Polygyny in the pied flycatcher,Ficedula hypoleuca: a test of the deception hypothesis

The deception hypothesis has been proposed as an explanation for polygyny in the pied flycatcher. According to this hypothesis, already-mated males hide their mating status with polyterritorial behaviour and thereby increase their chances of obtaining a second mate. In a study area at Oslo, Norway, secondary females raised 84% as many fledglings as did concurrent monogamous and primary females. The unmated males sang most of the time near their nest site, whereas the already-mated males frequently disrupted singing for longer periods in their secondary territories to visit their primary nest; such visits to the primary nest occurred both before and after the time of their second mating. The behaviour of the males suggests that deception of females is not an evolutionarily stable strategy, as an observant female would soon discern the male's status. Another difficulty with the deception hypothesis is that secondary females laid larger clutches than primary females. The number of young fledged from secondary nests was not dependent on the distance to the primary nest. The deception hypothesis was not supported by the data, and the reduced reproductive success of secondary females may be explained by the cost of searching for a mate.     

On the song resumption, polyterritorial behaviour and their population context in the Sedge Warbler Acrocephalus schoenobaenus

Mating tactics in species with facultative polygyny seem to be very flexible and to depend on local environmental conditions. We analysed the habitat and population contexts of territorial behaviour, associated with polygyny, in a population of Sedge Warblers Acrocephalus schoenobaenus inhabiting natural wetlands. Nearly one-third of all breeding males (46 individuals) resumed song after completing their mating with the first female, in order to attract another one. Resuming males were usually the earliest arrivals. There was a continuity in the territorial behaviour between resuming song on first territory and polyterritorial behaviour. Fifty-nine percent of resuming males set up second territories, clearly separated from the first. The second territory was usually located close to the primary female activity area. The quality of the first and second territories were correlated, with second territories being significantly inferior. However, their quality was not significantly different from the territories of non-breeding males. The quality of the second territories was also negatively related to the distance from the first territories. Polyterritorialism was influenced by population numbers: the higher the number of territorial males, the lower the number of second territories settled and the lower their average quality. Although the polygyny frequency in the studied population was very low, polyterritorial males were significantly more likely to be polygynous. We concluded that polygyny frequency can be significantly influenced by population numbers, which might be one of the main factors responsible for the variability in the mating system in this species.     

Female-female aggression and female mate choice on black grouse leks

We studied female-female aggression in relation to female mate choice in black grouse, Tetrao tetrix, in central Finland, in 1994-1998. Aggression occurred on average every other minute when there was more than one female on a territory, and aggressive behaviour was most prominent when several females attended the lek. Interactions tended to be proportionally most frequent on the territories of the highest-ranking males, although not significantly so. Females that were chased by other females did not mate with lower-ranking males than their aggressors did. Furthermore, chased females were only rarely (6% of cases) forced to move off the territory by agonistic interactions and copulations were disrupted by other females even less often (3% of cases). The choice of a mating territory did not depend on the outcome of aggression even though the aggressors were more likely to mate on the territory where aggression occurred than elsewhere. There was a marginally significant tendency for aggressors to mate earlier in the season. Females placed themselves further away from other females on the territory when soliciting a copulation than just before aggression. Our results suggest that aggression between females does not effectively constrain female choice in black grouse. Its function may be to aid females to secure undisturbed mating opportunities for themselves rather than to prevent others from mating with a particular male. Copyright 2000 The Association for the Study of Animal Behaviour.     

