Hi Steve, Further to Neil's comments, for the Tauranga area, shorebirds are probably the strong point. Maketu and Little Waihi are easily accessible from there, browse through the discussions in these forums for more info (use the Search tool). Pelagics are also promoted on this site fairly regularly, so keep an eye out for them, they're well worth doing, even if your stomach is a bit delicate, as mine is! For forest birds, you could try Otanewainuku (
http://kiwitrust.org). Or if you have time to go a bit further afield, Tiritiri Matangi is arguably the easiest place in the northern North Island to see a big range of endemics.
As for best time of year, as Neil says late spring is a time when most birds are active, the days are a good length, and you'll miss the peak of the tourist season. Do allow yourself plenty of time - my wife and I did a two-week road trip down to Stewart Island from near Hamilton in late November/early December, with no stops of any significance in the North Island at all, and though we had a ball and saw lots of birds it was a real rush! NZ's a long, narrow, mountainous country, and the roads aren't as good as you'll be used to in Britain, so travelling any distance takes more time than many overseas visitors realise.
