DOI: 10.5061/dryad.j3tx95xh7
title: Interpreting past trophic ecology of a threatened species, kea (Nestor notabilis), from museum specimens

description: When ecosystems are under severe pressure or environments change, trophic
 position and intraspecific niche width may decrease or narrow, signalling
 that conservation action is required. In New Zealand, alpine and
 sub-alpine ecosystems have been extensively modified through farming since
 19th century European settlement, with consequences for indigenous species
 such as the kea (Nestor notabilis). We investigated feather stable isotope
 values in the kea and predicted a lower trophic position in modern kea
 populations, to reflect reduced lowland habitat and a mixed diet with more
 plant material. We predicted that size and sex would influence trophic
 values in this sexually dimorphic species, with larger birds more likely
 to have a high protein diet. We examined potential dietary changes in 68
 museum collected kea from 1880s to 2000s, first recording accession
 details including provenance and sex, and measuring culmen length. We used
 bulk carbon and nitrogen stable isotopes analyses (BSIA) of feathers and a
 further feather subset using compound-specific stable isotopes analyses of
 amino acids (CSIA-AA) to obtain isotopic values and estimate trophic
 position. BSIA showed δ15N values in kea feathers declined through time,
 and could indicate that early century kea were highly omnivorous, with
 δ15N values on average higher than in modern kea. Variance in δ15N values
 was greater after 1950, driven by a few individuals. Few differences
 between males and females were evident, although females in the south
 region had lower δ15N values. There was a tendency for large male birds to
 have higher trophic values, perhaps reflecting dominant male bird
 behaviour noted in historical records. Nonetheless, CSIA-AA performed on a
 subset of the data suggested that variation in BSIA is likely due to
 baseline changes rather than relative trophic position which may be more
 homogenous than these data indicate. Although there was more variability
 in modern kea, we suggest caution in interpretation. Stable isotope data,
 particularly CSIA-AA, from museum specimens can reveal potential change in
 ecological networks, as well as sexually dimorphic feeding patterns within
 species. The data can reveal temporal and regional variation in species
 trophic position and changes in ecosystem integrity to inform conservation
 decision-making.
description: We examined kea specimens and skins from 5 natural history
 collections, at Auckland Museum, New Zealand; Te Papa National Museum, NZ;
 Canterbury Museum, NZ; and Otago Museum, NZ; and Naturhistorisches Museum
 Wien (the Vienna Natural History Museum), Austria. We recorded all
 accession details for kea where these were available, including collection
 location, year of collection, and sex if previously determined. Stable
 isotope analysis was conducted from feathers removed from the upper middle
 back between the shoulder blades on each bird skin, and were washed in 2:1
 chloroform:methanol solution for 24 h, agitated, rinsed and air dried in a
 fume cupboard for 48 h, before the top 1cm of the feather vane was finely
 clipped and weighed into tin capsules for bulk nitrogen and carbon isotope
 analysis. Further methods are reported in the paper.
description: Missing values do occur in this dataset; not all information
 required was available for all individuals. See the attached ReadMe
 file.