Figure 2: Cross-fostering of nestlings between collared (CF) and pied flycatchers (PF) on the Swedish island of Öland using two different approaches. (a) Complete clutches of eggs swapped between nests in three steps. (b) Partial cross-fostering of three day old nestlings between two nests. The left side (i) refers to the nests before swapping, and the right side (ii) refers to the same nests after swapping (collared flycatchers in white and pied flycatchers in grey).