Animals use interspecific cues as a source of information in decision-making, but the full costs and benefits of interspecific information use are unknown. We tested whether pied flycatchers use the body size and clutch size of great tits as cues in their reproductive decisions and what are the possible fitness consequences as a function of great tit size. The size of great tit females was positively associated with flycatchers’ probability to settle near a tit nest over a territory further away. Flycatcher egg mass was positively correlated with great tit female size regardless of flycatcher territory choice. However, in flycatchers that had chosen to nest near great tits, the size of nestlings decreased in relation to increasing great tit female size. Our results demonstrate the use of size of interspecifics as a cue in reproductive decisions and the trade-off between the value of information and costs of competition information users face when using interspecific information in decision-making.