OpenUCT :: Browsing by Author "Ryan, Peter G"

Browsing by Author "Ryan, Peter G"

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Open Access
The abundance, distribution and accumulation of plastic debris in Table Bay, Cape Town, South Africa
(2013) Lamprecht, Annerie; Moloney, Coleen; Ryan, Peter G
Stranded debris and beach litter were examined at two sites in Table Bay, South Africa, repeating a survey made at the same two beaches in 1994. One beach (Milnerton) is a popular recreational beach 12 km from the city centre, whereas the other (Koeberg) is situated in a nature reserve, with limited access by the general public, and is 27 km farther from the city. Daily accumulation rates of manufactured items (>1 cm diameter) were measured at both beaches for ten days in October, November and December 2012. Of the 124,646 items collected, 93% were made of plastic, but these items comprised only 59 % of the total weight. There was generally consistent but large within-site variability in accumulation rate; the within-site coefficients of variation (CVs), which range from 23.7 % to 101.5 %, respond in the same way across months. There was also considerable daily variation (CVs range from 13.6 % to 92.8 %). The mean density of items decreased with distance from Cape Town. Since 1994, the composition, abundance and accumulation rate of debris has changed on these two beaches. The mean (s.e) accumulation rate of plastic articles at Milnerton increased 257 %, from 378 (72.3) plastic items.day-1.100 m-1 of beach to 1350 (126.7) items.day- 1.100m-1. The increase at Koeberg was from 44 (2.7) items.day-1.100 m-1 to 100 (17.3) items.day-1.100 m-1. Evidence of increased input during the peak holiday season (December) was recorded at both beaches. The mean accumulation rates of most materials had increased at Milnerton since 1994 and the composition of the materials had also changed. The non-plastics were numerically dominated by cloth, paper and wood in 1994 but cigarette butts dominated in 2012. In contrast, at Koeberg the accumulation rates of most non-plastic materials decreased since 1994 and there were small differences in composition. No correlation was found between total weights and total counts of plastic items on the beaches. Daily variability (accumulation rate and accumulating weight) was generally not correlated with weather conditions. Since 1994, the accumulation rate of small, unidentified plastic fragments increased by more than 200- fold at Milnerton and by a factor of 80 at Koeberg. To improve our understanding of the vertical distribution, abundance and composition of microplastics (articles < 10 mm), samples were taken at 5 cm depth intervals (0 to 25 cm) on Milnerton. The number of microplastics, sized 2 mm- 10 mm, found in each layer decreased with depth. Smallest plastic items (0.5 - 2 mm) were randomly distributed in the surface layers (top 10 cm) but had low densities in the bottom layers. Plastic pellets had the same decreasing trend with depth. Amounts of plastic litter have increased by two orders of magnitude over an 18-year period, reflecting both accumulation of plastic debris in coastal environments and increased use of plastics during the past decades.
Open Access
African penguin (Spheniscus demersus) distribution during the non-breeding season : preparation for, and recovery from, a moulting fast
(2016) Roberts, Jennifer; Ryan, Peter G; Pichegru, Lorien; Wanless, Ross M; Hagen, Christina
Little is currently known about the spatial ecology of the endangered African penguin during the non-breeding season. As foraging success during this period is critical to adult survival, this project explores their dispersal patterns, as well as the degree of overlap with commercial purse-seine fisheries which target the same prey. African penguins from two colonies (Bird Island, Algoa Bay, south coast and Dassen Island, west coast) were tracked over 3 non-breeding seasons using Platform Terminal Transmitters and Global Positioning System devices to explore their pre- and post-moult dispersal patterns. Dispersal trips varied greatly between individuals, but there were still significant differences in the dispersal patterns found between islands and between life history-stages at Dassen Island. Bird Island penguins tended to make frequent, short trips, returning to their breeding colony in between, whereas Dassen Island penguins followed one of two strategies: either making few (up to 3) very long trips (up to 4000km), or adopting a central-place foraging pattern based at a point along the coast, distant from their breeding colony. At Dassen Island a clear spatial divide is evident with most pre-moulters dispersing south whereas most post-moult birds dispersed north, off the west coast. Bird Island penguins all moulted at their breeding colony and seldom visited either the adjacent coastline or other islands. During pre-moult, Dassen Island birds often spent nights close to shore along the coast or at other colonies and about a quarter of them moulted at another colony, most often at Stony Point, on the mainland east of Cape Point. Five dispersal patterns (defined in terms of the direction and distance of the furthest point reached) were identified for birds from Dassen Island and there is some indication that different dispersal patterns have distinct survival implications. Over 60% of PTT loss (a proxy for penguin mortality) occurred in a small area in the northern part of St Helena Bay, offshore from Lambert's Bay and Strandfontein and could be due to high levels of seal predation, which has been previously documented in the area. Commercial small pelagic fishing data were analysed over three years (2012-2014). Average fishing effort decreased each month from September to December (when hardly any fishing occurred in any of the three years) and there was much greater fishing effort along the west coast than on the south coast. Commercial fishing effort was compared to penguin track data to assess the degree of potential overlap between these two pelagic predators. Firstly, the spatial overlap between core penguin non-breeding dispersal areas and core fishing areas was assessed on a broad temporal scale (three years). Bird Island penguins were found to be more spatially removed from fishing activity with no overlap in core fishing and dispersal areas on the south coast. Compared to the size of their dispersal area, Dassen Island penguins which stayed along the lower west coast showed the highest overlap with core fishing areas. The two most common dispersal patterns exhibited by Dassen Island penguins both involve journeying to areas outside the range of purse-seine fishing, indicating the possibility of avoidance behaviour once the pressures of breeding are lifted. Direct (daily) overlap between commercial fishing effort and penguin tracks was studied although the low frequency of the penguin position data restricted the analysis to a 20 km scale. The results were similar to those described above, with most direct overlap occurring between Dassen Island and Gansbaai.
