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Thesis Abstract – Sueda (1997)


The Effect of Testosterone in Wintering White-Crowned Sparrows, Zonotrichia leucophrus gambelii, and Their Effect on Conspecific Aggression

Author and college:

Karen L. C. Sueda, Pomona College


May 2, 1997


Bachelor of Arts in Biology


Rachel Levin, Pomona College


Recent studies have demonstrated that high levels of aggression can occur in the absence of high testosterone levels, however the opposite situation in which there is little aggressive behavior in the presence of high testosterone levels has not been well documented (Wingfield et al., 1989; 1990; Gwinner et al., 1994). Because previous studies have found that white-crowned sparrows (WCSs) (Zonotrichia leucophrus gambelii) require testosterone for pre-migratory fat deposition and experience increases in circulating testosterone at the end of winter, they may be used to test whether aggression levels can remain stable in the presence of increasing testosterone (Schwabl and Farner, 1989a; 1989b). Unfortunately, not much is known about testosterone levels in wintering WCSs. The purpose of this experiment was to determine testosterone levels in wintering WCSs and to establish whether WCSs undergo a change in aggressive behavior as their pre-migratory testosterone levels increased. Blood samples from both captive and free-living birds were used to determine overall androgen levels during the months of February, March and April. Aggression among captive WCSs was also monitored. Fat levels of both captive and wild birds and the flock size of free-living birds was recorded. Neither aggression rates nor androgen levels significantly changed during the late winter months monitored. These findings suggest that the hormone levels of wintering birds may be far different and more complicated than what is currently being assumed. Further experiments are needed to determine unequivocally if low levels of aggression can remain constant as testosterone increases.

For more information:

Contact Rachel Levin – rachel.levin@pomona.edu

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