Costly reproductive competition between females in a monogamous cooperatively breeding bird.

In many cooperatively breeding societies, only a few socially dominant individuals in a group breed, reproductive skew is high, and reproductive conflict is common. Surprisingly, the effects of this conflict on dominant reproductive success in vertebrate societies have rarely been investigated, especially in high-skew societies. We examine how subordinate female competition for breeding opportunities affects the reproductive success of dominant females in a monogamous cooperatively breeding bird, the Southern pied babbler (Turdoides bicolor). In this species, successful subordinate reproduction is very rare, despite the fact that groups commonly contain sexually mature female subordinates that could mate with unrelated group males. However, we show that subordinate females compete with dominant females to breed, and do so far more often than expected, based on the infrequency of their success. Attempts by subordinates to obtain a share of breeding impose significant costs on dominant females: chicks fledge from fewer nests, more nests are abandoned before incubation begins, and more eggs are lost. Dominant females appear to attempt to reduce these costs by aggressively suppressing potentially competitive subordinate females. This empirical evidence provides rare insight into the nature of the conflicts between females and the resultant costs to reproductive success in cooperatively breeding societies.

The costs of keeping cool in a warming world: implications of high temperatures for foraging, thermoregulation and body condition of an arid-zone bird.

Recent mass mortalities of bats, birds and even humans highlight the substantial threats that rising global temperatures pose for endotherms. Although less dramatic, sublethal fitness costs of high temperatures may be considerable and result in changing population demographics. Endothermic animals exposed to high environmental temperatures can adjust their behaviour (e.g. reducing activity) or physiology (e.g. elevating rates of evaporative water loss) to maintain body temperatures within tolerable limits. The fitness consequences of these adjustments, in terms of the ability to balance water and energy budgets and therefore maintain body condition, are poorly known. We investigated the effects of daily maximum temperature on foraging and thermoregulatory behaviour as well as maintenance of body condition in a wild, habituated population of Southern Pied Babblers Turdoides bicolor. These birds inhabit a hot, arid area of southern Africa where they commonly experience environmental temperatures exceeding optimal body temperatures. Repeated measurements of individual behaviour and body mass were taken across days varying in maximum air temperature. Contrary to expectations, foraging effort was unaffected by daily maximum temperature. Foraging efficiency, however, was lower on hotter days and this was reflected in a drop in body mass on hotter days. When maximum air temperatures exceeded 35.5 °C, individuals no longer gained sufficient weight to counter typical overnight weight loss. This reduction in foraging efficiency is likely driven, in part, by a trade-off with the need to engage in heat-dissipation behaviours. When we controlled for temperature, individuals that actively dissipated heat while continuing to forage experienced a dramatic decrease in their foraging efficiency. This study demonstrates the value of investigations of temperature-dependent behaviour in the context of impacts on body condition, and suggests that increasingly high temperatures will have negative implications for the fitness of these arid-zone birds.

Inbreeding avoidance mechanisms: dispersal dynamics in cooperatively breeding southern pied babblers.

1. Breeding with kin can reduce individual fitness through the deleterious effects of inbreeding depression. Inbreeding avoidance mechanisms are expected to have developed in most species, and especially in cooperatively breeding species where individuals may delay dispersal until long after sexual maturity. Such potential mechanisms include sex-biased dispersal and avoidance of kin known through associative learning. 2. The investigation of inbreeding avoidance through dispersal dynamics can be enhanced by combining fine-scale population genetic structure data with detailed behavioural observations of wild populations. 3. We investigate possible inbreeding avoidance in a wild population of cooperatively breeding southern pied babblers (Turdoides bicolor). A combination of genetic, geographic and observational data is used to examine fine-scale genetic structure, dispersal (including sex-biased dispersal) and inheritance of dominance in cooperatively breeding groups. 4. Unusually, sex-bias in dispersal distance does not occur. Rather, individuals appear to avoid inbreeding through two routes. First, through dispersal itself: although both males and females disperse locally, they move outside the range within which genetically similar individuals are usually found, going twice as far from natal groups as from non-natal groups. Second, through avoidance of familiar group members as mates: individuals inherit a dominant position in the natal group only when an unrelated breeding partner is present. 5. This study uses spatial genetic analyses to investigate inbreeding avoidance mechanisms in a cooperative breeder and shows that individuals of both sexes can avoid inbreeding through a dispersal distance mechanism. While it appears that dispersal allows most individuals to move beyond the range of closely related kin, matings may still occur between distant kin. Nevertheless, any costs of breeding with a distant relative may be outweighed by the benefits of local dispersal and the immense fitness gains available from attaining a breeding position.

