Can it be done at all?

I've had a rather humbling expierence yesterday. Went to a small island that's being returned to nature. Loads of birds there including a varied assortment of ducks and geese.

Tried to shoot them in flight and found myself failing rather miserably a lot of the time. Up untill now I fancied myself a decent shot with my D300 and 70-300VR. I get decent fallow deer shot most of the time (like http://www.flickr.com/photos/j_wijnands/4094589595/) and every now and then a pic like these:
http://www.flickr.com/photos/j_wijna...7622854098515/
http://www.flickr.com/photos/j_wijna...7622854098515/

But I am now realizing that there's a big difference between shooting in a nature area that features a lot of vegetation and where every day dozens (on weekends often hunderds) of people walk by and an open landscape where there's perhaps a dozen visitors each day and no cover to speak of.

So...

I already figured out shutter speed is vital when shooting something in flight. I know my fieldcraft needs work. I will not have the option to lug a hiding place with me and spend hours waiting. I will not have the option to fork out cash for a longer lens.

Am I p****ng in the wind? Is it at all possible to get decent bird shots with my gear?