Egg morphology of Swift Terns in South Africa

Morphology of Swift Tern Thalasseus bergii bergii eggs was examined on Robben Island, South Africa. A recently formed colony was found abandoned en masse, probably following human disturbance, and 146 freshly laid eggs were collected. The mean±SD nest density was 7±2.5 nests m?2 and 3% of nests contained two eggs. Eggs ranged in shape from oval to pyriform and displayed black markings (blotched, streaked, scrawled or speckled) overlaying the eggs’ colour. The mean length and width of a sample of 105 eggs was 62.2?mm (56.3–66.9?mm) and 42.3?mm (39.8–45.3?mm), respectively. All collected eggs were weighed and the mean mass was 57.9±3.72?g. Estimated volume of eggs was calculated to be 56.3±3.74 cm3. This is the first report of mass measurements obtained from freshly laid eggs Swift Tern eggs and provides insight on egg morphology, for which knowledge is limited for this species.     

Diving patterns of female macaroni penguins breeding on Marion Island, South Africa

Despite the large biomass of macaroni penguins Eudyptes chrysolophus in the Southern Ocean, their feeding ecology is poorly known at some important breeding localities. We investigated the diving behaviour and diet of female macaroni penguins feeding small chicks on Marion Island (46o52′S, 37o5′E), South Africa, one of the species’ most northerly breeding sites, supporting 4% of their global population. We then compared our results with similar studies from other localities. In December 2008, we collected information on 12 foraging trips from 6 individuals using time-depth recorders, as well as diet from 42 individuals. Median trip duration was 22.8 h (5.6–80.8 h). Penguins performed 42.8 ± 15.9 dives per hour at sea, with dive depths averaging 24.6 ± 8.6 m and lasting 40.8 ± 12.1 s, although 74.3% of dives were <10 m. Euphasids dominated their diet (86% by mass), mainly Thysanoessa vicina. A second peak in dive depths at 55–80 m might reflect the 12% of fish in their diet. The substantial proportion of shallow night dives (30% of total dives) suggests some foraging occurs at night. Differences in diving patterns of individual macaroni penguins in this study confirmed the behavioural flexibility of these birds reported from other breeding localities. However, most other studies assumed that dives <3–5 m were commuting dives whereas our study suggests that at least some prey are caught during shallow dives. We highlight how different analytical methods can change the outcome of studies. Despite macaroni penguins’ apparent flexibility in foraging behaviour during the breeding season, their numbers are decreasing globally. Further investigations of their foraging behaviour are needed to assess potential competition with other predators and krill fisheries.     

Cats and seabirds: effects of feral Domestic Cat Felis silvestris catus eradication on the population of Sooty Terns Onychoprion fuscata on Ascension Island, South Atlantic

The population of Sooty Terns Onychoprion fuscata breeding on Ascension Island in the Atlantic Ocean was monitored over 17 years (1990–2007). This period spanned the programme of feral Domestic Cat Felis silvestris catus eradication from the island, which commenced in 2001 with the last Cat recorded in 2004. We report on the abundance of Sooty Terns and Black Rats Rattus rattus before and after Cat eradication. The Sooty Tern breeding population in the 1990s averaged 368 000 and Cats were killing Terns at an average rate of 33 adults per night. Following Cat eradication, adult Terns are no longer predated. However, egg predation by both Rats and Common Mynas Acridotheres tristis has continued with Mynas destroying more eggs than Rats. Unexpectedly, we observed a change in Rat predatory behaviour. Following Cat eradication, Rats have become a major predator of Sooty Tern chicks. Despite this change, the Tern population has shown a season-on-season increase since Cat eradication, 48.8% in 2005, 8.2% in 2006 and 6.1% in 2007, and the breeding population increased to 420 000 birds in 2007. Incubation success improved from 66.0 to 84.4% during Cat eradication, before dropping down again to 67.9% after Cats were eradicated and Rat control measures were introduced. Index traplines were set for Rats and Rat numbers fluctuated widely immediately after Cats were eradicated but there were no significant differences that could be attributed to changes in Cat numbers. Ascension Island Sooty Terns breed every 9.6 months and juveniles defer breeding for seven seasons. Hence 2008 is the first year in which an increase in the breeding Sooty Tern population directly attributable to Cat eradication is likely to be detected. We conclude that long-term monitoring is essential to guide conservation practice even in this relatively simple predator–prey system.     