Open Access
Breeding and dispersal implications for the conservation of the Southern Ground Hornbill Bucorvus leadbeateri
(2017) Carstens, Kate; Ryan, Peter G; Little, Rob M; Thomson, Robert
Populations of secondary tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. For the Southern Ground Hornbill Bucorvus leadbeateri that typically nests in natural tree cavities, the shortage of nesting sites is one factor potentially limiting population growth. The species is listed as endangered in South Africa, and vulnerable throughout the rest of its range. Nest boxes can improve the conservation status of threatened birds that are limited by nest-site availability. However, nest boxes or other types of artificial nests are not always beneficial to the target species, and their value as a conservation tool needs to be tested for each species. Wooden nest boxes were installed for ground hornbills in a study area in north eastern South Africa with a paucity of natural nest sites. In this thesis, I assess productivity, timing of breeding, and dispersal in the Southern Ground Hornbill in a study area supplemented with nest boxes and discuss the implications for the conservation of this endangered species. Nest boxes are an effective conservation tool to improve productivity in areas lacking natural tree cavity nesting sites. Breeding success (calculated as the proportion of nesting attempts that fledged a chick) and predation levels were similar for groups using nest boxes and natural nests. Natural nests were more buffered against cooling night temperatures, but otherwise nest boxes provided nesting conditions that were no better than natural nests. Timing of breeding for nests in natural tree cavities and nest boxes were similar. However, groups with access to a nest box attempted breeding more often than groups with access to a natural nest only, resulting in an 15 % increase in the number of fledglings per group compared to an adjacent protected area with no artificial nests. The number of breeding groups in the study area increased by 460 % over 12 years. However, there is a limit to the density of breeding groups. Breeding success was highest when breeding density was one breeding group per 90-120 km², so nests should be spaced ~10 km apart. Given that the threats to ground hornbills include persecution and poisoning, increasing the reproductive rate by providing nest boxes should assist in slowing the decline by the increased recruitment of offspring into the population. Timing of breeding varied across years. The first eggs laid each year ranged from 9 September to 14 November, and median lay date was 03 November. Breeding attempts that were initiated early in the season were more likely to fledge a chick than those initiated later in the season. Timing of breeding was delayed during warmer springs, particularly under dry conditions. In savannas, hotter spring temperatures could limit food availability, for example, if higher temperatures cause the vegetation to dry out, resulting in a rapid decline in insect flush, especially in the phytophagous insect groups that form a large part of the ground hornbill diet. Factors to consider when constructing and placing nest boxes include thickness of the cavity walls, entrance height above ground and density of nest boxes placed in the landscape. Breeding attempts in natural nests and nest boxes with thicker nest walls and those positioned with higher entrances above the ground increased breeding success. Therefore, nests should be constructed with cavity walls at least 6 cm thick and placed so that the entrances are situated > 6 m above the ground. With 186 ringed chicks fledging from the study area after the installation of nest boxes, it was possible to observe their dispersal within the study area and farther away into the adjacent Kruger National Park. There was no evidence for sex-biased dispersal. Males and females dispersed at similar ages, and over similar distances, raising interesting questions about inbreeding avoidance mechanisms in this species. If females do not disperse beyond the range of related males, how do related individuals avoid pairing, and what forms of individual recognition exist?
Open Access
Comparative breeding biology of the Northern Rockhopper penguin Eudyptes moseleyi on Gough and Nightingale Islands
(2014) Johaadien,Rukaya; Ryan, Peter G; Steinfurth, Antje
The Northern Rockhopper Penguin Eudyptes moseleyi is listed as Endangered due to an estimated 57% decrease in breeding numbers over the past 37 years. Approximately 85% of the global population breeds at the Tristan da Cunha archipelago (Tristan, Inaccessible and Nightingale Islands) and nearby Gough Island in the central South Atlantic Ocean. The population on Gough Island declined by 50-60% between 1982 and 2005, but in the Tristan da Cunha archipelago the population trend over the last few decades is believed to be stable despite long-term human exploitation (particularly egg collection on Nightingale Island in recent years).This study compares aspects of the breeding biology on Gough Island (where population numbers are decreasing) and Nightingale Island (where numbers are thought to be stable) based on data gathered from five colonies in the 2012/13 and 2013/4 breeding seasons. On Nightingale Island, breeding success was 6.5% lower and 40-day old chick mass 47% less(implying poor juvenile recruitment)compared to on Gough Island. Poor foraging conditions for birds on Nightingale Island is the most probable explanation for these results, and future studies should focus on the foraging locations used by birds on both islands. Additionally, egg collection practices on Nightingale Island may have had a negative impact on the population, and I recommend that the temporary ban on egg-collection at Nightingale Island is made permanent. It is also possible that the population on Gough Island is no longer in decline, or is declining for reasons unrelated to breeding success; to verify this and confirm the findings of this study, future population trends and chick fledging mass on both islands should be monitored over the long-term.
