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Assessing waterbird conservation objectives: An example for the Burry Inlet, UK
Abstract
We use an individual-based model to assess the conservation objectives for knot Calidris canutus L. and oystercatcher Haematopus ostralegus L. on the Burry Inlet Special Protection Area (SPA), UK. Population monitoring has identified a decline in oystercatcher numbers, but cannot determine whether this is due to a decline in site quality. Long term data on cockle stocks show that the biomass of the large-sized cockles consumed by oystercatcher declined after 2004, whereas a similar decline was not observed in the smaller cockles consumed by knot. The model postdicts that during the winters of 2005/2006 to 2008/2009 the site was unable to support the number of oystercatcher present at the time it was designated (i.e. the SPA population). Large cockle biomass remained low during 2009/2010, but increases in mussel biomass meant that the model postdicted that the site could support the SPA population of oystercatcher. Knot food supplies remained high during most years, except 2008/2009 during which the model postdicted that the SPA population could not be supported. The model postdicted that the stock reserved for oystercatchers after shellfishing needed to be 2–4 times the amount consumed by the birds in order to support the bird population. We recommend that where necessary, the conservation objectives of waterbirds should be assessed using a combination of thorough population size and behaviour monitoring to identify sites with population declines, and individual-based modelling on these sites to determine whether reduction in site quality may contribute to the site-specific population decline.
... Most of the case-studies use precautionary measures. These include the low catch limit for Antarctic krill, which is intended to limit competition between krill predators and the fishery (Hill et al., 2016); the partial closure of the North Sea sandeel fishery, which was prompted by low black-legged kittiwake breeding success and potential overfishing of the adjacent sandeel subpopulation (International Council for the Exploration of the Sea, 1999); fishing restrictions near Steller sea lion rookeries and African penguin colonies (Jemison, Pendleton, Hastings, Maniscalco, & Fritz, 2018;Pichegru, Grémillet, Crawford, & Ryan, 2010); and reservation of a fixed allocation of cockles in the Burry Inlet (Stillman et al., 2010). These examples are all fixed rather than tactical measures. ...
... All of the case-studies had at least one of the extra components required in a predator feedback loop, that is regular predator mon-Inlet cockle fishery has a legally designated target for the number of Eurasian oystercatchers that the site should support(Stillman et al., 2010). Finally, CCAMLR, the Convention on which management of the Antarctic krill fishery is based, is explicit about the need to restore depleted predator populations. ...
Ecosystem‐based management of fisheries aims to allow sustainable use of fished stocks while keeping impacts upon ecosystems within safe ecological limits. Both the FAO Code of Conduct for Responsible Fisheries and the Aichi Biodiversity Targets promote these aims. We evaluate implementation of ecosystem‐based management in six case‐study fisheries in which potential indirect impacts upon bird or mammal predators of fished stocks are well publicized and well studied. In particular, we consider the components needed to enable management strategies to respond to information from predator monitoring. Although such information is available in all case‐studies, only one has a reference point defining safe ecological limits for predators and none has a method to adjust fishing activities in response to estimates of the state of the predator population. Reference points for predators have been developed outside the fisheries management context, but adoption by fisheries managers is hindered a lack of clarity about management objectives and uncertainty about how fishing affects predator dynamics. This also hinders the development of adjustment methods because these generally require information on the state of ecosystem variables relative to reference points. Nonetheless, most of the case‐studies include precautionary measures to limit impacts on predators. These measures are not used tactically and therefore risk excessive restrictions on sustainable use. Adoption of predator reference points to inform tactical adjustment of precautionary measures would be an appropriate next step towards ecosystem‐based management.
... The Natura 2000 network does not facilitate the distributional changes -either by a lower increase or higher decrease in numbers inside the network -in two criteria Annex I species (Great White Egret and White-tailed Sea-eagle), and in several northern species (Eurasian Wigeon, Greater Scaup and Velvet Scoter), both these groups preferably wintering in Natura 2000 sites. However, this does not necessarily mean that there has been a decrease in the quality of the network; rather, it could simply be due to increases in the suitability of other sites outside (Stillman et al., 2010), or that the carrying capacity of the Natura 2000 network has been reached. In a previous study , the carrying capacity of the wintering sites has been indicated as being reached, mean total numbers per site having not increased since the 1990s -whereas waterbird numbers have been increasing in areas traditionally deemed 'cold'. ...
... For example, the designation of suitable wetlands as protected areas that border with Natura 2000 sites would help to solve the carrying capacity issue. Moreover, Natura 2000 designation should consider the behaviour and habitat requirements of the species concerned, as well as the effects of human disturbance (López-López et al., 2007;Briggs et al., 2012); certainly the population dynamics of species along with habitat changes brings together a more complicated issue (Stillman et al., 2010;Hiley et al., 2013;Guillemain et al., 2013). A low preference of Natura 2000 was demonstrated in invertebrateeaters and species declining on the flyway level. ...
Evaluating the species use of protected area networks is of considerable worldwide importance, especially as a feedback for policy-makers and the conservation community. Based on the data of an annual, citizen-science monitoring programme of long tradition (2004–2015), we test the hypothesis that the European Natura 2000 network protects high quality habitats preferentially settled by wintering waterbird species in a central European State (the Czech Republic). We analysed species-specific variables (protection status, flyway population trend and numbers, geographical distribution, and foraging guild) explaining the proportions of numbers in Natura 2000 and individual-species changes in numbers inside and outside Natura 2000. The proportions of numbers in individual species were generally low in Natura 2000 sites. The observed pattern revealed the expected higher preference of protected Annex I species for Natura 2000 sites compared to other species and showed foraging guilds having significant differences in Natura 2000 preference, with high preference in herbivores and fisheaters and low preference in invertebrate-eaters compared to omnivores. Northern species also showed a high preference for Natura 2000. The predicted prevalence of a higher rate of increase, or lower rate of decrease, inside Natura 2000, indicating that Natura 2000 facilitated the species' distribution changes, was not shown; instead, the positive and negative trends inside Natura 2000 were almost equivalent. We concluded that the low preference for Natura 2000, the distribution changes shifting species outside Natura 2000, and limits to the carrying capacity of the protected network sites, could all make an issue in effectively safeguarding the nonbreeding populations of waterbirds. The extension of the Natura 2000 network to facilitate their wintering requirements and distribution changes is therefore a high priority.
... Wetland birds play a vital role in maintaining the ecological system stability; therefore, these birds are important components of the wetland ecosystem and are good indicators for assessing wetland restoration (Mistry et al. 2008;Reid et al. 2013). Water birds as a group consume a wide range of food sources; therefore, changes in the assemblage composition and abundance should reflect the changes in the water, vegetation, and food web of the wetland (Fox et al. 2010;Stillman et al. 2010). Because the habitats that support water birds vary considerably in time and space, these birds must travel long distances to access suitable resources (Roshier et al. 2001a, b;Kingsford et al. 2010). ...
... In March and April, with the recovery of vegetation and the addition of other migratory water birds, the species and number recover slightly. Therefore, food and water are the most important factors influencing the distribution of water birds (Erwin 1983;Stillman et al. 2010;Arthur 2012). ...
