Female aggressive response and hormonal correlates—an intrusion experiment in a free-living passerine |
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Authors: | Henrik Pärn Karin M Lindström Maria Sandell Trond Amundsen |
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Institution: | 1. Department of Biology, Norwegian University of Science and Technology, 7491, Trondheim, Norway 2. Department of Ecology and Evolutionary Biology, Princeton University, 106 Guyot Hall, Princeton, NJ, 08544, USA 4. Population Biology and Conservation Biology Department of Ecology and Evolution, Norbyv?gen 18D, 752 36, Uppsala, Sweden 3. Department of Animal Ecology, Lund University, Ecology Building, 223 62, Lund, Sweden
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Abstract: | The optimal mating system is rarely the same for males and females—whereas males usually benefit from attracting additional
females to the territory, this could incur costs for the resident female. Females should therefore prevent prospecting females
from settling on the territory. We studied the male and female behavioral and hormonal responses to simulated female territorial
intrusions in free-living bluethroats during the pre-laying period. In the study population, polygyny occurs with potential
fitness costs for the resident female. We recorded different aspects of aggressive behavior before and after presentation
of a live female decoy and playback of female song. These behaviors were compared with a set of intrusions using a male decoy.
At the end of a trial, the birds were captured, and blood samples were analyzed for androstenedione, testosterone, estradiol
and corticosterone. During the pre-intrusion period, none of the females were observed. Females generally responded strongly
to the female decoy by increased flight rate, vocalizations, and by conspicuous perching. Nearly half of the males displayed
to the female decoy but never while the resident female was present. We suggest that resident female aggression in bluethroats
prevents courtship by her mate and signals her mating status to the female intruder. Female aggression could therefore prevent
additional females to settle on the territory and shape the mating system. Females that responded with song had higher levels
of estradiol. These findings suggest that estradiol may support aggression in breeding female birds. |
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Keywords: | Female aggression Female ornamentation Territorial intrusion Monogamy Sexual conflict Estradiol Testosterone |
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