Do male breeding displays function to attract mates or defend territories?The explanatory role of mate and site fidelity

Many shorebirds show elaborate breeding displays that include aerial flight s and ground displays accompanied by song. The mate attraction hypothesis s uggests that breeding displays function to attract mates and maintain pair bonds, whereas the territory defense hypothesis suggests breeding displays function in defining and defending nesting and feeding territories. We test ed these hypotheses in the Western Sandpiper (Calidris mauri) by contrastin g the duration and level of male breeding displays among pairs that differe d in their mate and site fidelity. As predicted by the mate attraction hypo thesis, males performed the highest number of song sequences during pair fo rmation, and males paired with their mate of a prior year sang less than ma les paired to new mates. Further, site-faithful males mated to a new but ex perienced mate displayed significantly more than remated males or males new to the area. This suggests a male's prior familiarity with an area and his neighbors does not lessen his display rate as was predicted under the terr itory defense hypothesis. Limited support for the territory defense hypothe sis came from observations of males performing breeding displays with neigh boring males along nest territory boundaries. This behavior was short-lived , however, as males abandoned nesting areas after pair-formation and used a djacent or disjointed feeding areas during egg-laying and incubation. Male aggression (i.e., aerial and ground chases), as opposed to breeding display s, appeared to be the principal means of maintaining territory boundaries. Indeed, the rate at which males chased other males remained fairly constant and high throughout the breeding season. Male chasing behavior may also se rve as a paternity guard to protect against extra-pair copulations. Our stu dy also found that a female's prior breeding experience in an area correlat ed with a reduced display rate by her mate, particularly if that mate was n ew to the area. This indicates female characteristics may not only drive ne st initiation, as has been shown in other studies, but are important in det ermining the duration and extent of male display.