A long-term monitoring and restoration study was implemented from 2008 to 2014 at the watershed scale in the Napahai wetland, a typically degenerative closed and half-closed alpine wetland in the Northwest Yunnan Plateau, China. After restoration, the vegetation of the swamp, swamp meadow, and meadow in the transitional zone improved constantly, as well as the soil properties, such as water content, soil organic matter, and TN. The vegetation in the lakeside zone increased from 10 families, 11 genera, and 14 species before the restoration to 15 families, 21 genera, and 26 species after the restoration. The removal rate of total nitrogen, total phosphorus, and chemical oxygen demand in the wetland remained greater than 45, 80, and 55 %, respectively; and the transparency in the outlet of the lake increased 171.1 %. Due to the improvement of habitats, the species and number of wintering water birds increased considerably. According to a Canonical Correspondence Analysis (CCA), the soil water content, soil organic matter, total phosphorus and pH were the most important factors that influenced the distribution of vegetation in the transitional zone. Based on the correlation analysis, the bird was positively correlated with the wetland age and the water quality. The evaluation results indicate that the restoration was effective and could act as a guideline for the further ecological restoration of alpine wetlands in the future.
... In the IS, shellfish beds provide a number of ecosystem services including sediment stabilisation, seawater filtration, and human food provision and serve as important feeding grounds for flatfish, birds and various invertebrates (e.g. Stillman et al. 2010). Shellfish beds in the IS can also be of high nature conservation importance where they are heterogeneous and thereby of high biodiversity importance Sanderson et al. 2008) or where they provide food for species of international conservation importance (Stillman et al. 2010). ...
... Stillman et al. 2010). Shellfish beds in the IS can also be of high nature conservation importance where they are heterogeneous and thereby of high biodiversity importance Sanderson et al. 2008) or where they provide food for species of international conservation importance (Stillman et al. 2010). ...
The Irish Sea represents a valuable resource to numerous industries, communities, and other stakeholders particularly in the areas of shellfisheries and aquaculture, energy development and ecosystem services. Climate change poses a substantial threat to marine environments in the region, with impacts exacerbated by struggles for ever limited space and resources, a pronounced need for conservation of important and vulnerable marine ecosystems, and lack of unified management. A concerted effort is required to: i) determine the impacts of climate change and potential risks to marine industry; ii) advise marine industries of future opportunities and areas of collaboration; and iii) develop coordinated marine management across the region to ensure the resource is exploited in an economically and environmentally sustainable manner. We propose that an Irish Sea Marine Research Forum be created that promotes a multi-disciplinary holistic research approach linking industry and research to identify and mitigate the socioeconomic and environmental impacts of climate change. Additionally, we propose that an integrated jurisdiction for the Irish Sea be formed to serve as a regulatory body on fisheries and marine policy for the entire region. Management and policy directives should consider both potential for economic development as well as protection of key environmental features and ecosystem services. Such concentrated efforts on the Irish Sea could then be used as a management model for other regional seas and resources.
... Across the breeding and nonbreeding ranges of oystercatchers, there are multiple threats including habitat loss or damage by land reclamation, sea level rises, and agricultural intensification of field habitats, food shortages through bait-digging, commercial shell-fisheries, or encroachment and competition by invasive Pacific oyster Crassostrea gigas, and human disturbance by activities such as hunting, walking, and watersports (van de Pol et al., 2014). Prior work has modeled how oystercatcher populations may be affected by such external forcing factors including prey biomass requirements, disturbance, and commercial shellfishing (Durell et al., 2008;Goss-Custard et al., 2019;Goss-Custard, Durell, Sitters, & Swinfen, 1982;Stillman et al., 2010), and now, biologging allows detailed investigation of how individuals within a population are likely to be affected by environmental change, which can be used to further optimize such models. ...
Globally, habitat loss or degradation is a major threat to many species, and those with specific habitat requirements are particularly vulnerable. Many species of wading birds (Charadrii) are dependent upon intertidal sites to feed, but, as a result of anthropogenic pressures, the prey landscape has changed at many estuaries. Behavioral adaptations may be able to buffer these changes. In this study over multiple seasons, we aimed to investigate the foraging behaviors of wintering Eurasian oystercatchers in the Exe Estuary where mussel beds, the preferred prey at this site, have almost disappeared in the last decade. From 2018 to 2021, GPS tracking devices were deployed on 24 oystercatchers, and the foraging locations of adults, sub-adults, and juveniles were determined. Of the 12 birds tracked over multiple winter periods, 10 used the same foraging home ranges but a juvenile and sub-adult changed locations interannually. The dominant prey species at key foraging sites were assessed, and we found that younger birds were more likely to visit sites with lower quality prey, likely due to being at a competitive disadvantage, and also to explore sites further away. Individuals were generally consistent in the areas of the estuary used in early and late winter, and over 90% of locations were recorded in the protected area boundary, which covers the sand and mudflats of the Exe. These findings suggest high specificity of the current protected area for oystercatchers in the Exe Estuary, although, if the prey landscape continues to decline, younger individuals may provide the potential for adaptation by finding and foraging at additional sites. Continued monitoring of individual behavior within populations that are facing dramatic changes to their prey is essential to understand how they may adapt and to develop suitable management plans to conserve threatened species.
... Estimates of cockle biomass recorded in November each year from 1993−2008 were obtained from annual surveys of the Burry Inlet undertaken by the Centre for Environment Fisheries & Aquaculture Science (CEFAS) and as reported in Stillman et al. (2010). More recent data (to 2016) were obtained from NRW reports (Vanstaen 2009, Firmin 2010, Moore 2011, Grubb et al. 2014, Clarkin & Grubb 2015, Smith 2016. ...
With coastal wader populations exhibiting long-term declines globally, understanding how they respond to changes in their preferred prey is important for future predictions, especially given the potential for warming seas to affect invertebrate populations. The cockle Cerastoderma edule population in the Burry Inlet Special Protection Area (SPA) in south Wales, UK, declined from 1997-2004 before an abrupt ‘crash’ in stocks between 2004 and 2010. While there has been some recovery since, stocks of larger cockles are still very low. Using survey data from the UK Wetland Bird Survey and analyses of apparent survival and biometrics from ringing, we investigated how the Burry Inlet SPA’s wintering Eurasian oystercatcher Haematopus ostralegus population responded to this crash. Our analysis showed that both body condition and apparent survival of wintering adult oystercatchers were reduced in the years following the cockle crash but both recovered. The number of birds using the Burry Inlet SPA decreased through the course of the cockle stock decline whilst numbers of birds in the adjacent Carmarthen Bay increased, indicating the importance of adjacent sites for buffering the effects of such changes, i.e. protected secondary habitats can be a vital component of a resilient site network. Our findings are useful in understanding how a predator copes with a serious decline in its preferred food stocks. This study has wide applicability in planning the management of coastal wetlands and shellfisheries as well as the design of resilient protected area networks in the light of environmental change.