Use of basic biological information for rapid prediction of the response of species to habitat loss.

Much research has focused on identifying traits that can act as useful indicators of how habitat loss affects the extinction risk of species, and the results are mixed. We developed 2 simple, rapid-assessment models of the susceptibility of species to habitat loss. We based both on an index of range size, but one also incorporated an index of body mass and the other an index combining habitat and dietary specialization. We applied the models to samples of birds (Accipitridae and Bucerotidae) and to the lemurs of Madagascar and compared the models' classifications of risk with the IUCN's global threat status of each species. The model derived from ecological attributes was much more robust than the one derived from body mass. Ecological attributes identified threatened birds and lemurs with an average of 80% accuracy and endangered and critically endangered species with 100% accuracy and identified some species not currently listed as threatened that almost certainly warrant conservation consideration. Appropriate analysis of even fairly crude biological information can help raise early-warning flags to the relative susceptibilities of species to habitat loss and thus provide a useful and rapid technique for highlighting potential species-level conservation issues. Advantages of this approach to classifying risk include flexibility in the specialization parameters used as well as its applicability at a range of spatial scales.

Habitat use and life history as predictors of bird responses to habitat change.

In theory the consideration of life-history characteristics should provide a way of making predictive generalizations about the responses of different species to environmental modification. Nevertheless, few studies have tested the validity of this assumption or attempted to apply it across large numbers of related species. We explored both quantitative and qualitative contrasts between species of waterbirds that have either expanded or contracted their ranges in southern Africa over the past 40 years to test the hypothesis that expansionists and contractionists, respectively, should share life-history characteristics and/or ecological attributes. Similarities and differences in life history and ecology were explored through multivariate statistics. Overall, life-history traits provided an inadequate explanation of whether species would be range expansionists or contractionists. By contrast, ecological attributes of species that related to habitat use correlated well with range changes. In particular, waterbird species that inhabit pans seemed to be preadapted to using human-made dams and impoundments. The ability of many species to use artificial wetlands has aided their westward range expansions into arid regions of southern Africa. By contrast, species that rely on vegetated wetlands and that require reeds for nesting were predisposed to range contraction because their habitats have been severely affected by agricultural development and urbanization. In direct contrast to range expansions, most range contractions were west to east, the eastward contraction reflected the high level of wetland loss and degradation in the eastern lowlands of South Africa. Based on analysis of ecological attributes of regional contractionists, several additional species were identified as of potential conservation concern, although such concern may not as yet have been expressed.

Geographic variation in factors that influence timing of moult and breeding in waterfowl.

Waterfowl flight-feather moult is expected to occur when energy is not needed for breeding and when a suitable safe habitat is available. Flight-feather regrowth is an energetically costly stage in the annual cycle of waterfowls. In this study, we tested the hypothesis that moult will coincide with the time of year when food and aquatic habitats are most abundant. We investigated how the timing of rainfall relates to the timing of breeding and flight-feather moult in five common southern African waterfowl at two sites in South Africa with opposite rainfall regimes (one summer, one winter). We then incorporated published data to compare and contrast the relative timing of breeding and moult in southern hemisphere (southern African and Australian) waterfowl with northern hemisphere (European and North American) species. Our results showed that southern African waterfowl breed in the wet season and moult during the dry season. Tadorna cana was an exception, breeding in the dry season and moulting during the wet season in the summer-rainfall area. There was also a long lag period between peak breeding and peak moult in southern hemisphere waterfowl species, the longest lag being that of birds in the summer-rainfall area. By comparison, northern hemisphere waterfowl species breed and moult during the warm season, with a shorter lag period between peak breeding and peak moult compared to southern hemisphere species. We concluded that waterfowl in southern Africa (with the exception of T. cana), southeast Australia, Europe and North America time their breeding period to coincide with peaks in the availability of both food and breeding sites. Northern hemisphere species moult where chances of predation are low, when temperatures are warm, and before food and aquatic habitats approach their winter minima. By contrast, southern hemisphere waterfowl delay the onset of moult until the dry season, opting to moult when both food and aquatic moulting habitats are scarce.

