Walter,
The tail bobbing and colour narrow it down to two likely suspects: American Pipit and Palm Warbler (both of which are likely visitors to the park at this time of year). Unfortunately the beak is blocked by a leaf in the photo which makes it more difficult to identify, however there seems to be a yellowish tinge to the undertail coverts. This tinge suggests Palm Warbler as opposed to Pipit as does the fairly plain back and wings. I would go with Palm Warbler but by no means is this a positive id.
Iain
