Cavity Depth, Not Experience, Determines Nest Height In Eastern Bluebirds

The functional consequences of nest size variation in cavity nesting birds have been thoroughly investigated in recent years. However, it is unknown whether recent nest-building experience influences subsequent nest architecture. By providing Eastern Bluebirds (Sialia sialis) with either deep or shallow nest boxes for their initial nest of the breeding season, we tested whether the height of their subsequent nest in the same breeding season reflected the height of their initial nest or whether they built nests to match their current nest cavity regardless of their previous nest height. We found that second nests built in deep boxes were significantly taller than first nests built in shallow boxes by the same females. This difference could be because of nest date, cavity depth, or experience. We tested each possible driver and found that cavity depth better explains variation in nest height than either nest date or prior experience. We conclude that, for this multi-brooded secondary cavity nesting passerine, the roles of learning and experience are secondary to the importance of behavioral plasticity.