Articles by Author: Ra Dyer

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  1. Assessment of recent drought severity for natural grassland at three locations

    Assessment of recent drought severity for natural grassland at three locations

    Item type: Journal Article • Journal: South African Journal of Plant and Soil
    The relative severity of drought in natural grassland during three growing seasons was analyzed for three South African weather stations. Computer simulation of grassland water use, based upon weather records, was used to quantify drought and to compare the conditions...
  2. Age at first breeding and change in plumage of kelp gulls <em>Larus dominicanus</em> in South Africa

    Age at first breeding and change in plumage of kelp gulls <em>Larus dominicanus</em> in South Africa

    Item type: Journal Article • Journal: South African Journal of Marine Science
    In South Africa, kelp gulls Larus dominicanus first breed when 4 years old. At least 50% of 4-year-olds breed; virtually all older birds breed annually. Most chicks leave natal colonies in the austral autumn and winter, when about 6 months...
  3. Top predators in the Benguela ecosystem — implications of their trophic position

    Top predators in the Benguela ecosystem — implications of their trophic position

    Item type: Journal Article • Journal: South African Journal of Marine Science
    Many top predators in the Benguela ecosystem feed on prey species targeted by commercial fisheries. Their roles as indicators of the state of exploited prey resources, as competitors with commercial fisheries for resources, and as susceptible to impact from commercial...
  4. Conservation of an increasing population of great white pelicans <em>Pelecanus onocrotalus</em> in South Africa's Western Cape

    Conservation of an increasing population of great white pelicans <em>Pelecanus onocrotalus</em> in South Africa's Western Cape

    Item type: Journal Article • Journal: South African Journal of Marine Science
    Unlike many pelican populations, that of the great white pelican Pelecanus onocrotalus in the Western Cape, South Africa, has increased in size, from 20–30 pairs in the first half of the century to over 500 in 1993. The population increase...
  5. Absence of breeding by African penguins at four former colonies

    Absence of breeding by African penguins at four former colonies

    Item type: Journal Article • Journal: South African Journal of Marine Science
    African penguins Spheniscus demersus no longer nest at four suspected previous breeding localities: Neglectus Islet (Hottentot Bay), North Reef and Albatross Island off Namibia and Jacob's Reef off South Africa. This brings to 10 the number of localities where breeding...
  6. Trends of African penguin <em>Spheniscus demersus</em> populations in the 20th century

    Trends of African penguin <em>Spheniscus demersus</em> populations in the 20th century

    Item type: Journal Article • Journal: South African Journal of Marine Science
    The entire nesting population of African penguins Spheniscus demersus was about 575 000 adults at the start of the 20th century. Numbers halved by the 1950s and continued to fall to about 220 000 by the late 1970s and about...
  7. Predation by snakes on seabirds at three South African islands

    Predation by snakes on seabirds at three South African islands

    Item type: Journal Article • Journal: South African Journal of Marine Science
    During 1989–1994, adult mole snakes Pseudaspis cana at Robben Island were recorded eating eggs of African penguin Spheniscus demersus and Hartlaub's gull Larus hartlaubii, as well as those of helmeted guinea-fowl Numida meleagris. Juvenile mole snakes ate clicking stream frogs...
  8. Age at breeding of crowned cormorants <em>Phalacrocorax coronatus</em>

    Age at breeding of crowned cormorants <em>Phalacrocorax coronatus</em>

    Item type: Journal Article • Journal: South African Journal of Marine Science
    Between 1991 and 1995,242 crowned cormorant Phalacrocorax coronatus chicks were banded at Malgas Island with metal and colour rings. At least 10 subsequently bred before 4 April 1996. First-year birds had juvenile plumage, but when about one year old they...
  9. SHORT NOTES

    SHORT NOTES

    Item type: Journal Article • Journal: Ostrich: Journal of African Ornithology