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Fixed-plot monitoring as a tool to assess population trends of underground nesting seabirds: an example with Cory’s Shearwater at its world’s largest colony

Published online by Cambridge University Press:  20 January 2025

Paulo Catry Open the ORCID record for Paulo Catry [Opens in a new window] ,
Maria Dias ,
Dília Menezes ,
Paulo Oliveira ,
Daniel Lopes Open the ORCID record for Daniel Lopes [Opens in a new window] ,
Maria Alho ,
Letizia Campioni ,
Teresa Catry Open the ORCID record for Teresa Catry [Opens in a new window] ,
Marie Claire Gatt  and
Francesco Ventura
...Show all authors
Paulo Catry*
Affiliation:
Marine and Environmental Sciences Centre (MARE)/Aquatic Research Network (ARNET), Ispa - Instituto Universitário, 1149-041 Lisbon, Portugal
Maria Dias
Affiliation:
Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências da Universidade de Lisboa, 1749-016, Lisbon, Portugal
Dília Menezes
Affiliation:
Instituto das Florestas e Conservação da Natureza da Madeira, Governo Regional da Madeira, 9050-027 Funchal, Portugal
Paulo Oliveira
Affiliation:
Instituto das Florestas e Conservação da Natureza da Madeira, Governo Regional da Madeira, 9050-027 Funchal, Portugal
Daniel Lopes
Affiliation:
Marine and Environmental Sciences Centre (MARE)/Aquatic Research Network (ARNET), Ispa - Instituto Universitário, 1149-041 Lisbon, Portugal
Maria Alho
Affiliation:
Marine and Environmental Sciences Centre (MARE)/Aquatic Research Network (ARNET), Ispa - Instituto Universitário, 1149-041 Lisbon, Portugal
Letizia Campioni
Affiliation:
Marine and Environmental Sciences Centre (MARE)/Aquatic Research Network (ARNET), Ispa - Instituto Universitário, 1149-041 Lisbon, Portugal
Teresa Catry
Affiliation:
Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, 1749-016, Lisbon, Portugal
Marie Claire Gatt
Affiliation:
Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, 1749-016, Lisbon, Portugal
Francesco Ventura
Affiliation:
Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
Joana Romero
Affiliation:
Department of Coastal Systems, Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
José Pedro Granadeiro
Affiliation:
Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, 1749-016, Lisbon, Portugal
*
Corresponding author: Paulo Catry; Email: [email protected]
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Summary

Medium to small petrels that mostly nest in burrows or crevices represent a large fraction of the world’s seabirds, yet their population trends are largely unknown. This lack of knowledge, which has implications for conservation planning, results mostly from methodological difficulties and from the approaches that have been used for their monitoring. Here, we present the surveying scheme created to monitor Cory’s Shearwater Calonectris borealis breeding numbers at their largest known colony, Selvagem Grande (Portugal). We defined 60 circular plots at fixed locations on this 2.45 km2 island and counted nests with eggs annually at the end of laying. Results show that the population increased at 1.45% (95% confidence interval [CI]: 0.72–2.01%) per year between 2009 and 2023. We estimate that the current population size is 38,830 pairs (95% quantile CIs = 34,373–43,713). To the best of our knowledge, this study provides the first systematic information (using fully repeatable methods and providing CIs for the estimates) on population trends of Cory’s Shearwaters, one of the most abundant seabirds in the warm temperate and subtropical North Atlantic and one of the most studied petrels globally. Monitoring using the approach detailed here requires two days of work (by 2–3 persons) per year. Our results and simulations indicate that this is a powerful methodology, with narrow confidence limits for estimated trends and an ability to detect small population changes over short time spans. We suggest that more monitoring protocols similar to this one (with necessary site-specific adaptations, particularly for potential colony expansion where suitable habitat exists) should be developed and implemented in a range of colonies with crevice and burrowing nesting petrels to improve our knowledge on the population status of a broad fraction of the world’s seabirds.

Keywords

Burrow nestingCalonectris borealisSelvagens Islands
Type
Research Article
Information
Bird Conservation International , Volume 35 , 2025 , e3
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of BirdLife International

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