Did I miss something in the movie The Silence?

I ended up watching The Silence on a trip in an airplane. So not sure if I missed something or if my son sitting next to me - not even watching - figured out a huge huge plot issue...

So these dinosaur birds attack everything that makes noise... Why wouldn't people just build a cage and kill them by the thousands sitting behind bars and rebar with machine guns (and the guns would attract more)? It would seem like this predator would be easy to combat since they were too aggressive. Did I miss something that said this wouldn't work? Or did a 9 year old break the plot of a multimillion dollar production?

Since this hasn't received any answers I will summarize a point from the comments. These are super dumb birds/dinosaurs/whatever... Yes there are millions of them. But... if I am in a military base and I start shooting them then supposedly any of them that can hear will attack. Meaning one bunker and machine gun would wipe out the area. Remember these birds had a hard time getting in a regular car. So to mobilize you could have heavy armored trucks or tanks just roam and wipe out. People would die from the birds at first but then the deaths should be more along the lines of starvation if there is a long-term issue in an area. Nothing in the movie makes sense because they are simply too aggressive not to wipe out.