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ItemParental behaviour and mating system of the fairy martin, Hirundo Ariel(University of Melbourne, 1997)The birds are unique among the major animal taxa in that biparental care is common, occurring in about 90% of the 9000 or so extant species. Among these biparental species there is dramatic variation, both across and within taxa, in the extent to which males and females contribute to incubation and nestling care. However, despite considerable interest, the causes of this variation generally remain poorly understood. The aim of this thesis was to examine a range of factors that may contribute to variation in the participation of males and females within a population of the socially monogamous fairy martin, Hirundo ariel. Fairy martins are endemic to Australia and nest colonially in aggregations of enclosed mud nests. The sexes are morphologically similar, although only the female acquires a brood patch during the breeding season. In the Yarra Valley, where this study was conducted, colonies ranged in size from 8 to 29 nests. Over the three years from 1993 to 1996, birds arrived in the study area in September and usually commenced laying in October, although nesting activities were generally asynchronous both between and within colonies. Most colonies contained active nests until February. An average of at least 16% of adults and 5% of fledglings returned to the study area in the following year. Returning adults generally nested at the same colony site as the previous year (68%), while most first year birds nested at sites other than their natal colony (75%). Adult males were more likely to return than adult females. Similarly, fledgling males were more likely to return than fledgling females (assuming an equal sex ratio at fledging). Both sexes participated in building the mud nest, incubating the clutch and feeding the nestlings. Clutch size ranged from two to five (mean = 3.5) and declined during the course of the season. The clutch was attended for an average of 88% of the time during daylight hours, although attendance generally declined during the course of the day. Females were more attentive of the clutch than males (56%), resulting primarily from longer incubation bouts, but also shorter recess periods. Females almost invariably attended the clutch overnight, and were usually accompanied by the male. Total clutch attendance did not vary with clutch size, however, male attendance increased with clutch size while female attendance decreased. Total attendance increased with clutch age resulting from an increase in female but not male attentiveness. Both sexes were more attentive of the clutch on cooler days, especially in the early morning and late afternoon. The duration of the incubation period varied from 12 to 18 days (mean = 13.7), and was shorter if the clutch was attended for a greater proportion of the day. A mean of 1.8 chicks fledged per completed clutch, while 60% of these clutches produced at least one chick. The period from hatching to fledging varied from 17 to 32 days (mean = 22.1), and was longer for larger broods. Fledging success was highest during the middle of the breeding season (December). Adverse weather conditions, resulting in clutch and brood abandonment, were the most common cause of nest failure, and on several occasions also resulted in adult mortality. Pairs produced from zero to eight fledglings per season (mean = 2.8), with those that commenced nesting earlier in the season having higher annual productivity. Parents visited larger broods more frequently, although the visit rate per chick declined with brood size. Visit rate generally increased with brood age, reaching a plateau between days 8 and 16, before declining until the chicks fledged. The relative contribution of the sexes did not vary with brood size or brood age. Brood visit rate generally increased with ambient temperature and decreased during periods of rainfall. Male participation in incubation (both absolute and relative to his mate) declined with an increase in the proportion of fertile females in the colony. Males were most 'responsive' to the availability of fertile females in the early morning, when copulations are likely to occur most frequently. Furthermore, the decline in male contribution with the proportion of fertile females was greater among males with smaller than average clutches. Male contribution to brood visits also tended to decline with an increase in the proportion of fertile females over the most demanding days of the nestling period. These patterns, each demonstrated for the first time, provide strong support for the presence of a reproductive trade-off for males between parental and extra-pair copulation effort. This trade-off may be widespread among the 90% of bird species where males contribute to parental care. Microsatellite parentage analysis revealed that 14% (29/207) of young were not sired by the putative father, while 2% (4/207) appeared to be the result of conspecific brood parasitism. The frequency of extra-pair fertilizations was not influenced by nesting synchrony, but tended to increase with colony size. The genetic fathers of extra-pair young had larger tarsi, greater previous breeding experience, and were more attentive to their own clutch than both the male that they cuckolded and the other males in the colony. Moreover, males with previous breeding experience had greater paternity of their own brood than those without. These results are consistent with female extra-pair mate choice for 'good genes'. Male incubation attendance, both across and matched for bird, was lower for clutches with reduced paternity. Furthermore, males with reduced paternity took longer in returning to their clutch after a disturbance than males with complete paternity. Together, these results suggested that males may adjust their level of parental investment in relation to their confidence of paternity. However, these results were confounded by the relationship between male contribution to incubation and the availability of fertile females in the colony. Mean nestling mass was lower in broods with reduced paternity however there was no evidence that this resulted from a reduced rate of feeding by cuckolded males. Among the Hirundinidae, and birds in general, species with male incubation are usually sexually monomorphic and have relatively low frequencies of extra-pair paternity. This study indicates that the biparental fairy martin conforms to this pattern. The evolution/ maintenance of male incubation in fairy martins may, in part, relate to the small body size and high nesting density of this species.
