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A modelling framework for integrating reproduction, survival and count data when projecting the fates of threatened populations

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Abstract

A key goal of ecological research is to obtain reliable estimates of population demographic rates, abundance and trends. However, a common challenge when studying wildlife populations is imperfect detection or breeding observation, which results in unknown survival status and reproductive output for some individuals. It is important to account for undetected individuals in population models because they contribute to population abundance and dynamics, and can have implications for population management. Promisingly, recent methodological advances provide us with the tools to integrate data from multiple independent sources to gain insights into the unobserved component of populations. We use data from five reintroduced populations of a threatened New Zealand bird, the hihi (Notiomystis cincta), to develop an integrated population modelling framework that allows missing values for survival status, sex and reproductive output to be modelled. Our approach combines parallel matrices of encounter and reproduction histories from marked individuals, as well as counts of unmarked recruits detected at the start of each breeding season. Integrating these multiple data types enabled us to simultaneously model survival and reproduction of detected individuals, undetected individuals and unknown (never detected) individuals to derive parameter estimates and projections based on all available data, thereby improving our understanding of population dynamics and enabling full propagation of uncertainty. The methods presented will be especially useful for management programmes for populations that are intensively monitored but where individuals are still imperfectly detected, as will be the case for most threatened wild populations.

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Acknowledgements

This study has only been possible through the participation of a large number of students and volunteers, and through the ongoing support of the New Zealand Department of Conservation, Supporters of Tiritiri Matangi Inc., Zealandia, Maungatautari Ecological Island Trust, Bushy Park Trust, Rotokare Scenic Reserve Trust and the Hihi Recovery Group. We wish to acknowledge the major field contributions from N. Anderson, E. Bemelmans, C. Devine, B. Ebert, P. Frost, R. Gribble, F. Gordon, T. Henry, S. Hunua-Soeder, S. Jack, M. Low, T. Makan, F. Moore, J. Panfylova, K. Richardson, J. Taylor, R. Thorogood, L. Walker and L. Wilson, as well as the extensive pedigree work carried out by P. Brekke for the Tiritiri Matangi population. We also thank two anonymous reviewers for their constructive comments on the manuscript and the many organisations (listed below) that have provided funding for this study.

Funding

This work was funded by the Royal Society of New Zealand (Marsden grant no. 17-MAU-09), the New Zealand Department of Conservation, the New Zealand Lotteries Board, the Zoological Society of London, the Natural Environment Research Council UK, the Royal Society UK, the Research Council UK, the Association for the Study of Animal Behaviour UK, the Leverhulme Trust, the Supporters of Tiritiri Matangi Inc., Zealandia, Maungatautari Ecological Island Trust, Bushy Park Trust, Rotokare Scenic Reserve Trust and Massey University.

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Contributions

DPA conceived the idea and led development of the integrated modelling framework. EHP, JGE and KAP contributed to conceptual development of the study. JGE oversaw data collection. MM carried out fieldwork. EHP, MM and DPA cleaned and formatted the data for analysis. EHP and DPA analysed the data. EHP led the writing of the manuscript. DPA contributed to writing the manuscript. All authors provided input on the drafts.

Corresponding author

Correspondence to Elizabeth H. Parlato.

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Conflict of interest

E.P., M.M., K.P. and D.A. have received research funding from the Royal Society of New Zealand. M.M. has also received funding from Maungatautari Ecological Island Trust, Bushy Park Trust, Rotokare Scenic Reserve Trust and the New Zealand Department of Conservation. J.E has received research funding from the New Zealand Department of Conservation.

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All applicable institutional and/or national guidelines for the care and use of animals were followed.

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Communicated by Ola Olsson.

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Parlato, E.H., Ewen, J.G., McCready, M. et al. A modelling framework for integrating reproduction, survival and count data when projecting the fates of threatened populations. Oecologia 195, 627–640 (2021). https://doi.org/10.1007/s00442-021-04871-5

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  • DOI: https://doi.org/10.1007/s00442-021-04871-5

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