... However, many waterbirds that utilise intertidal areas are highly mobile and local declines of benthic prey may result in predator redistribution patterns to other foraging areas (Atkinson et al., 2003), as exemplified by how the winter distribution patterns of Common Eider (Somateria mollissima) appear to be linked to available food stocks (Cervencl et al., 2015). Stillman et al. (2010) also highlighted how a decline in population at a local site may not necessarily be due to in situ declining benthic fauna, but instead due to an improving situation in neighbouring areas. Studies that relate shorebird populations to benthic fauna should therefore not only consider benthic fauna at local sites, but also benthic stocks available in the wider landscape. ...
Shorebird populations, especially those feeding on shellfish, have strongly declined in recent decades and identifying the drivers of these declines is important for conservation. Changing food stocks are thought to be a key driver of these declines and may also explain why trends have not been uniform across Europe's largest estuary. We therefore investigated how winter population trends of Eurasian oystercatchers (Haematopus ostralegus) were linked to food availability in the Dutch Wadden Sea. Our analysis incorporated two spatial scales, a smaller scale focused on roost counting areas and food available to birds in these areas and a larger spatial scale of tidal basins. A novelty in our study is that we quantify the connectivity between roosting and foraging areas, identified from GPS tracking data. This allowed us to estimate food available to roosting birds and thus how food availability may explain local population trends. At the smaller spatial scale of roost counting areas, there was no clear relationship between available food and the number of roosting oystercatchers, indicating that other factors may drive population fluctuations at finer spatial scales. At the scale of tidal basins, however, there was a significant relationship between population trends and available food, especially cockle Cerastoderma edule,. Mortality and recruitment alone could not account for the large fluctuations in bird counts, suggesting that the site choice of wintering migratory oystercatchers may primarily drive these large fluctuations. Furthermore, the relationship between oystercatcher abundance and benthic food stocks, suggests winter shorebird counts could act as ecological indicators of ecosystem health, informing about the winter status of food stocks at a spatial scale of tidal basins.
... This may be a feature that is due to the short time that the MSC program has been in operation, and the learning involved in the early years of the scheme resulting in changes to the assessment methodology since the first assessment was completed in 2000. Alternatively, it may be a feature that can be anticipated to always pertain, as some fisheries experience externally driven shocks such as the unexplained mortality events in the Burry Inlet cockle fishery (Stillman et al., 2010). The results from the present study, however, suggest that certification improvements will continue to be required in a few indicators. ...
... Given the long-term impacts of dredging on mollusc abundance, we urge managers to ensure that shellfish harvesting is limited in order to secure sufficient adult stock, both as prey for waterbird populations and as a source of larval supply and for future population viability. In fact, much work has been done on the subject of calculating the amount of bivalve prey required to support waterbird populations over winter (Goss-Custard et al. 2004, Stillman et al. 2010, 2016, Stillman & Wood 2013. Whether this is achieved through spatial and temporal restrictions, by assigning allowable catches or through effort limitations would likely be driven by local circumstance. ...
Harvesting of marine invertebrates in intertidal areas often comes into conflict with conservation objectives for waterbird populations of the orders Anseriformes and Charadriiformes. We present a meta-analysis of the relationships between benthic invertebrate communities and various sources of intertidal harvesting disturbance to investigate impacts and recovery in bird prey resources. The effect size (Hedges' d) of harvesting on benthic species abundance, diversity and biomass was calculated for 38 studies in various locations globally, derived from 16 publications captured through a systematic review process that met the meta-analysis inclusion criteria. A negative response to harvesting disturbance was found for all taxa, including both target and non-target species, that represent important types of waterbird prey. Impacts appear most severe from hand-gathering, which significantly reduces the abundance of target polychaete species, a key prey group for many bird species. Across all gear types, non-target species demonstrate a larger reduction in abundance compared to target species. Recovery trends vary, with differences observed between taxonomic groups and gear/habitat combinations. Abundance of bivalve molluscs, a potentially highly profitable bird prey item, is suppressed for >60 d by mechanical dredging in intertidal mud, while annelid and crustacean abundances demonstrate near recovery over the same period. Data suggest that recovery following harvesting in sandier habitats may in some cases take as long as or longer than in muddy sediments. We recommend management measures to minimise disturbance to benthic prey resources and support conservation objectives for waterbird populations to meet international legal requirements.
... One approach capable of linking behaviour to individual, population and environmental processes is individual-based ecology and can be implemented as Agent-Based/Individual-Based Models (ABM) 23 . MORPH is an ABM platform operating on optimal-foraging and fitness maximising principles; virtual 'animals' adapt their behaviours to feed or to rest based on bioenergetic rules, within virtual environments 24 and has been successfully applied to coastal bird systems 25,26 . Elsewhere, non-MORPH salmonid ABMs have been developed and applied for fish populations in North America 27 . ...
Predicting fish responses to modified flow regimes is becoming central to fisheries management. In this study we present an agent-based model (ABM) to predict the growth and distribution of young-of-the-year (YOY) and one-year-old (1+) Atlantic salmon and brown trout in response to flow change during summer. A field study of a real population during both natural and low flow conditions provided the simulation environment and validation patterns. Virtual fish were realistic both in terms of bioenergetics and feeding. We tested alternative movement rules to replicate observed patterns of body mass, growth rates, stretch distribution and patch occupancy patterns. Notably, there was no calibration of the model. Virtual fish prioritising consumption rates before predator avoidance replicated observed growth and distribution patterns better than a purely maximising consumption rule. Stream conditions of low predation and harsh winters provide ecological justification for the selection of this behaviour during summer months. Overall, the model was able to predict distribution and growth patterns well across both natural and low flow regimes. The model can be used to support management of salmonids by predicting population responses to predicted flow impacts and associated habitat change.
... The averaged data of all sites were used to determine the bird community every month Fig. 4 The number of wintering water birds significantly decreased in the newly formed lakeside from 2006 to 2011 foraging behavior, roosting locations, species composition and populations of water birds (Wan et al. 2001;Armitage et al. 2007;Forcey et al. 2007). Studies confirmed that wetlands with more vegetation species and shallow water tend to attract more birds (Lindegarth and Chapman 2001;Hoover 2006;Riffell et al. 2006;Cui et al. 2009), and food is the most important factor that influence the distribution of water birds (Erwin 1983;Stillman et al. 2010;Reid et al. 2013). ...
Whether dam impoundment for water resource purposes improves wetland ecosystems is heavily disputed. In this study, we investigated the effects of dam impoundment from 2006 to 2011 on wetland plant communities and wintering water birds in Lashi Lake, a typical closed wetland in Northwest Yunnan, China. The surface area of the water body increased from 933 hm2 before impoundment to 1262 hm2 after impoundment; the area of meadows and emergent, submerged and floating vegetation increased from 1006 to 1149 hm2. After the dam impoundment and with the rising water level, formerly dominant plant communities, such as Com. Phragmites australis, Com. Potamogeton pectinatus and Com. Nymphoides peltatum, disappeared. New communities, such as Com. Polygonum hydropiper, Com. Acorus calamus and Com. Leersia hexandra, rapidly expanded into the newly formed lakeside. During these changes, the species and number of wintering water birds slightly increased, but the populations and distributions of birds were altered. Some birds chose the newly formed lakeside as habitat, while others disappeared or decreased greatly. Notably, the major protected birds, such as species of Ciconia nigra, did not appear in the new area, and the species number of Grus grus decreased. The results showed that damming impacted wetland ecosystems. Given the importance and complexity of dam impoundment in alpine wetlands, the effects of food-chain modifications on plants, water birds, aquatic organisms, and humans could be extensive.
