In my opinion, of all the species that are on the Hunter Region list (or will be, if this tern is accepted by BARC) this would get my vote as the 'most unexpected bird' on the Hunter Region list, above Juan Fernandez Petrel, Torresian Imperial Pigeon, White Wagtail and just above New Zealand Storm-petrel and Aleutian Tern. I have only seen the last two of those, but I would expect to see any of the other three before I saw a Black-fronted Tern here.
Nearly all seabirds are prone to vagrancy given the environment that they live in, where they're in the firing line of major weather systems and affected by enormous shifts in preferred food, water temperature etc. Plus they're amazing travellers that can find themselves in the wrong ocean.
White Wagtails, Kentish Plovers, Buff-breasted Sandpipers, Northern Shovelers etc are all long-distance migrants and there are constantly migrating birds that are overshooting their migratory targets. The absolute vast majority of those individuals either never get found by birders or perish undetected, so we don't know about them - but they're out there - all the time.
Aleutian Terns are long-distance migrants but they're clearly not overshooting; they're choosing to come here. So that's different.
But long-distance migrants (be they shorebirds or passerines) and seabirds always feature in predictions for the next new species for Australia. Black-fronted Tern wouldn't have been in the top fifty predictions by any birder having a stab at this. Yes, the species makes post-breeding movements but that's mostly to coastal areas on the South Island of New Zealand where it breeds. Some birds make it to the North Island, but from what I have read, it doesn't sound like proper 'migration'.
I've been talking to researchers in New Zealand and they've told me that there have been seasons in the past where 100+ birds have been found on the North Island (e.g 2009). But despite that it still doesn't sound like something that's prone to vagrancy.
And this is the first record away from New Zealand.
There was a low pressure system in the Tasman Sea that resulted in the strong south-westerly winds that got people out seawatching but it didn't emanate from close to New Zealand. Maybe this bird was foraging a long way offshore and got blown towards the east coast? How far do these things forage out to sea? How far do our Aleutian Terns go to forage at sea?
It's also a species with a very small population (2500-10,000 individuals) and is listed under IUCN criteria as Endangered. The population is also said to be declining.
Further, it's a very distinct bird - even for a tern! And that's at any age too. I very much doubt that birds have been overlooked in Australia before.