Open Access
Comparative ecology of Pachyptila species breeding sympatrically at Gough Island
(2018) Jones, Christopher Warrick Price; Ryan, Peter G
Prions (Pachyptila spp.) are one of the most abundant seabird groups of the Southern Ocean but their taxonomy, at-sea distribution and foraging ecology are poorly known. There has been considerable confusion surrounding the taxonomy of prions and their identification at sea is problematic. Recent studies have confirmed the presence of two very similar prion species breeding sympatrically, approximately three months apart, on Gough Island: Pachyptila vittata and P. macgillivrayi. This discovery raised several questions about the ecological segregation of these species. My thesis compares the breeding distribution, at-sea movements, phenology, foraging ecology and trophic segregation of the two species at Gough Island, and compares Gough birds with the P. vittata from Tristan da Cunha. In 2000/01 it was estimated that 1.5–2.0 million pairs of prions bred on Gough Island, suggesting that this site supports the largest populations of both species in the world. However, the contribution of each species to this total as well as spatial and temporal segregation of the two species required further investigation. To investigate the breeding distribution and relative species proportions across Gough Island, 2227 prion specimens were collected opportunistically over several years at various sites. Most birds were caught at night or found dead, thus only provide an inference of breeding distribution. However, observations of incubating birds at several sites indicate that the data are representative of nesting distributions. At most sites there was evidence for consistent dominance of one or other species, although this need not mean local allopatry; a few P. vittata breed in Prion Cave, where P. macgillivrayi is by far the most abundant species. A few sites had both species in similar proportions, but these tended to be sites with relatively few birds and/or represent areas where the two species’ ranges abut. Weighting each site equally suggested a roughly equal ratio of P. vittata/P. macgillivrayi, but there was little coverage of the northern and eastern glens, where P. vittata appears to predominate. The habitat area occupied by P. macgillivrayi comprises ~40% of Gough Island, suggesting they comprise ~40% of the prion population if the density of breeding birds is roughly similar for both species. Based on these proportions and the previous population estimate, some 600 000 to 1 000 000 P. macgillivrayi and 750 000 to 1 200 000 P. vittata are estimated to breed on Gough Island Additional investigation is required to elucidate the spatial segregation of the two species at a finer scale. Additional detailed categorizing of habitat types is needed to determine the fine-scale drivers for their spatial segregation. The prions’ phenology, foraging ecology and trophic segregation was examined through geolocation technology, salt-water immersion sensors (recording time on the water), stable isotope analyses as well as a comparison of bill morphology. Breeding adults of both species were tagged with geolocators/immersion sensors on Gough Island and breeding adults of P. vittata were tagged at Tristan da Cunha. During their respective breeding seasons P. vittata largely remained within 1500 km to the north-east of the colony and P. macgillivrayi occupied waters within 1000 km to the south of the colony. At Gough Island, P. vittata departed and returned to the colony on average 91±9 days earlier than P. macgillivrayi. The length of the non-breeding period did not differ between species and all tracked individuals except one P. vittata engaged in a pre-laying exodus lasting 13-49 days. The P. vittata population from Tristan da Cunha departed, moulted and returned 15-17 days later than their counterparts from Gough Island. After breeding, both species showed a well-defined outward migration, with all moving west until the start of moult, except one P. vittata individual that moved east. Moulting was inferred from a marked reduction in the time spent in flight, which occurred shortly after arrival on the non-breeding grounds by both species (i.e. November– February for P. vittata and February–June for P. macgillivrayi). Moulting birds targeted specific areas with little overlap between species within the Argentine Basin. Both species briefly returned to their burrows after moulting. During the remainder of the non-breeding period both species were distributed more widely over the South Atlantic Ocean. Interspecific spatial segregation was observed for most of the tracking period, especially in core use areas. Pachyptila macgillivrayi spent more time flying, during both daylight and darkness, than P. vittata. Stable isotope signatures of prion flight feathers from tracked birds and additional samples from each population indicated that movements of tracked individuals were representative of the adult population, and were similar over years. Higher δ 15N values found in P. macgillivrayi feathers is consistent with the hypothesis that P. vittata, being the more specialist filter feeder, targeting copepods, should forage at a lower trophic level than the more generalist P. macgillivrayi. This is also consistent with the greater time in flight for P. macgillivrayi i.e. more time actively searching for food, rather than sitting on the water filtering. Across both species, bill width was positively correlated with the number of palatal lamellae with P. vittata having a wider bill containing more palatal lamellae and thus better equipped for filter feeding. Habitat analysis revealed biologically meaningful, speciesspecific preferences for distance from the breeding colony, chlorophyll-a and sea surface temperature, but not distance to seamount or for water depth. This study contributes to the growing number of studies tracking small petrels and provides information on the strategies employed by extremely similar and abundant seabirds, most notably allochrony for P. vittata and P. macgillivrayi, allowing ecological segregation as well as furthering the understanding of moult in prions. The findings of this thesis advance the knowledge of the ecology of these poorly studied species of prions.
Open Access
Comparative foraging ecology of macaroni and rockhopper penguins at the Prince Edward Islands
(2017) Whitehead, Thomas Otto; Ryan, Peter G
Penguins are one of the largest consumers of marine resources in the Southern Ocean and spend most of their lives at sea. Although the last four decades have seen technological advancements that have considerably expanded our knowledge about their at-sea behaviour, there is still much to be learned. Given the rapid ongoing ecosystem changes in the Southern Ocean, it is vital to better understand, firstly, how penguins respond to environmental variability, and secondly, how such changes alter ecological relationships between sympatric species. Being flightless, travel is slower and more costly for penguins than flying seabirds. This constrains their ability to find resources, particularly during the breeding season when they must regularly return to the colony to provision offspring. As penguins are colonial nesters, high foraging pressure near the colony can limit available resources, enhancing potential intra- and interspecific competition. At many localities, ecologically similar penguin species breed sympatrically. In such cases, co-existence is only thought possible through ecological segregation in space, time and/or diet. At the Prince Edward Islands, approximately 302,000 pairs of macaroni Eudyptes chrysolophus and 80,000 pairs eastern rockhopper E. chrysocome filholi