Bias in estimated breeding-bird abundance from closure-assumption violations

The closure assumption of many abundance models, that individual animals are present throughout the survey season, often is inconsistent with field data. The effects of closure-assumption violations on estimators of abundance and associations between abundance and covariates are not fully understood...

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Autores principales:	Frank A. Fogarty, Erica Fleishman
Formato:	article
Lenguaje:	EN
Publicado:	Elsevier 2021
Materias:	Emigration Great Basin Immigration Movement N-mixture model Point count Ecology QH540-549.5
Acceso en línea:	https://doaj.org/article/7f7f4afb508b4ac0a4135a9009fbb27c
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spelling	oai:doaj.org-article:7f7f4afb508b4ac0a4135a9009fbb27c2021-12-01T04:59:57ZBias in estimated breeding-bird abundance from closure-assumption violations1470-160X10.1016/j.ecolind.2021.108170https://doaj.org/article/7f7f4afb508b4ac0a4135a9009fbb27c2021-11-01T00:00:00Zhttp://www.sciencedirect.com/science/article/pii/S1470160X21008359https://doaj.org/toc/1470-160XThe closure assumption of many abundance models, that individual animals are present throughout the survey season, often is inconsistent with field data. The effects of closure-assumption violations on estimators of abundance and associations between abundance and covariates are not fully understood. Furthermore, one’s definition of abundance affects these estimates. We used simulated data on breeding birds to explore how permanent, non-random immigration and emigration that violate the closure assumption affect estimates from N-mixture abundance models and naïve models (models that do not account for imperfect detection). This is the first work to evaluate the effect of permanent immigration and emigration on estimates from N-mixture models, and to compare these effects among definitions of abundance (initial, season-long, and superpopulation). We also collected and analyzed point-count data on breeding bird species in the Great Basin (USA) to evaluate the frequency of within-season movement. When detection probability was high (ρ ≥ 0.65), estimators of superpopulation abundance from N-mixture and naïve models were relatively unbiased. By comparison, in many cases, even relatively small violations of the closure assumption biased estimates of initial and season-long abundance by > 20%. Naïve abundance models generally were less biased than N-mixture models when ρ ≥ 0.65, but highly biased when ρ ≤ 0.4. In both model types, estimators of the association between abundance and an environmental covariate were minimally biased. The magnitudes of assumption violations tested in our simulations were consistent with those in our field data. Movement of individuals (availability) strongly affected detection probability of nearly all species and, in 7 of 34 species-region combinations, was temporally heterogeneous, suggesting that closure-assumption violations are common in our study system. Our results highlight that permanent movement of individuals within a season may be a substantial source of bias in studies of breeding birds that are based on count data, and that the definition of abundance affects the magnitude of these biases.Frank A. FogartyErica FleishmanElsevierarticleEmigrationGreat BasinImmigrationMovementN-mixture modelPoint countEcologyQH540-549.5ENEcological Indicators, Vol 131, Iss , Pp 108170- (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Emigration Great Basin Immigration Movement N-mixture model Point count Ecology QH540-549.5
spellingShingle	Emigration Great Basin Immigration Movement N-mixture model Point count Ecology QH540-549.5 Frank A. Fogarty Erica Fleishman Bias in estimated breeding-bird abundance from closure-assumption violations
description	The closure assumption of many abundance models, that individual animals are present throughout the survey season, often is inconsistent with field data. The effects of closure-assumption violations on estimators of abundance and associations between abundance and covariates are not fully understood. Furthermore, one’s definition of abundance affects these estimates. We used simulated data on breeding birds to explore how permanent, non-random immigration and emigration that violate the closure assumption affect estimates from N-mixture abundance models and naïve models (models that do not account for imperfect detection). This is the first work to evaluate the effect of permanent immigration and emigration on estimates from N-mixture models, and to compare these effects among definitions of abundance (initial, season-long, and superpopulation). We also collected and analyzed point-count data on breeding bird species in the Great Basin (USA) to evaluate the frequency of within-season movement. When detection probability was high (ρ ≥ 0.65), estimators of superpopulation abundance from N-mixture and naïve models were relatively unbiased. By comparison, in many cases, even relatively small violations of the closure assumption biased estimates of initial and season-long abundance by > 20%. Naïve abundance models generally were less biased than N-mixture models when ρ ≥ 0.65, but highly biased when ρ ≤ 0.4. In both model types, estimators of the association between abundance and an environmental covariate were minimally biased. The magnitudes of assumption violations tested in our simulations were consistent with those in our field data. Movement of individuals (availability) strongly affected detection probability of nearly all species and, in 7 of 34 species-region combinations, was temporally heterogeneous, suggesting that closure-assumption violations are common in our study system. Our results highlight that permanent movement of individuals within a season may be a substantial source of bias in studies of breeding birds that are based on count data, and that the definition of abundance affects the magnitude of these biases.
format	article
author	Frank A. Fogarty Erica Fleishman
author_facet	Frank A. Fogarty Erica Fleishman
author_sort	Frank A. Fogarty
title	Bias in estimated breeding-bird abundance from closure-assumption violations
title_short	Bias in estimated breeding-bird abundance from closure-assumption violations
title_full	Bias in estimated breeding-bird abundance from closure-assumption violations
title_fullStr	Bias in estimated breeding-bird abundance from closure-assumption violations
title_full_unstemmed	Bias in estimated breeding-bird abundance from closure-assumption violations
title_sort	bias in estimated breeding-bird abundance from closure-assumption violations
publisher	Elsevier
publishDate	2021
url	https://doaj.org/article/7f7f4afb508b4ac0a4135a9009fbb27c
work_keys_str_mv	AT frankafogarty biasinestimatedbreedingbirdabundancefromclosureassumptionviolations AT ericafleishman biasinestimatedbreedingbirdabundancefromclosureassumptionviolations
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Bias in estimated breeding-bird abundance from closure-assumption violations

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