Rene A. Navarro

The impact of commercial afforestation on bird populations in Mpumalanga Province, South Africa - insights from bird-atlas data.

Bird-atlas data were used & conjunction with information on the extent of commercial afforestation with alien trees in Mpumalanga Province, South Africa, to assess the effect of afforestation on the avifauna of this region. Ninety species of birds characteristic of grassland habitats occur in the province. Twenty-five of these species are of conservation concern and 10 are globally threatened. A separate suite of 65 species associated with woodlands or forests occurs in the province and benefits from afforestation or at least the spread of alien trees. The areas of highest species diversity of grassland birds overlap extensively with the areas of greatest afforestation and potential additional afforestation. The species diversity of grassland birds generally, and globally threatened grassland birds in particular, is significantly and negatively correlated with the extent of afforestation. Afforestation apparently has a negative impact on grassland bird diversity even when the percentage area under plantation is relatively small. A comparison of the avifaunas negatively and positively impacted by afforestation reveals that the grassland community has more species and is richer in both endemics and threatened species than the plantation community. Any further afforestation in Mpumalanga Province is likely to contribute substantially to the potential extinction of many bird species there, including several globally threatened species. Copyright

The Riddle of the Sands: Why are Shorebird Densities so High in Southern Estuaries?

Population data for migratory waders (Aves: Charadrii) during the middle of the nonbreeding season at 31 coastal wetlands in the western Palearctic and Ethiopian regions were analyzed to examine the relationships between bird density and energy intake, intertidal foraging area, and latitude. Wader density is closely linked to population energy intake at individual sites during the nonbreeding season and increases from northern to southern latitudes independently of wetland size. A simple mathematical model linking the variations in the seasonalities of invertebrate production and bird predation is used to provide a mechanistic explanation of the observed variation in bird density with latitude. Results are discussed in the light of current competition- and survival-based models of wader distribution, and, contrary to predictions of some models, we conclude that wader populations track the carrying capacities of coastal wetlands across a wide latitudinal range.

Return to Robben Island of African Penguins that were rehabilitated, relocated or reared in captivity following the Treasure oil spill of 2000

Following an oil spill from the Treasure off the coast of South Africa in June 2000, about 19 000 oiled African Penguins Spheniscus demersus, including 14 825 from Robben Island, were caught for rehabilitation and subsequent release. A further 19 500 penguins that were not oiled — mostly birds in adult plumage, including 7 000 from Robben Island — were relocated some 700km to the east, to prevent them becoming oiled. Additionally, 3 350 orphaned chicks, including 2 643 from Robben Island — were collected for rearing in captivity and release to the wild. Some four years later — by the end of December 2004 — 70% of rehabilitated adults, 40% of relocated birds and 34% of captive-reared chicks had been seen back at Robben Island. Another 7% of birds relocated from Robben Island had been sighted at other localities. Rates of resighting rehabilitated birds were similar at Robben and Dassen Islands, but a greater proportion of relocated birds was seen at Dassen Island, where birds collected for relocation were mostly from breeding areas. The lower proportion of relocated birds seen at Robben Island is thought to result from this intervention causing some pre-breeding birds to move to other colonies. All three conservation interventions are considered to have been successful, but it is premature to assess their relative contributions to the conservation of the species. Three relocated birds tracked by satellite took 15–21 days to return to their home colonies. This rapid return may have resulted from breeding attempts being interrupted. After remaining at their home islands for 4–5 days, two of the tracked birds then left these islands for 19–36 days. We surmise that, after they had searched unsuccessfully for their mates, they abandoned breeding for the year 2000.

