Yolanda van Heezik
Bio: Yolanda van Heezik is an academic researcher from University of Cape Town. The author has contributed to research in topics: Spheniscus demersus & Biodiversity. The author has an hindex of 4, co-authored 6 publications receiving 72 citations.
01 Jan 1999
TL;DR: Houbara Bustards showed seasonally changing habitat preferences that appeared to be influenced primarily by vegetation phenology, abundance and cover, and more densely vegetated areas (10-17% cover) were preferred as discussed by the authors.
Abstract: Habitat preferences by Houbara Bustards Chlamydotis [undulata] macqueenii in Harrat al-Harrah reserve, in northern Saudi Arabia were determined from sightings of birds in all seasons over three years. Vegetation and crawling invertebrate abundance were sampled in each habitat. Houbara Bustards showed seasonally changing habitat preferences that appeared to be influenced primarily by vegetation phenology, abundance and cover. More densely vegetated areas (10–17% cover) were preferred. Seasonal and inter-habitat variations in invertebrate numbers were not reflected in differential habitat use by Houbara Bustards. The highest selection ratio for a single habitat (dry lakes) occurred in summer, coinciding with the fruiting of Shafallah Capparis spinosa. Selectivity of habitats was least in spring, when green vegetation was most widespread. Changes in Houbara Bustard habitat preferences in response to marked seasonal changes in habitats brought about by well-defined patterns of rainfall indicate that studies of habitat selection should consider the entire annual cycle. The importance of vegetative cover and the sensitivity of Houbara Bustards to human disturbance suggest that reserves set aside for Houbara Bustards should be extensive, diverse and largely free of livestock, human occupation and its associated disturbances.
01 Jan 2012
TL;DR: In this article, the influence of habitat and two covariates (observer and whether birds were seen or heard) on detectability of urban birds was evaluated, and the authors concluded that habitat did not appear to influence detectability for most species.
Abstract: Urban areas can support significant bird populations, including species of conservation concern, but urban ecologists have been slow to apply detectability-based counting techniques. We compared abundances and relative abundances of eight urban birds, derived using two commonly applied techniques (fixed-radius point and strip sampling) and distance sampling. We evaluated the influence of habitat and two covariates (observer and whether birds were seen or heard) on detectability. Due to built-up structures in urban areas, point counts are appropriate. Unavoidable and sometimes complex but necessary interactions with multiple property owners may compromise the number of points able to be counted and therefore the precision of estimates. Abundances from strip and fixed-radius point counts were on average only one-third (strip) and less than one-half (fixed-radius point) those obtained using distance sampling, with interspecific variation in the degree to which densities were underestimated. Rankings of relative abundances were mostly similar, although distance sampling ranked silvereye (Zosterops lateralis) and grey warbler (Gerygone igata) relatively higher in residential habitat. Habitat did not appear to influence detectability for most species, but the two covariates (observer and seen/heard) improved model fit for a number of species, indicating it is useful to record this information. Well-standardised non-detectability-based counts could provide useful information on community structure and relative abundances in urban areas, but distance sampling is necessary to track the population status of species, although it cannot usefully be applied to rare species.
TL;DR: The ontogeny of Jackass Penguin Spheniscus demersus chick behaviour follows the order of development determined for Adelie Pygoscelis adeliae and Yelloweyed Megadyptes antipodes Penguins.
Abstract: Summary Seddon, P. J. & Y. van Heezik. 1993. Behaviour of the Jackass Penguin Chick. Ostrich 64:8-12. The ontogeny of Jackass Penguin Spheniscus demersus chick behaviour follows the order of development determined for Adelie Pygoscelis adeliae and Yelloweyed Megadyptes antipodes Penguins. Feeding and comfort behaviours occur from day one, followed by locomotion and aggressive behaviours. Jackass Penguin chicks are largely inactive during both the day and at night; chicks less than 20 days old are usually prone beneath the attending adult. Begging, feeding and preening are the major chick activities. Begging and feeding become restricted to late afternoon and evening following the commencement of the post-guard phase when chicks are between 26–45 days old. Feeding episodes last on average less than 30 minutes. The frequency of preening increases as chicks moult from about 40 days.
01 Jan 2009
TL;DR: Investigation of movements of Critically Endangered kaki reveals equal proportions of 2-year old survivors that had been released as juveniles and subadults returning and being observed consistently at release sites, emphasizing the value of long-term monitoring in informing release strategies for population restorations.
Abstract: Translocation outcomes for mobile species can be affected by post-release movement of individuals, yet few population reintroduction and supplementation projects con- sider propensity to move as a selection criterion when selecting individuals to release or sites for release. We investigate the influence of release age (juvenile or subadult), the size of the release group and the size of the wild population at the release site on movements of Critically Endangered kaki (black stilt) Himantopus novaezelandiae .O ver 460 subadult and juvenile kaki have been released during 12 years at nine sites in the Waitaki Basin, New Zealand, with the aim of supplementing specific sub-populations. Among the survivors that reached breeding age, 32% of released kaki ended up away from their release sites, i.e. away from the subpopulations they were intended to augment and 15% of these birds were in un- manageable areas where monitoring cannot take place. Kaki released as juveniles (2-3 months) made more long moves and moved further from the release site during 2 months post- release. The presence of conspecifics affected behaviour after release: released birds were more likely to remain closer to the release site when the size of the wild population at the release site was large, and kaki released in larger groups were more likely to make more longer moves. Despite initial differences in mobility, long-term monitoring revealed equal proportions of 2-year old survivors that had been released as juveniles and subadults returning and being observed consistently at rele- ase sites, emphasizing the value of long-term monitoring in informing release strategies for population restorations.