... Since the mid-1990s individual-based models (IBMs) have been developed which account for these factors when predicting the quantity of shellfish that a bird population needs to survive the winter. These IBMs have been used in the process of setting TACs for some UK shellfisheries, most recently the Burry Inlet in Wales (Stillman et al., 2010). However, specialist computational knowledge is required to run the models and they have typically been applied on a site-by-site basis, limiting more widespread use. ...
The intertidal areas of UK coasts are important habitats for shellfish species, such as cockles Cerastoderma edule and mussels Mytilus edulis. Commercial harvesting of shellfish is worth an annual £250 million to the UK economy, providing both food and employment (DEFRA, 2013). These shellfish are also the principal food resource for overwintering shorebirds such as oystercatchers Haematopus ostralegus and knots Calidris canutus. Shorebirds are key components of UK coastal biodiversity and are protected under the European Union Wild Birds Directive (2009/147/EEC), which legally obligates the UK government to maintain healthy shorebird populations. Thus, many estuaries have been designated estuarine Special Protection Areas (SPAs) which must be managed to sustain overwintering shorebird populations. Additionally, shorebirds are popular with bird watchers and, therefore, benefit tourism in coastal areas. Thus, a conflict has occurred since the 1970s between those desiring to conserve shorebirds and those desiring to harvest shellfish commercially.
... They are speciose->120 species have been recorded in the Murray-Darling Basin-easy to identify, long-lived and, due to their size and mobility, require large areas of habitat. Waterbirds as a group consume a wide range of food sources, so changes in assemblage composition and abundance ought to reflect changes to aquatic food web structure ( Fox et al., 2010;Stillman et al., 2010). Various waterbird guilds have different feeding and breeding requirements, and healthy diverse communities require a range of habitats that enable both breeding and survival between breeding events ( Leslie, 2001). ...
... This may be a feature that is due to the short time that the MSC program has been in operation, and the learning involved in the early years of the scheme resulting in changes to the assessment methodology since the first assessment was completed in 2000. Alternatively, it may be a feature that can be anticipated to always pertain, as some fisheries experience externally driven shocks such as the unexplained mortality events in the Burry Inlet cockle fishery (Stillman et al., 2010). The results from the present study, however, suggest that certification improvements will continue to be required in a few indicators. ...
There is ongoing debate regarding the value of market-based instruments, such as certification schemes, as an approach to improving the environmental impact of fisheries. This article evaluates the effects of the Marine Stewardship Council on the environmental performance of fisheries over the period before and after certification. A large number of fisheries (n = 447) have undertaken pre-assessments, and in most cases (83%), the auditors recommended that significant improvements should be made before entering full assessment. In cases where substantial improvements were required, the proportion of performance indicators scoring over 80 (considered by the Marine Stewardship Council to be the point of best practice) increased by 22% between pre-assessment and certification. Significant improvements continued after certification, characterized by a 16% increase in the proportion of performance indicators scoring over 80 over a period of five years. Increases in scores assigned by auditors were significantly correlated with increases in real environmental performance (such as increases in stock biomass or the development of protected areas) and improvements in information, which led to increasing certainty that impacts were within sustainable limits. Although results show that certification is associated with real environmental benefits, most improvements are made by fisheries that require significant changes to enter the program.[Supplementary materials are available for this article. Go to the publisher's online edition of Reviews in Fisheries Science for the following free supplemental resources: information and references used in order to analyze the trends related to each fishery performance indicator]
Coastal ecosystems are undergoing unprecedented rates of environmental change. Many of these changes are anthropogenically-driven and linked to long-term, climate-related phenomena. This thesis focusses on ecological change in soft sediment intertidal habitats. One of the largest harbours in Europe, Poole Harbour, is used as a case study. It contains a variety of important habitats including intertidal mudflat and non-tidal saline lagoon.
The two main themes of the thesis are 1) assessing the physical and ecological factors that determine benthic invertebrate abundance, distribution and community structure, which is examined at the scale of the whole harbour, and at the scale of individual habitats: an intertidal mudflat and a saline lagoon; and 2) predicting the response of an overwintering shorebird population, the pied avocet (Recurvirostra avosetta), to future environmental changes, such as sea-level rise and habitat loss. This is achieved by development of an individual-based model (IBM) and consideration of the species’ unique foraging behaviour.
This study contributes to the understanding of the factors structuring soft sediment benthic communities, including the use of data from fine-scale hydrodynamic models. It offers a unique comparison of the spatial and temporal variables driving community structure of a saline lagoon and an intertidal mudflat. It also provides insight into the foraging ecology of the pied avocet at a level of detail that has not previously been considered, including a comparison of foraging behaviour in a tidal and non-tidal habitat, the importance of social foraging, and the novel application of an IBM to this species.
Drivers of environmental change are causing novel combinations of pressures on ecological systems. Prediction in ecology often uses understanding of past conditions to make predictions to the future, but such an approach can breakdown when future conditions have not previously been encountered. Individual‐based models (IBMs) consider ecological systems as arising from the adaptive behavior and fates of individuals and have potential to provide more reliable predictions. To demonstrate potential, we review a lineage of related IBMs addressing the effects of environmental change on waterbirds, comprising 53 case studies of 28 species in 32 sites in 9 countries, using the Drivers‐Pressures‐State‐Impact‐Response (DPSIR) environmental management framework. Each case study comprises the predictions of an IBM on the effects of one or more drivers of environmental change on one or more bird species. Drivers exert a pressure on the environment which is represented in the IBMs as changes in either area or time available for feeding, the quality of habitat, or the energetic cost of living within an environment. Birds in the IBMs adapt to increased pressure by altering their behavioral state, defined as their location, diet, and the proportion of time spent feeding. If the birds are not able to compensate behaviorally, they suffer a physiological impact, determined by a decrease in body energy reserves, increased mortality, or decreased ability to migrate. Each case study assesses the impact of alternative drivers and potential ways to mitigate impacts to advise appropriate conservation management responses. We overview the lessons learned from the case studies and highlight the opportunities of using IBMs to inform conservation management for other species. Key findings indicate that understanding the behavioral and physiological processes that determine whether or not birds survive following a change in their environment is vital, so that mitigation measures can be better targeted. This is especially important where multiple hazards exist so that sensitivities and worse‐case scenarios can be better understood. Increasing the involvement of stakeholders to help inform and shape model development is encouraged and can lead to better representation of the modeled system and wider understanding and support for the final model.
In UK estuaries conflicts have routinely occurred between economic and conservation interests regarding shellfish such as cockles Cerastoderma edule and mussels Mytilus edulis. The harvest of these species is economically important, but shellfish also constitute the main overwinter food supply of the oystercatcher Haematopus ostralegus. In this report we use a simplified spreadsheet model to predict the overwinter food requirements of oystercatchers in the Dee Estuary and compare the predictions of this model with those of an individual-based model which has been used to advise the setting of Total Allowable Catch in the Dee Estuary over recent years.