Food Addition and Twinning Experiments in the Cape Gannet: Effects on Breeding Success and Chick Growth and Behavior

-Breeding success and growth of single and twinned Cape Gannet (Morus capensis) chicks under natural and supplementary food regimes were studied at Malgas Island, Saldanha Bay, South Africa. Age differences between chicks in artificially twinned broods were set at 0, 5, and 10 days in 1986-87, and 0 and 5 days in 1987-88. The additional food supplied was ca 5% of the body mass (25% of chicks daily food intake). The number of fledglings per nest (singletons and twins pooled) by controls (0.72 ? 0.07 (S.E.), N = 85) and food supplemented birds (0.78 ? 0.07, N = 78) did not differ significantly. A total of 159 (out of 273) chicks died, of which 75% died by starvation. Mortality was high during the first 20 days and decreased significantly with age. No significant differences in mortality rate were observed between control and food supplemented chicks. Masses of twinned chicks did not differ from masses of singletons. The growth parameters of fledging mass, length of fledging period, and age at maximum body mass did not differ significantly between control chicks and those provided with extra food. Brood-type effect was significant only on maximum body mass attained by chicks. Chick begging frequency was higher in 0-5twins than in 0-0twins or singletons, however, the number of parental feeds per chick was similar in all brood types. Success rate (the percentage of begging bouts that resulted in parental feeding) was significantly higher in 0-0twins and singletons than in 0_5twins. Success rate, begging frequency and priority ratio (the probability that one chick obtained food first when both chicks begged simultaneously) were similar between aand b-chicks in twins. The results suggest that chicks regulate their food intake and cannot increase their growth rate in response to the extra food. The mechanism for this is probably a behavioral feed-back link to adult provisioning rate. The study does not support the hypothesis of Cape Gannet numbers being limited by food during the breeding season (Ashmoles hypothesis), suggesting instead high food availability during the study period. Received 26 June 1990, accepted 25 March 1991.

Foraging of a coastal seabird: flight patterns and movements of breeding Cape gannets Morus capensis

Cape gannets Morus capensis are predatory seabirds in the coastal waters of southern Africa where they feed on commercially important fish species. Using a combination of intensive monitoring at nest sites, tracking of radio-tagged birds and diet sampling, we determined the foraging ranges and foraging areas used by breeding gannets, and whether links existed between the broad-scale spatial distribution of foraging birds and the distribution of prey or the predominant wind regime. A total of 270 Cape gannets dispersing to forage from Malgas Island, South Africa, were tagged over three consecutive breeding seasons. Modal durations of foraging flights were six or 24 hours, depending on whether birds returned on the same day they left or remained at sea overnight. Few birds remained continuously at sea over two consecutive nights. Non-radio-tagged birds more frequently undertook shorter foraging trips than radio-tagged birds, indicating a behavioural response to handling. Some 23% of radio-tagged gannets triangulated throughout a complete foraging trip foraged within a maximum of about 60km of Malgas Island, 44% foraged between about 60km and 120km of the island and the remaining 33% flew beyond 120km, travelling a total of at least 240km. Flight directions of gannets departing from the island were non-random in two of the three seasons. Return flight directions were non-random in all three seasons. Most foraging flights were to the south-west of the island, birds generally returning with the prevailing wind and from the same general direction in which they departed. Birds returning with saury Scomberesox saurus did so significantly more frequently from a west-south-west direction. Birds feeding on the other two prey species were equally likely to return from any direction. Under average conditions, the energy benefit associated with returning under load with a tailwind as opposed to a headwind was equivalent to 12% of the average stomach sample mass. The observed distribution of flights probably reflects the large area of suitable foraging habitat to the south and south-west of the island and the energetic advantages of returning with the prevailing wind.

Opportunistic Subsistence Strategies among Late Holocene Coastal Hunter-Gatherers, Elands Bay, South Africa

ABSTRACT Hunting and gathering was practiced for many hundreds of thousands of years in South Africas Western Cape region, until ceramics and a stock-keeping economy first appeared c. 2,000 years ago, and in the Elands Bay and Lamberts Bay areas 200 years later. Subsistence and settlement patterns in this part of the West Coast of South Africa changed dramatically after this date, but the nature of interactions between indigenous groups engaging with these two types of subsistence practices is still poorly understood. The cultural-contact scenarios so far proposed view this interaction as basically competitive, with forager groups living at the margins of herder society and compelled to change their subsistence and settlement choices by focusing on small food parcels and having to move to less accessible areas. Observations from Borrow Pit Midden and other sites in the study area do not support this scenario. Instead, their records suggest flexible adaptive responses among foragers when at coastal and pericoastal locations. Overall, an opportunistic subsistence strategy was practiced mostly within the immediate surrounding environment of camps with high mobility, characterizing forager settlement. The components of a new cultural-contact model are emerging, but much remains to be done before it is established on a reliable empirical foundation.