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ItemParental behaviour and mating system of the fairy martin, Hirundo Ariel(University of Melbourne, 1997)The birds are unique among the major animal taxa in that biparental care is common, occurring in about 90% of the 9000 or so extant species. Among these biparental species there is dramatic variation, both across and within taxa, in the extent to which males and females contribute to incubation and nestling care. However, despite considerable interest, the causes of this variation generally remain poorly understood. The aim of this thesis was to examine a range of factors that may contribute to variation in the participation of males and females within a population of the socially monogamous fairy martin, Hirundo ariel. Fairy martins are endemic to Australia and nest colonially in aggregations of enclosed mud nests. The sexes are morphologically similar, although only the female acquires a brood patch during the breeding season. In the Yarra Valley, where this study was conducted, colonies ranged in size from 8 to 29 nests. Over the three years from 1993 to 1996, birds arrived in the study area in September and usually commenced laying in October, although nesting activities were generally asynchronous both between and within colonies. Most colonies contained active nests until February. An average of at least 16% of adults and 5% of fledglings returned to the study area in the following year. Returning adults generally nested at the same colony site as the previous year (68%), while most first year birds nested at sites other than their natal colony (75%). Adult males were more likely to return than adult females. Similarly, fledgling males were more likely to return than fledgling females (assuming an equal sex ratio at fledging). Both sexes participated in building the mud nest, incubating the clutch and feeding the nestlings. Clutch size ranged from two to five (mean = 3.5) and declined during the course of the season. The clutch was attended for an average of 88% of the time during daylight hours, although attendance generally declined during the course of the day. Females were more attentive of the clutch than males (56%), resulting primarily from longer incubation bouts, but also shorter recess periods. Females almost invariably attended the clutch overnight, and were usually accompanied by the male. Total clutch attendance did not vary with clutch size, however, male attendance increased with clutch size while female attendance decreased. Total attendance increased with clutch age resulting from an increase in female but not male attentiveness. Both sexes were more attentive of the clutch on cooler days, especially in the early morning and late afternoon. The duration of the incubation period varied from 12 to 18 days (mean = 13.7), and was shorter if the clutch was attended for a greater proportion of the day. A mean of 1.8 chicks fledged per completed clutch, while 60% of these clutches produced at least one chick. The period from hatching to fledging varied from 17 to 32 days (mean = 22.1), and was longer for larger broods. Fledging success was highest during the middle of the breeding season (December). Adverse weather conditions, resulting in clutch and brood abandonment, were the most common cause of nest failure, and on several occasions also resulted in adult mortality. Pairs produced from zero to eight fledglings per season (mean = 2.8), with those that commenced nesting earlier in the season having higher annual productivity. Parents visited larger broods more frequently, although the visit rate per chick declined with brood size. Visit rate generally increased with brood age, reaching a plateau between days 8 and 16, before declining until the chicks fledged. The relative contribution of the sexes did not vary with brood size or brood age. Brood visit rate generally increased with ambient temperature and decreased during periods of rainfall. Male participation in incubation (both absolute and relative to his mate) declined with an increase in the proportion of fertile females in the colony. Males were most 'responsive' to the availability of fertile females in the early morning, when copulations are likely to occur most frequently. Furthermore, the decline in male contribution with the proportion of fertile females was greater among males with smaller than average clutches. Male contribution to brood visits also tended to decline with an increase in the proportion of fertile females over the most demanding days of the nestling period. These patterns, each demonstrated for the first time, provide strong support for the presence of a reproductive trade-off for males between parental and extra-pair copulation effort. This trade-off may be widespread among the 90% of bird species where males contribute to parental care. Microsatellite parentage analysis revealed that 14% (29/207) of young were not sired by the putative father, while 2% (4/207) appeared to be the result of conspecific brood parasitism. The frequency of extra-pair fertilizations was not influenced by nesting synchrony, but tended to increase with colony size. The genetic fathers of extra-pair young had larger tarsi, greater previous breeding experience, and were more attentive to their own clutch than both the male that they cuckolded and the other males in the colony. Moreover, males with previous breeding experience had greater paternity of their own brood than those without. These results are consistent with female extra-pair mate choice for 'good genes'. Male incubation attendance, both across and matched for bird, was lower for clutches with reduced paternity. Furthermore, males with reduced paternity took longer in returning to their clutch after a disturbance than males with complete paternity. Together, these results suggested that males may adjust their level of parental investment in relation to their confidence of paternity. However, these results were confounded by the relationship between male contribution to incubation and the availability of fertile females in the colony. Mean nestling mass was lower in broods with reduced paternity however there was no evidence that this resulted from a reduced rate of feeding by cuckolded males. Among the Hirundinidae, and birds in general, species with male incubation are usually sexually monomorphic and have relatively low frequencies of extra-pair paternity. This study indicates that the biparental fairy martin conforms to this pattern. The evolution/ maintenance of male incubation in fairy martins may, in part, relate to the small body size and high nesting density of this species.