penguins breed sympatrically. These populations are closer to parity than at any other locations where two eudyptid species breed sympatrically. Populations of both species at the Prince Edward Islands have declined in the last two decades, but drivers of these declines are poorly understood. The primary aim of this thesis was to better understand the foraging strategies of macaroni and rockhopper penguins at the islands and identify aspects of their ecology that allow them to co-exist. The secondary focus was to investigate how each species responds to environmental variability and assess how ecological interactions between species might be altered in an era of rapid global change. To study the at-sea habitat use and diving behaviour of penguins during chick-rearing and pre-moult periods, I used GPS loggers and time-depth recorders. To track penguins during the winter I used geolocation loggers and satellite transmitters. Stable isotope analyses were used to investigate trophic ecology during late winter, summer and pre-moult periods. During the breeding season, both species primarily foraged in pelagic waters beyond the shelf break (> 3000 m), with macaroni penguins foraging slightly farther offshore on average. However, rockhopper penguins breeding adjacent to the inter-island shelf foraged in shallow waters (< 200 m) over the shelf. Both species dived to similar depths (40 to 60 m), but macaroni penguins dived deeper more often. The diet of both species was dominated by two krill species (Thysanoessa vicina and Euphausia vallentini). Diving behaviour varied between years, with both species diving deeper when the SAF was located farther away and geostrophic flow was reduced. During these conditions, macaroni penguins fed on a larger proportion of myctophids whereas rockhopper penguins resorted to less energy-dense nototheniids. This highlights contrasting responses to periods of low krill availability. During the pre-moult period, habitat preferences were similar between species, with penguins travelling up to 1000 km south to forage in Antarctic Zone waters (SST 3-4 °C). However, a three-week difference in departure dates minimised spatiotemporal overlap between species. Diving behaviour was similar between species, but macaroni penguins performed more deep dives and encountered thermoclines more often. Stable isotope analyses revealed that macaroni penguins fed on a greater proportion of fish than rockhopper penguins, and revealed species-specific spatial responses to changes in primary productivity, with macaroni penguins travelling farther south in less productive years. During the 6-month long winter sojourn, macaroni penguins generally foraged in cooler waters (SST ~ 3 °C) compared to rockhopper penguins (5-6 °C). However, stable isotope analyses revealed that trophic and spatial overlap were high during late winter. Both species associated with mesoscale eddies and submesoscale filaments, suggesting that these features play an important role in aggregating prey during the resource-limited winter months. In summary, it appears that subtle differences exist to minimise competitive overlap between macaroni and rockhopper penguins. The three-week difference in the onset of breeding is integral to minimising competitive overlap during late winter, brood-guard/crèche, pre-moult and immediately following the moult. This allochrony staggers the peak energy demands of rockhopper penguins to reduce overlap with macaroni penguins. The larger-bodied macaroni penguins are capable of diving deeper, for longer and more efficiently than rockhopper penguins, which increases their behavioural flexibility and fitness by minimising stresses associated with reduced krill availability. Such differences in diving behaviour may explain contrasting population trends at the islands and suggests that rockhopper penguins may continue to decline at a faster rate than macaroni penguins if ongoing climate change continues to reduce prey availability around the Prince Edward Islands.
Open Access
Comparing body condition and foraging ecology of two populations of Cape Gannets on Bird and Malgas Islands
(2010) Moseley, Christina; Grémillet, David; Pichegru, Lorien; Ryan, Peter G
Cape gannets (Morus capensis) are one of the dominant seabirds in the Benguela current ecosystem and feed mainly on sardines (Sardinops sagax) and anchovy (Engraulis encrasicolus). Starting in the late 1990s the distribution of these fish shifted from the west coast of South Africa to the south-east coast. This has resulted in gannets on the west coast feeding extensively on fishery wastes, which slows the growth of chicks and decreases their fledging mass. I compared the foraging ecology, diet and body condition of adult Cape gannets from two colonies, one where individuals have been feeding on fishery wastes (hake) for several years (Malgas Island; west coast) and the other where individuals feed on natural prey (Bird Island; south coast). In October and November 2009, through the use of GPS loggers I compared the foraging behaviour of birds from the two colonies. I compared the diet of gannets at the two colonies, using stomach contents samples and an isotopic mixing model using stable isotope ratios of carbon and nitrogen in blood, feathers and potential prey. I also compared the body condition of adults by measuring pectoral muscle thickness and other morphological parameters. These results were analysed with data from a concurrent hydro-acoustic survey of the distribution and abundance of pelagic fish along the coast of South Africa. The hydro-acoustic survey showed that more than half of the sardine and anchovy stocks were present on the west coast for the first time in several years but that the overall biomass of these two species remained low in the southern Benguela. Stomach samples and isotopic analysis of blood showed that gannets at both colonies fed mainly on sardines during the study period. Long-term diet estimates from feather isotopes suggest that there was little hake in the diet of birds at Malgas Island, despite the direct diet samples showing that hake and saury dominated the diet over the preceding 10 months. This could be due to insufficient prey sampling or the diet samples not being representative of the gannet population as a whole. Gannets from Bird Island made longer foraging trips and flew further from their colony than did those from Malgas Island. Individuals from this colony had slightly greater pectoral muscle thicknesses and body masses (after controlling for size) than those from Bird Island, but 4 this was not significant. Despite gannets from Malgas Island relying on fishery wastes for a number of years, there has been little effect on body condition among breeding birds when compared with Bird Island gannets feeding on pelagic fish. Two possible reasons for this are that (1) when feeding on fishery wastes, adults decrease their reproductive effort to preserve body condition or (2) gannets on the west coast have regained body mass and pectoral muscle rapidly since the local recovery of sardines. It is likely that the gannets from Bird Island have greater foraging costs due to intra-specific competition for food as the colony has increased five-fold in size over the last 50 years. However, chick growth and adult body condition have been affected only marginally. Despite the presence of sardine and anchovy on the west coast, it is likely that Cape gannets are food limited, especially since there is also a strong spatio-temporal overlap of gannet foraging with the large commercial purse-seine fishery. Better spatial management of this fishery is necessary to ensure the persistence of seabirds and other top predators in the southern Benguela.
