S Craig Roberts
Bio: S Craig Roberts is an academic researcher. The author has contributed to research in topics: Bulbul. The author has an hindex of 2, co-authored 2 publications receiving 12 citations.
TL;DR: Scent-marking is a ubiquitous form of olfactory signaling in male mammals and both territorial males in resource-defense mating systems and dominant males in dominance mating systems scent-mark, and it is argued that the mechanisms are used conditionally, depending on information available and potential costs and benefits to receivers.
Abstract: Summary Scent-marking is a ubiquitous form of olfactory signaling in male mammals and both territorial males in resource-defense mating systems and dominant males in dominance mating systems scent-mark. A large body of evidence suggests a link between scent-marking by male mammals and intrasexual competition. Resource holders appear to mark to help establish and maintain their status. They may do this because scent marks allow potential opponents to assess the status or RHP of the signaler. Nonresource holding competitors benefit because they can adjust the level of escalation in relation to potential costs and benefits and avoid risky contests. Resource holders benefit through reduced costs because many nonresource holders withdraw to avoid escalated contests. Three basic mechanisms allow receivers to make decisions after detecting scent marks. Receivers may (1) detect intrinsic properties of scent marks (e.g., concentrations of androgen-dependent volatiles), (2) remember past contests and the odor of each individual involved and associate these with the odor of scent marks, and (3) remember the smell of marks recently encountered and match this smell with potential opponents that they meet subsequently. It is now known that all of these mechanisms are used, sometimes within one species (e.g., mice) and we argue that the mechanisms are used conditionally, depending on information available and potential costs and benefits to receivers. Game theoretical analysis has recently shown how territorial intruders may switch from using intrinsic properties of marks to scent-matching when making decision about whether to remain in a territory. Scent-marking may be a uniquely cheat-proof signal of status because males must be able to defend their territory or dominance status over the time taken to mark it. A pattern of marks is thus a signal of status that has been tested in intrasexual competition. It also seems likely that marks are intrinsically costly both in energetic terms and by increasing predation risk. Mice can detect whether urine is from a parasitized or nonparasitized individual and these odors could potentially signal immunocompetence if mediated by variation at the MHC region of the genome. This remains to be tested. It is known that mice can detect relatedness via urine volatiles mediated by the MHC and it has been predicted that males should modify their competitive behavior in the light of this information. Again this remains to be tested. Information about disease status and genetic relatedness does not explain why males maintain patterns of scent marks. Most, perhaps all, territories are scent-marked. This may be because most intruders are of lower RHP than resource holders and these males should usually withdraw after assessing the resource holder by its scent marks. The costs of defending a territory may thus be substantially reduced. The obligate link between scent-marking and territoriality suggests that resource-defense polygyny in mammals may not be economically viable without this reduction in the costs of area defense. A little information is available to show that females use information from patterns of scent marks and a great deal of information shows that they use intrinsic information. It is not known whether males signal to females to enable mate choice or if females eavesdrop on signals sent between male competitors. Most known responses are to male urine by female rodents. For example, females show physiological (priming) responses to male odors (e.g., advancing and synchronizing estrus, inducing abortion). Other research has identified factors responsible for female mate preferences in choice tests. For example, the dominance status of the signaling male is a predictor of female interest and such studies have identified androgen-dependent volatiles responsible for the response. More recently, females have been shown to use odor mediated by the MHC locus to choose mates in relation to their genetic relatedness and to use odor to distinguish healthy and diseased mates. Most of these studies have been on mice and most use male urine, but the effect of patterns of urine scent marks has not been investigated. The only studies that explicitly use scent marks are those showing that females match the odor of potential mates with marks previously found in the environment to select mates. Future research should aim to clarify how information about the quality of potential mates is transmitted and how females trade-off such information against genetic relatedness.
01 Jan 1997
TL;DR: In this paper, a major work covering the breeding and non-breeding birds of the Southern African sub-region is presented, which sets new standards in its scope and in its methods, for setting a measured baseline against which to judge environmental trends across the great range of southern Africa.
Abstract: This is a major work covering the breeding and non-breeding birds of the Southern African sub-region. Published in two volumes, Volume One includes introductory chapters describing methodology and the 'avi'-geography of the region, with habitat photos, and coverage of the non-passerines, whilst Volume Two covers the passerines. Some 900 species are covered in total, including 200 vagrants, with detailed species accounts, maps and statistics for at least 500 species. Conservation issues are discussed for most species. '...sets new standards in its scope and in its methods...it will come to be valued ever more as years go by, for setting a measured baseline against which to judge environmental trends across the great range of southern Africa.' - Colin Bibby, "BirdLife International".