SEASONAL MIGRATION OF TERRESTRIAL BIRDS ALONG THE SOUTHERN AND EASTERN COASTS OF SOUTHERN AFRICA

Summary Berruti, A., Harrison, J.A. & Navarro, R.A. 1994. Seasonal migration of terrestrial birds along the southern and eastern coasts of southern Africa. Ostrich 65: 54–65. Several species of ter...

Energy Expenditure of Free-Ranging Chicks of the Cape Gannet Morus capensis.

The Cape gannet Morus capensis, a large fish-eating seabird, is endemic to southern Africa. To study the energetics of nestling growth, we used the doubly labeled water technique to measure field metabolic rate (FMR) of nestlings, from hatchings to large partly feathered chicks (n = 17) at Malgas Island, Saldanha Bay, South Africa. At the same time, the growth rate of a large sample of chicks was measured (n = 338). These data, together with literature values on resting metabolic rate and body composition, were used to construct and partition the nestling energy budget. Nestling FMR (kJ d−1) increased with body mass according to FMR = 1.23m0.923, r2 = 0.944. Mass-specific FMR (FMRratio; kJ d−1 g−3/4) was independent of chick age (r2 = 0.20, P > 0.05); mean mass-specific FMR was 4.11 ± 1.28, n = 17. Peak daily-metabolized energy (DME), which represents the maximum rate at which parents must supply their nestlings, occurred at age 71 d and was 2,141 kJ d−1. Between the ages 51 and 92 d (43% of the fledging period), the DME of Cape gannet chicks was equal to or surpassed 90% of adult FMR at the nest. Energy demand during this period of peak DME represented 58% of the total metabolized energy, which was estimated at 150.1 MJ for an average chick during a 97-d period, from hatching to fledging. Sensitivity analysis of the energy budget indicated that the model was robust; the biggest source of error (±15%) was for the mass-FMR equation used in the model.

Extreme water efficiency of Cape gannet Morus capensis chicks as an adaptation to water scarcity and heat stress in the breeding colony

Abstract Cape gannet Morus capensis chicks depend entirely on fish prey and metabolic water for water requirements during development. Water loss through evaporative cooling due to heat stress is substantial. We measured water flux and field metabolic rates (FMR) of Cape gannet chicks and adults to determine if gannets developed water saving strategies. The water economy index (WEI, g kJ−1) decreased with chick age according to the model WEI = 0.676 – 0.272 × log10(t), indicating that water efficiency increased with age. At fledging, the WEI of chicks was at the level expected of adult desert birds. Desert birds maintain a low WEI by also having a low FMR, whereas Cape gannet chicks have FMR comparable to other seabird species’ nestling requirements. We propose that maintaining low WEI is adaptive for Cape gannets because (1) chicks need to balance water loss through evaporative cooling, (2) fledglings need to overcome a period of up to a week when they cannot ingest any water and (3) adults spend extended periods in the breeding colony during which water can become a limiting factor. Understanding the physiological mechanism of maintaining low WEI will become increasingly important with future rising temperatures.

Helm Field Guides — Birds of Chile including the Antarctic Peninsula, the Falkland Islands and South Georgia by Albaro Jaramillo with illustrations by Peter Burke and David Beadle

Christopher Helm, A&C Black, 37 Soho Square, London, W1D 3QZ, UK, e-mail: vharrison@acblack.com 20 pages, 96 colour plates, softcover ISBN 0 7136 4688 8, price £19.99 Ostrich 2004, 75(1&2): 77