Open Access
A conservation genetic study of threatened, endemic southern African seabirds
(2014) Nupen, Lisa Jane; Bishop, Jacqueline M; Ryan, Peter G
Molecular techniques have a broad, and growing, application in the field of wildlife conservation, ranging from the systematic identification and classification of taxa, through studying genetic connectivity between populations, to parentage and individual barcoding. While they are applied to a wide range of spatial- and temporal-scales, molecular approaches complement traditional methods used to classify, investigate and understand the natural world. This study uses multiple lines of evidence, at various scales, to investigate how seabird biology influences population-level responses to changing environments. The focal area is the Agulhas-Benguela Ecosystem (ABE) along the south-western coast of Africa. Globally, biodiversity loss due to environmental change in marine ecosystems is significantly affecting the phenology, distribution, dispersal patterns, and demographic rates of organisms across trophic-levels. Broad-scale changes are occurring that have consequences for both commercial fisheries and threatened marine top-predators. Seabirds are valuable indicators of the state of marine ecosystems, and changes in their distribution and dispersal patterns may reflect those of species in lower trophic-levels. This is the case in the ABE, where some endemic seabird species are better at responding to changes in their environment than others. Twentieth century shifts in the distribution of key pelagic prey species in the ABE have had serious consequences for endemic seabirds. The African Penguin Spheniscus demersus, Cape _ Gannet Moms capensis and Cape Cormorant Phalacrocorax capensis rely on these pelagic fish, and all three species are threatened and in decline. In this study population genetic and phylogeographic methods are used to: (i) quantify levels of genetic diversity, and determine regional-scale structure within all three focal species; (ii) explore fine-scale population structure in African Penguin; and (iii) compare wild and captive populations of African Penguins. The conservation of genetic diversity is essential for the long-term persistence of species. Population genetics can help us to understand the evolutionary processes that have shaped patterns of genetic diversity in the focal species, and predict how they might respond to further environmental changes. Comparative phylogeography, combined with capture-mark- recapture models based on ringing data and annual census counts, provide the most complete picture of the micro-evolutionary forces at play in this unique ecosystem, and highlight seabird life-history characteristics may facilitate adaptation and survival under novel conditions. This is the first conservation genetic study of endemic seabirds in the ABE. Although the three focal species differ in a number of aspects of their breeding and foraging ecology, and in some life-history characteristics, they have evolved under similar selective pressures across their shared range, and represent natural replicates that allow us to determine the dominant drivers of population genetic change. Flexibility in foraging behaviour and the degree of breeding site fidelity exhibited by each of the three focal species affect the rate and effectiveness of their demographic responses to changes in their environment. Understanding connectivity among seabird populations is crucial for their long-term conservation, and has been investigated in numerous studies of seabird species from around the world. Similar to many of these, this study found very low levels of genetic structure among populations of all three focal species based on DNA sequence data, suggesting long-term gene-flow among them, despite potential physical and non-physical barriers. Overall, the patterns observed suggest that high connectivity characterises their breeding regions, and most breeding colonies, buffering the respective populations against environmental variability. These results were supported by fine-scale analyses of the African Penguin using microsatellite markers that also suggested high levels of gene-flow, which may have masked genetic signatures of the regional- and colony-level bottlenecks experienced by this species. Microsatellite-based genetic diversity and fine-scale structure were also compared among wild and captive populations of African Penguins to assess the genetic consequences of a planned conservation breeding program. The genetic composition of birds in captivity largely reflects that found in wild populations. The success of reintroduction in terms of decreasing extinction risk in the wild is uncertain, and should be implemented as part of a broader management plan that addresses the primary threats to wild populations. Further research is required to improve our understanding of many aspects of endemic southern African marine avifauna and better inform our ability to ensure their continued persistence in this system.
Open Access
Cranes and crops: investigating the viability of blue cranes in agricultural lands of the Western Cape
(2016) Van Velden, Julia; Ryan, Peter G; Smith, Tanya
The Western Cape population of Blue Cranes (Anthropoides paradiseus) is of great importance as the largest and most stable population throughout its range. This species is strongly associated with agricultural lands in the Western Cape, and therefore may come into conflict with farmers who perceive them as damaging to crops. Blue Cranes are suspected to be locally nomadic, but little information has been collated to support this and they are also relatively understudied in terms of demographic parameters. This project investigates the viability of the Blue Crane population in three ways: exploring farmer attitudes towards cranes in two regions of the Western Cape (Swartland and Overberg) using 40 semi-structured interviews, generating estimates of survival using Mark-Recapture methods and exploring movement patterns using a long-term data set of resightings of marked individuals. These three components all add important aspects to the overarch ing goal of achieving a better understanding of threats to Blue Cranes in the Western Cape, and thus the population's long-term viability. Perceptions of cranes differed widely between regions: farmers in the Swartland perceived cranes to be particularly damaging to the feed crop sweet lupin (65% of farmers reported some level of damage by cranes), and 40% of these farmers perceived cranes as more problematic than other common bird pests. Farmers in the Overberg did not perceive cranes as highly damaging, although there was concern about cranes eating feed at sheep troughs. Survival was age-structured: individuals in their first year had a survival of 0.6, those in their second and third years that of 0.87 and adult individuals (4+) that of 0.72. The adult survival estimate is suspected to be underestimated due to ring loss. Resightings of colour-ringed cranes suggest that movements in the Western Cape were localized, with an average displacement of 24.6 km from their natal point. Only 3.8% of marked individuals were resighted in both the Overberg and the Swartland regions, indicating that movement between these regions was low and regional fidelity was high. There was significant movement within the Overberg however, and 90% of movements of >10 km were made within this region. This species therefore appears to be resident to locally nomadic in nature. Evidence for natal philopatry was also found: 57% of adults returned at least once to the area where they were ringed as juveniles. These results highlight the need for location-specific management solutions to crop-damage by cranes, and contribute to the understanding of basic demographics for this vulnerable species.
Open Access
Diet and foraging behaviour of Macaroni and Chinstrap penguins at Bouvetøya, South Atlantic Ocean
(2000) Huyser, Onno Adrian Wallace; Wilson, Rory; Ryan, Peter G
Bibliography: leaf 195.