An experimental analysis of mate choice in the wren: a monomorphic, polygynous passerine

Male wrens (Troglodytes troglodytes) construct nests that areused in their display to females. Previous work has suggestedthat the number of vacant nests may be used as a mate choicecue. Correlational data from 1992 confirmed that females appearedto be assessing die number of vacant nests on a male's territoryand preferentially mating with males with more nests. Male taillengdi was also correlated widi mating success. In 1993 thenumbers of nests on territories was experimentally manipulated,the female setdement patterns confirmed that die number of vacantnests did mediate mate choice. Male tail length failed to explainadditional variance in mating success when die variance explainedby the experimental manipulation was removed, suggesting diatdie original correlation arose because both tail length andmating success were correlated widi a confounding variable.The structure of the vegetation in a male's territory influencedmating success. This appeared to be due to nests surviving betterin territories widi dense vegetation. Males on territories inwhich nests survive well had longer tails. Male-male competitionfor good territories may explain die observed effects of malemorphology on mating success. Furdier analysis of die nest choicedata showed diat all nests had an equal chance of being usedby a female. The fact diat all nests had an equal probabilityof being chosen by a female means diat each additional nestbuilt by a male wren results in die same increase in matingsuccess. This suggests diat die benefits to males of nest buildingincrease linearly. The number of nests on a territory will beaffected by various factors such as predation pressure, nestbuilding rate, and vegetation structure. The information diatfemales are getting by assessing such a signal is discussed.     

Effects of a food supplementation experiment on reproductive investment and a post-mating sexually selected trait in magpies Pica pica

Food availability is an important factor affecting breeding success in birds. Food supplementation experiments in birds have in general focused on the effects on reproductive success in terms of female investment (laying date, clutch size, egg size), however, it is also known that the estimation of mate quality based on sexually selected signals influences female reproductive investment. In the particular case of magpies, females use nest size, a post-mating sexually selected signal, to assess male's likelihood to invest in reproduction, and accordingly adjust reproductive investment (clutch size). Then, the possible effects of food supplementation on female reproductive investment could be mediated by other variables related to parental quality, such as nest size in magpies. In the present study, we explore if higher food availability in a magpie territory affected both male sexually selected traits (i.e. nest size) and female reproductive investment (laying date, egg size, clutch size). We performed a food supplementation experiment in which we experimentally increased food availability in several magpie territories, keeping others as controls. In food-supplemented territories, males built significantly larger nests and females significantly increased egg size by 4.1% compared to control females. Results suggest that the continuous provisioning of protein rich food allowed magpie females to increase egg size. However, laying date and clutch size did not differ between control and food-supplemented magpie pairs. Food availability also affected the relationship between female reproductive investment and nest size. In control territories, females decreased their egg size in response to a larger nest, whereas a tendency for the opposite relationship was revealed in food-supplemented territories. We discuss the possibility that magpie females adopt different strategies for reproductive investment according to food availability.     

Breeding Season Aggression of Female and Male Eastern Bluebirds (Sialia sialis) to Models of Potential Conspecific and Interspecific Egg Dumpers

Naturally occurring aggression between female eastern bluebirds (Sialia sialis) is dramatic, resulting in severe injuries and even death. Furthermore, aggression among bluebirds is usually sex specific: males attack males, females attack females. We hypothesized that the primary function of female-female aggression is to guard against the threat of intraspecific egg dumping and that, in this context, same sex aggression is related to the possibility of advantages for males of parasitism (egg dumping) of their nests. Our hypotheses to explain variation in naturally occurring aggression predict temporal variation in aggressive tendency within nest cycles and between the sexes depending on asymmetries in threats to the residents. We report the results of experimental trials in the field designed to determine temporal variation in the aggressive tendencies of resident females to models of intruder females of two species, eastern bluebirds and brown-headed cowbirds (Molothrus ater). Both species dump eggs in the nests of bluebirds. Female aggression to eastern bluebird models is greatest during early stages of nest cycles; the patterns are most consistent with protection against egg dumping and protection of nest sites from usurpation. Male residents seldom attack female eastern bluebird models, but often attack models of female brown-headed cowbirds, a result inconsistent with the hypothesis that patterns of differential parental care control aggression of female and male residents.     