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ItemMale germ cell transplantation(University of Melbourne, 1995)This thesis has explored the success of male germ cell transplantation in rats. Busulfan-treated black and white Long Evans rats were used as the germ cell-recipients, and white Sprague Dawley fetal and neonatal rats were used to provide donor germ cells which were transplanted by 2 different routes. Adult Long Evans male rats were injected intraperitoneally once or twice with busulfan, an alkylating agent, at a dose of 10 mg/kg body weight. Forty four days after the first busulfan treatment, their testes were essentially devoid of spermatogenic cells and therefore suitable as germ cell recipients. Following exposure to busulfan during intrauterine life on which primordial germ cells (PGCs) were exclusively destroyed, the rats at days 4 - 5 of age were devoid of germ cells and therefore used as newborn recipients. Donor fetal and newborn testes were excised and dissociated by trypsin-EDTA (fetal tissues) or collagenase/trypsin-EDTA (neonatal tissues) treatment. PGCs and gonocytes were purified by equilibrium centrifugation on a discontinuous Percoll gradient column. Alkaline phosphatase activity was used as a marker for both PGCs and gonocytes. Trypan blue exclusion was used to determine cellular viability. The donor germ cells were injected into the testes of the anaesthetised recipients by retrograde injection into the rete testis, or random multiple testicular injections. A total of 74 recipient rats were transplanted with either primordial germ cells or gonocytes. Forty eight of them were paternity tested with 563 fertile Sprague Dawley females, and they produced 2,280 progeny. However, none of the progeny was derived from the donor germ cells, as judged by coat colour. However, a detailed histological analysis of the recipient testes showed that the donor germ cells had apparently differentiated into mini-tubules or irregular segments of seminiferous epithelium within the lumen of the host�s seminiferous tubules, and exhibited qualitatively normal spermatogenesis in 13 out of 19 animals following rete testis injections. The stage of spermatogenesis of the donor intraluminal seminiferous epithelium was closely synchronised with that of the host�s epithelium, suggesting that the spermatogenic cycle is regulated locally by the intraluminal microenvironment. None of 15 neonatal or adult recipients given random multiple intratesticular injections showed any evidence of intraluminal spermatogenesis, suggesting that the donor germ cells were unable to migrate through the basement membrane of the host seminiferous tubules. In summary, this thesis has demonstrated that it is possible to transplant purified PGCs and gonocytes from one rat to another. Male germ cell transplantation therefore provides an interesting new tool for investigating the control of spermatogenesis, and if the success rate of the procedure can be improved, so that the donated germ cells all integrated with the host�s Sertoli cells, it could become an invaluable technique for manipulating the male germ cell line.
