Territorial bequeathal by red squirrel mothers: A dynamic model

Female red squirrels (Tamiasciurus hudsonicus) sometimes bequeath their territory to their offspring. Late-breeding females are more likely to leave than are early-breeding females. Early-breeding females tend to lose weight during reproduction while late-breeding females do not. Early-born juveniles are more successful at winning territories than are those born late. I use dynamic programming to investigate the trade-offs involved in territorial bequeathal from the female's perspective as a function of breeding date, litter size and female body condition. The model predicts that two classes of females are more likely to bequeath: those in good condition early in the season, and those in poor condition at the season's end. Only versions of the model incorporating a function improving the female's ability to win a territory over the season mimicked the pattern of bequeathal observed in the field. A seasonal effect is likely an important factor in driving the pattern of strategies observed.     

Red coloration of male northern cardinals correlates with mate quality and territory quality

I investigated how mate quality and territory quality influencean extravagant ornament in a socially monogamous species thatdefends multipurpose territories. Northern cardinals (Cardinaliscardinalis) are a highly dichromatic, socially monogamous species,and males are a brilliant red. I conducted a 3-year field studyof northern cardinals and found that redder males produced moreoffspring in a breeding season. Two selective factors mediatedthis fitness gain. Redder males were paired with earlier breedingfemales, an established measure of mate quality in birds. Second,redder males obtained territories of higher quality, as measuredby vegetation density. Interactions among these factors werealso important in explaining variance in male reproductive success.Multivariate analysis indicated that earlier breeding increasedreproductive success independent of territory quality. In turn,territory quality contributed to male reproductive success throughits effect on nest survival and possibly through its role in attractingan earlier breeding female.     

Nest and mate choice in the red bishop (Euplectes orix) : female settlement rules

We investigated female settlement in a colony of red bishops(Euplectes orix), a territorial and highly polygynous weaverbirdwidely distributed over sub-Saharan Africa. An earlier studyshowed that male reproductive success is mainly determinedby the number of nests a male builds in his territory, whichappeared to be a good indicator of male quality. Because malesprovide no parental care or food resources within the territory,females sharing a territory do not compete for material resourcesand might therefore be expected to settle preferentially interritories of males that build many nests to gain the possiblegenetic benefit of high-quality offspring. An analysis of femalesettlement, however, revealed that females did not show a preferencefor territories of males with many nests and that the distribution of female breeding attempts with regard to the number of vacantnests within a territory could be explained best by randomfemale settlement in 3 out of 4 years. Females settled moreoften than expected by chance (in 3 out of 4 years) in territoriesalready containing occupied nests, indicating that residentfemales did not discourage settlement of additional females.However, sharing a territory with other females might imposecosts in terms of an increased predation risk because nestsin territories that contained other nests with young sufferedfrom higher predation than nests in territories that did notcontain other nests with young. Females therefore might tradethe possible benefits of settling in territories of males withmany nests against the costs of sharing a territory with otherfemales. This might result in the mating pattern found withrandom female settlement and male reproductive success beingdirectly proportional to the number of nests built. We discuss possible implications of this mating pattern for sexual selectionon males.     

Post-breeding dispersal by female red squirrels (Tamiasciurus hudsonicus): the effect of local vacancies

Red squirrels (Tamiasciurus hudsonicus) defend food-based territoriesyear round, and juveniles must acquire a territory before winterto survive. We experimentally removed territory owners duringthe time that juveniles were becoming independent to examinethe effect of local vacancies on dispersal patterns. Juvenilesattempted to take over removal territories most frequently.However, females with offspring still on the natal territoryactually took over twice as many territories as juveniles. Thesefemales did not appear to move because of low reproductive potentialor to increase territory quality. Instead, moving to a removalterritory allowed more of their offspring to remain on the natalterritory, which appeared to increase juvenile survival.     

