I studied the Puerto Rican Bullfinch (Loxigilla portoricensis), a frugivorous island endemic, in two sites in southwestern Puerto Rico in 2009 and 2010. I modeled nest survival of 37 nests to better understand the effects of several biological factors on daily nest survival. Predation was the most important cause of nest failure. Six models, all including some measure of fruit abundance, received approximately equal support. Constant, linear, and quadratic time trends in nest survival during seasons were all supported in these top six models. Results suggested that Coccoloba microstachya fruit abundance had a significant negative relationship, Bursera simaruba fruit abundance had a weak positive relationship, and Bourreria succulenta fruit abundance had a nearly significant positive relationship with nest survival. I radio-tracked bullfinches and estimated the breeding season home ranges and core areas of 17 adults. Median home range and core area for both sites were 31.4 y 30.0 ha and 13.2 y 15.7 ha, respectively. Home ranges and core areas did not differ in size between males and females or between pre-nesting and nesting periods. These findings increase our understanding of the breeding-season biology of the bullfinch, and will ultimately help inform future studies and conservation efforts of bullfinches and other passerines in southwestern Puerto Rico.