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ItemMale germ cell transplantation(University of Melbourne, 1995)This thesis has explored the success of male germ cell transplantation in rats. Busulfan-treated black and white Long Evans rats were used as the germ cell-recipients, and white Sprague Dawley fetal and neonatal rats were used to provide donor germ cells which were transplanted by 2 different routes. Adult Long Evans male rats were injected intraperitoneally once or twice with busulfan, an alkylating agent, at a dose of 10 mg/kg body weight. Forty four days after the first busulfan treatment, their testes were essentially devoid of spermatogenic cells and therefore suitable as germ cell recipients. Following exposure to busulfan during intrauterine life on which primordial germ cells (PGCs) were exclusively destroyed, the rats at days 4 - 5 of age were devoid of germ cells and therefore used as newborn recipients. Donor fetal and newborn testes were excised and dissociated by trypsin-EDTA (fetal tissues) or collagenase/trypsin-EDTA (neonatal tissues) treatment. PGCs and gonocytes were purified by equilibrium centrifugation on a discontinuous Percoll gradient column. Alkaline phosphatase activity was used as a marker for both PGCs and gonocytes. Trypan blue exclusion was used to determine cellular viability. The donor germ cells were injected into the testes of the anaesthetised recipients by retrograde injection into the rete testis, or random multiple testicular injections. A total of 74 recipient rats were transplanted with either primordial germ cells or gonocytes. Forty eight of them were paternity tested with 563 fertile Sprague Dawley females, and they produced 2,280 progeny. However, none of the progeny was derived from the donor germ cells, as judged by coat colour. However, a detailed histological analysis of the recipient testes showed that the donor germ cells had apparently differentiated into mini-tubules or irregular segments of seminiferous epithelium within the lumen of the host�s seminiferous tubules, and exhibited qualitatively normal spermatogenesis in 13 out of 19 animals following rete testis injections. The stage of spermatogenesis of the donor intraluminal seminiferous epithelium was closely synchronised with that of the host�s epithelium, suggesting that the spermatogenic cycle is regulated locally by the intraluminal microenvironment. None of 15 neonatal or adult recipients given random multiple intratesticular injections showed any evidence of intraluminal spermatogenesis, suggesting that the donor germ cells were unable to migrate through the basement membrane of the host seminiferous tubules. In summary, this thesis has demonstrated that it is possible to transplant purified PGCs and gonocytes from one rat to another. Male germ cell transplantation therefore provides an interesting new tool for investigating the control of spermatogenesis, and if the success rate of the procedure can be improved, so that the donated germ cells all integrated with the host�s Sertoli cells, it could become an invaluable technique for manipulating the male germ cell line.
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ItemThe role of Customary Marine Tenure and local knowledge in fishery management at West Nggela, Solomon Islands( 1998-04)A proper understanding of the management of small-scale subsistence and artisanal fisheries requires not only detailed sociocultural study, but comprehensive analysis of the state of the fished population(s) using rigorous stock assessment and other fisheries biology tools. This study comprises such an interdisciplinary approach taken in an attempt to understand subsistence and artisanal fishing at West Nggela, with a particular focus on the management of the artisanal trochus fishery. The importance of an understanding of Customary Marine Tenure is dealt with in some detail. An analysis of the various categories of fishers’ ecological knowledge about marine fauna, with an emphasis on trochus, is also presented, and discussed with respect to the categories of biological and ecological information considered by most fisheries biologists as essential to the assessment and management of a fishery. The theoretical basis of my approach to the study of local knowledge, which could broadly be termed “rationalist”, is discussed and defended against “postmodernist” criticisms. Trochus are currently overfished at most of the reefs I studied at West Nggela. Densities measured using mark-recapture were apparently low compared to well-managed fisheries elsewhere in the Pacific. The current market demand, and the ease of capture, storage and marketing of the product, indicate that pressure on the fishery (which includes some poaching) is likely to remain high, and some improvement in management is required. Egg-per-recruit and yield-per-recruit modeling indicates that enforcement of a minimum size limit of 8cm basal diameter would bring about immediate improvement in yields and recruitment in the fishery. Such a measure would not only be practical and expedient but also more culturally sensitive than many of the alternatives. The system of customary marine tenure at West Nggela, which includes a system of serial prohibitions on harvesting, appears not to be adapted to the high levels of pressure currently being exerted on this valuable species. An analysis of the property tenure system at Nggela, including two case studies of formal disputes, outlines some of the reasons for this problem. Local ecological knowledge about marine fauna in general, and trochus in particular, appears to mostly concur with, and in some cases extend, scientific knowledge. However, there appear to be subject areas in which local knowledge is lacking, and these typically include parameters related to yield and recruitment, such as growth, natural mortality, lifespan and reproductive ecology. In particular, for broadcastspawning species such as trochus, the relationship between dwindling stock densities and recruitment failure is usually not recognised by most fishers at West Nggela. Customary manne tenure and local ecological knowledge thus appear to be insufficient for maximising and sustaining yields of trochus at current levels of fishing pressure. Nevertheless, any new management measures, or fisheries developments, should remain sensitive to the dynamic and competitive nature of the property tenure system. Collaboration between fishery biologists and local fishers is recommended wherever possible. Efforts by fishery biologists to extend, to rural fishers, their knowledge of reproductive biology and ecology of broadcast spawning organisms are encouraged. Outside knowledge is likely to be embraced by fishers only if it is communicated in a way that is compatible with the cognitive framework in which most local knowledge is situated. Such an input of expertise, when combined synergistically with the extensive local knowledge of rural fishers, cannot fail to result in improvements to strategies for community-based fishery management.