Mate acquisition tactics in polyandrous spotted sandpipers (Actitis macularia): the role of age and experience

We consider resource-defense polyandry and mate-access polyandryas female mating tactics in spotted sandpipers (Actitis macularia).These tactics can be distinguished by the resource females defend,female interclutch movement, expected reproductive success aftermoving, and male and female dispersion. We examine these characteristicsrelative to patterns observed in a 17-year study of spottedsandpipers, a species traditionally considered resource-defensepolyandrous. On average, 26% of spotted sandpiper females eachyear were monogamous. Older females were more likely to be polyandrous,and polyandrous females of each age employed different matingtactics. Yearlings were typically sequentially resourcedefensepolyandrous. Two-year-olds were primarily simultaneously polyandrous,exhibiting equivalent proportions of resource-defense and mate-accesspolyandry. Older females were primarily simultaneously resource-defensepolyandrous. Females tended to stay on territories where theyand/or their mates had greater breeding experience (i.e., manyclutches laid for females, many clutches diat hatched for males);females that moved went to territories where their mates hada history of breeding success. Location changes between clutchesby polyandrous females were better described by breeding experienceon a territory than by age.     

Sexual conflict over breeding substrate causes female expulsion and offspring loss in a cichlid fish

Females of the Lake Tanganyika cichlid Lamprologus callipterusexclusively breed in empty snail shells that males collect intheir territories. Male–male competition for shells issevere, leading to frequent shell stealing and territory takeover.As a consequence, males have breeding females in their shellsthat spawned with competitors. In this field study, we investigatedboth naturally occurring and experimentally induced encountersof territorial males with females that had spawned with othermales. We found that the breeding success of females that weretaken over by a different male was significantly reduced. Behavioralobservations after experimental shell relocation further showedthat males recognized females that they had not spawned with:males directed more exploration and manipulation behavior towardsuch shells compared with controls. Reoccupation rate of emptiedexperimental shells was significantly higher than that of unmanipulatedempty shells. This indicates that shell stealing and nest takeover,followed by female expulsion, contribute to the reproductivesuccess of L. callipterus males. We also found that female matechoice reduces expulsion risk: females preferred to mate withlarge males, and male size correlated with dominance. We concludethat the limited availability of breeding substrate is a keydeterminant of both intrasexual competition and intersexualconflict in this species.     

Accepting unrelated broods helps replacement male yellow-headed blackbirds attract mates

Replacement male yellow-headed blackbirds (Xanthocephalus xanthocephalus)did not destroy broods sired by the previous territorial maleand they showed no aggression toward females with unrelatedbroods. To test whether their tolerance of unrelated young wasmisdirected normal parental care, we removed males from experimentalterritories after primary nests were completed but before secondarynests were initiated. Replacement males fed young that theypresumably had sired in secondary nests and ignored foster youngin primary nests, whereas control males fed young in their primarynests. To identify potential benefits of accepting unrelatedyoung, we analyzed patterns of within-season breeding dispersaland of female settlement on territories following nest lossesto predators. Although some female yellowheads do renest onthe same territory following nest failures, the number of nestsinitiated on territories after a predation event was significantlylower than the number initiated on territories without predationover the same period of time. This implies that late-settlingfemales use the number of active or failed nests and/or thenumber of females on a territory when choosing where to breed.If replacement males that accepted unrelated offspring attractmore new females in the remainder of the current breeding seasonthan infanticidal males, then tolerance of unrelated young byreplacement males may be adaptive in some polygynous birds.     

Black holes, mate retention, and the evolution of ungulate leks

In some ungulates living in unstable herds, females in estrusleave their usual groups and join males defending mating territories.During the 12-24 h before mating, females commonly move severaltimes between males. These movements are commonly caused byharems being disrupted by young males or by overenthusiasticcourtship by the territorial male. When females leave a territorythey typically move to its nearest neighbor. Under these circumstances,clusters of territories can retain estrous females until theymate and leave the lek. This paper develops a model to investigatethe benefits of defending clustered versus dispersed territoriesto males and the consequences of variation in the rate of femalemovement between territories (P_m) and the tendency for femalesto move from one territory to a neighboring territory (a). Wherefemales move between territories at least once every 24 h (P_m< 0.04) and usually move to neighboring territories (a <0.5), the mating success of males is inversely related to thedistance from their territory to its nearest neighbor, and malesdefending clustered territories have higher mating rates thanthose defending dispersed territories. This process may be importantin the initial evolution of ungulate leks, which may resembleblack holes, attracting and retaining estrous females untilthey mate and their estrus ceases. It provides one possibleexplanation of the evolution of ungulate leks that does notrely on female preferences for mating with particular phenotypiccategories of males.     

