Male and female conspecifics constitute a second class of potential eavesdroppers. Experimental evidence from a number of songbird SB705498 has confirmed that conspecific males do indeed eavesdrop on neighbouring singers (Ak?ay et?al., 2010, Naguib et?al., 1999, Peake, 2005, Peake et?al., 2001 and Peake et?al., 2002). Unlike eavesdropping by predators, which seems likely always to be disadvantageous to a signaller, eavesdropping by competitors may sometimes be beneficial. For example, if neighbouring males overhear a territory owner defeating an intruder, the eavesdroppers may subsequently be discouraged from confronting that owner themselves (Johnstone, 2001 and Johnstone and Bshary, 2004). Territory owners thus might benefit from encouraging eavesdropping by using broadcast song, rather than soft song, when countering intruders. Conversely, ozone may be advantageous for intruders to use soft vocalizations when they trespass on territories of others. There is experimental evidence from song sparrows that territory owners that appear to intrude on a neighbour's territory pay a retaliation cost from other eavesdropping males (Akçay et al., 2010). If that is true, then intruders would benefit from limiting eavesdropping by competitors.