Polygyny and extrapair fertilizations in eastern red-winged blackbirds (Agelaius phoeniceus)

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Parentage of nestling red-winged blackbirds (Agelaius phoeniceus) from an eastern population was determinedusing DNA fingerprinting techniques. Of 235 nestlings surveyed, 58 had fingerprints excludingthe male, but none excluded the female tending the nest. Data on pairing status during the female's fertilizable period was available for 232 offspring; 55 (25%of 1988 nestlings, 23% of 1989 nestlings) of those were sired through extrapair copulations. Of these 55 offspring, 33 could be assigned to nearby territory holders; 16 of the remaining nestlings may have been sired by nearby males that were not captured. During both years, 44% of territorial males had more than one female nesting simultaneously on their territory. The number of extrapair fertilizations gained by males increased significandy with harem size in 1 year. Paternity (die proportion of nesdings on the territory sired by die territory holder) showed a positive but nonsignificant increase widi harem size in bodi years. There was no apparent cost in paternity for males guarding two or more fertilizable females at the same time. The broods of females that were fertilizable at die same time anodier female was setding on die same territory tended to have a greater proportion of extrapair fertilizations (0.37) than did die broods of odier females within harems (0.15). Established fertilizable females were chased significantly more by die territory owner and by extrapair males when a new female was setding. There were no associations between a male's paternity or success at gaining extrapair fertilizations and his age or color-band combination. Overall, extrapair fertilizations had litde effect on die relationship between fledgling success and harem size and appeared to have a minimal impact on die overall intensity of sexual selection on males.

Original languageEnglish
Pages (from-to)49-60
Number of pages12
JournalBehavioral Ecology
Issue number1
StatePublished - Mar 1993

Bibliographical note

Funding Information:
I am deeply indebted to C. F. Aquadro, B. Noon, H. K. Reeve, J. Coleson, C. Yoon, and T. Boyce for their advice and support in developing the fingerprinting techniques. I thank AlecJeffreys and the Lister Institute, Roy Carter, lisle Gibbs, and Mike Young for generously supplying the fingerprinting probes. B. Johnson and N. Hairston were a tremendous help with the logistics of using Cornell's ponds facility. L. Breen and G. Crutcher completed much of the lab work, and C. Corson and C. Butler worked very hard in the field. I also thank A. B. Clark for her collaboration on the Ithaca blackbirds. Capture and banding activities were authorized under federal banding permit no. 2213, federal collecting permit no. PRT-725174, and New York State permit no. SCL 88-010. Finally, I appreciate the helpful comments of Paul Sherman, Jeff Dickhaut, Greta Crutcher, Bob Montgomerie, Patrick Weatherhead, and an anonymous reviewer on previous drafts of the manuscript. This study was funded by National Science Foundation grants BSR 8700159 and BSR 890-06562, indirect assistance from a National Institutes of Health grant to C. F. Aquadro, and support from Cornell University and the University of Kentucky.


  • DNA fingerprinting
  • Extrapair copulations
  • Mating systems
  • Paternity
  • Reproductive strategy
  • Reproductive success
  • Sexual selection

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


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