Territory and male quality do not influence settlement of yearling female willow ptarmigan

A common assumption in territory and mate selection models isthat individuals evaluate the qualities of territories and/orpartners and then choose the best ones. We determined whetherthis assumption was correct for yearling female willow ptarmigan(Lagopus lagopus). Yearling females did not choose partnersbased on the characteristics of the territories or of the malesthat we measured. In addition, the first females to settle didnot appear to obtain better territories or better partners thanthose settling later; date of settling was not related to subsequentsurvival, reproductive success, or quality of chicks produced.To evaluate whether choices of territories and partners wereconsistent among females, we manipulated settlement such thattwo sets of yearling females had the same suite of territoriesand males available. We found no consistent patterns of territoryand mate choice. We concluded that, in this population, yearlingfemales did not choose where to settle based on the relativequalities of territories or partners. Females may have beenunable to assess differences among territories when settlingbecause all territories were covered with snow.     

Breeding success in Blue Tits: good territories or good parents?

Territorial quality and parental quality are usually assumed to be the main sources of variation in the reproductive success of passerine birds. To evaluate their relative importance for variation in breeding time (itself an important factor for breeding success), clutch size and offspring condition at fledging, we analysed six years of data from a Blue Tit Parus caeruleus population breeding on the island of Gotland, Sweden. Hatching dates and the condition of offspring were consistent for territories between years and accounted for 30% and 33% of the variation in these variables, respectively. After removing the effect of territory quality, none of the breeding parameters were significantly repeatable for individual females, but offspring condition was repeatable for males, accounting for 28% of variation. For females breeding on the same territory in subsequent seasons (combined effect of individual and territory quality) only hatching date was repeatable (45% of variation accounted for). In males, the combined effect of individual and territory quality was repeatable for offspring condition and accounted for 33% of variation, but this result was only marginally significant. Consistency of the peak frass-fall date for individual frass collectors over the study period suggests that repeatable hatching dates on territories may be related to the relationship between timing of breeding and timing of peak food availability on territories. Our results suggest that territory quality is more important than parental quality for breeding success in the Blue Tit, and that male (but not female) quality makes a considerable contribution to reproductive success.     

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.     

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex‐specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.     

Female mate choice based on territory quality in barn swallows

Female mate choice based on territory quality is difficult to study because territories often contain many resources, which are difficult to quantify. Here, using the barn swallow (Hirundo rustica gutturalis) breeding at an outdoor breeding site in Japan, where each male defends only a small territory containing old nests, we studied whether females choose social mates based on territory quality. Since the territories of this species contain few other resources, territory quality can easily be assessed by quantifying old nests in the territory. We made the following four observations: (1) male swallows displayed old nests in their territories to females; (2) the old nests used for the first clutch were less broken than the other old nests within the same territory; (3) territory quality, defined by the number of old nests weighted by the intactness of each old nest, predicted the productivity of the territory; and (4) males with better territories paired with females earlier, and hence bred earlier, than those with inferior territories. The relationships remained significant even after controlling for male morphological traits. Based on these results, we can infer that female swallows choose their mates based, in part, on territory quality.     

