Three fledglings per nest are produced in Argentina (Mezquida 2002), two per nest in Santa Cruz Department, Bolivia (AEJ, A.M. Mamani, and V. Bejarano, unpublished data), and one per nest in central Brazil (Marini et al. 2009). In central Brazil, the nest success rate from 2003 to 2007 was ca 53% (Marini et al. 2009). During three years (2010-2012) at a site in Buenos Aires Province, Argentina, it was 48% (DTT and AEJ, unpublished data), and in Santa Cruz Department, Bolivia it was 44% over two years (2010 and 2011; AEJ, A.M. Mamani, and V. Bejarano, unpublished data). There is currently no information available on such variables as age at first breeding, life span and survivorship, dispersal, or population regulation for Fork-tailed Flycatcher.
Fork-tailed Flycatcher is parasitized by the feather mite Trouessartia savanae (Hernandes 2014).