Nutritional Constraints Determine the Expression of a Sexual Trait in the House Sparrow, Passer domesticus

• Published in: Proceedings of the Royal Society. B, Biological sciences Biological sciences, 1996-02, Vol.263 (1367), p.229-234
• Main Authors: Veiga, José P., Puerta, Marisa
• Format: Article
• Language: English
• Subjects: Aviary birds; Aviculture; Birds; Blood proteins; Feathers; Male animals; Molting; Phenotypic traits; Sparrows; Wild birds
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.1996.0036

Many birds have distinctive patches of feathers that in some cases have been shown to function as reliable signals of phenotypic quality. It has generally been assumed that these called ‘badges’ are inexpensive to produce, so other kind of costs have been invoked to explain how they are maintained as honest signals. In the present study we addressed the hypothesis that the black throat badge of male house sparrows functions as an honest signal of condition because it is nutritionally costly to produce, a possibility not yet evaluated for badges showing status. While under field conditions adult birds exhibited larger badges than juveniles, individuals of both age classes developed badges of similar size when moulting in an aviary with ad libitum food. Fat reserves, blood proteins and body mass records of free ranging birds at the start of moult suggest that juveniles were in poorer condition than adults. The reduction of blood proteins during moult negatively correlated with badge size after moult in juveniles but not in adults, and only the variation of blood proteins, but not fat reserves, correlated with the size of the badge when using multiple regression analysis. The results suggest that: (i) a limited access to food sources during moult may account for the smaller badge size of juveniles as previously reported in the same study population; and (ii) the use of more blood proteins, that seems to depend on a worse nutritional condition, constrains the production of a larger badge. The results give support for the hypothesis that badges are costly to produce, though the magnitude of the costs may be age dependent.