“…However, more studies from species with differing levels of sperm competition are needed to assess whether this is a general trend (Snook 2005, Kleven et al 2008, Rowe and Pruett-Jones 2011. For example, although it is commonly predicted that tropical species experience lower sperm competition than temperate species-because of differences in life history traits such as life span, clutch size, breeding synchrony, migration, and promiscuity rates (Ricklefs and Wikelski 2002)-data on sperm variation in tropical passerines are rare, and a recent review found little evidence for such a distinction (Albrecht et al 2013). Furthermore, although the level of sperm competition is often predicted to be relatively low in lekking systems, given that no pair bonds restrict females from all mating with the most attractive male, evidence for multiple mating and multiple paternity in lekking species indicates that postcopulatory sperm-competition levels may be higher than previously thought (Petrie et al 1992, Lank et al 2002, Hess et al 2012.…”