The forest communities of Table Mountain,South Africa

Summary The forest communities of Table Mountain have been classified using the Braun-Blanquet technique together with numerical analysis. Three major communities, termed associations, have been recognised. Some of these associations have been subdivided. Each community has been described in terms of floristic, structural and environmental factors. The dominant factors affecting the distribution of forest communities appear to be moisture conditions, soil rockiness and soil depth. Information from other South-Western Cape forest areas is discussed. The forests from Table Mountain are similar to these.However, two forest communities are not found on the Cape Peninsula and extensive areas of Cassine dominated forest on deep soils referred to as the Scolopia mundii — Cassine capensis varlant do not appear to be foun outside Orange Kloof.Nomenclature follows that used in the Bolus Herbarium, University of Cape Town.The authors wish to thank the Course III Botany classes of 1974 and 1975 for assisting in collecting some of the field data, and the South African Council for Scientific and Industrial Research and Smuts Scholarship Board for some financial assistance (B. M. Campbell).     

The Griqua of Campbell, Cape Provice, South Africa.

The Griqua of Campbell in the Cape Province of South Africa are reputed to be descended from an amalgam of Khoi ("Hottentots") with various Caucasoid, Negroid and East Asian elements at the Cape of Good Hope. A stormy history of migration and deprivation has left this small residuum on the edge of the Kalahari Desert. It was hoped that a sero-genetic study of these people, who proudly preserve their identity, might provide further insights into the genetic consitution of their Khoi forebears. Despite the retention of the language of their own, an social mores distinct from of other Mixed populations, they have been shown, however, to have received an appreciable inflow of non-Khoisan genes. This has probably resulted from social factors such as the prestige attaching to Griqua membership and the willingness of the Griqua to assimilate outsiders, combined with the tendency of Campbell Griqua to migrate elsewhere. There are no significant differences between "Griqua" members of the population and those who are not recognized as "Griqua."     

The occurrence and ecology of a marine hydrobiid mudsnail in the southern hemisphere: the Knysna Estuary, South Africa

Earlier published records of the gastropod Hydrobia from the warm temperate Knysna Lagoon on the Indian Ocean coast of South Africa are in error. Nevertheless, an animal hitherto identified as an Assiminea (Assimineidae) or as a Tomichia (Pomatiopsidae) is in fact a Hydrobia s.l., and it does occur intertidally within the Knysna system. The same species also occurs in salt pans in the cool temperate Great Berg Estuary on the Atlantic coast of South Africa. This extends the distribution of confirmed species of the dominant coastal hydrobiid mudsnails of the northern hemisphere into the southern hemisphere. H. knysnaensis (Krauss) occurs patchily at low density near the head of the Knysna Estuary in waters of low salinity. This appears to be a suboptimal habitat, and it is suggested that Hydrobia is restricted to this zone as a result of interference competition from potamidid mudwhelks and ocypodid crabs. The prevalence of potamidids and ocypodids in the tropics and in the temperate southern hemisphere may account for the rareness or absence of hydrobiids in these areas. Unlike its equally intertidal relative, the widespread North Atlantic/Arctic H. ulvae, H. knysnaensis develops directly like other Hydrobia.     

