As we're now, alledgedly, in summer time most of the bird life in St.Ives will have youngster in tow. There should be many large parties moving through the tree tops. You're probably more likely to hear them rather than see them because of the foliage on the trees. If you do encounter parties crossing the path in front of you during a walk, it's worth just standing quietly and counting how many birds you see. Birds such as Long-tailed Tits can have upto 14 young following them around.
On the sunnier days it's also worth watching for Butterflies and Dragonflies. There are several species of both in St.Ives.