Burying beetles, Nicrophorus defodiens, reproduce on vertebrate carcasses, and the number of beetles of either sex on a carcass is known to be highly variable. Field and laboratory studies were conducted to examine how sexual advertisement by males is affected by resource quality and number of mates, and to determine the reproductive output of males in different breeding associations. Carcass size had a strong influence on the reproductive benefits of polygyny to males, and on male sexual advertisement. In the field, polygynous groups produced more young and a greater brood mass than monogamous or polyandrous groups when using a large carcass (40-60 g). On a small carcass (15-18 g), however, no differences in reproductive output between the three breeding associations were found. In light of these findings, advertisement for mates was monitored when males were provided: (1) a small carcass and one female; (2) a large carcass and one female; and (3) a large carcass and four females. Most males that were paired with a female on a large carcass released pheromone even after copulating with the resident femalae. Pheromone emission was rare, however, in males that were paired with a single female on a small carcass, or in males that were given access to four females. Male N. defodiens thus assess both resource quality and number of mates when deciding whether to emit pheromone, and this decision appears to agree with the reproducitve interests of males but not necessarily that of resident females.