Fractionation,mobility and multivariate statistical evaluation of metals in marine sediments of Cape Town Harbour,South Africa

Abstract

Distribution of possible chemical forms of Al, Si, Sn, Pb, Zn, Fe, Hg, Cd and Cu in marine sediments of Cape Town harbour was investigated using a modified Tessier’s sequential extraction procedure and ICP-MS and ICP-AES for heavy metals determination. The mean fractions for all metals at all locations were: 1.5–7196 mg kg^-1 for Si, 7.79–7266 mg kg^-1 for Al, 161-639 mg kg^-1 for Cu, 19–41978 mg kg^-1 for Fe, 2.83–5864 mg kg^-1 for Zn, 1.45–13.26 mg kg^-1for Cd, 9.87–223 mg kg^-1 for Sn, 11.98-979 mg kg^-1 for Pb and 0.13–5.93 mg kg^-1 for Hg. Si, Al and Zn were mostly associated with Fe–Mn oxides, whereas Sn and Hg were mainly bound to residual and organic matter. Pb existed mainly in the residual and iron/manganese oxide phases while Cd was evenly distributed in all the five phases. The loading plots of heavy metals bound to the various chemical forms, as well as Pearson correlation coefficients, enabled the determination binding relationship. Pb, Sn and Hg exhibited similar binding behaviour which indicated an anthropogenic point source from wastes from the ship maintenance workshop, and the presence of Sn in the organic phase can be identified with the use of anti-fouling paints at the harbour, whereas Al, Fe, Si, Cu and Zn would probably be of natural origin. Lastly Cd probably came from a diffuse pollution sources in the harbour due to its unique binding characteristic. The mobility of heavy metals varied depending on location and the heavy metal type. The mobility of metals followed the order: Si > Zn > Fe > Cu> Al> Cd> Pb > Sn > Hg. The high percentage of Cd and Pb in the bioavailable forms suggested the need to keep close surveillance on these metals because of their high toxicity.     

The nutrient status of the Kromme River estuary,South Africa

The Kromme is a small estuary in rural eastern Cape, South Africa with a relatively unpopulated and undisturbed catchment. Physical and chemical variables including the major nutrients and E. coli were examined. It was found to be a well oxygenated, well mixed estuary with some stratification in its upper reaches. Nutrient levels were generally low with nitrate values higher in winter than during summer. While no overt seasonality was detected for phosphorus, levels were comparatively high. Faecal E. coli levels were low with a mean count of 26 per 100 ml for the estuary. Along the Kromme, nutrients were highest at the confluence of the Geelhoutboom tributary suggesting it was a major nutrient contributor. At the head of the Kromme, silicate and E. coli were significantly linked to riverflow, while nitrate was correlated with rainfall. In the Geelhoutboom, only nitrate was correlated with riverflow and rainfall. When nutrient gradients (total inorganic nitrogen, total phosphorus and silicate) were correlated against salinity, significant relationships were observed for nitrogen and silicate (Kromme and Geelhoutboom) and for phosphorus along the Geelhoutboom, but not the Kromme, reflecting differences in sub-catchments. An overall N:P atomic ratio of 0.89:1 was found for the system, with more nitrogen relative to phosphorus at the head of the Kromme and vice versa for the Geelhoutboom and mouth. The Kromme is low in nitrogen, conservative in silicate and low in phosphorus while the Geelhoutboom supplies nitrogen, phosphorus and silicate to the system. Although there may be nutrient absorption by sediments in the upper estuary, and by macrophytes in the lower estuary, the Kromme may be classified as a non-conservative mesotrophic marine-dominated estuary which probably exhibits some nutrient recycling.     

The effects of herbivory by a mega- and mesoherbivore on tree recruitment in sand forest, South Africa

