GEE, JM; GEE, ; GEE, ; GEE, ; GEE, ; GEE, ; GEE, ; GEE, ; Cornell University: GREGARIOUS SPECIES AND THE TENDENCY TO HYBRIDIZE

Many studies have revealed the circumstances that create hybrid zones, such as secondary contact between once isolated species. Others have shown how dispersal and selection maintain hybrid zones and limit their size. Why some populations or individuals hybridize while others do not is still a matter of considerable debate. I have found that the formation of social groups prior to the breeding season explains the high incidence of hybridization between California and Gambel�s Quail (Callipepla californica and C. gambelii). Instead of holding individual territories, both species form coveys, which are flocks of 4-6 fused family groups. Reproductive barriers break down due to the formation of mixed species coveys, in which pairing occurs. Pairs forming within the local covey breed with greater reproductive success than pairs outside the local covey. Based on this case study, here I investigate whether flock and covey formation is a general phenomenon that can explain the common occurrence of hybridization among at least some species of birds. To investigate this possibility, I examine the tendency to hybridize among 19 phasianid species that were reported to be solitary, forming loose groups, or forming coveys. My results provide insight into the ways in which life history and mating system traits affect the ease of hybridization between distinct populations and determine their evolutionary trajectories.