Contrasting interference functions and foraging dispersion in two species of shorebird (Charadrii)

Yates, M. G.; Stillman, Richard A.; Goss‐Custard, J. D.

doi:10.1046/j.1365-2656.2000.00394.x

Cited by 52 publications

(50 citation statements)

References 20 publications

(59 reference statements)

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“…The reduced intake rate in shorebirds eating prey that could retreat into a burrow may imply that this antipredator behaviour is effective in reducing intake rate in shorebirds, and also introduces the possibility that interference through prey depression may have occurred in our sample (Yates, Stillman & Goss-Custard, 2000). Interference from intra-specific and inter-specific kleptoparasitism may also have occurred.…”

Section: Discussion (1 ) Phylogenetic Effectsmentioning

confidence: 95%

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

Goss‐Custard¹,

West²,

Yates³

et al. 2006

Biol. Rev.

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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 x2 ). 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 ostralegus eating 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 shore...

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Section: Discussion (1 ) Phylogenetic Effectsmentioning

confidence: 95%

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

Goss‐Custard¹,

West²,

Yates³

et al. 2006

Biol. Rev.

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“…Values given in bold are statistically significant inactive may remain closer to the surface and more active during low tide. The intake rate of redshank foraging on Corophium volutator is reduced when the latter retreat down their burrows (Selman & Goss-Custard 1988, Yates et al 2000. Thus, although the absolute abundance of e.g.…”

Section: Hypothesismentioning

confidence: 99%

Effects of intertidal mussel cultivation on bird assemblages

Caldow¹,

Beadman²,

McGrorty³

et al. 2003

Mar. Ecol. Prog. Ser.

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Mussel Mytilus edulis cultivation on intertidal flats affects the invertebrate community, often adversely, and this may have detrimental consequences for shorebirds. Here we present the results of an experimental study to quantify the effects of intertidal mussel cultivation on shorebirds. A study area of 4.32 ha, comprising experimental plots and control plots, was laid out in summer 1999 on the mudflats of the Menai Strait in Wales. Regular counts throughout winter of 1999/2000 established pre-cultivation patterns of bird usage. Mussels were laid in the experimental plots in April 2000 and bird usage in these plots and the controls was monitored over the 2 subsequent winters. Although no species were lost from the experimental plots, the bird assemblage in them changed. This reflected variation in the distribution of the 5 most abundant species. However, none of these key species declined in abundance following the laying of mussels. Curlew Numenius arquata and redshank Tringa totanus increased in abundance, although, unexpectedly, oystercatchers Haematopus ostralegus did not. At this study site, commercial mussel cultivation may have beneficial effects, not just for the birds that eat mussels, but also for other species that can take advantage of the associated changes to the benthic fauna and habitat complexity. However, features of conservation interest at other localities may mean that bottom cultivation of mussels will have detrimental rather than beneficial effects. The environmental effects of proposals to initiate or expand bottom cultivation of mussels need to be assessed on a case-by-case basis.

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“…Bird species differ in their body and fat store sizes, daily energy requirements, the size ranges of each food consumed, their intake rates from different foods and their susceptibility to intraspecific interference through food-fighting or prey depression (e.g. Yates et al 2000). Individuals within a species differ in their foraging efficiency and dominance, which influences susceptibility to interference.…”

Section: Methodsmentioning

confidence: 99%

“…The influence of conspecific competitors on a bird's intake rate was incorporated using the following interference function : (3) where IR = intake rate (mg s -1 for all systems in which interference was assumed to occur, as this is the approximate threshold in a number of systems in which interference occurs through either kleptoparasitism , Triplet et al 1999 or a reduction in prey availability due to prey-avoidance behaviour (prey depression; e.g. Yates et al 2000). The aggregation factor accounts for the fact that birds will usually be aggregated in a patch, rather than spread uniformly.…”

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confidence: 99%

“…(which are mobile and can often escape rapidly into the sediment as birds approach) was assumed to occur through prey depression. Interference in these systems was assumed to be independent of dominance (m max = 0.48, m min = 0.48) with the same strength as that observed between Corophium spp.-feeding common redshanks (Yates et al 2000), the only system in which the strength of interference through prey depression has been measured. For Cerastoderma edule and Macoma balthica, interference was assumed to occur through prey-stealing and hence to depend on dominance, being absent for the most dominant birds (m max = 0) and strongest for the least dominant.…”

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confidence: 99%

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Predicting site quality for shorebird communities: a case study on the Humber estuary, UK

Stillman¹,

West²,

Goss‐Custard³

et al. 2005

Mar. Ecol. Prog. Ser.

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The conservation importance of estuaries is often measured by bird numbers, but monitoring numbers is not necessarily a reliable way of assessing changes in site quality. We used an individual-based model, comprised of fitness-maximising individuals, to assess the quality of the Humber estuary, UK, for 9 shorebirds; dunlin Calidris alpina, common ringed plover Charadrius hiaticula, red knot Calidris canutus, common redshank Tringa totanus, grey plover Pluvialis squatarola, blacktailed godwit Limosa limosa, bar-tailed godwit L. lapponica, Eurasian oystercatcher Haematopus ostralegus and Eurasian curlew Numenius arquata. We measured site quality as predicted overwinter survival. The model accurately predicted the observed shorebird distribution (if non-starving birds were assumed to feed on any prey or patch on which intake rate equalled or exceeded their requirements), and the diets of most species. Predicted survival rates were highest in dunlin and common ringed plovers, the smallest species, and in Eurasian oystercatchers, which consumed larger prey than the other species. Shorebird survival was most strongly influenced by the biomass densities of annelid worms, and the bivalve molluscs Cerastoderma edule and Macoma balthica. A 2 to 8% reduction in intertidal area (the magnitude expected through sea level rise and industrial developments) decreased predicted survival rates of all species except the dunlin, common ringed plover, red knot and Eurasian oystercatcher. This paper shows how an individual-based model can assess present-day site quality and predict how site quality may change in the future. The model was developed using existing data from intertidal invertebrate and bird monitoring schemes plus new intertidal invertebrate data collected over 2 winters. We believe that individual-based models are useful tools for assessing estuarine site quality. KEY WORDS: Climate change · Estuary management · Behaviour-based model · Site quality · WadersResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 305: 203-217, 2005 site depend not only on the conditions at the site, but also the conditions at other sites both within the nonbreeding and breeding seasons (e.g. Goss-Custard 1993, Goss-Custard et al. 1995b, Gill et al. 1997. A reduction in numbers at a site might be due to a decrease in the site's quality, but might also be due to an increase in the quality of other sites. A decrease in reproductive rate or an increase in overall mortality rate will reduce the overall population size, which could reduce the number of birds using the site even though its quality had not changed. Another drawback of assessments using bird numbers is that they are not predictive and so it is often too late to take remedial action by the time the change has been detected.Because bird numbers are not a reliable way of assessing the quality of a site, another method is required. In migratory shorebirds (Charadrii), population size is a function of the interaction between (1) the...

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Contrasting interference functions and foraging dispersion in two species of shorebird (Charadrii)

Cited by 52 publications

References 20 publications

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

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

Effects of intertidal mussel cultivation on bird assemblages

Predicting site quality for shorebird communities: a case study on the Humber estuary, UK

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