Herbivory by megaherbivores on woody vegetation in general is well documented; however studies focusing on the individual browsing effects of both mega- and mesoherbivore species on recruitment are scarce. We determined these effects for elephant Loxodonta africana and nyala Tragelaphus angasii in the critically endangered Sand Forest, which is restricted to east southern Africa, and is conserved mainly in small reserves with high herbivore densities. Replicated experimental treatments (400 m(2)) in a single forest patch were used to exclude elephant, or both elephant and nyala. In each treatment, all woody individuals were identified to species and number of stems, diameter and height were recorded. Results of changes after two years are presented. Individual tree and stem densities had increased in absence of nyala and elephant. Seedling recruitment (based on height and diameter) was inhibited by nyala, and by elephant and nyala in combination, thereby preventing recruitment into the sapling stage. Neither nyala or elephant significantly reduced sapling densities. Excluding both elephant and nyala in combination enhanced recruitment of woody species, as seedling densities increased, indicating that forest regeneration is impacted by both mega- and mesoherbivores. The Sand Forest tree community approached an inverse J-shaped curve, with the highest abundance in the smaller size classes. However, the larger characteristic tree species in particular, such as Newtonia hildebrandtii, were missing cohorts in the middle size classes. When setting management goals to conserve habitats of key importance, conservation management plans need to consider the total herbivore assemblage present and the resulting browsing effects on vegetation. Especially in Africa, where the broadest suite of megaherbivores still persists, and which is currently dealing with the 'elephant problem', the individual effects of different herbivore species on recruitment and dynamics of forests and woodlands are important issues which need conclusive answers.     

Surface-feeding on cephalopods by procellariiform seabirds in the southern Benguela region, South Africa

Cephalopod beaks recovered from stomach samples taken from 14 seabird species in the southern Benguela region off Southern Africa and from one species at Sub-Antarctic Marion Island, were identified as far as possible, counted and the lower rostral lengths (LRLs) measured. Dorsal mantle lengths (DMLs) and body masses of the cephalopods eaten were estimated. The results of analyses by percentage frequency of occurrence and numerical abundance are discussed with reference to present knowledge of the distribution of cephalopods eaten by seabirds in the areas studied. Division of the cephalopod component of seabird diets into species which float, and species which sink, after death indicates that the birds forage on dead or moribund cephalopods on the surface, rather than catching live bioluminescent cephalopods at night.     

The effects of agriculture on farmland bird assemblages on the Agulhas Plain, Western Cape, South Africa

Coastal Fynbos on the Agulhas Plain of the Western Cape, South Africa, has been transformed extensively by crop and pastoral agriculture. Many bird species, e.g. sunbirds, nightjars and mousebirds have consequently been affected negatively by the reduction of suitable habitat for daily requirements. However, populations of certain bird species, especially granivores and omnivores, such as sparrows, larks and pipits, as well as Egyptian Geese and Helmeted Guineafowl have proliferated on the Agulhas Plain. This study investigates the effects of agricultural development on overall bird diversity on the Agulhas Plain. In 1998, twice monthly transect counts at 13 farmland sites recorded 106 bird species. Fifteen species occurred at 75% or more of the sites. Highest avian diversity was recorded at the sites with a mixture of crops and Coastal Fynbos (Mixed regime). A small number of species, e.g. sunbirds, are reliant on the natural Coastal Fynbos for their survival. With the exception of the Mixed regime that gained 50 species, all the other agricultural regimes reflected a loss of diversity when compared with Fynbos. To provide more suitable habitat for a greater diversity of birds, mixed landscapes should be maintained, and further destruction of natural Fynbos habitat should be prevented.     

The effects of fire on grassland bird communities of Barberspan,North West Province,South Africa

Considering the frequent nature of fires and resultant drastic change in habitat following fire, research on the effects of fire on birds in the grasslands of South Africa is surprisingly scarce. For at least five months after burns we followed the changes in bird species composition, species richness and densities of two controlled burns and one accidental fire at the Barberspan Nature Reserve in grasslands that had not been burned or grazed in 10 years. Compared with the control areas, species richness and densities increased in the burned areas immediately following the burns, with more species and birds recruited to the burned areas than were lost. Immediate post-burn opportunists tended to be larger species, and the biomass increase mirrored the increases in species richness and densities in burned areas. Avian species richness, densities and biomass tended to return to the initial conditions after a number of months. Although the bird communities from two controlled-burns differed before the burns, they converged to a characteristic immediate post-burn composition. Five months after the burns however, the bird communities reflected a pre-burn composition. Indications were that birds in an area larger than that burned were affected. Mosaic burning, with shifting large and small patches, should be considered on a landscape scale.