Talk about paying at the pump.Exxon-Mobil had a bad day in court in Denver yesterday. The firm pleaded guilty to killing migratory birds in five states, including Colorado. The size of the fine and community-service payments Exxon-Mobil has agreed to pony up -- $600,000 -- is, to use an avian reference, chicken feed given the profits the company has reaped in recent years. Nonetheless, the corporate behmoth is also having to invest in a plan to prevent such slayings in the future. These p