Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Influence of Food on Numbers Breeding, Colony Size and Fidelity to Localities of Swift Terns in South Africa's Western Cape, 1987-2000

Robert J. M. Crawford
Waterbirds: The International Journal of Waterbird Biology
Vol. 26, No. 1 (Mar., 2003), pp. 44-53
Published by: Waterbird Society
Stable URL: http://www.jstor.org/stable/1522465
Page Count: 10
  • Read Online (Free)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Influence of Food on Numbers Breeding, Colony Size and Fidelity to Localities of Swift Terns in South Africa's Western Cape, 1987-2000
Preview not available

Abstract

During 1987-2000, the numbers of Swift Terns (Sterna bergii) breeding in South Africa's Western Cape varied between 1,449 and 5,668 pairs, distributed at 13 localities. Numbers were significantly related to the combined biomass of Anchovy (Engraulis capensis) and Sardine (Sardinops sagax), two of the main food items. In years when food was scarce, numbers breeding decreased by up to 67%. The sizes of breeding aggregations of Swift Terns were significantly related to the combined biomass of Anchovy and Sardine. Numbers of Swift Terns breeding at a locality ranged from 1-4,192 pairs, with an average of 750. Numbers breeding in discrete colonies ranged from 1-3,000 pairs, with an average of 513. Swift Terns showed low fidelity to breeding areas, 61% of which were used just once. This is attributed to their requirement to breed near to fish prey, and its variable distribution from year to year. Breeding by other seabirds probably often indicated safe sites for nesting. Swift Terns bred by themselves in 17%, with Hartlaub's Gulls (Larus hartlaubii) in 77%, and with Crowned Cormorants (Phalacrocorax coronatus) in 18% of breeding attempts.

Page Thumbnails

  • Thumbnail: Page 
44
    44
  • Thumbnail: Page 
45
    45
  • Thumbnail: Page 
46
    46
  • Thumbnail: Page 
47
    47
  • Thumbnail: Page 
48
    48
  • Thumbnail: Page 
49
    49
  • Thumbnail: Page 
50
    50
  • Thumbnail: Page 
51
    51
  • Thumbnail: Page 
52
    52
  • Thumbnail: Page 
53
    53