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.

Factors Affecting Prey Preparation by Adult Magpies Feeding Nestlings

Adrián Ponz, José A. Gil-Delgado and Emilio Barba
The Condor
Vol. 101, No. 4 (Nov., 1999), pp. 818-823
DOI: 10.2307/1370069
Stable URL: http://www.jstor.org/stable/1370069
Page Count: 6
  • 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.
Factors Affecting Prey Preparation by Adult Magpies Feeding Nestlings
Preview not available

Abstract

We collected 1,138 prey items from the guts of nestling Magpies (Pica pica) using neck collars. We noted the alterations (appendages missing, breakage) shown by the prey, and gave an index of preparation to the most abundant prey types (adult beetles and grasshopper nymphs). We then related these indices to prey size, age of the nestlings, brood size, and sampling date. Fifty-seven percent of the beetles were prepared, most of them being broken. The probability of breaking a beetle increased as the difference between clutch size and brood size increased, and as the residuals of prey size on sampling date increased. The probability of having at least one elytra removed increased as the beetle size increased and as the difference between clutch size and brood size increased. The degree of preparation of beetles decreased as their size decreased, as the nestlings grew older, and as the difference between clutch size and brood size decreased. Seventy-one percent of the grasshopper nymphs were prepared, the degree of preparation decreasing as their size decreased and as the season progressed. We conclude that the degree of prey preparation by Magpies feeding nestlings is the result of a trade-off between the benefits obtained by the nestlings and the costs to the parents.

Page Thumbnails

  • Thumbnail: Page 
818
    818
  • Thumbnail: Page 
819
    819
  • Thumbnail: Page 
820
    820
  • Thumbnail: Page 
821
    821
  • Thumbnail: Page 
822
    822
  • Thumbnail: Page 
823
    823