Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

John D Goss-Custard, Andrew D West, Michael G Yates, Richard WG Caldow, Richard A Stillman, Louise Bardsley, Juan Castilla, Macarena Castro, Volker Dierschke, Sarah EA Le V Dit durell, Goetz Eichorn, Bruno J Ens, Klaus-Michael Exo, PU Udayangani-Fernando, Peter N Ferns, Philip AR Hockey, Jennifer A Gill, Ian Johnstone, Bozena Kalejta-Summers, Jose A MaseroFranciso Moreira, Rajarathina Velu Nagarajan, Ian PF Owens, Cristian Pacheco, Alejandro Perez-Hurtado, Daniel Rogers, Gregor Scheiffarth, Humphrey Sitter, William J Sutherland, Patrick Triplet, Dave H Worrall, Yuri Zharikov, Leo Zwarts, Richard A Pettifor

Research output: Contribution to journalArticle

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Abstract

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching. A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m'2). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote. A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81% of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3%), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostraleguseating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93% of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.
Original languageEnglish
Pages (from-to)501-529
Number of pages29
JournalBiological Reviews
Volume81
Issue number4
Publication statusPublished - 2006

Fingerprint

Charadriiformes
Birds
Invertebrates
Macros
Eating
invertebrates
ingestion
Raptors
Bivalvia
Breeding
Ashes
birds
Multivariate Analysis
Mytilus edulis
Grooming
multivariate analysis
Ecology
mussels
foraging
preening

Cite this

Goss-Custard, J. D., West, A. D., Yates, M. G., Caldow, R. WG., Stillman, R. A., Bardsley, L., ... Pettifor, R. A. (2006). Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates. Biological Reviews, 81(4), 501-529.
Goss-Custard, John D ; West, Andrew D ; Yates, Michael G ; Caldow, Richard WG ; Stillman, Richard A ; Bardsley, Louise ; Castilla, Juan ; Castro, Macarena ; Dierschke, Volker ; Dit durell, Sarah EA Le V ; Eichorn, Goetz ; Ens, Bruno J ; Exo, Klaus-Michael ; Udayangani-Fernando, PU ; Ferns, Peter N ; Hockey, Philip AR ; Gill, Jennifer A ; Johnstone, Ian ; Kalejta-Summers, Bozena ; Masero, Jose A ; Moreira, Franciso ; Nagarajan, Rajarathina Velu ; Owens, Ian PF ; Pacheco, Cristian ; Perez-Hurtado, Alejandro ; Rogers, Daniel ; Scheiffarth, Gregor ; Sitter, Humphrey ; Sutherland, William J ; Triplet, Patrick ; Worrall, Dave H ; Zharikov, Yuri ; Zwarts, Leo ; Pettifor, Richard A. / Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates. In: Biological Reviews. 2006 ; Vol. 81, No. 4. pp. 501-529.
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abstract = "As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching. A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m'2). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote. A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81{\%} of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3{\%}), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostraleguseating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6{\%}, but this discrepancy was reduced to 0.2{\%} when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93{\%} of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.",
author = "Goss-Custard, {John D} and West, {Andrew D} and Yates, {Michael G} and Caldow, {Richard WG} and Stillman, {Richard A} and Louise Bardsley and Juan Castilla and Macarena Castro and Volker Dierschke and {Dit durell}, {Sarah EA Le V} and Goetz Eichorn and Ens, {Bruno J} and Klaus-Michael Exo and PU Udayangani-Fernando and Ferns, {Peter N} and Hockey, {Philip AR} and Gill, {Jennifer A} and Ian Johnstone and Bozena Kalejta-Summers and Masero, {Jose A} and Franciso Moreira and Nagarajan, {Rajarathina Velu} and Owens, {Ian PF} and Cristian Pacheco and Alejandro Perez-Hurtado and Daniel Rogers and Gregor Scheiffarth and Humphrey Sitter and Sutherland, {William J} and Patrick Triplet and Worrall, {Dave H} and Yuri Zharikov and Leo Zwarts and Pettifor, {Richard A}",
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Goss-Custard, JD, West, AD, Yates, MG, Caldow, RWG, Stillman, RA, Bardsley, L, Castilla, J, Castro, M, Dierschke, V, Dit durell, SEALV, Eichorn, G, Ens, BJ, Exo, K-M, Udayangani-Fernando, PU, Ferns, PN, Hockey, PAR, Gill, JA, Johnstone, I, Kalejta-Summers, B, Masero, JA, Moreira, F, Nagarajan, RV, Owens, IPF, Pacheco, C, Perez-Hurtado, A, Rogers, D, Scheiffarth, G, Sitter, H, Sutherland, WJ, Triplet, P, Worrall, DH, Zharikov, Y, Zwarts, L & Pettifor, RA 2006, 'Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates', Biological Reviews, vol. 81, no. 4, pp. 501-529.

Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates. / Goss-Custard, John D; West, Andrew D; Yates, Michael G; Caldow, Richard WG; Stillman, Richard A; Bardsley, Louise; Castilla, Juan; Castro, Macarena; Dierschke, Volker; Dit durell, Sarah EA Le V; Eichorn, Goetz; Ens, Bruno J; Exo, Klaus-Michael; Udayangani-Fernando, PU; Ferns, Peter N; Hockey, Philip AR; Gill, Jennifer A; Johnstone, Ian; Kalejta-Summers, Bozena; Masero, Jose A; Moreira, Franciso; Nagarajan, Rajarathina Velu; Owens, Ian PF; Pacheco, Cristian; Perez-Hurtado, Alejandro; Rogers, Daniel; Scheiffarth, Gregor; Sitter, Humphrey; Sutherland, William J; Triplet, Patrick; Worrall, Dave H; Zharikov, Yuri; Zwarts, Leo; Pettifor, Richard A.

In: Biological Reviews, Vol. 81, No. 4, 2006, p. 501-529.

Research output: Contribution to journalArticle

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T1 - Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

AU - Goss-Custard, John D

AU - West, Andrew D

AU - Yates, Michael G

AU - Caldow, Richard WG

AU - Stillman, Richard A

AU - Bardsley, Louise

AU - Castilla, Juan

AU - Castro, Macarena

AU - Dierschke, Volker

AU - Dit durell, Sarah EA Le V

AU - Eichorn, Goetz

AU - Ens, Bruno J

AU - Exo, Klaus-Michael

AU - Udayangani-Fernando, PU

AU - Ferns, Peter N

AU - Hockey, Philip AR

AU - Gill, Jennifer A

AU - Johnstone, Ian

AU - Kalejta-Summers, Bozena

AU - Masero, Jose A

AU - Moreira, Franciso

AU - Nagarajan, Rajarathina Velu

AU - Owens, Ian PF

AU - Pacheco, Cristian

AU - Perez-Hurtado, Alejandro

AU - Rogers, Daniel

AU - Scheiffarth, Gregor

AU - Sitter, Humphrey

AU - Sutherland, William J

AU - Triplet, Patrick

AU - Worrall, Dave H

AU - Zharikov, Yuri

AU - Zwarts, Leo

AU - Pettifor, Richard A

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PY - 2006

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AB - As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching. A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (<150/m'2). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote. A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81% of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3%), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostraleguseating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93% of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.

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Goss-Custard JD, West AD, Yates MG, Caldow RWG, Stillman RA, Bardsley L et al. Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates. Biological Reviews. 2006;81(4):501-529.