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ItemThe evolution and ecology of the Gadopsis marmoratus complex( 1986)The Family Gadopsidae is the only family of fishes in South-eastern Australia which is both endemic to this region, and strictly confined to fresh water. Although several species of Gadopsis have been proposed, prior to the commencement of this study only one species, G. marmoratus Richardson, was formally recognised. This species was known to exhibit considerable geographic variation in morphology, colouration patterns, and size; and it had been suggested that the taxonomy of the genus was in need of review. This study is an attempt to: (i) determine the number of species in the, G. marmoratus complex; (ii) assess the relationships between G. marmoratus and any additional taxa in the complex; (iii) Formulate a biogeographic hypothesis to account for the geographic distributions and phylogenetic relationships of the taxa in the G. marmoratus complex; and, (iv) examine ecological characteristics of a population of Gadopsis from each side of the Great Dividing Range in Victoria. Analysis of meristic variation revealed that two sympatric taxa of Gadopsis were present in north-eastern Victoria. No evidence of hybridization between these taxa was found. The two taxa have different numbers of spines in the dorsal fin, and the specific status of the taxon with only two spines in the fin was recognised by the formal description of G. bispinosus Sanger. By adoption of an evolutionary species concept, and using univariate and multivariate statistical analyses of meristic variation, it was shown that G. marmoratus was comprised of two divergent taxa. It was proposed that these taxa be recognised as separate species, and for the purposes of this study are referred to as northern G. marmoratus and southern G. marmoratus. Multivariate statistical analyses of morphometric variation supported the proposal to recognise northern G. marmoratus and southern G. marmoratus as separate species. Electrophoretic analysis of protein variation also supported the recognition of northern G. marmoratus and southern G. marmoratus, and confirmed that hybridization was not occurring between G. bispinosus and northern G. marmoratus. The level of genetic divergence between northern G. marmoratus and southern G. marmoratus was less than that between both of these taxa and G. bispinosus. This result was interpreted to indicate a close phylogenetic relationship between northern G. marmoratus and southern G. marmoratus, and supported the relationships suggested by the phenetic analysis of meristic and morphometric variation. A biogeographic hypothesis to explain the geographic distributions and phylogenetic relationships of the three taxa was proposed. The ancestry of the Family Gadopsidae has been the subject of some dispute, and the alternative views on this subject were critically reviewed. Support was found for a basal percoid relationship for the family, and this result suggested that Gadopsis may have been of Gondwanan origin. The freshwater life-cycle of all the members of the family was interpreted as further support for a freshwater origin for Gadopsis. Several ecological characteristics of a population of G. bispinosus from the King Parrot Creek and G. marmoratus from the Yarra River system were compared. Gadopsis bispinosus in the King Parrot Creek is a small, lightly-built, short-lived species compared to G. marmoratus from the Yarra River system. The two species were found to have similar reproductive biologies. The discovery of additional species of Gadopsis has created the need for further examination of the evolution and ecology of the G. marmoratus complex, and suggestions for such further study are included at the end of this study.