Uncertainty in territory quality affects the benefits of usurpation in a Mediterranean wrasse

Individuals should defend sites when the expected benefits ofthe territory exceed the cost of defense. However, if territoryqulaity is unpredictable or difficult to assess, the expectedpattern of territorial behavior is less clear. In a Mediterraneanwrasse, Symphodus ocellatus, mating success is skewed with 2%of nesting males getting more than 20% of the spawning success.Yet, variation in mating success is not explained by any knownphysical characteristic of males or their territories. Instead,females prefer nests with a recent history of mating successbecause males are less likely to desert the offspring she leavesbehind. Thus, territory quality is transient and determinedby interactions between the sexes. I measured the frequencyof territorial takeovers and the uncertainty in mating successamong days at a nest. Observations indicated that S. ocellatusmales usurped their neighbor's successful nests when males wereunsuccessful and larger than their successful neighbor. Sitesthat achieved mating success had a significantly higher probability(0.84) of remaining sucessful between consecutive days thanunsuccessful territories had of becoming successful (0.30).Unsuccessful males obtained higher and more certain fitnessreturns if they usurped a successful neighbor's territory. Interactionswithin and between the sexes drive uncertainty in success, whichinfluences territorial behavior in this species.     

The mating system of the White-throated Magpie-jay Calocitta formosa and Greenwood's hypothesis for sex-biased dispersal

Greenwood explained the different sex bias in dispersal of birds (usually female biased) and mammals (usually male biased) by a difference in mating systems: male birds primarily defend resources while male mammals primarily defend females. The White-throated Magpie-jay Calocitta formosa is unusual among birds in that females are philopatric and jointly defend permanent resource territories while males disperse before they are 2 years of age. One female in a group is the primary breeder. One male joins the group permanently as her mate. Males that do not have a permanent breeding position circulate among groups and attempt to mate with both the primary breeding female and other group females. Other females feed the primary breeder and her offspring and also pursue other reproductive behaviour, including secondary nesting in the territory and egg dumping into the primary breeder's nest. I argue that the unusual dispersal pattern in this species is a result of the alternative reproductive strategies that can be pursued by males and females excluded from being primary breeders. The White-throated Magpie-jay conforms to Greenwood's predictions: males pursue a mate defence rather than resource defence mating system and they are the dispersing sex. The primary factor influencing alternative reproductive tactics may be asynchronous reproduction among groups during the long breeding season arising from frequent renesting in an area of high nest predation.     

The social organization of a sexually dimorphic honeyeater: the Crescent Honeyeater Phylidonyris pyrrhoptera,at Wilsons Promontory,Victoria

The social organization of the sexually dimorphic and dichromatic Crescent Honeyeater Phylidonyris pyrrhoptera (Latham 1801) was studied at Wilsons Promontory National Park between January 1994 and January 1997. All breeding attempts at one site were followed during the spring and summer of 1996. Most pairs were multibrooded, with pair-bonds maintained throughout the study. Breeding males held well-defined territories. Females, although generally restricting their activities to within their mate’s territory, visited other males’ territories more frequently than did their mates and did so close to the time of egg laying. Males aggressively chased intruding males, but appeared to permit intrusions by non-mate females. Circumstantial evidence suggests some males may kill neighbour’s nestlings. Female Crescent Honeyeaters are solely responsible for nest construction and incubation. While both sexes attended nestlings, males contributed to parental care significantly less than females. Males also provided significantly less parental care than has been reported for monomorphic species of honeyeater. Single syllable calls are given throughout the year. Peaks in the rate of double and multisyllable calls corresponded with peaks in breeding activity. Only males were observed uttering loud multisyllable calls. In contrast to predictions arising from sexual selection theory and observations of the mating system of sexually dimorphic hummingbirds, the population of Crescent Honeyeaters studied exhibited a socially monogamous mating system. However, the very limited male role in parental care and non-observance of male territory boundaries by females suggest the genetic mating system may not be one of monogamy.     