THE EVOLUTION OF FEMALE BODY SIZE IN RED-WINGED BLACKBIRDS: THE EFFECTS OF TIMING OF BREEDING,SOCIAL COMPETITION,AND REPRODUCTIVE ENERGETICS

We examined opposing selective forces on female body size in the sexually dimorphic red-winged blackbird: social competition favoring larger females, and energetic advantages favoring smaller females. Downhower proposed that selection might drive female birds to be smaller than the optimum for survival, if smaller females were able to exceed their energetic requirements for self-maintenance earlier in the season and therefore breed earlier. Since in most birds the earliest breeders fledge the most young, this could favor the evolution of smaller female size, and therefore contribute to the magnitude of sexual size dimorphism in these birds. We tested this hypothesis in 1987 and 1988 by comparing the size and breeding date of female red-winged blackbirds. Consistent with our preditions, early-nesting females had much higher nesting success, but contrary to prediction, larger females bred earlier. We then examined the effects of female size on competition. If large females have an advantage in social competition, and if competition influences breeding date and reproductive success, then larger females might breed earlier. Primary females, the first females to arrive and nest on a territory, were more aggressive than lower ranked females; more aggressive females settled on better territories and laid earlier than less aggressive females; and larger females were more aggressive. Social competition between females may therefore favor large females. Finally, we tested the prediction that selection favoring large females might be limited by energetic constraints on large females. We found that large females had less fat than small females during breeding, and that the levels of fat that females of a given size carried affected breeding date and egg size. Therefore, social competition may favor large females, but reproductive energetics favoring smaller females may constrain selection for large female body size.     

Causes and consequences of individual variation in territory size in the American red squirrel

For most territorial species that defend food or other resources, territory size is inversely related to resource density. However, in some food-based territorial species, larger territories are known to contain greater absolute resource availability. For these latter species, both the specific determinants of territory size, and the relationship between territory size and fitness, remain unclear. We predicted that in American red squirrels ( Tamiasciurus hudsonicus ), where larger territories tend to hold increased food resources, survival should be correlated positively with territory size and that both individual (body mass, sex, duration of territory ownership) and habitat-specific (population density) attributes would contribute to variation in territory size. We monitored survival and territory size of 58 squirrels during a two-year period using live-trapping and radio-telemetry. Survival and territory size were correlated positively, with each 0.1 ha decrease in territory size typically resulting in a 16.6% increase in mortality risk; mortality risk for squirrels with the smallest versus largest territories differed by up to 23-fold. Territory size was negatively related to local population density, but not to any attributes of individual squirrels, implying that, in this species, territory size may not be influenced strongly by individual quality. We conclude that while larger territories may confer a survival advantage to squirrels, territory size is unrelated to individual physical attributes, likely because costs associated with the acquisition of a larger or richer territory outweigh potential benefits of increased food access.     

Mate choice by marsh wrens: the influence of male and territory quality

If females choose breeding situations to maximize their fitness, then those features of the male and/or territory that are important in mate selection by females should affect female fitness, be assessable prior to mating, and vary among males. The purpose of this study was to identify characteristics of male quality and territory quality that fit these criteria for marsh wrens Cistothorus palustris. The male's contribution to nest defence appeared not to affect female success or choice. However, females that received male assistance with feeding young produced more and heavier fledglings than females without assistance. Males that fed young did not attract more mates. Few males in this population fed young, and no relationship was found between feeding effort and physical or behavioural features of the male. Results of multivariate analyses suggest that, within sites, the measures of territory quality used here cannot explain the variance in the number of young fledged per female or male harem size. The examination of arbitrary territories showed that male pairing success, female settlement order and predation patterns were not significantly correlated between years. The results suggest that territory quality does not influence female success or choice. These results are discussed in the light of earlier attempts to relate features of males and territories to mate selection by female passerines.     

Uganda kob prefer high-visibility leks and territories

In lekking species, where males provide estrous females withlittle more than sperm, it has been widely supposed that theonly possible benefits to females of mate choice are genetic.We studied female choice of leks and territories in a reduncineantelope, the Uganda kob (Kobus kob thomasi), and found thatfemales consistently preferred high-visibility mating sites.Leks were elevated and had shorter grass and fewer thicketsthan the surrounding areas. Changes in the number of male andfemale kob on 10 leks were correlated with changes in surroundinggrass height, and both females and males preferred leks withexperimentally reduced grass height over neighboring controls.Within a lek, territory popularity was the primary determinantof male daily mating success, and females preferred territoriesrelatively far from thickets, but removal of thickets did notaffect female territory preferences. Because lion hunting successon kob increases with grass height and thicket density, femalesmay benefit directly from these preferences by reducing therisk of predation.     

