| the importance of indirect cues for white-browed sparrow-weaver (plocepasser mahali) risk assessment. | both direct cues that provide information about the actual presence of a predator and indirect environmental cues that provide information about the probability of encountering a predator may be used by animals assessing predation risk, but relatively few studies manipulate both simultaneously to study their relative importance. we conducted two experiments to study the foraging decisions of white-browed sparrow-weavers (plocepasser mahali). the first experiment manipulated both direct and indir ... | 2009 | 21874088 |
| avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern african arid-zone passerines. | many birds can defend body temperature (tb) far below air temperature (ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (mb), phylogeny or ecological factors. we determined maximum rates of evaporative heat dissipation and thermal end points (tb and ta associated with thermoregulatory failure) in three southern african ploceid passerines, the scaly-feathered weaver (sporopipes squamifrons, mb≈10 g ... | 2015 | 26041032 |
| seasonal metabolic acclimatization varies in direction and magnitude among populations of an afrotropical passerine bird. | avian metabolic responses demonstrate considerable diversity under fluctuating environmental conditions, a well-studied example being the seasonal upregulation of basal metabolic rate (bmr) and summit metabolism (msum) in temperate species experiencing harsh winters. fewer studies have examined seasonal metabolic acclimatization in subtropical or tropical species. we investigated seasonal metabolic variation in an afrotropical ploceid passerine, the white-browed sparrow-weaver (plocepasser mahal ... | 2017 | 28277960 |
| sexually selected sentinels? evidence of a role for intrasexual competition in sentinel behavior. | although the evolutionary mechanisms that favor investment in cooperative behaviors have long been a focus of research, comparatively few studies have considered the role that sexual selection may play. for example, evolutionary explanations for sentinel behavior (where 1 individual assumes an elevated position and scans the surroundings while other group members forage nearby) have traditionally focused on the inclusive fitness benefits arising from its effects on predation risk, while its pote ... | 2017 | 27656086 |
| dominance-related seasonal song production is unrelated to circulating testosterone in a subtropical songbird. | circulating testosterone (t) is widely considered to play a key role in the production of sexual displays by male vertebrates. while numerous studies support a role for circulating t in promoting the production of song in male birds, this understanding is based primarily on evidence from seasonally breeding northern temperate species, leaving it unclear whether this mechanism generalizes to other regions of the world. here we investigate whether variation in circulating levels of t can explain t ... | 2016 | 27179883 |
| dominant male song performance reflects current immune state in a cooperatively breeding songbird. | conspicuous displays are thought to have evolved as signals of individual "quality", though precisely what they encode remains a focus of debate. while high quality signals may be produced by high quality individuals due to "good genes" or favourable early-life conditions, whether current immune state also impacts signalling performance remains poorly understood, particularly in social species. here, we experimentally demonstrate that male song performance is impaired by immune system activation ... | 2016 | 26811745 |
| seasonal and geographical variation in heat tolerance and evaporative cooling capacity in a passerine bird. | intraspecific variation in avian thermoregulatory responses to heat stress has received little attention, despite increasing evidence that endothermic animals show considerable physiological variation among populations. we investigated seasonal (summer versus winter) variation in heat tolerance and evaporative cooling in an afrotropical ploceid passerine, the white-browed sparrow-weaver (plocepasser mahali; ∼ 47 g) at three sites along a climatic gradient with more than 10 °c variation in mid-su ... | 2016 | 26787477 |
| the oxidative costs of reproduction are group-size dependent in a wild cooperative breeder. | life-history theory assumes that reproduction entails a cost, and research on cooperatively breeding societies suggests that the cooperative sharing of workloads can reduce this cost. however, the physiological mechanisms that underpin both the costs of reproduction and the benefits of cooperation remain poorly understood. it has been hypothesized that reproductive costs may arise in part from oxidative stress, as reproductive investment may elevate exposure to reactive oxygen species, compromis ... | 2015 | 26582023 |
