Master of Science
Date of Defense
Patricia Parker, PhD
The Galapagos Hawk (Buteo galapagoensis) is endemic to the Galapagos Islands, where it is the top predator and only resident diurnal raptor. On most islands, Galapagos hawks form polyandrous breeding groups with one female with up to eight males. Before entering a breeding group, individuals spend 3-4 years as non-breeding floaters. I studied the hawks on Santiago Island, where introduced goats had been recently eradicated, leading to drastic changes in the ecology of the island. Using mark-recapture procedures, we assessed the size of the juvenile component of the population over time. In addition, using software MARK with a 12-year demographic database on this population to model annual survivorship of breeding adults. I also used this database as well as current observations to describe natal dispersal patterns and patterns of floater sociality. The population size of the floater fraction of the population declined at the end of the goat eradication program, with an apparent disappearance in 2007 and 2008, and an apparent recovery in 2009. Territorial adult survivorship probability is a function of sex, body size, territory vegetation type and breeding group size per year, but the relative importance of these factors changes between years. The lowest annual adult survivorship through the 12 years monitored was 2005-2006, the final year that the goats were eradicated. In the component focusing on juvenile behavior, I found that individuals do tend to disperse to territories neighboring their natal territories (p<0.05), but they showed no statistical preference for territories with similar vegetation (p>0.05). Individuals in the four-year juvenile period do not form stable coalitions with particular individuals even though they are often highly aggregated. The eradication of goats from Santiago Island had an effect on the Hawk’s population; further monitoring is needed to better understand possible long term effects still to be seen and better understand the relationship of survivorship estimates with possible unaccounted variables such as prey abundance.
Rivera, Jose Luis, "Galapagos Hawk: Demographic and Social Effects in a Changing Environment" (2010). Theses. 29.