2015 bird report:
The open grasslands on either side of the Colne on the South side comprising of steeply sloping banks are frequently used by up to 50 crows, magpies, wood pigeons and sea gulls. In the river there are often up to 40 mallards and 10 moor hens. We have 2 kingfishers frequenting the Mercedes side of the river and also have 2 swans with a signet using the river in the park (late January) a heron is also often seen in the river.

Oxhey Park Bird List (In or Over Park 2014) from Chris:
House Sparrow, Hedge Sparrow (Dunnock), Starling, Black Bird, Wren, Robin, Blue Tit, Great Tit, Long Tailed Tit, Coal Tit, Goldcrest, Tree Creeper, Nuthatch, Great Spotted Woodpecker, Green Woodpecker, Magpie, Jay, Crow, Rook, Black Headed Gull, Lesser Black Back Gull, Herring Gull, Soung Thrush, Mistle Thrush, Chaffinch, Bull Finch, Greenfinch, GoldFinch, Common Redpoll, Chiff Chaff, Willow Warbler, Garden Warbler, BlackCap, Redwing, Fieldfare, Waxwing, Pied Wagtail, Grey Wagtail, Kingfisher, Heron, Little Egret, Mallard, Moorhen, Coot, Sparrowhawk, Kestrel, Red Kite, Buzzard, Tawny Owl, Ring Necked Parakeet, Feral Pigeon, Wood Pigeon, Collard Dove.
Suspect there may be a handful of other species in the park at some point in the year (especially around spring or Autumn migration) but as yet not recorded/confirmed.