ORIGINAL RESEARCH article
Front. Conserv. Sci.
Sec. Animal Conservation
Volume 6 - 2025 | doi: 10.3389/fcosc.2025.1564661
Fine-grained temporal population monitoring of a declining, critically endangered Hawaiian honeycreeper
Provisionally accepted
- 1Pacific Island Ecosystems Research Center, United States Geological Survey (USGS), Hawai‘i, United States
- 2Pacific Cooperative Studies Unit, University of Hawai‘i - Mānoa, Honolulu, Hawaii, United States
- 3Hawaiʻi Cooperative Studies Unit, University of Hawaii at Hilo, Hilo, California, United States
- 4Department of Land and Natural Resources-Division of Forestry and Wildlife, State of Hawaii, Hilo, California, United States
- 5American Bird Conservancy, Volcano, United States
- 6Department of Land and Natural Resources-Division of Forestry and Wildlife, State of Hawaii, Honolulu, Hawaii, United States
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Annual point counts are commonly used to monitor birds to track population densities across space and time. Palila (Loxioides bailleui) are surveyed annually in the first quarter, but we recently instituted quarterly sampling that offers a unique opportunity to improve estimator precision. We conducted point-transect distance sampling point counts during the first quarter of 2020 through 2024, and the second through fourth quarters in 2022 and 2023, and the second quarter in 2024. The reduced sampling intensity during the quarterly counts, however, requires model-based methods to estimate abundance to the entire sampling frame. We modeled spatial and temporal correlation using a soap film smoother within a generalized additive modeling framework, a density surface model, fitted to palila counts each quarter for the five-year timeseries to track changes in population abundances. Our results indicate that palila maintained a high-density hotspot throughout the fiveyear timeseries; however, the extent of the hotspot declined substantially over the timeseries while densities within the hotspot declined from about 3 birds/ha in 2020 to about 1 bird/ha in 2024, which resulted in a 66% decline in palila abundances over 5 years. Density surface model estimates give on average a confidence interval width that was 74.7% shorter than the associated distance sampling confidence interval widths. Our results indicate that palila may benefit most if management actions were applied within the remaining hotspot. Additionally, this temporally fine-grained sampling provides information on seasonal movement patterns and resource tracking, and population response to management and conservation actions. Our spatially explicit, model-based approach is applicable to a wide range of monitoring programs, particularly those with inconsistent, opportunistic spatial coverage.
Keywords: abundance, Density surface modeling, distribution, Generalized additive model, Hawai'i, Loxioides bailleui, Palila, Spatio-temporal model
Received: 21 Jan 2025; Accepted: 07 May 2025.
Copyright: © 2025 Camp, Asing, Hunt, Wang, Farmer, Neitmann and Banko. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Richard Camp, Pacific Island Ecosystems Research Center, United States Geological Survey (USGS), Hawai‘i, United States
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