Open Access
Disturbance effects of boat-based tourism on waterbirds at the Ramsar-designated De Hoop Vlei, Western Cape, South Africa
(2017) De Blocq Van Scheltinga, Andrew; Ryan, Peter G; Thomson, Robert
Recreation and ecotourism activities are growing in demand worldwide, especially in biodiversity hotspots. Protected area managers may seek to introduce novel activities in order to generate revenue. However, disturbance effects brought about through encounters between humans and wildlife can have negative consequences, which conflict with conservation goals. De Hoop Vlei is a large coastal lake within the De Hoop Nature Reserve. It is a Ramsar site as well as a key feature of a BirdLife Important Bird Area (IBA). Proposals for motorized boat tours and kayak tours on the vlei have been made, for which this study provides an impact assessment. Repeated counts were performed in order to characterize the waterbirds present during the high water level conditions required for boating. Birds were concentrated in areas with aquatic vegetation and shallow water, mainly along the vlei's western shoreline and southern and northern ends. Two routes were designed for boat tours that would minimize disturbance by avoiding these areas as well as breeding sites. Count data were also used to revise the Ramsar and IBA assessments, which underestimated the site's conservation value. Boat tours were monitored to estimate the number of birds disturbed, and to measure agitation distances (ADs) and flight initiation distances (FIDs) in response to the boat as well as a kayak. Post-disturbance recovery was investigated, as was the likelihood of habituation using a space-for-time substitution at a site with regular boat traffic. Boat tours did not typically disturb more than 10% of birds present at the vlei, and largely avoided disturbing species of conservation concern. Responses to the kayak were more severe than to the boat, which is most likely due to the similar speeds of the two boats are similar and the kayak is more easily perceived as a threat due to its shape and stealth, the presence of a paddler, and the consistent paddling motion. Post-disturbance recovery of species was slow and incomplete after an hour, meaning that there are likely costs for foraging opportunities and breeding if important areas are disturbed. Most species did allow a closer approach at the site with regular boating, but AD did not differ between them for most species. From these results it would be dangerous to assume that habituation will mitigate against disturbance impacts. Recommendations made included that kayak tours should not be permitted. Boat tours, with correct management, can be conducted in a manner that will not be too disruptive to birds. This study is the first to document such a large difference in responses of birds to two differing boat types, and is a rare example of disturbance of birds being studied in an African context.
Open Access
Diving of great shearwaters (Puffinus gravis) in cold and warm water regions of the South Atlantic Ocean
(Public Library of Science, 2010) Ronconi, Robert A; Ryan, Peter G; Ropert-Coudert, Yan
BACKGROUND: Among the most widespread seabirds in the world, shearwaters of the genus Puffinus are also some of the deepest diving members of the Procellariiformes. Maximum diving depths are known for several Puffinus species, but dive depths or diving behaviour have never been recorded for great shearwaters ( P. gravis ), the largest member of this genus. This study reports the first high sampling rate (2 s) of depth and diving behaviour for Puffinus shearwaters. METHODOLOGY/PRINCIPAL FINDINGS: Time-depth recorders (TDRs) were deployed on two female great shearwaters nesting on Inaccessible Island in the South Atlantic Ocean, recording 10 consecutive days of diving activity. Remote sensing imagery and movement patterns of 8 males tracked by satellite telemetry over the same period were used to identify probable foraging areas used by TDR-equipped females. The deepest and longest dive was to 18.9 m and lasted 40 s, but most (>50%) dives were <2 m deep. Diving was most frequent near dawn and dusk, with <0.5% of dives occurring at night. The two individuals foraged in contrasting oceanographic conditions, one in cold (8 to 10°C) water of the Sub-Antarctic Front, likely 1000 km south of the breeding colony, and the other in warmer (10 to 16°C) water of the Sub-tropical Frontal Zone, at the same latitude as the colony, possibly on the Patagonian Shelf, 4000 km away. The cold water bird spent fewer days commuting, conducted four times as many dives as the warm water bird, dived deeper on average, and had a greater proportion of bottom time during dives. Conclusions/Significance General patterns of diving activity were consistent with those of other shearwaters foraging in cold and warm water habitats. Great shearwaters are likely adapted to forage in a wide range of oceanographic conditions, foraging mostly with shallow dives but capable of deep diving.
Open Access
Does the availability of shade limit use of water troughs by desert birds?
(2015) Abdu, Salamatu; Cunningham, Susan J; Ryan, Peter G; McKechnie, Andrew E
Climate change poses a major threat to living organisms, with maximum temperatures expected to continue to rise over the next few decades. Hot desert environments are particularly at risk because they experience high environmental temperatures, scarce vegetation, low productivity and unpredictable water sources. Endotherms such as birds face the challenge of maintaining a stable body temperature while avoiding dehydration. This study was carried out in the southern Kalahari, in South Africa's Northern Cape, where about 50% of bird species (36 species) depend on free-standing drinking water. Livestock farms within this area provide artificial water points, which benefit birds as well as livestock. This study determined the role of shade and cover in the use of these artificial water points by birds. An experiment was conducted at six waterholes using the Before-After, Control-Impact (BACI) design. After an initial baseline was established, three waterholes were shaded while the other three were left unshaded. Camera traps were used to record the pattern and intensity of water use by bird species at different times of the day and at varying air temperatures. A total of 36 bird species drank at the water holes, but data analysis was confined to the ten most abundant species. Of the ten, six species responded to the presence of shade/cover, with four species reacting positively (Cape Glossy Starling Lamprotornis nitens , Red - headed Finch Amadina erythrocephala , Black - throated Canary Serinus atrogularis , and Laughing Dove Spilopelia senegalensis ), four showing no significant change in drinking patterns, and two showing a decrease in visitor numbers when the site was shaded (Cape Turtle - Dove Streptopelia capicola, Namaqua Dove Oena capensis). This suggests that providing shade at waterholes is not a universal solution to the problem of increasing heat stress experienced by birds coming to drink. Certain species such as the Laughing Doves and Cape Turtle-Doves avoided waterholes during the warmest time of the day while the Namaqua Doves were frequent visitors at this time. However, the Laughing Dove took advantage of the shade provided at midday (warmest temperatures) as their numbers increased. The Red-headed Finch and Black-throated Canary also increased at water holes with temperature irrespective of the time of day. These patterns imply that the provision of shade modifies the behavior of some bird species in response to predation risk or heat stress. These species utilized shade at different times of day and with varying intensities as temperatures rose.
