous T or pharmacological agents that block the action of T in nonterritorial floaters and territory owners. Floaters with artificially elevated plasma T levels were unable to obtain territories. Territory owners implanted with T did not expand their territories, although they engaged in more aggressive behavior than did control males. Flutamide, which binds to T receptors in target areas, had no effect on territoriality. However, most territory owners given a combination of flutamide and ATD, an aromatization blocker, lost portions of their territories even though they actively defended them. Our results 1) suggest that, although T influences aggressive behavior, elevated plasma levels alone are insufficient to overcome previously-established social relationships between territory owners or between owners and floaters; 2) indicate that impairing the action of T leads to reduced abilities of territory owners to maintain territories against vigorous challenges: and 3) support recent findings that T acts on reproductive behavior in birds through both androgenic and estrogenic metabolites.     

Colony-specific territorial marking with the metapleural gland secretion in the ant Solenopsis geminata (Fabr)

S. geminata workers mark the areas they explore with a secretion from the metapleural gland. The territorial mark lasts for more than 6 h. Territories without the chemical mark induce the workers to initiate recruitment to that territory. Ants on their own territory or on territories impregnated with metapleural gland extract from workers of their colony, initiate more intraspecific combats than ants on territories of a different colony or on territories without the chemical mark.     

Intruder Pressure Affects Territory Size and Foraging Success in Asymmetric Contests in the Water Strider Gerris lacustris

The theory of evolutionarily stable strategies (ESS) in asymmetric contests predicts that the propensity of an individual to expose itself to risk during contests depends on the individual's resource-holding-potential (RHP) and on the value of the disputed resource (V) for the individual compared with that for an opponent. If encounters of a territory owner with individuals of high RHP and high food demands (V) increase in frequency, one should expect a decrease in total aggressiveness of the territory owner, and in consequence a decrease of its territory size. Such a decrease should result in a lower amount of food consumed by the territory owner. Using natural variability in RHP and V in Gerris lacustris, I experimentally tested these predictions. The average prey item has higher value (V) for reproductive female water striders (which probably transform most of their food into eggs), than for nonreproductive females and for males. Because males are smaller, they have lower RHP than females, as RHP depends on size. Thus the reproductive females are the class of individuals of high RHP and high food demands (high V). Most nonreproductive females defend food-based territories. I observed two groups of water striders in a seminatural laboratory setting. As predicted, there was a negative correlation between the rate of encounter with reproductive females and size of the territory, and a positive correlation between territory size and number of Drosophila flies consumed by the owner. Territories were smaller in the group with high rates of encounter between territory owners and reproductive females. Territory owners caught the same number of Drosophila flies as non-territorial individuals in this group. In contrast, in the group with fewer encounters between territory owners and reproductive females, territories were larger, and territory owners gained more food than non territorial water striders.     

Why long-lived species are more likely to be social: the role of local dominance

Recent studies have shown that individuals of species that livein groups tend to have high annual survival, but this link haslacked a theoretical explanation. We evaluate two hypothesesthat explain how longevity could have led to the evolution ofgroup living. The first is the territory inheritance hypothesis,and it proposes that longevity increases the probability ofnonbreeding subordinates surviving long enough to have the opportunityof inheriting their natal territory. Second, we propose a novelhypothesis, the reciprocal altruism hypothesis, which is thatlongevity increases local dominance by favoring nonaggressionpacts among neighboring residents because longevity increasesthe likelihood of reciprocal altruism. Birds thus accept subordinateresidency because the exclusion of nonlocal birds will meanthat, if they survive long enough, they will be likely to actuallyachieve territory inheritance. The reciprocal altruism hypothesisis supported by a wider array of evidence; becomes progressivelymore powerful as longevity increases, thus producing a positivefeedback; explains the evolution of local dominance (whereasthe territory inheritance hypothesis assumes its existence);and provides an explanation for why cooperative breeding shouldbe found more often in aseasonal environments.     

Pathway-specific genetic attenuation of glutamate release alters select features of competition-based visual circuit refinement

A hallmark of mammalian neural circuit development is the refinement of initially imprecise connections by competitive activity-dependent processes. In the developing visual system retinal ganglion cell (RGC) axons from the two eyes undergo activity-dependent competition for territory in the dorsal lateral geniculate nucleus (dLGN). The direct contributions of synaptic transmission to this process, however, remain unclear. We used a genetic approach to reduce glutamate release selectively from ipsilateral-projecting RGCs and found that their release-deficient axons failed to exclude competing axons from the ipsilateral eye territory in the dLGN. Nevertheless, the release-deficient axons consolidated and maintained their normal amount of dLGN territory, even in the face of fully active competing axons. These results show that during visual circuit refinement glutamatergic transmission plays a direct role in excluding competing axons from inappropriate target regions, but they argue that consolidation and maintenance of axonal territory are largely insensitive to alterations in synaptic activity levels.