Subspecific split of NZ falcon

[Neil Fitzgerald]

This new paper proposes North Island and South Island NZ falcon (currently considered different races) should be classified as subspecies. Falco novaeseelandiae novaeseelandiae (South Island), and Falco novaeseelandiae ferox (North Island). I kinda like that ferox name.

Trewick and Olley 2016. Spatial size dimorphism in New Zealand's last endemic raptor, the Kārearea Falco novaeseelandiae, coincides with a narrow sea strait. Ibis

Abstract

Although New Zealand's avifauna includes many unusual birds, species-level diversity within lineages is typically low. There are, however, several instances where different allied forms are recognized in each of the two main islands. Among them is the Kārearea Falco novaeseelandiae, which is the only surviving endemic raptor species in New Zealand. Recent analysis confirms it to be a distinct lineage in the global radiation of this genus and most closely related to the Aplomado Falcon Falco femoralis of South America. We examined body size metrics and neutral genetic markers in Kārearea sampled across New Zealand to assess subspecific variation within the species. We found strong evidence using linear modelling and Bayesian clustering for two distinct sizes within Kārearea, in addition to the recognized sexual dimorphism. The boundary between the size clusters coincides closely with the Cook Strait, a narrow seaway between the two largest islands. However, analysis of mitochondrial sequence data and nuclear microsatellites showed no compelling partitioning at neutral loci. These data suggest adaptive change along a stepped environmental cline. Lineage splitting in Kārearea has either yet to become apparent in the distribution of neutral genetic variation and/or regional adaptation is proceeding despite gene flow.

And the important last paragraph

Formal recognition of distinct subspecies in Karearea places appropriate emphasi s on their different evolutionary potential, and for conservation management supports an existing strategy to avoid translocation and cross-breeding in captivity of falcons from the two islands. We there fore propose Falco novaeseelandiae novaeseelandiae as the nominotypical subspecies from the South Island and Falco novaeseelandiae ferox for the smaller North Isla nd form. The name Falco ferox was proposed in 1848 from material collected during the United States Exploring Expedition (1838–1842) in the Bay of Plenty, North Island, and retained for the smaller North Island ‘bush hawk’ (Buller 1888).

[Pat Miller]

Why aren't there 3 subspecies corresponding to "Bush", "Eastern" and "Southern" falcons currently recognised? And the "Bush" falcon distribution includes the North Island and NW of the South Island, so Cook Strait doesn't appear to be a distributional boundary under current knowledge. Do these authors answer these questions in the rest of their paper?

[Davidthomas]

There has been little difference shown genetically to give the distinct forms a subspecies status which is why they are just classed as forms not subspecies as far as i know. Based on the neutral genetic markers they used they found NI birds and SI birds distinct enough to be classified as separate subspecies while there was not sufficient evidence to split them into forms. Seems weird from my point of view based on visual morphological differences but i know the Author and i trust her science.

Interestingly the Auckland Island population was found to be not that dissimilar from the mainland birds even though they are a long way from the mainland!

[Neil Fitzgerald]

Pat, the morphometrics used (mainly wing-length as a proxy for body size) shows a clear change with latitude corresponding with Cook Straight. There doesn't appear to be the same East-West SI clustering. This inter-island dimorphism is explained as dense forest vs open/dry forest, which does make the lack of east/west distinction a bit surprising.
The genetics is basically summed up by

The exact test of population differentiation based on allele frequencies (Raymond & Rouset 1995) found no significant differentiation among regions or zones.

[Ian Southey]

Looking forward to reading this in full. Nice to finally see an opinion backed up with data but did they look at colour too? That's what's obviously different between the east and west coast birds in the South Island.

Ian

[Ian Southey]

So, a little bird dropped a copy of this paper into my inbox today and it's a bit of an eye opener.

There's not much acknowledgement of Nick Fox's Bush, Southern and Eastern Falcon http://notornis.osnz.org.nz/distributio ... seelandiae. The "Bush Falcon" was supposed to be in the North Island and the North-western part of the South Island but in the South Island there are no birds examined from north west of a line between Nelson and Westport so it is not absolutely clear if the cut off is Cook Strait or not. "Southern Falcons" were found from Fiordland and the Auckland Islands while much of the West Coast seemed to be "Eastern Falcons" - also found in Canterbury and Otago. There are birds from the Auckland Islands but nothing from Fiordland although some from South Westland (closest is Big Bay) may fit the bill or they may be Eastern Falcons as would be those around Te Anau which appears to be the next closest so Southern Falcons are probably not well represented either.

The confusion indicated by the names in the old literature is more about difficulties in the really early workers seeing each other's work and specimens then and perhaps less care about the application of names then. The Victorian New Zealanders had a better handle on it and did recognise real variation but Smith 1884 is not to my mind a clear indication of this, Buller 1888 is better and this http://nzetc.victoria.ac.nz/tm/scholarl ... y1-d5.html indicates that he was more or less distinguishing "Eastern Falcons" from the eastern plains and foothills of the South island from the other two forms as "Bush Hawks" found in the North Island and from around the main divide and westward.

The geographic divisions used for morphometric analysis are cut off from east to west rather than north to south in the South Island so these could sometimes include two forms of the birds. In the field I wasn't able to see a size difference but there is an obvious colour difference with the Southern Falcons of Fiordland and Waitutu being very dark and a few intermediate birds (or dark Eastern Falcons) in western Southland just east of Lake Hauroko. It is clear in the pictures of skins shown in the paper but was not analysed.

So the science may be good and the conclusions may be correct but they don't quite lay the ghosts of the past as there are key gaps in the analysis that won't let me move on although I very much want to. Some better scholarship with the taxonomy please, it gives the "science" more meaning.

Ian

[Neil Fitzgerald]

Always appreciate your critique of these things, Ian.
N

[fras444]

Very interesting article, I have been very fascinated with this "three forms" thing since I was young and the difference between them. On a subnote... The southern falcon is one that fascinates me the most!!! guess cause of it's rarity... Is there any research or interest in insuring that this form doesn't become extinct...? being the rarer of the three forms??? Ideas such as breeding programs with the aim of.. (being a exposed island bird) starting new populations of these birds on Islands such as the Campbells or the Snares etc... Some of these could be classed as reintroduction's...? Didn't the Campbells and the Chats have recently dated fossil evidence of NZ Falcons...?
How is the population of Southern Falcons...? Another one I'm interested in, that is their status on Stewart Island??? One would think a pristine environment for them to have read that report saying that, there were falcons obserbed in the past to, today where I have read somewhere that are now no concrete evidence that they are still present on the Island