| immune response in a wild bird is predicted by oxidative status, but does not cause oxidative stress. | the immune system provides vital protection against pathogens, but extensive evidence suggests that mounting immune responses can entail survival and fecundity costs. the physiological mechanisms that underpin these costs remain poorly understood, despite their potentially important role in shaping life-histories. recent studies involving laboratory models highlight the possibility that oxidative stress could mediate these costs, as immune-activation can increase the production of reactive oxyge ... | 2015 | 25815888 |
| population genetic structure and direct observations reveal sex-reversed patterns of dispersal in a cooperative bird. | sex-biased dispersal is pervasive and has diverse evolutionary implications, but the fundamental drivers of dispersal sex biases remain unresolved. this is due in part to limited diversity within taxonomic groups in the direction of dispersal sex biases, which leaves hypothesis testing critically dependent upon identifying rare reversals of taxonomic norms. here, we use a combination of observational and genetic data to demonstrate a rare reversal of the avian sex bias in dispersal in the cooper ... | 2014 | 25346189 |
| singing in the moonlight: dawn song performance of a diurnal bird varies with lunar phase. | it is well established that the lunar cycle can affect the behaviour of nocturnal animals, but its potential to have a similar influence on diurnal species has received less research attention. here, we demonstrate that the dawn song of a cooperative songbird, the white-browed sparrow weaver (plocepasser mahali), varies with moon phase. when the moon was above the horizon at dawn, males began singing on average 10 min earlier, if there was a full moon compared with a new moon, resulting in a 67% ... | 2014 | 24429683 |
| extra-group mating increases inbreeding risk in a cooperatively breeding bird. | in many cooperatively breeding species, females mate extra-group, the adaptive value of which remains poorly understood. one hypothesis posits that females employ extra-group mating to access mates whose genotypes are more dissimilar to their own than their social mates, so as to increase offspring heterozygosity. we test this hypothesis using life history and genetic data from 36 cooperatively breeding white-browed sparrow weaver (plocepasser mahali) groups. contrary to prediction, a dominant f ... | 2013 | 24118639 |
| adaptive thermoregulation during summer in two populations of an arid-zone passerine. | heterothermy plays an important role in lowering the costs of thermoregulation in endotherms by reducing water and energy requirements. we tested predictions that birds in arid habitats should express fine-scale variation in their thermoregulatory patterns as a function of prevailing climatic conditions. we assessed effects of air temperature (tair) and water vapor pressure deficit (d) on body temperature (tb) in free-living white-browed sparrow-weavers (plocepasser mahali) during summer in two ... | 2013 | 23858654 |
| testosterone-dependency of male solo song in a duetting songbird--evidence from females. | for male songbirds of the temperate zone there is a tight link between seasonal song behaviour and circulating testosterone levels. such a relationship does not seem to hold for tropical species where singing can occur year-round and breeding seasons are often extended. white-browed sparrow weavers (plocepasser mahali) are cooperatively breeding songbirds with a dominant breeding pair and male and female subordinates found in eastern and southern africa. each group defends an all-purpose territo ... | 2013 | 23085444 |
| social status affects the degree of sex difference in the songbird brain. | it is thought that neural sex differences are functionally related to sex differences in the behaviour of vertebrates. a prominent example is the song control system of songbirds. inter-specific comparisons have led to the hypothesis that sex differences in song nuclei size correlate with sex differences in song behaviour. however, only few species with similar song behaviour in both sexes have been investigated and not all data fit the hypothesis. we investigated the proposed structure-function ... | 2011 | 21687671 |
| socially induced brain differentiation in a cooperatively breeding songbird. | birds living in social groups establish dominance hierarchies, and taking up the dominant position influences behaviour and physiological parameters. in cooperatively breeding white-browed sparrow weavers (plocepasser mahali), the transition from subordinate helper to dominant breeder male induces the production of a new type of song. this song contains a large number of new syllables and differs in temporal pattern from duet songs produced by all other group members. here we show that this chan ... | 2007 | 17785271 |
| simple roost nests confer large energetic savings for sparrow-weavers. | white-browed sparrow-weavers (plocepasser mahali, body mass 40 g) are group-living passerines adapted to the semi-arid environment of north-eastern and south-western africa. during winter, the nocturnal ambient temperature of these regions often falls below 0 degrees c. imposing conditions demanding an increase in thermoregulatory heat production. individuals roost throughout the year in inverted u-shaped roost nests. we investigated the energetic advantages of roosting by measuring nest and amb ... | 2002 | 11924563 |
