A Strange Mating System

The behavior in which multiple unrelated males feed dependent nestlings is common in only one other North American bird species, Smith's Longspur. In our study, 75% of broods were sired by multiple males and 78% of broods were fed by multiple males. Some males had parentage in multiple broods in the same year, but females did not. Twelve of 14 males (86%) sired offspring in the broods that they fed. Females typically provided about half of feeds for a brood, while males appeared to adjust feeding in response to the number of male co-feeders. Multiple male feeders may allocate parental effort to broods based on probability of paternity, to enhance mating access, as misdirected parental care, or via some combination of these factors. A harsh environment which exceeds the polyandry threshold, and a strongly male-biased sex ratio may also influence the number of feeders. Many aspects of this secretive bird's breeding ecology remain obscure, in particular the effects of food availability, female dispersion, female reproductive synchrony, mating access, and kinship.

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