The models are based on the energy requirements of the birds and the energy value of their shellfish food. The spreadsheet model predicts the amount of shellfish required to maintain high survival rates within the oystercatcher population. The individual-based model predicts how the survival rate within the oystercatcher population is related to the amount of shellfish food and the amount removed by shellfishing. Although more complicated, the individual-based model represents the system in a more realistic way and can simulate specific shellfishing scenarios.
The models produced relatively similar predictions, especially when it was assumed that birds fed on upshore and terrestrial food in addition to cockles. As the biomass of cockles has declined since 2008, the models predicted that the amount required by the birds became close to the total available in 2012. The cockle biomass during 2013 was lower than that during 2012 and the spreadsheet model predicted that the birds required virtually all of the cockle stocks available.
The purpose of this project was to assess the mussel (Mytilus edulis) food requirements of oystercatcher (Haematopus ostralegus) in the Exe Estuary, which has been designated a Special Protection Area for overwintering waterbirds, including oystercatcher. The overwintering oystercatcher population of the Exe Estuary has been well-studied, and the birds are known to feed predominantly upon mussels in intertidal areas. There have been recent declines in the population size of oystercatcher in the Exe Estuary, mirroring wider declines throughout Europe, the reasons for which are unknown.
The study comprised:
• The collection of new data on the area of mussel beds, the density and size distribution of mussels on these beds, and the numbers and behaviour of oystercatcher on these beds;
• The collation of existing data on the food supply of oystercatchers in the Exe Estuary;
• The development of models to predict the food requirements of oystercatcher;
• Running simulations of the models to predict whether there is / could be any effect on oystercatcher survival of the current / potential future ways of managing the mussel fishery on the Exe Estuary.
The current mussel fishery on the Exe provides a feeding resource for oystercatcher on intertidal lays that are exposed on spring tides. Two potential management options that could be effective at improving the feeding conditions of oystercatcher would be to increase the number and area of intertidal mussel lays, and / or to place mussel discards at a relatively high shore level close to the oystercatcher roost.
This project documented a number of changes that have occurred to the Exe Estuary mussel and oystercatcher populations including:
• The number and size of mussel beds have decreased since traditional methods of maintaining mussel beds in the estuary have ceased.
• The density of mussels within the size range consumed by the birds has generally decreased, but the density of the larger mussels within this size range, which are more profitable to oystercatcher, has generally increased.
• Oystercatcher lose a higher proportion of mussels to attacks by carrion crows and herring gulls than they have in the past.
• The number of oystercatcher wintering in the estuary has declined, but the number of birds feeding on the mussel beds has been relatively stable.
The models developed in the project predict that the present day mussel population is sufficient to support the number of oystercatcher that were observed to feed on mussels.
The presence of mussel lays provides extra food for oystercatcher when these lays are exposed on spring tides. The present area, or increases in the area of mussel lays could increase the survival rate of oystercatcher if the number of birds feeding on mussels was over 2000. Below this threshold, starvation was predicted to affect 0 % of the population and so additional food resources cannot further reduce the starvation. The effect over 2000 birds is relatively small because the lays are only exposed for a short time, and so oystercatcher will obtain the majority of their food from mussel beds that are higher on the shore, and hence exposed for longer. Simulations were not run in which lays were positioned higher on the shore because this would not be commercially viable from a fishery perspective; the growth rate of mussels declines as they are positioned further up the shore because they are inundated with water for less time and so have less time to feed.
Factors that would affect the beneficial effect of discards include the size of the discards, the size of the discard bed and the date from which discards are replenished. Our simulations predicted that larger discards spread at lower density over a larger bed increased oystercatcher survival by the greatest amount. This happened because interference competition excluded some birds from smaller patches, and oystercatcher can maintain high intake rate down to low mussel densities. It is unlikely that the size of discards could be increased, but the simulations suggest that the greatest benefit to oystercatchers could be achieved by spreading discards over a larger area. Our simulations predicted that making discards available from January increased oystercatcher survival by the same amount as making them available from September. This was because the feeding conditions of birds deteriorate through winter as, for example, the ash-free dry mass of prey declines, interference competition intensifies and day length shortens. The intake rate of birds feeding on discards was not measured during the study, but we recommend that this is done to between understand the potential benefit of discards. We recommend that the best place for the discard bed would be along the top of the shore on an area of gravel (and hence of relatively low food value to the birds), to the south of Cockwood. This is south of an area where discards have been laid and exploited by oystercatcher in the past, but would experience lower levels of disturbance from human activity.
In this report we use a recently-developed spreadsheet model to predict the overwinter food requirements of two shorebird species, oystercatcher (Haematopus ostralegus) and red knot (Calidris canutus), within the Solway Firth. The model is based on the energy requirements of the birds together with the energy value of their shellfish food. The model predicts the quantity of shellfish required to maintain high survival rates, and hence avoid significant mortality events within the oystercatcher and knot populations.
Knot were assumed to consume 5-14mm cockles (Cerastoderma edule L.), 5-24mm mussels (Mytilus edulis L.) and 8-16 mm tellin (Macoma balthica L.). Oystercatcher were assumed to consume >15mm cockles, 30-60mm mussels and >12mm tellin. The biomasses of invertebrate prey were derived from intertidal surveys of the site. The population sizes of the bird species were derived from Wetland Bird Survey (WeBS) core counts. Predictions were for the winter of 2013-2014. Shellfishing was assumed to exploit >28mm cockles.
The food requirements of oystercatcher and knot were predicted for different combinations of food supply. All scenarios assumed that the birds could consume cockles, mussels and tellin. Alternative scenarios assumed that knot and oystercatcher could consume other food from upshore areas, or that oystercatcher could consume food from terrestrial habitats. Cockle and tellin biomasses were estimated within Solway Firth, and at Wigtown Bay, a site outside the area in which bird population sizes were estimated. Further scenarios therefore assumed that birds either could, or could not, consume food from Wigtown Bay.
In each scenario the model initially predicted the amount of shellfish biomass not required by the birds. This was then converted into the biomass potentially available for fishing, accounting for the fact that the size range exploited by fishing did not overlap completely with that consumed by the birds. In the case of knot there was no overlap, and so the amount available to fishing was only calculated from the biomass of shellfish not required by oystercatcher.
The model predicted that approximately 700 tonnes of >28mm cockles could potentially be exploited by shellfishing during the winter of 2013-2014, after taking into account the food requirements of the birds, excluding cockle and tellin biomass in Wigtown Bay, and assuming that oystercatcher consumed cockles, mussels, tellin and prey from upshore areas and terrestrial habitats. This was considered to be the most realistic scenario given that oystercatcher can potentially feed on terrestrial and upshore habitats, and given the distance between Wigtown and the area in which oystercatcher population size was estimated. The cockle, mussel and tellin surveys did not cover the entire extent of the Solway Firth, not recording cockles or tellin in English waters or mussels or the Scottish side, and so it is likely that a higher biomass of shellfish food is available to the birds in reality. However, without a more extensive survey it is not possible to quantify this.