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ItemEcological effects of the introduced fanworm, Sabella spallanzanii, on hard substratum epifaunal assemblages( 1999)Observations on the impacts of introduced species abound, but little experimental work bears on the nature and mechanisms of these impacts. The recent invasion of the sabellid polychaete Sabella spallanzanii into several embayments on the south coast of Australia provides an opportunity to test hypotheses about the effects of this exotic species on the invaded assemblage. The large size (30 cm long) and high density S. spallanzanii results in a structurally complex canopy of feeding fans above the substratum. I investigated the effect of the canopy on various life history stages of co-occurring marine invertebrates in epifaunal assemblages on hard substrata. The effects of Sabella on recruitment of sessile taxa were complex, but a number of generalisations could be made. Recruitment of some barnacle, bryozoan, spirorbid and ascidian taxa to large experimentally cleared areas (pilings) was higher than on uncleared areas. On the scale of individual 20 by 20 cm settlement plates, where I controlled for the effect of physical structure using fanworm mimics, most of the effects were caused by the presence of physical structure on the plate. Barnacles responded negatively, and sponges and one bryozoan responded positively to structure in one experiment, while a spirorbid, a bryozoan and three ascidians all responded negatively in another. Recruitment on to tubes increased the abundance of several taxa on plates with fanworms, but not all taxa recruited to tubes. Effects were not consistent within taxonomic groups or between sites. Longer term experiments revealed fewer changes to the structure of the understorey assemblage. A two month experiment showed fewer effects of the fanworms on the smaller plate scale, and a six month experiment found few effects on either plate or piling scales. The apparent disappearance of canopy effects with time could be caused by processes associated with assemblage development such as overgrowth and senescence of early recruits. Alternatively it could simply be caused by differences in the composition of assemblages between experiments. Multivariate analyses showed that spatial variation in recruitment on the scale of 10’s of metres was important in determining the composition of the assemblage in both early and later stages. The planktonic abundances of larval solitary ascidians, spionid polychaetes and pooled larval taxa adjacent to the substratum were significantly reduced by the presence of a fanworm canopy, suggesting that larval flux to these areas may be lower. Little difference in overall recruitment between cleared and uncleared areas suggests that settlement rates may be enhanced or post-settlement mortality rates might be lower beneath canopies. Growth of the arborescent bryozoan Bugula stolonifera and an encrusting bryozoan, Watersipora subtorquata, were affected by the presence of a canopy, but these effects were not consistent between experiments. B. stolonifera growth increased beneath the canopy in one experiment and decreased in another, while W. subtorquata grew less in response to physical structure on the plates. Survivorship of B. stolonifera and a serpulid polychaete were lower beneath the canopy in one experiment each, but not in others, and survivorship of W. subtorquata was not affected. The variable results suggested that canopies may act in different ways at different times. The overall impact of Sabella spallanzanii on other species at the scales I looked at can be explained by its modification of the habitat. The use of tubes as settlement sites, and the predominance of small scale responses to physical structure support this idea. Traditional models of the ecological impacts of exotic species, which focus on competitive species replacement, may not be relevant in this system. Any impacts of Sabella spallanzanii must also be evaluated in the light of observations that the canopy was not constant through time, clue to population crashes that occurred a number of times and places.
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ItemThe acoustic repertoire of the bell miner, Manorina melanophrys( 1989)Acoustic communication was studied in a population of the cooperatively-breeding Bell Miner, Manorina melanophrys (Family Meliphagidae), from March 1985 to May 1988 at Bundoora, Victoria. The study aimed to describe the acoustic repertoire of the Bell Miner and to investigate the function of vocalizations in the repertoire. An additional aim was to examine whether there were functional specializations of vocal signals associated with a cooperatively-breeding social organization. Eighteen adult calls and four juvenile calls were distinguished in the acoustic repertoire of the Bell Miner. Six adult calls were given only by females and one adult call was given only by males. For calls that were given by both sexes, there were no differences between males and females. Most calls that were analyzed showed difference s between individuals in some characteristics; however, only two calls showed strong evidence of individuality. The characteristic tink call appears to function as an interspecific territorial call, deterring other species of birds from entering the area occupied by a Bell Miner social unit. The tink call may also act as a contact call between birds. Female-specific calls are believed to function in courtship of males (assisting a female in obtaining a breeding position), in synchronizing reproduction between mates, in reinforcing the pair-bond between mates, in acoustic mate-guarding, and as contact calls during nesting (ensuring that the female’s mate and other birds in the social unit are aware of the female's activities). The individuality of the female-specific chuk-a-choo call may enable males to recognize their mates. The male-specific oar call is believed to function in establishing and reinforcing a pair bond. The mew call given by both sexes appears to function to elicit a begging response from young; to induce a bird to leave young when the caller is approaching; to signal to other birds that the caller is leaving the young; to encourage nestlings to fledge; and to lead fledglings away from danger. Observations also suggest that the mew call functions in advertising male helping behaviour. Recognition of males on the basis of this individually distinctive call may occur. Calls of the Bell Miner also function as alarm calls, mobbing calls (to confuse an intruder and to encourage it to move on, and to alert and attract other birds to a mobbing), distress calls (to attract birds to a caller held by a predator) and distraction calls (to attract an intruder's attention away from young). Juvenile calls are believed to function in soliciting food from adults, to signal a juvenile's location to adults and to attract adults. Other potential functions of calls are discussed. The specificity of vocal functions of the Bell Miner in the context of a cooperatively-breeding social organization was evaluated by comparisons with vocalizations reported in the literature for other species. Several vocal adaptations were identified that may be restricted to, or most prominent in, species with a cooperatively-breeding social organization: these include the possession of a general interspecific territorial call, acoustic courtship of males by females, and vocal advertising of helping behaviour. Vocal components of communal display behaviour of the Bell Miner may also have functions adapted to a cooperatively-breeding social organization.
