Rats climbing up bird feeder?

I have a bird feeder similar to this (http://www.wyevale.co.uk/Heavy%20duty%20wild%20bird%20feeder%20pole%20+single/1170001054,default,pd.html) and there is a family of five rats that climb up it and eat all the food. I stopped putting food on the ground as soon as I realised I had a rat problem but this did not help. How do I deter the rats? They are the size of small rabbits so I think the only way to get rid of them would be to shoot them. How about vaseline up the pole? Would that stop them climbing?

rat trap
wild rats carry disease
any time you see rodents, multiply the number by 10 to estimate how many there are in the area.
check out the site

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html

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