Preliminary study on female choice of mates versus sites in a wrasse, Cirrhilabrus temminckii

Female choice of mates versus sites was studied in a wrasse, Cirrhilabrus temminckii. Males had territories within a restricted area on a rocky slope at which females visited and pair-spawned pelagic gametes. Females visited several males or territories before spawning, suggesting the opportunity of female choice. Of the four characteristics of territorial males examined—body size, ratio of pelvic fin length to body size, courtship, frequency and territory depth—only territory depth was significantly correlated with daily mating success of males. The former three male characters were not related to territory depth. These results suggest that female C. temminckii chooses deep sites rather than specific mates in mating.     

Influences on variation in territorial tenures of male white-faced dragonflies (Leucorrhinia intacta) (Odonata: Libellulidae)

Some individuals in species with extended periods of territorial occupancy may change territory locations within a single bout of territorial activity. Length of occupancy of mating territories among males in a local population of white-faced dragonflies (Leucorrhinia intacta) varied from more than 6 h to 15 min or less. Males with short tenures often established territories in several locations on the pond during a day. Several hypotheses have been proposed to explain shifting territorial sites rather than remaining in a single site during one bout of territoriality. We attempted to test the hypothesis that males shift to leave low-quality sites. Site quality may be affected by costs of defense in relation to intruder rate and the mating benefits of holding the territory. To test whether variation in these possible effects of benefits and costs of territoriality influenced tenure, we manipulated local quality of oviposition substrate and perch density. The quality of oviposition substrate, but not perch density, influenced both potential benefits and costs of territoriality. Female density was higher in areas with good substrate, but so were rates of males intruding into the territories, rates of chasing by territorial males, and local density of territorial males. More matings occurred in areas with good substrate, but among males with tenures of 15 min or more, mating success per male and tenure lengths did not differ statistically among treatments. Defense costs were low for all treatments and perhaps were not an important influence on tenure duration. Territorial males in this population probably adjusted local density to expected mating success by initial choice of site rather than by varying tenure length. Variation in tenure length at a site resulted, in part, from stochastic external factors, such as predation attempts.     

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.     

Territoriality and Male Mating Success in the Dart-poison Frog,Epipedobates femoralis (Dendrobatidae,Anura)

The social and reproductive behaviour of the dart-poison frog, Epipedobates femoralis, was studied in Amazonian Peru for 14 months. Males defended territories with advertisement calls and, ultimately, fighting. Territory size ranged from 0.25 to 26 m² and was positively correlated with duration of residence and calling activity of the owner. Females were not territorial and were never attacked when approaching calling males. Males and females only mated once and females sampled calling males before mating. Male mating success was closely correlated with territory size and calling activity. No correlation was found between male body size and mating success. Territories provide residents with sufficient space for mate attraction and reproduction without interference from rivals. Since territory size is dependent on calling activity which involves high energetic costs, it is suggested that territory size reveals male quality.     

Mating systems and territory in Lapwings Vanellus vanellus

In a population of Lapwings Vanellus vanellus studied for 5 years near Bergen, southwester Norway, 23–41% of the males were polygynous, having two and sometimes three mates, whereas 50–77% were monogamous and 0–21% remained unmated. Bachelors held territories in or immediately adjacent to the study area each of the years. As predicted from the Polygyny Threshold model, primary females generally laid eggs earlier than monogamous females, but the overlap in laying dates was substantial between these two classes. The number of females and start of breeding on the territories were analysed in relation to nine variables pertaining to safety from predation and to food. Of these, territory size correlated most consistently with number of females (positively) and the laying of first egg (negatively). Numbers of females observed were not significantly different from numbers expected from territory size in 4 out of 5 years; however, earlier start of breeding on large territories indicated that females did not settle according to the Neutral Mate Choice model. The Female-biased Sex Ratio hypothesis was refuted, unmated territorial males being available throughout the breeding seasons.     

