Fast moving animals

I'm having another go at using the incredibly light weight but very slow 75-300mm zoom today. I have a few minutes in Covent Garden before my shiatsu appointment.

I'm going to be photographing some potentially dangerous animals in Mexico, so am still undecided as to wether to take this versatile but poor quality lens or a prime 100mm or 200mm. Both the latter are nice wide aperture lenses, but heavy in comparison.