Open Access
Dominance, social organisation and cooperation in the sociable weaver (Philetairus socius)
(2015) Rat, Margaux Emilie Therese; Ryan, Peter G; Covas, Rita; Doutrelant, Claire; van Dijk, Rene E
Sociality and cooperation are universal features of life, yet cooperative societies are highly vulnerable to conflicts-of-interests which may lead to societal collapse. Dominance may function as a central mechanism behind the maintenance of cooperative societies, because it may reduce conflict by the establishment of hierarchies, and may act in concert with kin selection, enforcement or signalling mechanisms to promote cooperation. Yet, the significance of dominance in the evolutionary routes that maintain cooperation remains poorly understood (Chapter 1). Sociable weavers Philetairus socius are highly social, cooperative passerines. The species is particularly prone to conflicts because of their year-round coloniality and thus year round sharing of resources. Using extensive field-data on individual behaviour, I examine in this thesis whether dominance may mitigate conflict and maintain cooperation, and how it may inform our understanding of the evolutionary mechanisms underlying cooperation. In Chapter2, I investigate whether hierarchies and phenotypic traits allowing the assessment of social status may have evolved to mediate conflicts. I show that weavers establish ordered hierarchies within colonies and that the size of a melanin-based plumage trait, the black bib, is correlated to social status. In Chapter 3, experimental manipulation supports my proposition of a status signalling function of the bib. In Chapter 4, I investigate the benefits of achieving high social status and whether these are shared with relatives through nepotism. Both dominants and their offspring gain enhanced access to resources. Dominants had more access to breeding positions, although this was not reflected by increased reproductive success. In Chapter 5, I explore how dominance and kinship predict individual cooperativeness to three tasks, nestling provisioning, nest construction and predator mobbing. I find that both explain variation in cooperativeness, yet some results follow opposite directions, revealing multiple routes to cooperation. Finally, in Chapter 6, I examine how dominance and kinship structure weavers' social network and whether network position are linked to cooperativeness. Social network analyses reveal that more central birds are more, related, dominant and cooperative. Chapter 7 concludes that dominance acts in concert with kinship to promote the societal lifestyle of sociable weavers highlighting the potential significance of dominance in the evolution of cooperation.
Open Access
The effects of colony dynamics and climate on a declining population of sociable weavers, Phlietairus Socius
(2010) Marais, Michael; Covas, R; Altwegg, Res; Ryan, Peter G
Open Access
The effects of prey availability on the endangered bank cormorant Phalacroxorax neglectus
(2014) Botha, Philna; Underhill, Les; Ryan, Peter G; Sherley, Richard; Cook, Timothée
The bank cormorant Phalacrocorax neglectus is a seabird endemic to the south-western coast of southern Africa and the Benguela Upwelling System and has suffered a decline of more than 50% over three generations. Main threats include displacement by Cape fur seals Arctocephalus pusillus, direct human disturbance, pollution, climate change and food shortage. This thesis focuses on the bank cormorant’s response to food shortage, both directly and indirectly. Four colonies (Jutten Island, Dassen Island, Robben Island and Stony Point) were studied in terms of responses on population level in relation to the spatial distribution of prey surrounding the various colonies, foraging behaviour and breeding success. First, I tested the response of the bank cormorant ’ s population dynamics in relation to the availability of West Coast rock lobster Jasus lalandii in different spatial scales around three colonies (Jutten Island, Dassen Island and Stony Point) over a subset of years. I found that birds at Dassen Island showed the strongest response to the availability of rock lobster. Birds also showed strongest response to the availability of rock lobster in an accumulative distance around colonies, and their largest response was to rock lobster within 30 km distance from the colony. Various aspects including the life - history traits and moulting stages of this particular rock lobster species may be the reason to this response. Second, I present foraging effort data of bank cormorants in localities known to be situated in areas with different prey availability. I found that at Jutten Island, situated in an area where West Coast rock lobster have dramatically decreased, bank cormorants spent significantly longer time at sea than at Robben Island and Stony Point, which were situated in areas where rock lobster were known to be abundant at the time of the study. Third, I tested the effect of food availability on the breeding success of bank cormorants at Jutten Island, Robben Island and Stony Point. There was no significant relationship between food availability and the survival probability of the birds. The number of chicks fledged per successful nest, however was significantly related to the availability of rock lobster during the relevant breeding season, as well as during the relevant month of hatching.
Open Access
Effects of temperature on gular fluttering and evaporative water loss in four sympatric cormorants in southern Africa
(2014) Campbell, Greg Thomas; Cook, Timothée; Sherley, Richard; Ryan, Peter G
Climate change continues to cause rising air and sea surface temperatures and changes in precipitation patterns across the globe. Many seabirds will be challenged by increasing temperatures because they must balance conflicting adaptations for dealing with cold environments when foraging and hot environments when nesting. Heat stressed seabirds often gular flutter for thermoregulation, a behaviour that is effective for dissipating heat but expensive in terms of evaporative water loss. This study examined gular fluttering behaviour of four species of southern African cormorants, crowned ( Microcarbo coronatus ), Cape ( Phalacrocorax capensis ), bank ( Phalacrocorax neglectus ), and white-breasted ( Phalacrocorax carbolucidus) cormorants. Results show that gular fluttering is influenced by temperature, body position and body size. Gular fluttering increases with temperature and larger cormorant species spend a greater proportion of time gular fluttering for a given temperature. Threshold temperatures for initiating gular fluttering are lower for large than for small cormorant species. Proportions of time spent gular fluttering are higher when birds are sitting than when crouching over the nest. Water loss shows the same pattern as gular fluttering, with the larger species estimated to lose a higher percentage of their daily water intake. Larger cormorant species can lose as much as 40% of their daily ingested water after eight hours of gular fluttering. These findings indicate that temperature increases from climate change will likely have serious direct impacts on nesting cormorant colonies in southern Africa. Gular fluttering could increase by as much as 25% by 2100 under current projected temperature increases, and increases in water loss could reach nearly 10%. Some species may shift their breeding dates to compensate for increasing temperatures, but if breeding activities are timed to coincide with peaks in their main prey specie s, this may result in poorer diets or increased competition from other species.
