The eavesdropping risk of conspicuous sexual signaling in humpback whales

Abstract

Conspicuous signals, such as acoustic sexual signals, can be “risky” in that they may be overheard by competitors. This means the signaller must balance the benefits of signaling to the intended receiver with the costs of providing information to these competitors. Depending on the signaller context, this balance may change. Male humpback whales produce long, high amplitude songs. This conspicuous sexual signal is presumably used for advertisement when alone and possibly aimed at females when escorting. Regardless of which animal is the intended receiver, as it is conspicuous, it also available to multiple eavesdropping competitors. Here, we show a singing behavior in humpback whales that comprises of a series of “decisions” which depend on the singer’s context (advertising alone versus escorting a female) and the eavesdropping risk. In lone males not with a female, eavesdropping risk was not a significant factor in determining the “decision” to start singing and for how long. Escorting singers, however, were presumably at risk of losing a female to a competitor and were less likely to invest effort into singing as eavesdropping risk increased. Results suggest signaling males seem to be capable of assessing eavesdropping risk, and modifying their signaling behavior, according to the trade-off between the costs and benefits of signaling within each context. Given male humpback whales are using long-range communication signals available to a network of competitors, these trade-off “decisions” are likely to be complex.

Significance statement

Humpback whale males use song as a long-range sexual signal. However, for any long-range conspicuous sexual signal, there is a direct trade-off between the advantages of using a conspicuous signal, with the cost of signaling to eavesdroppers such as rival males. Here, we showed that the “decisions” made by humpback whale singers depended on a combination of social factors including a social “trigger,” eavesdropping risk, and whether the singer was escorting a female. Results suggest male humpback whales are selecting the most appropriate singing strategy based on their assessment of a constantly changing, complex social environment.