For his doctoral degree, Peter Grant studied the relationship between
ecology and
evolution and how they were interrelated. The Grants travelled to the
Tres Marias Islands off Mexico to conduct field studies of the birds that inhabited the island. On average, the birds on the islands had larger beaks. The Grants attributed these differences to what foods were available, and what was available was dependent on competitors. The bigger beaks indicated a greater range of foods present in the environment. In his article "Interspecific Competition Among Rodents", he concluded that competitive interaction for space is common among many rodent species, not just the species that have been studied in detail. The island provided the best environment to study natural selection; seasons of heavy rain switched to seasons of extended drought. With these environmental changes brought changes in the types of foods available to the birds. The Grants would study this for the next few decades of their lives. In 1973, the Grants headed out on what they thought would be a two-year study on the island of Daphne Major. There they would study evolution and ultimately determine what drives the formation of new species. The lack of rain caused major food sources to become scarce, causing the need to find alternative food sources. The smaller, softer seeds ran out, leaving only the larger, tougher seeds. The finch species with smaller beaks struggled to find alternate seeds to eat. They called this bird Big Bird. It had many different characteristics than those of the native finches: a strange call, extra glossy feathers, it could eat both large and small seeds, and could also eat the nectar, pollen, and seeds of the cacti that grow on the island. Big Bird lived for thirteen years, initially interbreeding with local species. His descendants have only mated within themselves for the past thirty years, a total of seven generations. Whole genome studies have enabled scientists to trace changes in the genome as the species became distinct. Genes for beak shape (ALX1) and beak size (HMGA2) have been determined to be crucial in separating the hybridized species from local finches. Genes relating to the finches' song may also be involved. Over the course of 1982–1983,
El Niño brought a steady eight months of rain. In a normal rainy season Daphne Major usually gets two months of rain. The excessive rain brought a turnover in the types of vegetation growing on the island. The seeds shifted from large, hard to crack seeds to many different types of small, softer seeds. This gave birds with smaller beaks an advantage when another drought hit the following year. ==Significant findings==