Bill Trait Variation in Kākāpō, Strigops Habroptilus (Gray): Differences Between Contemporary and Historical Birds

1 Notornis, 2017, Vol. 64: 1-12 0029-4470 © The Ornithological Society of New Zealand Inc. Bill trait variation in kākāpō, Strigops habroptilus (Gray): differences between contemporary and historical birds LINDSEY J. GRAY School of Life and Environmental Sciences, Charles Perkins Centre, and Macleay Museum, Macleay Building (A12), Science Road, University of Sydney, New South Wales, Australia, 2006 ANDREW DIGBY DARYL K. EASON Kākāpō / Takahē Recovery Programme, Department of Conservation, P.O. Box 734, Invercargill 9840, New Zealand Abstract Museum study-skins are an important though under-utilised resource for studying the biology of endangered birds. This study compares the bill and cere morphology of female and male kākāpō (Strigops habroptilus) from three provenances: 1) “historical wild-origin” museum specimens collected from the North and South islands of New Zealand over 100 years ago; 2) the “modern wild-origin”, predominantly ex-Stewart Island Kākāpō Recovery Programme (KRP) founder population; and 3) the “modern non-wild” descendants of the founder population raised and maintained under the conservation management of the KRP. Bill length and gape was found to be smaller in the historical wild-origin birds than in the two contemporary groups. In comparison, historical wild-origin male kākāpō had larger ceres than both contemporary groups. As bird bills can show rapid morphological adjustment to diet over generational time scales, we evaluate whether bill size differences measured could be due to differences in the nutritional environments experienced by the birds either across their life-times or over recent evolutionary time. We also discuss whether regional variation in sexual selection might account for the provenance related variation in cere size. Gray, L.J.; Digby, A.; Eason, D.K. 2017. Bill trait variation in kākāpō, Strigops habroptilus (Gray): differences between contemporary and historical birds. Notornis 64 (1): 1-12. Keywords kākāpo; Strigops habroptilus; museum study-skins; endangered species; nutrition; adaptation; parrots INTRODUCTION to species rarity (Lane 1996; Gill 2006), or requisite Natural history museums in Australia and New access restrictions on remnant populations. Data Zealand hold more than half a million bird obtained from museum specimens collected from specimens, the majority of which are study-skins dispersed times and places can also be incorporated (Gill 2006). For many endangered species, more into comparative analyses with contemporary data, individuals exist as study-skins than living birds. allowing for the dynamics of endangered species These skins are therefore a valuable resource for biogeography, ecology and evolution to be described studying aspects of the endangered species biology, and understood (Smith et al. 1995; Lane 1996; for example plumage or morphology, that may be Stockwell et al. 2003; Hendry et al. 2007; Rolshausen otherwise challenging to conduct research on due et al. 2009). Despite the potential benefits of working with skins, owing to some common challenges such Received 14 June 2016; accepted 17 October 2016 as specimen provenance accuracy (Gray & Renner Correspondence: [email protected] 2016), unspecified specimen sex (Lee & Griffiths 2 Gray et al. 2003) and the meaningfulness of comparing data and reproductive state. Comparing the KRP data from long-dead museum specimens to those from against those from museum study-skins from living or fresh specimens (Winker 1993), study- different geographical and temporal populations skins are typically under-utilised by ornithologists can therefore facilitate hypothesis-driven research (Smith et al. 1995; Russell et al. 2013). on kākāpō evolutionary ecology. Attempting to overcome these challenges is Characters associated with the bill present as worthwhile when studying skins might yield amenable for study when choosing what to compare biological insights relevant to endangered species between living kākāpō and museum specimen management, or when the rare species has birds. Parrots are adapted to varied food, including exceptional ecological and evolutionary novelty. tough vegetation, hard nuts and seeds. To facilitate The kākāpō (Strigops habroptilus) is a good candidate this their rhamphotheca is comprised of hardened, species for which careful examination of museum dense keratin (Stettenheim 2000) that fits snugly over study-skins could generate interesting results. the underlying maxilla bone (Summers 1976). The Kākāpō are unique among the Psittaciformes, post-mortem shrinkage experienced by museum being very large, flightless and nocturnal, and the specimens in bird species with softer “fleshier” bills only known lek breeding parrots (Henry 1903; (Summers 1976; Winker 