Testosterone in Tropical Birds: Effects of Environmental and Social Factors

Abstract

Previous investigations suggest that male tropical birds have lower plasma testosterone concentrations than northern latitude species. To test whether this generalization is valid, we analyzed all currently available plasma testosterone data of tropical birds. We focused on peak breeding testosterone levels using phylogenetic and conventional statistics. Explanatory variables considered were social mating system, type of territoriality, breeding season length, and altitude. On average, tropical birds had lower mean peak testosterone levels than northern temperate birds. However, in several tropical species, testosterone levels were well within the range of northern latitude birds. Without controlling for phylogeny, breeding season length, type of territoriality, and altitude explained a significant proportion of the variance in testosterone levels. The shorter the breeding season, the higher the testosterone levels. Tropical birds that defend a breeding season territory had higher testosterone levels than birds that were year-round territorial or colonial, and testosterone levels were positively correlated with altitude. When controlling for phylogeny, only breeding season length predicted testosterone levels. In conclusion, we propose to refine previous notions of low plasma testosterone levels in tropical birds: short breeding seasons and perhaps environmental conditions at high altitudes precipitate conditions under which high testosterone levels are beneficial in the tropics.

Androgen and the elaborate courtship behavior of a tropical lekking bird

“…In the few lekking species that have been studied, males have high levels of androgen as long as they are actively displaying on their leks (Alatalo et al, 1996;Lisano and Kennamer, 1977). In general, tropical birds differ from their temperate-breeding counterparts by having relatively low levels of circulating T throughout the reproductive season (Goymann et al, 2004;Gwinner and Scheuerlein, 1999;Hau et al, 2000;Levin and Wingfield, 1992;Wikelski et al, 2003). This is particularly the case of species that, like the golden-collared manakin, live at low altitudes and have a long breeding season (Goymann et al, 2004).…”

“…In general, tropical birds differ from their temperate-breeding counterparts by having relatively low levels of circulating T throughout the reproductive season (Goymann et al, 2004;Gwinner and Scheuerlein, 1999;Hau et al, 2000;Levin and Wingfield, 1992;Wikelski et al, 2003). This is particularly the case of species that, like the golden-collared manakin, live at low altitudes and have a long breeding season (Goymann et al, 2004). Golden-collared manakins seem to differ also from lekking species in the temperate-zone in that plasma levels of T declined significantly although the males continued to court females and interact with neighboring males.…”

“…T decreases afterwards, probably because elevated T concentrations are costly in terms of parental care (reviewed in Wingfield et al, 2001) and immunocompetence (Folstad and Karter, 1992). By contrast, males of many tropical species with prolonged breeding seasons typically have low levels of plasma T (reviewed by Goymann et al, 2004;Levin and Wingfield, 1992;Wikelski et al, 2003), unless they live at high elevations (Moore et al, 2002). However, high levels of T have been found in some tropical species during courtship (Chastel et al, 2005;Levin and Wingfield, 1992;Wiley and Goldizen, 2003).…”

Social environment affects testosterone level in captive male blue–black grassquits

“…Hormones and Behavior 59 (2011) 51-55 The study of the reproductive physiology and behavior of tropical birds is still in its infancy, but data obtained to data present strikingly different patterns from those found for temperate birds (Martin and Rubenstein, 2008;Wikelski et al, 2003a,b). In the few tropical birds studied to date, those that exhibit year-round territoriality and longterm pair bonding do not exhibit high T levels, although territorial aggression is sustained (reviewed in Gwinner and Dittami, 1990;Goymann et al, 2004;Hau et al, 2000;Wikelski et al, 2000). The key factor underlying life-history traits of tropical birds is the duration of the breeding season, which may be the chief determinant of their low T levels: if the breeding season is short, the T peak should be higher, but if the breeding season is long, the T peak is expected to be lower (Goymann et al, 2004).…”

“…In the few tropical birds studied to date, those that exhibit year-round territoriality and longterm pair bonding do not exhibit high T levels, although territorial aggression is sustained (reviewed in Gwinner and Dittami, 1990;Goymann et al, 2004;Hau et al, 2000;Wikelski et al, 2000). The key factor underlying life-history traits of tropical birds is the duration of the breeding season, which may be the chief determinant of their low T levels: if the breeding season is short, the T peak should be higher, but if the breeding season is long, the T peak is expected to be lower (Goymann et al, 2004). This happens because the maintenance of high and prolonged T levels may have an excessive physiological cost to the individual (Wingfield et al, 2001).…”