Why many animals display several different kinds of ornaments has been of recent interest in animal-communication research. Three key hypotheses have been suggested: multiple ornaments can function as (1) multiple messages (each ornament provides different information), (2) redundant messages or back-up signals (all ornaments provide the same information), and (3) unreliable signals (no information). Here we tested the signal properties of ornamental traits of male House Sparrows (Passer domesticus) to better resolve the potential information different ornaments reveal. We repeatedly measured badge size, wingbar area and color, bill color, and leg color in 170 captive males over 3 years. We found that (1) badge size and wingbar area were related to condition (to mass, tarsus length, and the interaction of both), (2) badge size, wingbar area, and bill color were related to testosterone levels, (3) all ornaments except bill color were related to age, and (4) origin had only minor effects. We conclude that badge size, wingbar area, and bill color may function as multiple messages of different testosterone-related behaviors and that badge size, wingbar area, and leg color have the potential to function as back-up signals of age. However, the empirical categorization of ornaments as either multiple messages or back-up signals is not clear, and we suggest instead it is more informative to view multiple ornaments as providers of varying degrees of overlapping types of information.
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Vol. 114 • No. 4