Some birds migrate quite amazing distances, sometimes almost pole to pole. For example, I used to see Canada Geese in my tiny hometown in New Zealand every year.
So why are Canadian Geese considered Canadian native, and not New Zealand native? Or are they both? Is it determined by birth/nesting country? Or whoever names them first?
They’re not “Canadian Geese”, they’re “Canada Geese”, as you said in your first paragraph. It’s just a name, not a nationality. The Canada Geese you see in New Zealand are an introduced species, originally from North America, and the name stuck.
“Canada Goose,” as **Athena ** says, is just a common name. They are a native breeder in much of the US and part of Greenland, besides Canada. They have been introduced, and are now breeding, in NZ and Europe. The European Starling has been introduced in North America for many years, and it is still called the European Starling.
For birds, a distinction is often made between native breeding species, introduced breeding species, and migratory species that don’t breed in an area. But this doesn’t necessarily have anything to do with the name. Many migratory species are named after the place where they were first collected, rather than their breeding range. The Tennessee, Nashville, Cape May, and Connecticut Warblers don’t breed anywhere near their namesake localities.
While there are birds that migrate over distances equivalent to NZ - Canada, the Canada Goose isn’t among them. As noted by Athena & Colibri, the birds you saw spend the entire year in New Zealand.
Okay, maybe Canada Geese was a bad example.
I still am wondering what the determining factor is for ‘native’ when it’s a migratory species.
I’m not sure it’s a rigorously defined term - Colibri, as the resident bird expert, would probably be the right one to answer.
It seems reasonable to say that a migratory species is native to both the area where it spends the nesting season and where it spends most of the rest of its time. It seems a bit of a reach to say it’s ‘native’ to areas it visits only during migration. Any yet there are huge numbers of species that are seen annually in certain areas, but only briefly, on migration (in some cases, only in one migration direction).
I would say that “native” is a term that is only appropriate to use with respect to breeding species, to distringuish naturally occurring breeding species from those that have been introduced by humans. The real distinction, whether breeding or migratory species, is between those that occur naturally in an area and those that would not be present except for human intervention.
Species’ ranges change naturally too. Here in Panama, a number of new species have appeared in the country and bred over the past few decades. While not historically “native,” they are naturally occurring (although some have benefited by human-caused changes to the environment, such as deforestation).
As far as migrants go, if I am making up a bird checklist for an area, I distinguish regularly occurring migrants from those that appear only occasionally (referred to as “casual” species). Species which occur even more rarely, but which are assumed to have reached the area under their own power, are called “vagrants” or “accidentals.”
Species which are definitely known to have been brought in by humans, but which have not established breeding populations in the wild over the long term (such as escaped cage birds), are usually not counted on regional checklists. Species for which it is unknown for sure whether they arrived naturally, or with human assistance, are usually included on the “hypothetical” list. Here in Panama we have recorded a few individuals of number of species which do not normally migrate, but which probably arrived by hitchhiking on ships bound for the Panama Canal.
What about a species that is present annually for a couple of months, but breeds in the opposite hemisphere?
That’s a migrant (with respect to the area where it doesn’t breed).
Here in Panama a substantial part of the avifauna is made up of non-breeding migrants. Most come from the north, breeding in Canada and the US. A few come from South America (and many sea birds come from the South Pacific). Some are winter residents, which actually may spend more time in Panama (seven months) than they do up north (five months). Some are transients, which pass through Panama en route to wintering grounds farther south but don’t stay for any length of time. Some of these come through Panama only in the fall, returning back north in the spring another way. A small number of Panama birds are intertropical migrants - they breed in Panama, then migrate to South America for part of the year.
I would think that wherever the birds breed, nest and raise young would be considered “home.” However birds like the Arctic Tern that migrate from way north in the northern hemisphere to way south in the southern are hard to pin down.
Even harder is theStorm Petrel. Also sometimes referred to as Mother Carey’s Chickens, they spend all of their lives at sea except for brief times ashore (60 to 70 days) to nest and raise young.
There are lots of birds that spend more time away from their breeding area than at it. For larger seabirds, they may spend many years at sea before returning to
their original breeding area. Many shorebirds breed in Canada and migrate to Panama during the northern winter. Many juveniles do not return north when their parents do, but spend their first full summer in the tropics, only returning up north when they are nearly 2 years old.
Thanks, Colibri. That’s just what I was looking for - interesting to see there are words for each kind of ‘native’ or ‘migrant’ type, and also that it can be a bit vague even so.
An outstanding example is found near Dunedin, on the South Island of the OP’s New Zealand. On the Otago Peninsula is a colony of Royal Albatross (something like two dozen breeding pairs). When the young birds fledge (after about 9 months in & near their nest) they don’t return home - or indeed near land - for 5 to 6 years.
Anyone visiting NZ and interested by the sight of a giant bird with a 12-ft wingspan would find this place well worth a visit.
I’m actually from Dunedin 
Have you been out to Taiaroa to see the Albatross colony? How about the penguins?
I’ve been to Taiaroa Heads a lot, but never when the albatrosses were in. But I’ve seen the penguins a lot. Penguins are all over NZ, you just need to hang out at a rocky beach anywhere and a penguin will waddle up eventually. Or a sea lion. Or see whales and dolphins.
They’re in quite a lot - they have to mate, lay eggs, hatch them, then feed the chicks for 270 days before they fledge.