Cooperative Breeding and Group Structure in the Lake Tanganyika Cichlid Neolamprologus savoryi

As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding cichlid Neolamprologus savoryi. Breeding groups typically consisted of a large breeding male with one to four breeding females and three to 33 helpers (mean group size: 14.3 members). Group size was significantly related to breeding male and female body sizes, and larger males had more breeding females and larger sized male helpers. The size of the largest female in the group was positively related to the number and sizes of secondary breeding females and female helpers. In case of multiple breeding females, these females usually divided the group's territory into sub‐territories, each with its own helpers (subgroups). Interspersed between groups, independent fish were detected defending an individual shelter (4.4% of all fish). In 9% of the groups no breeding female was present. All group members participated in territory defence and maintenance, and showed submissive behaviours to larger group members. As expected, the level of between‐subgroup conflicts was high compared with the level of within‐subgroup conflicts. We compare these results with data available from other cooperatively breeding fishes.     

Fitness correlates of male coloration in a Lake Victoria cichlid fish

Sexual selection by female choice has contributed to the rapidevolution of phenotypic diversity in the cichlid fish speciesflocks of East Africa. Yet, very little is known about the ecologicalmechanisms that drive the evolution of female mating preferences.We studied fitness correlates of male nuptial coloration ina member of a diverse Lake Victoria cichlid lineage, Pundamilianyererei. In this species, male red coloration is subject tointraspecific sexual selection by female mate choice. Male nuptialcoloration plays a critical role also in reproductive isolationbetween this species and the closely related sympatric speciesP. pundamilia. Here, we show that P. nyererei male colorationis carotenoid based, illustrating the potential for honest signalingof individual quality. In a wild population, we found that variationin male coloration was not associated with variation in a setof strongly intercorrelated indicators of male dominance: malesize, territory size, and territory location. Instead, the 2male characters that predominantly determine female choice,territory size and red coloration, may be independent predictorsof male quality: males with bright red coloration and largeterritories had lower parasite infestation rates. As a result,female preferences tended to select against heavily parasitizedmales. Consistent with parasite-mediated sexual selection, maleshad higher and more variable parasite loads than females.     

Resource attractiveness of the male beaugregory damselfish and his decision to court or defend

We examined the decisions territorial male beaugregory damselfish (Stegastes leucostictus) make when presented with mating and aggressive situations simultaneously. Specifically, we testedhow males responded to simultaneous and consecutive presentationsof conspecific males and females in bottles. We hypothesizedthat (1) territorial males would show lower levels of courtshiptoward females when a competing male is also present comparedto when only the female is present and (2) territorial maleswould show higher levels of aggression toward intruding maleswhen a female is also present on their territories than whenonly the intruder is present. We predicted that males withhigh-quality breeding sites would court females and attackcompetitors more vigorously than males with low-quality breedingsites. Males on low-quality breeding sites exhibited fewerconspicuous courtship displays toward bottled females and alower bite rate toward bottled males than did the males onhigh-quality breeding sites. We concluded that poor breeding-sitequality was responsible for the decline in the most conspicuous aspects of both courtship and aggression. When presented simultaneouslywith a bottled male and a bottled female, defenders of bothbreeding-site types drastically reduced the number of courtshipdisplays and the amount of time they spent near the female.Thus, all aspects of courtship were reduced in the presenceof a male intruder. Time spent near the bottled male also decreased in these simultaneous presentations; however, this decreasewas less dramatic than the reduction in time spent near bottledfemales. Habitat quality did not affect these trade-off decisions,but the bite rate exhibited toward the bottled male increasedin the simultaneous presentations compared to the single presentations.Due to this increase in a territorial male's defensive behaviorwhen a female is present, we conclude that the presence of afemale temporarily increased the value of a territory. We suggestthat the possible loss of a territory to an intruding maletakes priority over the potential benefits of successfullycourting a single female and that it is a male's future reproduction,as well as his current reproduction, by which he assesses hisbenefits.