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.

Finch Flock Size and Risk of Hawk Predation at a Migratory Stopover Site

Åke Lindström
The Auk
Vol. 106, No. 2 (Apr., 1989), pp. 225-232
Stable URL: http://www.jstor.org/stable/4087716
Page Count: 8
  • Read Online (Free)
  • Download ($12.00)
  • 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.
Finch Flock Size and Risk of Hawk Predation at a Migratory Stopover Site
Preview not available

Abstract

I studied migratory flocks of finches (Fringilla coelebs and F. montifringilla) feeding during three autumn and two spring seasons at a stopover site in South Sweden. Raptors attacked flocks repeatedly, and the finches showed obvious adaptations to the risk. A total of 304 attacks were recorded, of which 270 were from European Sparrowhawks (Accipiter nisus). Attack frequency was significantly higher in autumn (1.9 attacks/h) than in spring (0.3 attacks/h). In autumn, finch flock size varied from 10 to 10,000. Both attack frequency and hunting success increased with flock size. The risk for an individual finch to be killed (successful attacks per hour and individual) showed no correlation with flock size. Thus predation seemed not to be the primary cause for formation of large finch flocks. Instead, patchy distribution of the preferred food presumably causes large numbers of finches to aggregate. Once aggregated at a field, the best antipredator strategy for the finches is probably to crowd into a dense flock with synchronized feeding. I estimated that ca. 10% of the finches were killed by raptors during the autumn migration.

Page Thumbnails

  • Thumbnail: Page 
225
    225
  • Thumbnail: Page 
226
    226
  • Thumbnail: Page 
227
    227
  • Thumbnail: Page 
228
    228
  • Thumbnail: Page 
229
    229
  • Thumbnail: Page 
230
    230
  • Thumbnail: Page 
231
    231
  • Thumbnail: Page 
232
    232