The spreadsheet model’s predictions for the winter of 2007-2008 were also compared with those of a more complex individual-based model that was developed for oystercatcher and knot in the Solway Firth based on shellfish biomass during 2005 to 2007. The individual-based model predicted that knot survival was 100% in all simulations for the winter of 2007-2008, consistent with the prediction of the spreadsheet model that 18038 tonnes of shellfish were not required by the birds during this winter. The spreadsheet model predicted that the oystercatcher population required all of the shellfish food available during the winter of 2007-2008. Similarly, the individual-based model predicted that oystercatcher were relatively sensitive to the amount of biomass removed by fishing during this winter. With a shellfishing Total Allowable Catch (TAC) set at 1000 tonnes there was a predicted reduction in survival and TACs set at 500, 750 and 1000 tonnes were predicted to reduce body mass. The spreadsheet model predicted that birds required all of the food during 2007-2008 and hence that any TAC would reduce survival. This demonstrates that the spreadsheet model is capable of producing broadly similar predictions to the more complex individual model, although the latter is more sensitive when stock levels are more critical.
In northwest Europe conflicts have routinely occurred between economic and conservation interests regarding shellfish such as cockles and mussels. The harvest of these species is economically important, but shellfish also constitute the main overwinter food supply of the oystercatcher Haematopus ostralegus. In this report we describe attempts to produced a simplified modelling approach to predict the quantities of shellfish which need to be left unharvested in order to ensure high overwinter survival of oystercatcher.
We review oystercatcher diet and prey selection in order to quantify the dependence of this species on shellfish, and determine the size ranges of shellfish which the birds consume. We also review the food requirements of oystercatchers, based on their energetic needs and the nutritional quality of shellfish. In general the data agree well with those used in previous oystercatcher modelling studies. However, there is a possibility that the daily energy requirements, calculated from an all bird allometric equation, may yield an underestimate of oystercatcher food requirements. A comparison of the physiological food requirements, i.e. the quantity directly consumed, and the ecological food requirements, i.e. the quantity required to avoid high mortality, indicated that the ecological food requirement was between 2.0 and 7.8 times greater, with the value depending on the proportion of cockles Cerastoderma edule and mussels Mytilus edulis in a site. These ratios are calculated from empirical data on oystercatcher survival and the predictions of individual-based models predicting the relationship between mortality rate and the abundance of the food supply. Data from the Burry Inlet indicated that the mean ecological food requirement was 3.3 times greater at this site.
We describe a simplified spreadsheet model, which we used to predict the food requirements of the oystercatcher population of the Burry Inlet, and thus the quantity of shellfish which must be left unharvested in order to maintain low mortality rate. The model is based on parameter values derived from the literature reviews in this study, including the energy requirements of the birds, the energy content of shellfish, the minimum size of cockles and mussels consumed, and the ratio of the ecological and physiological requirements. We describe the assumptions and limitations of the model, and compare the model with more detailed individual-based models that can be used to predict the mortality rate of shorebirds in relation to the amount of food available.
Hydroelectric dam have since empowering Malaysia’s development since 1900 Sempam Hydroelectric dam were built in Raub. However, its detrimental effect were well documented in degrading and modifying forest habitat. The objective for present study is to determine the recolonization of bird’s species after the construction of a hydroelectric dam in Peninsular Malaysia. Study of bird species number and composition were done using both mist-net and observation method for three period of research; pre-log, construction and operational. The result of this study show that the species number is declining from 275 species in Pre-Log phase to 67 species in Construction phase. Bird species number increases in Operational phase with 102 species. Different composition of bird species on each phases indicate that bird present on each phase are suited to that particular condition. The re-emergence of pre-log species and wintering bird during operational phase show the recovery process after habitat degradation during construction phase. New species were also found during operational phases indicates that the habitat have been modified to fit the requirements of different bird. It is expected that the species number will continue to climb as the forest recover and habitat become more stable.
The management of Arctic migrant geese is complex, because they frequently use landscapes under intensive human use, and are conflict species in multiple respects. Some populations are of high conservation concern, but they also cause agricultural damage, are quarry for hunters, and may be particularly sensitive to infrastructure developments. In Bulgarian Dobrudzha, large wintering populations of greater white-fronted geese Anser albifrons and red-breasted geese Branta ruficollis feed in agricultural land, and cause management dilemmas. We developed linear models to investigate fine- and meso-scale foraging habitat selection of geese foraging on winter wheat in the area, and used these models to make suggestions for zoning landscape use in order to reduce conflict and conserve geese. Habitat selection was scale-dependent. Geese selected fields that were near to major roosts and had low proximity to roads and tree-lines, which may be a proxy for hunting disturbance. We found some evidence for selection of wheat fields with high nutritional quality. Within fields, geese strongly avoided features which cause landscape ‘clutter’: power-lines, tree-lines and wind-turbines, but primarily over distances of less than a few hundred metres. Optimal management might involve encouraging goose populations to feed in areas close to roosts, by means of agri-environmental measures and creation of hunting-free refuges. This would allow efficient use of agri-environment funds, might reduce conflict with farmers, and would mean that infrastructure development—notably wind farms—could be sited at greater distance from roosts with relatively minor impact on foraging habitat availability.
Local alteration of species abundance in natural communities due to anthropogenic impacts may have secondary, cascading effects on species at higher trophic levels. Such effects are typically hard to single out due to their ubiquitous nature and, therefore, may render impact assessment exercises difficult to undertake. Here we describe how we used empirical knowledge together with modelling tools to predict the indirect trophic effects of a future warm-water outflow on populations of shorebirds and wildfowl. Of the main potential benthic prey used by the birds in this instance, the clam Macoma balthica was the only species suspected to be adversely affected by a future increase of temperature. Various scenarios of decreases in prey energy content, simulating various degrees of temperature increase, were tested using an individual-based model, MORPH, in order to assess the effects on birds. The survival and body condition of eight of the 10 bird species modelled, dunlin, ringed plover, turnstone, redshank, grey plover, black-tailed godwit, oystercatcher and shelduck were shown to be not influenced even by the most conservative prey reduction scenarios. Most of these species are known to feed primarily on polychaete worms. For the few bivalve-feeding species, the larger size-classes of polychaete worms were predicted to be a sufficient alternative food. Only knot was predicted to have a lower survival under the two worst case scenario of decreased M. balthica energy content. We believe that this is the first time such predicted cascade effects from a future warm-water outflow have been shown.
Recent decades have seen great advances in ecological modelling and computing power, enabling ecologists to build increasingly detailed models to more accurately represent ecological systems. To better inform environmental decision-making, it is important that the predictions of these models are expressed in simple ways that are straightforward for stakeholders to comprehend and use. One way to achieve this is to predict threshold values for environmental perturbations (e.g. climate change, habitat modification, food loss, sea level rise) associated with negative impacts on individuals, populations, communities or ecosystems. These thresholds can be used by stakeholders to inform management and policy. In this paper we demonstrate how this approach can use individual-based models of birds, their prey and habitats, to provide the evidence-base for coastal bird conservation and shellfishery management. In particular, we show how such models can be used to identify threshold values for perturbations of food abundance that can impact negatively on bird populations. We highlight how environmental thresholds could be used more widely to inform management of species and habitats under environmental change.