TL;DR: The parallels between the distributions of functions of vocal learning and brain nuclei suggest future research should clarify both how and why parrots are more extensive vocal learners than songbirds and whether there are in fact parallels with humans.
Abstract: Given that both sexes of most parrots learn new vocalizations throughout life and produce them in diverse social contexts, whereas few songbird species combine all these traits, why are parrots not a better model for the evolution of human speech than songbirds? We first note the technical constraints that have limited research on wild parrot communication and then review the discoveries that have accumulated in the last two decades as constraints were overcome. Vocal learning in wild parrots appears unrelated to sexual selection and mate competition but is used by parrot pairs to defend nest sites in ways similar to those of songbirds. Where parrots differ from songbirds is in their specialization on toxic and armored foods, the consequences of this diet on foraging and social dynamics, and the use of learned vocalizations to mediate those dynamics. Parrots thus use learned vocalizations for two quite different functions, only one of which they share with songbirds (and hummingbirds). Interestingly, recent neurobiological studies have shown that parrots have dual cortical pathway nuclei for vocal learning, only one of which is present in songbirds. The parallels between the distributions of functions of vocal learning and brain nuclei suggest future research that should clarify both how and why parrots are more extensive vocal learners than songbirds and whether there are in fact parallels with humans.
Percy FitzPatrick Institute of African Ornithology1, University of KwaZulu-Natal2, Manchester Metropolitan University3, United Nations Development Programme4, University of Dschang5, Seychelles Islands Foundation6, Wildlife Conservation Society7, University of Ghana8, University of the Witwatersrand9, University of Waikato10, University of Göttingen11
TL;DR: This review of developments since the production of the IUCN Parrot Action Plan published in 2000, identifies areas where critical knowledge is lacking and highlight opportunities to address them.
Abstract: Parrot populations in Africa and Madagascar are declining and the need for conservation actions to address threats is increasingly recognised. Effective conservation requires a robust knowledge base on which decisions over appropriate actions can be made, yet at present there is no current and readily accessible synthesis of the status of populations, the threats they face and knowledge gaps. Here we begin to address this shortfall for the larger species in the region belonging to the genera Coracopsis, Poicephalus, Psittacus and Psittacula. We review developments since the production of the IUCN Parrot Action Plan published in 2000, identify areas where critical knowledge is lacking and highlight opportunities to address them. While advances have been made over the last decade, progress has not been evenly spread, with a strong bias towards populations in southern Africa. To date much research has focused on describing aspects of ecology and behaviour and there remains a need for studies determining the current status of populations and the factors limiting distributions and abundance. This review aims to provide a basis upon which progress towards an improved understanding of the conservation needs of the larger parrots of Africa and Madagascar can be made.
TL;DR: Meyer's Parrot can be considered to be an opportunistic generalist that tracks resource availability across a wide suite of potential food items, resulting in significant positive correlations between Levins’ niche breadth, rainfall and food resource availability.
Abstract: The diet of Meyer’s Parrot Poicephalus meyeri in the Okavango Delta, Botswana, was distinctly seasonal, comprising 71 different food items from 37 tree species in 16 families. During 480 road transects over 24 months, food item preferences closely tracked fruiting phenology, resulting in significant positive correlations between Levins’ niche breadth, rainfall and food resource availability. Meyer’s Parrot can, therefore, be considered to be an opportunistic generalist that tracks resource availability across a wide suite of potential food items. Predispersal seed predation accounted for 62% of total feeding activity, of which 37% were seeds from ripe pods and fruits. Unripe seeds were, however, preferred when seasonally available. Seeds and parasites from fruits and pods accounted for 42% and 35% of total feeding bouts, respectively. Fruit pulp was predominantly consumed as a by-product of seed predation. Four arthropods, previously unknown in the diets of African parrots, were discovered during the breeding season. The most important tree species in their diet included (in order of magnitude): Kigelia africana , Diospyros mespiliformis , Combretum imberbe , Ficus sycomorus , Diospyros lycoides lycoides , Combretum hereroense and Berchemia discolor . Geophagy was reported in the questionnaire. There was no evidence to support any local migrations. OSTRICH 2009, 80(3): 153–164