Open Access
The endangered bank cormorant Phalacrocorax neglectus: the heat is on : understanding the effect of climate change and associated environmental variable changes on the breeding biology and population dynamics of the bank cormorant in the W. C., S. A
(2014) Meyer,Corlia; Underhill, Les; Ryan, Peter G; Sherley, Richard; Cook, T
The bank cormorant Phalacrocorax neglectus was listed as ‘Endangered’ in 2004, following a decrease of more than 60% in the total population from 1975-2011. It ranges from central Namibia to the Western Cape, South Africa, with most of the population occurring on offshore islands in Namibia. The main reason for this study was to determine if climate change could be identified as a factor which has influenced the decreasing numbers of bank cormorants. This involved research on the heat stress behaviour, breeding success and population trends of the bank cormorant in the Western Cape, South Africa. High environmental temperatures resulting in heat stress and storms with associated extreme environmental variables was predicted to cause breeding failures, decreasing breeding success. As a result, climate change can also affect long-term trends in the adult population of the bank cormorant, and this was examined using the population data of nine bank cormorant colonies in the Western Cape, South Africa. A link existed between ambient and operative temperature, and the latter was used for statistical analysis. Mean operative temperatures of over 30°C were experienced. Temperatures were highest at the bank cormorant colony at Robben Island when three colonies were compared (Robben Island, Jutten Island and Stony Point). Increased environmental temperatures resulted in the average bank cormorant increasing its time spent employing thermoregulatory behaviour. Bank cormorants were shown to start gular fluttering at 21°C on average and spend all their time gular fluttering when they experienced an operative temperature of 34.2°C or higher. The birds also started employing this thermoregulatory behaviour at a lower temperature when on eggs or small chicks. During the study period, the breeding success of the bank cormorant was not impacted by high temperatures at the three bank cormorant colonies studied. Wave and wind action, associated with storms, resulted in a lowered reproductive output during the breeding seasons of 2012 and 2013. Both incubation success and chick rearing success did not differ significantly between 2012 and 2013 for the three bank cormorant colonies at Robben Island, Jutten Island and Stony Point. The study of long-term trends in colony sizes of nine bank cormorant colonies in the Western Cape, South Africa revealed a decrease in the bank cormorants breeding population. The decrease could not be directly associated with climate change in the region. An increase in the mean maximum temperatures and a decrease in the annual rainfall did not affect the bank cormorant numbers, but rather the fecundity. This resulted in a lagged effect of climate change on the bank cormorant population. Climate change and extreme weather events can cause massive breeding failures.
Open Access
Fine-scale movements and habitat use of the Southern Ground Hornbill Bucorvus Leadbeateri
(2015) Zoghby, Blair Anthony; Ryan, Peter G; Little, Rob M; Hockey, Phil A R
Southern Ground-Hornbills Bucorvus leadbeateri are listed as Endangered in South Africa and there is a concerted effort to reverse their population decline. Understanding the factors affecting their movement patterns and how they interact with their habitat is useful to inform conservation and habitat management options for the species, to select sites for artificial nests and to identify suitable areas for reintroduction initiatives. In this study, I report daily and seasonal patterns of habitat use as well as patterns of roost site use of four Southern Ground-Hornbill groups in the Associated Private Nature Reserves, northeast South Africa, based on data from GPS-satellite tags collected over one year from October 2010 to September 2011. Home ranges varied from 5.9-10.3 km² and were larger in winter than during the summer breeding season. Daily travel distances were greater during the breeding season, when birds were constrained to forage close to their nest, and were lower in winter, when birds ranged more widely. Hourly travel distances were affected by time of day, season, air temperature and group. Birds travelled farthest per hour in the morning, decreasing in the afternoon in winter. However, in summer hourly travel distances were bimodally distributed, with a minimum during the middle of the day when ambient temperatures exceed 25⁰C. Acacia-dominated vegetation and riparian habitats were favoured disproportionately during the heat of the day in summer, presumably because they offer more shade than other habitats. The number of roost sites used per month decreased progressively throughout the Early Wet season (October-December) and was lowest during the Late Wet season (January-March) for three groups that bred successfully. Mean monthly nights per roost were highest for these groups in the Early Wet and Late Wet seasons, specifically over December and January, coinciding with the peak breeding period. Throughout the Early Wet season, all four groups frequently roosted in close proximity to the nest, with 54-83% of roosts being within 1 000 m of the nest. During the Wet season, riparian habitats were favoured for roosting by the three groups that bred successfully, while during the dry season, disturbed areas, combretum-dominated habitats and mopane-dominated habitats were used. I conclude that the optimal habitat configurations for ground-hornbills include a mosaic of habitat types, including open areas for foraging and dense trees for shade as well as adequate large trees for nesting and roosting, particularly in riparian habitats.
Open Access
Foraging ecology of the African Penguin Spheniscus demersus in relation to ocean physical processes.
(2012) Van Eeden, Rowen Brandon; Pichegru, Lorien; Ryan, Peter G
This research demonstrated the dual utility of bio-loggers as a method for generating accurate, high-resolution oceanographic data. These data can be used in future studies, generating a cross disciplinary platform for research. The thesis augments our knowledge base of the African Penguins foraging ecology. African Penguins show flexibility in their foraging behaviour by adjusting their dive behaviour to subsurface thermal structures. Penguins also demonstrated foraging optimization by using temperature cues and behavioral switching to maximize the probability of locating prey patches on a fine temporal and spatial scale.