Books recommended
Hi Big Phil,
Your Heather and Robertson is the best Fieldguide available for NZ birds. The latest revised edition of 2005 would be best. Even for the seabirds it is reasonable (though it is not detailed enough for all possible distinctions in sub-species which are in the process of getting a full species status. If you have the previous edition don't bother to replace it) Still it is the best on offer as far as NZ fieldguides is concerned.
If you can study the Handbook of Antarctic, Oz and NZ birds (Hanza) that would be a great oppertunity. Though I must state that the volume on Seabirds is outdated (again taxonomy) but still worth a read. Try a library?
The Harrison Pictorial seabirdguide is nice but I am pretty sure you will be lost at a pelagic trip using it, because of the number of species you will encounter. E.g. being surrounded by 4 - 6 species of shearwaters, fairy Prions, Cape doves, both Giant Petrel species and 5 species of albatross at the same time is quite overwhelming and if not experienced can be paralizing (certainly confusing!), but also very magic!!!
The seabirdguide issued by Helm and a special booklet on seabirds in the Southern Pacific are handy (I can't recaal authors names and I am traveling at the moment...). There is also a guide on NZ Seabirds by Brian Parkinson. Great photo's but to me it was not a substantial addition to the other books mentioned. Best advise for not missing on species "right under your nose" is a good guide familiar with the seabirds. But I am afraid these are few.
Compared to travel expenses to NZ the fee for a guide is a worthwile investment. Missing a bird in France is relatively easy "repaired" if you are living in Scotland. Missing e.g. broad-billed prion, Blue shag (subspecies of Spotted shag), or rifleman or a NZ Robin for that matter is a lot more difficult and expensive experience once you are back in Scotland! (and I do not regularly guide, so its not because of that.)
I have seen quite a few of the Seabirds by now but sometimes I am still wishing for a photographic memory!
Phil, enjoy your trip (I am sure you will!!!) and start studying the seabird plates and pictures!
Cheers,
Leo