| characterization of hypervariable microsatellites in the cooperatively breeding white-browed sparrow weaver plocepasser mahali. | | 1999 | 10368974 |
| hormonal responses to removal of a breeding male in the cooperatively breeding white-browed sparrow weaver, plocepasser mahali. | the white-browed sparrow weaver (plocepasser mahali) is a cooperatively breeding ploceid finch that lives in groups of up to 11 individuals. each group consists of a dominant breeding male and female and a varying number of nonreproductive birds that help feed young and defend the group territory. experimental removal of the dominant male resulted in attempts by other males to take over the group. removal of a subordinate, nonbreeding male, as a control, resulted in no change of status among gro ... | 1992 | 1612561 |
| seasonal metabolic acclimatization varies in direction and magnitude among years in two arid-zone passerines. | adaptive plasticity in avian thermal physiology is increasingly apparent, with a well-studied example being metabolic upregulation during cold winters in small birds inhabiting temperate and boreal latitudes. recent studies have revealed greater variation in the direction and magnitude of seasonal metabolic adjustments among subtropical/tropical birds experiencing milder winters compared with higher-latitude counterparts, suggesting that patterns could vary among years within populations. we qua ... | 2020 | 32027231 |
| morphological and molecular characterisation of isospora butcherae n. sp. in a silvereye (zosterops lateralis) (latham, 1801). | a new isospora (apicomplexa:eimeriidae) species is described from a silvereye (zosterops lateralis) in western australia. sporulated oocysts of this species are spherical, 24.2 (23.1-25.2) × 23.3 (22.8-23.9) μm, with a shape index (length/width) of 1.02, and with a smooth bi-layered oocyst wall, 1.2 μm thick (outer layer 0.9 μm, inner 0.3 μm). a polar granule is present, but the oocyst residuum and a micropyle are absent. the ovoid-shaped sporocysts are 16.1 (15.7-17.3) × 10.5 (15.7-17.3) μm and ... | 2018 | 29527641 |
| seasonal variation in body composition in an afrotropical passerine bird: increases in pectoral muscle mass are, unexpectedly, associated with lower thermogenic capacity. | phenotypic flexibility in avian metabolic rates and body composition have been well-studied in high-latitude species, which typically increase basal metabolic rate (bmr) and summit metabolism (msum) when acclimatized to winter conditions. patterns of seasonal metabolic acclimatization are more variable in lower-latitude birds that experience milder winters, with fewer studies investigating adjustments in avian organ and muscle masses in the context of metabolic flexibility in these regions. we q ... | 2020 | 32189062 |
| phenotypic flexibility of metabolic rate and evaporative water loss does not vary across a climatic gradient in an afrotropical passerine bird. | small birds inhabiting northern temperate and boreal latitudes typically increase metabolic rates during cold winters or acclimation to low air temperatures (taccl). recent studies suggest considerable variation in patterns of seasonal metabolic acclimatization in birds from subtropical and tropical regions with milder winters, but there remains a dearth of acclimation studies investigating metabolic flexibility among lower-latitude birds. we used short-term thermal acclimation experiments to in ... | 2020 | 32165435 |
| telomere attrition predicts reduced survival in a wild social bird, but short telomeres do not. | attempts to understand the causes of variation in senescence trajectories would benefit greatly from biomarkers that reflect the progressive declines in somatic integrity (si) that lead to senescence. while telomere length has attracted considerable interest in this regard, sources of variation in telomere length potentially unrelated to declines in si could, in some contexts, leave telomere attrition rates a more effective biomarker than telomere length alone. here, we investigate whether telom ... | 2019 | 31332860 |
| reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird. | there is increasing evidence for considerable phenotypic flexibility in endotherm thermal physiology, a phenomenon with far-reaching implications for the evolution of traits related to heat tolerance. numerous studies have documented intraspecific variation in avian thermoregulatory traits, but few have revealed the shapes of thermoregulatory reaction norms or how these might vary among populations. we investigated phenotypic flexibility in the ability of a model afrotropical passerine bird (the ... | 2019 | 31278988 |
| interactions between humidity and evaporative heat dissipation in a passerine bird. | environmental humidity is thought to be a major determinant of evaporative cooling capacity at high air temperatures (ta), but the technical challenges of experimentally manipulating humidity in respirometry chambers have resulted in far less being known about the effects of humidity compared to those of ta. we tested the prediction that at ta approaching and exceeding normothermic body temperature (tb), high humidity would result in higher tb, lower evaporative water loss (ewl) and/or higher re ... | 2019 | 30805750 |