Testosterone and behavior in neotropical birds: fundamental differences from high latitude species (#268)
Our understanding of the roles of testosterone in free-living animals has dramatically increased in the past few decades. From the hormone’s role in mediating aggression, to growth of the song control system, we probably know more about testosterone than any other hormone. However, most of what we know is from studies on mid- to high latitude species, which may not be representative of the majority of species, which are tropical. Tropical birds face very different challenges and display more varied life histories than species from higher latitudes. I will present data on the behavioral role of testosterone from two very different equatorial species of birds. In high elevation populations of the rufous-collared sparrow, Zonotrichia capensis, breeding is seasonal and occurs during an extended period of 3-4 months. Testosterone levels in males are high during the breeding season with levels comparable to high latitude species. However, territorial aggression is not associated with increased testosterone levels as predicted by the Challenge Hypothesis. However, elevated testosterone does inhibit paternal care of young, similar to high latitude species. In low elevation populations of the wire-tailed manakins, Pipra filicauda, territorial males on leks display higher testosterone than floaters but also cooperate with these floaters in an effort to attract females. Thus elevated testosterone is associated more with cooperation than aggression. It is clear that testosterone’s behavioral role in these equatorial birds contradicts much of what we understand about the hormone based on studies of high latitude species. Our future studies of these species and other tropical birds will continue to elucidate and expand our understanding of the behavioral role of testosterone.