Background/Question/Methods
The release in the wild of captive-raised animals (stocking) is a common tool used for the conservation of vulnerable species and the enhancement of exploited stocks, but conservationists require practical guidance to optimize its cost-effectiveness. A good example comes from freshwater fisheries as many rely on regular stocking of juveniles to sustain the subsequent catches of adults. Determining the individual patterns of mortality (e.g. predation, food resource shortage) and dispersal in the stocked fishes is crucial in evaluating stocking, but remains largely unknown. This is technically challenging, as small-bodied individuals cannot be monitored with conventional tools, and virtually no data exist on their fate after release. Existing habitat models rarely consider the ecological processes underlying species distribution (e.g. optimal habitat choice), and do not predict the movement, and survival of individuals. To have confidence in model predictions, they must operate on basic principles that still apply in new environmental conditions and under different stocking scenarios. Using individual-based models (IBMs) as a tool to provide a reliable basis for prediction, and northern pike (Esox lucius) as a model species, the study aims to: i) parameterize an IBM based on optimal foraging and game theories to determine the fate of stocked juveniles; ii) test these predictions using the results from an innovative field survey using PIT telemetry (individual tagging, and monitoring) and repeated stable isotope analyses (SIA); and iii) using outputs from the IBM, predict how individual fish will respond to different environmental conditions and stocking scenarios to define an optimised design.
Results/Conclusions
We found that the IBM could accurately predict the observed growth, mortality, and dispersal of juveniles. Specifically, we measured size-dependant dispersal and low survival (19.3% of the 192 PIT-tagged individuals). Based on PIT telemetry, we estimated that 59 individuals were predated by birds, and 68 suffered from another source of size-dependent mortality although SIA revealed this was not significantly caused by cannibalism. A selective use of the deepest areas was also observed and predicted. Using different environmental conditions and stocking scenarios, the IBM predicted the influence of the characteristics of released juveniles, release locations, stocking density, and timing on fish survival rates. The combined use of innovative field techniques with an IBM provides new insights into the management of vulnerable species and reveals the transferability of IBMs to other model species to provide realistic information for managers to optimise their stocking strategies.
Prey species have different morphological and behavioural adaptations to escape their predators. In this paper we review how these prey defenses affect prey profitability and intake rate for one predator, the Oystercatcher. Four rules govern profitability. First, within each species large prey are more profitable than small prey, because flesh content increases more steeply with prey size than handling time. Second, soft-bodied prey, such as worms and leatherjackets, which can be swallowed whole, are much more profitable than armoured prey, such as bivalves, which Oystercatchers have to open before the flesh can be extracted from the shell. Third, heavily armoured surface-dwelling prey, like Mussels and Cockles, are the least profitable prey of all, even if the armour is bypassed through stabbing the bill between the valves. Fourth, within the burying prey species, the profitability of prey decreases with depth. Hence burying bivalve species that bury in winter at larger depth than in summer, are in winter, if not out of reach of the bill, anyway less profitable. Despite the large differences between the profitabilities of the various prey species, the intake rates do not differ much when the prey species are compared, presumably because prey with a low profitability are only exploited if the search time is relatively short, i.e. if the density of harvestable prey is high. On the other hand, within each species, the intake rate goes up if larger, more profitable prey are taken. Thus, if the birds have to feed on smaller prey specimens, they fail to fully compensate for the low profitability by an increase in the rate at which these prey are found. Although the profitability of prey differs seasonally due to the variation in the prey condition, only a small seasonal variation in the intake rate was found. Because burying bivalves and soft-bodied worms bury deeper and are less active in winter, Oystercatchers necessarily rely on bivalves living at, or just beneath, the surface at that time of year.
We quantified the prey selection and intake rate of a wading bird, knot Calidris canutus, when 6 different, intertidal prey species, the mud snail Peringia ulvae and the bivalves Macoma balthica, Cerastoderma edule, Mya arenaria, Scrobicularia plana and Mytilus edulis, were abundant. Knot usually search for food by randomly probing into the mud. Prey selection may be described by 5 rules: (1) Prey are not ingestible by knot if the circumference is more than 30 mm. (2) Prey are not accessible to knot when they lie buried deeper than 2 to 3 cm. (3) The probability of a prey organism being detected depends on its surface area, measured in the horizontal plane. (4) Prey are ignored when they are unprofitable, i.e. when the rate of intake while handling the prey is below the current overall average intake rate during feeding. (5) Knot prefer thin-shelled to thick-shelled prey species, possibly because a high inorganic content has an inhibitory effect on the rate at which energy can be extracted from the food. The first rule of ingestion is set by the gape width, and is therefore invariable. The fraction of the prey which is accessible varies according to the probing depth of the bird. The lower size threshold of prey taken is determined by the profitability rule and so varies according to the current feeding rate of knot. Unfortunately for knot, the majority of the preferred thin-shelled prey live out of reach of the bill, whereas the thick-shelled species live at the surface. Medium-sized Macoma balthica is the best compromise available in the 6-species mix.
Measured basal metabolic rate (BMR), existence metabolism and costs of thermoregulation in oystercatcher Haematopus ostralegus, grey plover Pluvialis squatarola and turnstone Arenaria interpres. A high DEE (daily energy expenditure) mainly generated by the skeletal muscles, requires a high level of support by the organs in the abdominal cavity, which inevitably results in a high BMR. This interpretation provides a functional explanation for the constant ratio between BMR and DEE in many bird species and explains the existence of a "maximum sustained working level' of parent birds feeding their young at c4 times BMR. The high DEE of temperate wintering shorebirds must be considered in relation to peak energy demands during their annual cycle. Candidate times are the periods of pre-migratory fattening and mid-winter. From measurements of food intake the authors estimated the additional amount of energy needed for 1 g increase in body weight at 45.66 kJ. Using this value, the efficiency of energy deposition is 88%. -from Authors
The paper deals with the seasonal and annual variations in the weight of the soft parts of four bivalve species, Macoma balthica, Scrobicularia plana, Mya arenaria and Cerastoderma edule from tidal flats of the Dutch Wadden Sea. The paper reviews methodology and points to error sources. The variation in ash-free dry weight between individuals of the same size collected at the same time and place could be attributed to age, parasitic infestation, gametogenesis, burying depth and siphon size. The allometric relations between weight of soft parts and size are given in equations, averaged per month.The body weight of all four bivalve species peaked in May and June at a level approximately twice the lowest value, which occurred in November to March. The extent of this seasonal fluctuation varied, however, from year to year. The presence of gametes explained a part of the peak weight in summer. Winter losses of body weight were less at low temperatures, due to reduced energy expenditure when the animals are inactive. No large differences were found between the seasonal changes in body weight in the Wadden Sea and elsewhere in the temperate zone.
