Szukana fraza: [Abstract = "We predicted that \"Solo\" males would lose beak color faster than would \"Group\" males. We used digital images to monitor beak color once a week starting on 26 May. Beak blackness decreased more quickly and to a greater degree in \"Solo\" than in \"Group\" males. These results show that social environment in captivity affected beak color and suggest that male House Sparrows may require physical interactions to maintain breeding season levels of testosterone."]

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