Male dimorphism, territoriality and mating success in the tropical damselfly, Paraphlebia zoe Selys (Odonata: Megapodagrionidae)

The tropical damselfly Paraphlebia zoe has two male morphs: a black-winged (BW) male which is associated with territorial defense of oviposition sites; and a hyaline-winged (HW) male similar in appearance to females, and, compared to the black morph, less frequently found defending territories. In a wild population of this species, we first assessed the relationship between phenotypic traits [male morph, size and territorial status (being territorial or non-territorial)], their role on mating success, and the degree to which a particular territory may contribute to male mating success. Second, to relate a physiological basis of being territorial we compared both morphs in terms of muscular fat reserves and thoracic muscle, two key traits related to territory defense ability. Males of both morphs defended territories although the BW males were more commonly found doing this. BW males were larger than HW males and size predicted being territorial but only within HW males (territorial males were larger) but not in BW males. Male mating success was related to territorial status (territorial males achieved a higher mating success), but not to morph or size. Furthermore, territory identity also explained mating success with some territories producing more matings than others. The BW morph stored more fat reserves which may explain why this morph was more likely to secure and defend a place than the HW morph. However, the HW morph showed higher relative muscle mass which we have interpreted as a flexible strategy to enable males to defend a territory. These results are distant to what has been found in another male dimorphic damselfly, Mnais pruinosa, where the advantage of the non-territorial morph relies on its longevity to compensate in mating benefits compared to the territorial morph.     

The role of territory settlement,individual quality,and nesting initiation on productivity of Bell's vireos Vireo bellii bellii

Variation in habitat quality among territories within a heterogeneous patch should influence reproductive success of territory owners. Further, territory settlement order following an ideal despotic distribution (IDD) should predict the fitness of occupants if territory selection is adaptive. We recorded settlement order and monitored nests in territories occupied by individually marked Bell's vireos Vireo bellii bellii across a range of shrubland habitats in central Missouri, USA. We used an information theoretic approach to evaluate multiple hypotheses regarding the relationship between territory settlement order and seasonal territory productivity (productivity), which we define as the number of young fledged from all nest attempts in a territory. Territory settlement order and arrival date were not analogous and later arriving males displaced early settlers in 13 of 49 territories. Settlement order and lay date together were the best predictors of a territory's productivity; productivity decreased 2.08 young from earliest to latest settlement rank and lay date. Males that defended the same territory in successive years occupied territories with earlier settlement dates, but we found little evidence that age or prior ownership influenced productivity. Territory selection by male Bell's vireos was adaptive because males preferred to settle in territories that had high seasonal offspring production, but even though settlement rank was linked to territory quality, high productivity was only realized on high quality territory when also linked to early nest initiation date. While settlement rank was related to territory quality, obtaining a high quality territory had to be combined with early nest initiation to maximize productivity. We found support for the IDD hypothesis because the highest quality territories, (i.e. most productive), were settled earlier. Research that identifies high quality habitat by linking individual fitness with habitat characteristics may elucidate the importance of habitat quality, individual experience and temporal factors to productivity of Bell's vireos.     

Manipulations of male parental investment in polygynous pied flycatchers, Ficedula hypoleuca

We designed three experiments to identify important cues asto how bigamous male pied flycatchers (Ficedula hypoleuca) apportionnestling feeding between their broods. Normally, males givepriority to their primary brood, that is, the brood of theirfirst-acquired mate. In the first experiment, we reversed thehatching order of primary and secondary broods by substitutingeggs. Males responded by reallocating their efforts in favorof secondary broods. Males thus favored the brood that hatchedfirst, irrespective of female mating order. In the second experiment,carried out on the same males when the younger brood was 4 or5 days old, we transferred the older brood to the nest of theyounger, and vice versa; the males changed their investmentpattern accordingly, still giving priority to the older brood.In the third experiment, primary and secondary broods were madeto hatch on the same day. In these cases, males divided theirnestling feeding efforts fairly equally between the broods.The results reveal a remarkable flexibility of male investmentdecisions, which is discussed in light of parental investmenttheory. The fact that the degree of male assistance to secondarymates is variable and that it is to a large extent predictablefrom the nest initiation asynchrony of the two females has importantimplications for our understanding of the polyterritorial matingsystem of this species.     

