Spatial size dimorphism in New Zealand's last endemic raptor, the Kārearea Falco novaeseelandiae, coincides with a narrow sea strait

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.

Closing the gap: Avian lineage splits at a young, narrow seaway imply a protracted history of mixed population response

“…Passeriformes—Toutouwai, Petroica longipes and P . australis (Miller & Lambert, ); Casuariiformes—Kiwi, Apteryx mantelli and A. rowi (Shepherd et al., ); Gruiformes—Weka, Gallirallus australis (this study), Buff‐banded rail, Gallirallus philippensis (Garcia‐R et al., ); Anseriformes—Whio, Hymenolaimus malacorhynchos (Robertson, Steeves, et al., 2007); Ngiru‐ngiru/Miromiro— Petroica macrocephala (Miller & Lambert, ); Columbiformes—Kererū, Hemiphaga novaeseelandiae (Goldberg et al., ); Psittaciformes—Kaka, Nestor meridionalis (Dussex et al., ); Falconiformes—Kārearea, Falco novaeseelandiae (Trewick & Olley, ). Inset maps show approximate palaeogeography of central New Zealand during the last 4 million years including the last glacial maximum (20 thousand years), with present day coastline indicated (redrawn from Trewick & Bland, ).…”

“…Minimum‐spanning and median‐joining networks (Bandelt, Forster, & Röhl, ) were inferred for Weka haplotypes in PopArt (Leigh & Bryant, ) and colour‐edited in Adobe Illustrator. We downloaded published mtDNA Control Region sequence for seven other New Zealand bird taxa that span the Cook Strait (Dussex, Sainsbury, Moorhouse, Jamieson, & Robertson, ; Goldberg, Trewick, & Powlesland, ; Miller & Lambert, ; Robertson, Steeves, et al., ; Shepherd et al., ; Trewick & Olley, ) and inferred haplotype networks for each using minimum‐spanning and median‐joining networks.…”

“…Also, European bird species brought to mainland New Zealand by settlers have reached offshore islands in the region (>800 km away) by their own efforts (Heather & Robertson, ). Contrary to this evidence of numerous colonization and establishment, there are numerous endemic bird species and some have distinct races on different islands in the New Zealand region, including the two main islands separated by a sea strait (Buller, ; Trewick & Olley, ).…”

“…Gaps are conceptually linked with biogeographic boundaries or barriers where they are associated with biotic compositional differences, but may be coincidental not causal (Edwards, Crisp, Cook, & Cook, ). For example, phenotypic evidence for adaptive ecological partitioning across a seaway without correlated neutral genetic signal suggests the habitat gap acts as a region of low density, into which the frequency cline of ecological traits under selection has rapidly moved (Trewick & Olley, ). And, despite the absence of habitat gaps or species dispersal limitation, strong spatial genetic structure suggests animal behaviour can be influential in controlling gene flow (Morinha et al., ).…”

New Zealand falcon prey selection may not be driven by preference based on prey nutritional content

“…Falco novaeseelandiae, the New Zealand falcon or kārearea, is New Zealand's only remaining endemic bird of prey and consists of two subspecies (F. n. novaeseelandiae and F. n. ferox; Trewick & Olley 2016) both of which are classified as 'At Risk-Recovering' by the New Zealand Department of Conservation (Robertson et al 2017). The interaction between kārearea and potential prey is of considerable relevance to management of this species because of its potential effect on population increase.…”