01 Jan 2016
TL;DR: Differential attack rates between guarded, creching and unguarded chicks, and the response of chicks to attack, suggest that creching of unattended chicks may confer protection against adult aggression.
Abstract: Creching of penguin chicks is believed to offer protection from predators and/ or cold weather conditions. An alternative explanation is proposed for the close association of Jackass Penguin (Spheniscus demersus) chicks. The frequency of creching by Jackass Penguin chicks during the pre-independence phase was examined. Unguarded chicks of all ages may form creches of 4-11 chicks. Unguarded chicks may be exposed to high levels of aggression (maximum mean attack rate 3.8/h, range 0-12) from 1-6 adults at a time. Differential attack rates between guarded, creching and unguarded chicks, and the response of chicks to attack, suggest that creching of unattended chicks may confer protection against adult aggression.
TL;DR: This study directly demonstrates that the human pastime of bird feeding substantially contributes to the structure of avian community in urban areas, potentially altering the balance between native and introduced species.
Abstract: Food availability is a primary driver of avian population regulation. However, few studies have considered the effects of what is essentially a massive supplementary feeding experiment: the practice of wild bird feeding. Bird feeding has been posited as an important factor influencing the structure of bird communities, especially in urban areas, although experimental evidence to support this is almost entirely lacking. We carried out an 18-mo experimental feeding study at 23 residential properties to investigate the effects of bird feeding on local urban avian assemblages. Our feeding regime was based on predominant urban feeding practices in our region. We used monthly bird surveys to compare avian community composition, species richness, and the densities of local species at feeding and nonfeeding properties. Avian community structure diverged at feeding properties and five of the commonest garden bird species were affected by the experimental feeding regime. Introduced birds particularly benefitted, with dramatic increases observed in the abundances of house sparrow (Passer domesticus) and spotted dove (Streptopelia chinensis) in particular. We also found evidence of a negative effect on the abundance of a native insectivore, the grey warbler (Gerygone igata). Almost all of the observed changes did not persist once feeding had ceased. Our study directly demonstrates that the human pastime of bird feeding substantially contributes to the structure of avian community in urban areas, potentially altering the balance between native and introduced species.
TL;DR: From 1989 to 2004, the breeding success of African penguins Spheniscus demersus at Robben Island, South Africa was significantly related to estimates of the abundance of both their main prey species, anchovy and sardine, and to the combined biomass of these species.
Abstract: From 1989 to 2004, the breeding success of African penguins Spheniscus demersus at Robben Island, South Africa was significantly related to estimates of the abundance of both their main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax , and to the combined biomass of these species. When the combined spawner biomass of fish prey was less than 2 million ton, pairs fledged an average of 0.46 chicks annually. When it was above 2 million ton, annual breeding success had a mean value of 0.73 chicks per pair. Given previously estimated values of survival and age at first breeding, these levels of breeding success are inadequate to sustain the African penguin population. With the higher level of breeding success, an equilibrium situation might be attained if adult survival could be increased by 6–7% per annum. Attempts to reduce mortality of penguins have included the collection, cleaning and return to the wild of oiled birds, culling of Cape fur seals Arctocephalus pusillus pusillus seen preying on penguins around breeding localities and control of the spread of disease. Management of the purse-seine fishery should ensure adequate escapement of fish to maintain the combined biomass of anchovy and sardine above 2 million ton. The maintenance of suitable breeding habitat and removal of feral predators from breeding localities will also be important in improving breeding success.
TL;DR: Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony.
Abstract: Population trends of African penguins Spheniscus demersus in the Western Cape, South Africa, and their breeding success have been linked to the abundance of their main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. During the late 1990s and early 2000s, both fish species increased markedly in abundance, but after 2004, sardine biomass decreased to below average levels. In addition, adults of both stocks were principally located to the east of Cape Agulhas from 2001 to 2009 and were thus distant from seabird colonies on South Africa's West Coast. The number of African penguin pairs counted at Robben Island from 2001 to 2009 and the fledging period of chicks from successful nests increased and decreased in apparent response to the biomass of sardine prior to each breeding season, possibly linked through adult condition at the onset of breeding. Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony. In addi- tion, chick-fledging rates were depressed in 2-chick broods during years when anchovy con- tributed <75% by mass to the diet of breeding birds. Previously reported relationships between the overall abundance of forage fish in South Africa and penguin breeding success were not sup- ported. Taken together, these results highlight the combined importance of ensuring adequate local food availability for seabirds during the reproductive cycle and safeguarding regional prey abundance during the non-breeding season.
TL;DR: A quantitative framework for citizen surveillance calls for an integration of citizen science and crowdsourcing and provides a way forward to solve the statistical challenges inherent to citizen-sourced data.
Abstract: Citizen science and crowdsourcing have been emerging as methods to collect data for surveillance and/or monitoring activities They could be gathered under the overarching term citizen surveillance The discipline, however, still struggles to be widely accepted in the scientific community, mainly because these activities are not embedded in a quantitative framework This results in an ongoing discussion on how to analyze and make useful inference from these data When considering the data collection process, we illustrate how citizen surveillance can be classified according to the nature of the underlying observation process measured in two dimensions-the degree of observer reporting intention and the control in observer detection effort By classifying the observation process in these dimensions we distinguish between crowdsourcing, unstructured citizen science and structured citizen science This classification helps the determine data processing and statistical treatment of these data for making inference Using our framework, it is apparent that published studies are overwhelmingly associated with structured citizen science, and there are well developed statistical methods for the resulting data In contrast, methods for making useful inference from purely crowd-sourced data remain under development, with the challenges of accounting for the unknown observation process considerable Our quantitative framework for citizen surveillance calls for an integration of citizen science and crowdsourcing and provides a way forward to solve the statistical challenges inherent to citizen-sourced data