https://vital.seals.ac.za/vital/access/manager/Index en-us 5 https://vital.seals.ac.za/vital/access/manager/Repository/vital:5660 Wed 12 May 2021 23:31:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5789 Wed 12 May 2021 19:18:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5788 90% in the last 130 years), the cause(s)of which are unknown. There is a paucity of data on this species in the South Atlantic Ocean, therefore their trophic ecology at Tristan da Cunha was studied, specifically focusing on diet, using stomach content analysis and stable isotope analysis (SIA), in conjunction with an analysis of diving behaviour, assessed using temperature-depth recorders. In order to evaluate the influence of gender on foraging, a morphometric investigation of sexual dimorphism was confirmed using molecular analysis. Additionally, plasma corticosterone levels were measured to examine breeding stage and presence of blood parasites as potential sources of stress during the breeding season. Northern Rockhopper penguins at Tristan da Cunha displayed a high degree of foraging plasticity, and fed opportunistically on a wide variety of prey, probably reflecting local small-scale changes in prey distribution. Zooplankton dominated (by mass) the diet of guard stage females, whereas small meso-pelagic fish (predominantly Photichthyidae)dominated diet of adults of both sexes in the crèche stage, with cephalopods contributing equally in both stages. Adults consistently fed chicks on lower-trophic level prey (assessed using SIA), probably zooplankton, than they consumed themselves indicating that the increasing demands of growing chicks were not met by adults through provisioning of higher- quality prey. SIA also indicated that adults foraged in different oceanic water masses when feeding for self-maintenance and for chick provisioning, thus temporally segregating the prey consumed for different purposes. It is possible that adults ‘selected’ these higher quality prey for themselves, or this may be a reflection of opportunistic behaviour. At Tristan da Cunha sexual dimorphism was observed in culmen dimensions (length, depth, width), with males having larger beaks and feeding on larger individuals of squid and fish than females. No sexual segregation in terms of foraging habitat (i.e. different water masses, based on ð¹³N or trophic level ð¹⁵N) during the breeding season or pre-moult period was revealed through SIA, and stomach content analysis revealed no sexual differences in prey species targeted. The results of SIA of feathers indicate that during the pre-moult period birds foraged in different water masses than during the breeding period. The fact that throughout the breeding season birds foraged in similar habitats suggests no intra-specific competition, despite both sexes feeding on the same prey.Birds were generally diurnal, daily foragers (12 – 16 hr trips), with extended trips (maximum duration 35.5 hours) and nocturnal diving recorded in a few individuals. Birds dived well within their physiological limits, predominantly utilising the upper 20m of the water column, employing two different strategies to target different prey items. Long, deep (30 – 40 m), energetically costly dives were performed when targeting energy-rich prey (fish), and a greater number of shorter, shallower (5 – 20 m), energy-efficient dives were performed when targeting prey with a lower energy content (zooplankton). More than half of the sampled study population were infected with the intra-cellular blood parasite Babesia, but infection showed no relationship to body mass, corticosterone levels or breeding success. Fasting birds showed no signs of elevated corticosterone levels, suggesting they had acquired sufficient fat reserves prior to breeding. Failed breeders did not exhibit elevated corticosterone levels. Tristan skuas, Catharacta antarctica hamiltoni, were observed to be a significant cause of egg and chick mortality. The absence of sex-based differences in foraging, and the absence of any signs of stress in relation to body mass, presence of Babesia or breeding stage, suggest that there are no obvious signs of high levels of stress or food limitations during breeding at Tristan da Cunha.]]> Wed 12 May 2021 17:44:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5726 Wed 12 May 2021 17:21:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5893 Wed 12 May 2021 17:07:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5644 Wed 12 May 2021 16:23:44 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5766 1700m) sites within the Sneeuberg Mountain Complex (SMC) from June 2009 to May 2010. I also tested the effectiveness of five different bait types for measuring small mammal diversity (i.e. number of individuals caught, species richness, Shannon diversity index and Simpson index of diversity). Out of a total of 423 captures, 292 individuals of 12 small mammal species (one shrew, one elephant shrew and 10 rodents) were recorded over 5280 trap nights. The species richness and diversity of small mammals captured at the three sites were similar and this homogeneity was probably related to the regional processes (e.g. climate and latitude) that govern species richness and diversity. The most effective bait type in terms of capture success, species richness and diversity measurements was peanut butter and oats. In addition, the use of richness estimators revealed that peanut butter and oats was the most effective bait for sampling the species richness of small mammals. The effectiveness of peanut butter and oats was related to this bait having a more attractive scent, when compared to the other bait types. Future studies should focus on researching the range of local and regional processes that drive small mammal diversity at high altitudes in South Africa. I also recommend the use of more than one bait type when planning to survey small mammal communities.]]> Wed 12 May 2021 16:13:06 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5693 Thu 13 May 2021 07:16:52 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5767 Thu 13 May 2021 07:13:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5916 2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.]]> Thu 13 May 2021 04:32:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5636 Thu 13 May 2021 03:50:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5724 Thu 13 May 2021 03:05:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5661 Thu 13 May 2021 02:02:37 SAST ]]>