Why is it so difficult for Airports to remove birds?

From the Sacramento Bee:

The birds share airspace with commercial jets arriving and departing from Sacramento International Airport – and too frequently, the two groups of fliers collide.

That fact was highlighted two weeks ago in New York when a US Airways jet crash-landed on the Hudson River after a bird strike reportedly disabled both engines.

None of the 155 passengers was killed. But, fearing catastrophe here, Sacramento airport officials are reassessing their safety practices, and pushing for a state law that would assure them of one particular safety tool: full legal clearance to kill troublesome birds.

Dealing with birds is a daily, dawn to dusk job, they say. They fire air cannons and use screech boxes as deterrents. They employ "Bird Banger" firecrackers and even drive in trucks honking horns.

It's not enough, they say. They want "lethal take" rights. That may means traps or poison. Most often, it means a shotgun.

Sacramento, like other airports, has killed birds on its property for years, under federal permits. But state game officials told the airport to back off last year after receiving an anonymous complaint. Killing non-game birds is not authorized by state code, they said, and county employees can be prosecuted for doing it. . . .

The lives of some very common birds versus those of humans? Given the extremes to which the airport has gone to non-lethally get rid of the birds, why do they face such problems. My guess is that if you kill some of the birds, the other birds will stay away.