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ItemThe feeding and breeding biology of the sacred ibis Threskiornis aethiopicus in southern Victoria( 1984)This study aimed to elucidate the major selective factors affecting the biology, and particularly the breeding ecology of the Sacred Ibis (Threskiornis aethiopicus) in Australia. A comparative study of the breeding ecology of the Family Plataleidae in Australia was undertaken to define the ecological niche of the Sacred Ibis. The Australian ibis and spoonbills have very similar breeding ecology to their conspecifics and congeners elsewhere in the world. However, the breeding success of Australian birds appears to be limited by food supply whereas, in African members of the Family, for example, breeding success is limited by predation. In Australia, Sacred Ibis exhibit two broad responses to their environment: some populations showed adaptations in their breeding to an unpredictable environment; and, other populations have developed complex breeding strategies that are dependent on a highly predictable set of environmental conditions. In unpredictable environments, Sacred Ibis do not breed regularly but rather breeding is closely tied to the variable environmental conditions; the ibis move away from the breeding site when the area dries out. In unpredictable environments, clutch size is adjusted to the conditions and the ibis may employ multiple brooding. Where the environment is much more predictable, Sacred Ibis breed on a very regular cycle. In these environments, ibis are highly sedentary and clutch and brood size and multiple brooding are adjusted to maximise seasonal reproductive success, that is, Sacred Ibis raise fewer offspring per brood than the apparent maximum number possible as a trade-off against raising more broods in each breeding season. The timing and duration of the breeding attempts has had a major effect on the mating system. Sacred Ibis are essentially monogamous but one case of apparent polygyny was found. The mating system is also characterised by a high rate of promiscuous copulation and changes of mate between breeding attempts. The roles of male and female in post-fledging care of young and costs/benefits to life-time fitness are discussed. The selective factors maintaining colonial nesting are reviewed and the single most important evolutionary pressure affecting the breeding ecology of the Sacred Ibis is finding food; predation was shown to be unimportant.
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ItemIndividual variation in reproductive success in the sacred ibis( 1988)Factors affecting the reproductive success of individually colour-banded sacred ibis, Threskiornis aethiopicus stricitpennis (Gould), at Healesville Sanctuary, Victoria, were studied from November, 1983, to March, 1987. Although the majority of clutches were of three eggs, the modal fledging success was two young, due to starvation of the third chick. The likely adaptive value of brood reduction is discussed. Characteristics of individuals (e.g. weight, body condition, culmen length, estimated age and dominance status) had no discernible effect on the number of chicks raised to fledging from one attempt (fledging success). The structure of the dominance hierarchy among male sacred ibis at Healesville is described. Dominance relationships among females were not consistent and, therefore, analysis of dominance status was restricted to males. Weight was the major trait contributing to a male's dominance status. High-status males achieved a higher seasonal reproductive success than did low-status males in two seasons when resources were apparently at low levels. Reproductive success over five consecutive years was largely dependent on survival, but, no significant relationships between individual traits and survival were found. Male sacred ibis achieving high seasonal reproductive success tended to survive better than did less successful males. Thus, variation in success measured over a short term (one season) underestimated the variation between males in success measured over a long term (five years). Variation in success of females also increased with the longer sampling period, but not at as fast a rate as variation in male success. Variation in success is therefore significantly greater in males than females, even though the sacred ibis is a monogamous species. Variability in reproductive success and number of attempts among individuals is facilitated by the changes of mate frequently observed in individuals breeding more than once in a season. Female sacred ibis were found to invest more in any one attempt than were male ibis. Consequently, individual females averaged fewer nesting attempts per season than did males and, with the sex-ratio of unity, females were a limiting resource for males. The resulting opportunity for selection on males is apparently fulfilled to some degree, with high-status, heavy and old males being particularly successful in competition for mates.