Host specificity and co-speciation in avian haemosporidia in the Western Cape, South Africa.

Host and pathogen ecology are often closely linked, with evolutionary processes often leading to the development of host specificity traits in some pathogens. Host specificity may range from 'generalist', where pathogens infect any available competent host; to 'specialist', where pathogens repeatedly infect specific host species or families. Avian malaria ecology in the region remains largely unexplored, despite the presence of vulnerable endemic avian species. We analysed the expression of host specificity in avian haemosporidia, by applying a previously developed host specificity index to lineages isolated from wetland passerines in the Western Cape, South Africa. Parasite lineages were isolated using PCR and identified when possible using matching lineages deposited in GenBank and in MalAvi. Parasitic clades were constructed from phylogenetic trees consisting of Plasmodium and Haemoproteus lineages. Isolated lineages matched some strains of Plasmodium relictum, P. elongatum, Haemoproteus sylvae and H. lanii. Plasmodium lineages infected a wide range of hosts from several avian families in a generalist pattern of infection. Plasmodium spp. also exhibited an infection trend according to host abundance rather than host species. By contrast, Haemoproteus lineages were typically restricted to one or two host species or families, and displayed higher host fidelity than Plasmodium spp. The findings confirm that a range of host specificity traits are exhibited by avian haemosporidia in the region. The traits show the potential to not only impact infection prevalence within specific host species, but also to affect patterns of infection at the community level.

Temperatures in excess of critical thresholds threaten nestling growth and survival in a rapidly-warming arid savanna: a study of common fiscals.

Frequency, duration, and intensity of hot-weather events are all predicted to increase with climate warming. Despite this, mechanisms by which temperature increases affect individual fitness and drive population-level changes are poorly understood. We investigated the link between daily maximum air temperature (tmax) and breeding success of Kalahari common fiscals (Lanius collaris) in terms of the daily effect on nestling body-mass gain, and the cumulative effect on size and age of fledglings. High tmax reduced mass gain of younger, but not older nestlings and average nestling-period tmax did not affect fledgling size. Instead, the frequency with which tmax exceeded critical thresholds (tcrits) significantly reduced fledging body mass (tcrit = 33°C) and tarsus length (tcrit= 37°C), as well as delaying fledging (tcrit= 35°C). Nest failure risk was 4.2% per day therefore delays reduced fledging probability. Smaller size at fledging often correlates with reduced lifetime fitness and might also underlie documented adult body-size reductions in desert birds in relation to climate warming. Temperature thresholds above which organisms incur fitness costs are probably common, as physiological responses to temperature are non-linear. Understanding the shape of the relationship between temperature and fitness has implications for our ability to predict species' responses to climate change.

Identifying biologically meaningful hot-weather events using threshold temperatures that affect life-history.

Increases in the frequency, duration and intensity of heat waves are frequently evoked in climate change predictions. However, there is no universal definition of a heat wave. Recent, intense hot weather events have caused mass mortalities of birds, bats and even humans, making the definition and prediction of heat wave events that have the potential to impact populations of different species an urgent priority. One possible technique for defining biologically meaningful heat waves is to use threshold temperatures (T(thresh)) above which known fitness costs are incurred by species of interest. We set out to test the utility of this technique using T(thresh) values that, when exceeded, affect aspects of the fitness of two focal southern African bird species: the southern pied babbler Turdiodes bicolor (T(thresh) = 35.5 °C) and the common fiscal Lanius collaris (T(thresh) = 33 °C). We used these T(thresh) values to analyse trends in the frequency, duration and intensity of heat waves of magnitude relevant to the focal species, as well as the annual number of hot days (maximum air temperature > T(thresh)), in north-western South Africa between 1961 and 2010. Using this technique, we were able to show that, while all heat wave indices increased during the study period, most rapid increases for both species were in the annual number of hot days and in the maximum intensity (and therefore intensity variance) of biologically meaningful heat waves. Importantly, we also showed that warming trends were not uniform across the study area and that geographical patterns in warming allowed both areas of high risk and potential climate refugia to be identified. We discuss the implications of the trends we found for our focal species, and the utility of the T(thresh) technique as a conservation tool.

Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates.

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m-2). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote.A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81% of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3%), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93% of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.