Males Exhibit Novel Relationships of Dominance with Nest Departure in the Social Paper Wasp Mischocyttarus mastigophorus (Hymenoptera: Vespidae)

In many animal societies, an individual's opportunities to reproduce correspond to their position in a dominance hierarchy. In primitively eusocial paper wasps, female social dominance and direct reproduction are positively associated with taking food from nest mates, but both negatively correlate with foraging flights. Female paper wasps reproduce by laying eggs in their nest, while males reproduce by leaving the nest to copulate. Males of Mischocyttarus mastigophorus are unusual because they reside on their natal nests for prolonged periods, and males direct aggression towards female nestmates. Mischocyttarus mastigophorus males provide an opportunity to further analyse the relationships between dominance, nutrition and nest departure. We found males' rates of social aggression, food taking behaviour, and rates of nest departure were positively correlated. Furthermore, males that initiated aggression at younger ages also began flying earlier, and males engaged in all three behaviours at younger ages than females. Male social aggression may lead to nutrient acquisition, which enable males to depart from the nest. We hypothesise that male nest departure could be adaptive if it increases male mating opportunities. This could account for the positive relationship between dominance and nest departure for males.     

Anthropogenic noise affects female,not male house wren response to change in signaling network

Vocal signals mediate social relationships, and among networks of territorial animals, information is often shared via broadcast vocalizations. Anthropogenic noise may disrupt communication among individuals within networks, as animals change the way they vocalize in noise. Furthermore, constraints on signal transmission, including frequency masking and distance, may affect information exchange following a disruption in social networks. We tested the hypothesis that signaling interactions within networks of breeding male and female house wrens (Troglodytes aedon) depend on distance, ambient noise, and receiver nesting stage. We used playback experiments to simulate territorial intrusions with and without noise playbacks on the territories of established males and simultaneously recorded the vocal responses of neighbors. To examine whether intrusions impacted interactions between males, we used randomization tests to determine whether treatment, distance, noise, or nesting stage affected vocal coordination between challenged and neighboring males. We also quantified singing patterns to explore whether intrusions on territories of challenged males affected singing by males and females on neighboring territories. Males sang at the lowest rates and were less likely to overlap songs with the challenged male when their partner was laying, compared to males during early and late nesting stages. Noise and distance did not affect vocal coordination or male singing rates. Fewer females sang during the intruder-only treatment compared to the control and intrusions with noise. Added noise in the territories of challenged males may have masked signals, and as a result, females only changed their behavior during the intruder-only treatment. Our results suggest that the fertility of breeding partners may be more important to males than short-term changes on rival male territories. Elevated noise did little to alter male responses to threats within networks. Females appeared to eavesdrop on interactions involving neighboring males, but noise may have prevented detection of their interactions.     

Patterns of breeding behaviour and plasma levels of hormones in a free-living population of Pied flycatchers, Ficedula hypoleuca

Plasma levels of luteinizing hormone (LH) and steroid hormones were measured by radioimmunoassay in a series of plasma samples collected from a free-living population of Pied flycatchers, Ficedula hypoleuca. Both males and females have similar circulating levels of LH and testosterone when they arrive in the breeding area. However, as territories and pair bonds are established, and as courtship and nest-building ensue, the plasma levels of testosterone in males become elevated over those of females, although a lesser peak also occurs in females. As the egg laying phase and incubation begin, plasma levels of LH and testosterone decline sharply in both sexes. On the other hand polyterritorial males, that establish secondary territories, maintain higher levels of LH and testosterone than males remaining in the home-territory, at least until they return to the home-territory, usually at the middle part of the incubation period. By this time polyterritorial males also have basal levels of these hormones. Curiously, females on home-territories show a small, but significant, rise of circulating LH and testosterone at the time the males return.
In males, plasma levels of corticosterone are elevated from the time of arrival on the breeding grounds until the end of the nest-building period. Thereafter corticosterone levels decline in males staying on the home-territory but remain elevated in polyterritorial males until the latter return to the home-territory. In contrast, circulating levels of corticosterone in females are only elevated for brief period during egg laying.