1993) should therefore be Merton et al. 1984). Concordant with their lek-based reduced in parrots. Bill morphological traits are mating-system, kākāpō do not form monogamous also highly labile in response to habitat-dictated pairs as most parrots do, and males and females dietary changes, and display strong directional have very distinct life-histories (Merton et al. 1984; selection in birds (Herrera 1977; Caroll & Dingle Livezey 1992; Eason et al. 2006), the morphological 1996; Grant & Grant 2002; Herrel et al. 2010). Rapid and ecological correlates of which have not been inter-generational morphological adjustments extensively researched. Additional to their highly in response to local food environment change is derived behaviour, and further evidence of their particularly pronounced for bird species that have evolutionary novelty, kākāpō are one of only three life histories characterised by low dispersal and extant species of Strigopoidea, the most basal therefore low inter-population gene-flow (Baker et superfamily of Psittaciformes (Chambers & Worthy al. 1990; Bardwell et al. 2001; Hendry et al. 2007), as 2013). Kākāpō are endemic to New Zealand and in the flightless kākāpō. Rapid bill morphological classified as critically endangered by the IUCN change is also observed in species under quasi- (IUCN 2016) and Nationally Critical under the New natural selection settings, for example in response Zealand Threat Classification System (Robertson et to dietary shifts under domestication (Champagnon al. 2013). There are only 154 known birds alive, all of et al. 2010) and captive rearing (Clabaut et al. 2009). which are maintained under intensive conservation This phenomenom, whereby trait divergence management (Whitehead et al. 2012). Hundreds occurs over relatively short, ecological timeframes of kākāpō study-skins exist in museums world- is called contemporary or rapid evolution (Hendry wide however, and beginning to study these could et al. 2000; Hendry 2001; Stockwell et al. 2003; contribute to our understanding of this highly Rolshausen et al. 2009). For bird bills, this process unique parrot’s basic biology. is facilitated by the genes and genetic pathways Kākāpō became endangered due to predation which underpin bill shape being highly flexible in by introduced mammals introduced to New their expression, and by multiple distinct pathways Zealand (Henry 1903; Best & Powlesland 1985; being able to affect morphological change during Murphy & Dowding 1994; Clout & Craig 1995; bill development (Mallarino et al. 2012). Clout & Merton 1998). To save kākāpō from Given the responsiveness of bill morphology to extinction, in the late 20th Century the Kākāpō different physical and temporal food environments Recovery Programme Programme (KRP) removed experienced by individuals within bird species, all kākāpō from their remaining wild habitats kākāpō museum study-skins and KRP data were and established a breeding program on predator- used to test whether there were differences in the free off-shore islands, with the largest population bill traits among males and females from three established on Whenua Hou (Codfish Island) in environmentally-distinct groups: 1) historical a semi-captive situation (Whitehead et al. 2012). wild-origin birds likely to have been sourced from Ninety-eight percent of the breeding population’s either of New Zealand’s main islands (hereafter founders were birds removed from the last known the “mainland”); 2) the modern wild-origin KRP natural wild population, discovered in 1977 on founder population, 98% of which were sourced Stewart Island (Powlesland et al. 1992; Powlesland from Stewart Island where kākāpō may have et al. 1995). Today, the remaining founders and persisted naturally for 10,000 years (Cullen 1967; their descendants are all intensively managed Bull & Whitaker 1975; Powlesland et al. 1995); by the KRP who collect extensive data from each and 3) these founder’s descendants – the modern bird, including standard measures of morphology non-wild kākāpō raised by KRP under semi- Bill trait variation in kākāpō 3 captivity, predominantly on Whenua Hou. Habitat Table 1. Collection locations and collectors of Australian resources on Whenua Hou have not always allowed Museum kākāpō study skins used in this study (courtesy for kākāpō hens to raise their chicks without of the Australian Museum). nutritional intervention by KRP (Whitehead et al. 2012). These interventions have included the Specimen Collection location and Collector supplementary feeding of “muesli” (Powlesland & number date Lloyd 1994; Clout & Merton 1998; Elliot et al. 2001) 0.30429 Nelson, South Island, Unknown and proprietary pellets to kākāpō mothers who 1912 then pass these non-wild foods to their chicks, and 0.2299 Unknown, May 1888 W. Newman

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