Interference is an important component of food competition but is often difficult to detect and measure in natural animal populations. Although interference has been shown to occur between oystercatchers Haematopus ostralegus L. feeding on mussels Mytilus edulis L., four previous studies have not detected interference between oystercatchers feeding on cockles Cerastoderma edule L. In contrast, this study detected interference between cockle-feeding oystercatchers in the Baie de Somme, France. Prey stealing (kleptoparasitism), one of the main causes of interference between mussel-feeders, also occurred between oystercatchers in the Baie de Somme. The kleptoparasitism rate was related to the natural variation in the food supply, tending to be higher when cockles were rare. Feeding rate was negatively related to competitor density, so providing evidence for interference, but, as in mussel-feeders, only above a threshold density of about 50–100 birds ha−1. The strength of interference at a fixed competitor density was related to the cockle food supply, usually being greater when cockles were rare. Previous studies probably failed to detect interference between cockle-feeders because competitor densities were too low, or cockles were too abundant, or because they were not conducted during late winter when interference is most intense. The study shows that natural variation in the food supply can influence the strength of interference within an animal population and provides support for those behaviour-based interference models which predict that the strength of interference will be greatest when competitor densities are high and prey scarce.
Simulation models that describe autonomous individual organisms (individual based models, IBM) or agents (agent-based models, ABM) have become a widely used tool, not only in ecology, but also in many other disciplines dealing with complex systems made up of autonomous entities. However, there is no standard protocol for describing such simulation models, which can make them difficult to understand and to duplicate. This paper presents a proposed standard protocol, ODD, for describing IBMs and ABMs, developed and tested by 28 modellers who cover a wide range of fields within ecology. This protocol consists of three blocks (Overview, Design concepts, and Details), which are subdivided into seven elements: Purpose, State variables and scales, Process overview and scheduling, Design concepts, Initialization, Input, and Submodels. We explain which aspects of a model should be described in each element, and we present an example to illustrate the protocol in use. In addition, 19 examples are available in an Online Appendix. We consider ODD as a first step for establishing a more detailed common format of the description of IBMs and ABMs. Once initiated, the protocol will hopefully evolve as it becomes used by a sufficiently large proportion of modellers.
We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P < or = 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.
In a number of extensive coastal areas in northwest Europe, large numbers of long-lived migrant birds eat shellfish that are also commercially harvested. Competition between birds and people for this resource often leads to conflicts between commercial and conservation interests. One policy to prevent shellfishing from harming birds is to ensure that enough food remains after harvesting to meet most or all of their energy demands. Using simulations with behaviour-based models of five areas, we show here that even leaving enough shellfish to meet 100% of the birds' demands may fail to ensure that birds survive in good condition. Up to almost eight times this amount is needed to protect them from being harmed by the shellfishery, even when the birds can consume other kinds of non-harvested prey.
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.
The Wetland Bird Survey (WeBS) is a joint scheme of the British Trust for Ornithology (BTO), the Wildfowl & Wetlands Trust (WWT), Royal Society for the Protection of Birds (RSPB) and Joint Nature Conservation Committee (JNCC) to monitor non-breeding waterbirds in the UK. The principal aims of the scheme are to identify population sizes, to determine trends in numbers and distribution, and to identify important sites for waterbirds. WeBS Core Counts are made annually at around 2,000 wetland sites of all habitats; estuaries and large still waters predominate. Monthly coordinated counts are made mostly by volunteers, principally from September to March, with fewer observations during summer months. Data from other sources, e.g. roost counts of grey geese, are included in this report where relevant. This report presents total numbers counted for all species in the most recent year in Great Britain and Northern Ireland. Annual indices are provided for the more numerous species, as are monthly indices showing relative abundance during the winter. Species accounts provide yearly maxima for all sites supporting internationally and nationally important numbers. Sites with changed status are highlighted and significant counts are discussed. Counts are placed in an international context where possible, and relevant research is summarised. Waterbird totals are provided for all sites meeting criteria for international importance and species occurring in internationally important numbers on each are identified. WeBS Low Tide Counts are made on selected estuaries to determine the distribution of birds during low tide and to identify important feeding areas that may not be recognised during Core Counts, which are made mostly at high tide. A summary of results for these estuaries, and distribution maps for selected species, are provided. Waterbird totals recorded by the Irish Wetland Bird Survey, a similar scheme operating in the Republic of Ireland, are also included
1. Whether food intake is determined by the maximum rate at which animals can collect food, or by the rate at which this food can be processed, will strongly affect the organization of their behaviour. We investigated whether the digestive system imposes a constraint on (I) instantaneous rate of food acquisition, (2) total daily food consumption and (3) sustainable maximum energy expenditure in the Oystercatcher, Haematopus ostralegus. We measured the rate of food processing in captive birds from the cumulative loss of body mass after the consumption of various amounts of mussels, Mytilus edulis. 2, Mass loss associated with the digestion of food can be conveniently described by a three-parameter model. These parameters are: (1) latency time, the time interval that elapses between the ingestion of the first food item and the production of the first elapses (28.3 min), (2) evacuation rare, the rate with which digested fod is defecated (0.233 g min(-1)) and (3) absorption coefficient, the proportion of the food (fresh mass) which is not defecated (11.3%). The value of all three parameters was independent of the amount of food consumed, 3, Since the birds absorbed 11.3% of the food, the rate of food processing is slightly higher than the evacuation rate and amounts to 0.263 g min(-1). 4. Given the energy content of the food (3.58 kJ g(-1) fresh mass) and an assimilation efficiency of 85.4%, the instantaneous rate of energy assimilation is 13.4 W. 5. An 80-g food storage capacity in the oesophagus enables the bird to continue digestion during most of the high-water roosting period. Consequently, the maximum amount of energy that can be assimilated during a 24-h day with two low-water feeding periods amounts to 1067 ELT, which equals 4.25 times the basal metabolic rare. This figure probably reflects the maximum sustained working level. 6. Free-living Oystercatchers collect food much faster than they are able to process it. A digestive bottleneck forces them to interrupt their feeding at regular intervals, even when they attempt to collect the maximum amount of food that can be dealt with by the digestive tract. The main implication of such a digestive bottleneck is that a considerable amount of time becomes available for activities other than feeding. In practice, mast of this spare time is spent inactive and we will point out how some evolutionary oddities, such as laziness and individual differences in prey preferences, may have evolved as by-products of a digestive bottleneck.
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.
Birds are highly mobile animals and we need to understand the factors and processes that determine numbers throughout their range and annual life cycle. Most avian studies have concentrated on birds using one locality at a particular time of year, but the numbers breeding or wintering in any one locality may be affected by the size of the greater population of which the local group forms a part, as well as by local conditions. Equilibrium theory provides a useful framework within which to analyse populations at this larger scale, although the meaning and usefulness of some of the concepts used for investigating local groups may change. New approaches are required in which mathematical models are used to integrate the results of studies on the behavioural and population ecology of local groups with those of large-scale monitoring programmes of the kind conducted by the BTO.
Analysis of weight variation, based on monthly mean weights for ten wader species occurring on the Wash demonstrating the patterns of season weight variation. For each species the trends are interpreted in terms of adaptations and responses to specific life cycle events and potential feeding difficulties which arise from winter environmental conditions.
The Burry inlet, South Wales, supports a licensed cockle Cerastoderma edule fishery and occasional mussel Mytilus edulis fishery. It is also an important overwintering ground for oystercatchers Haematopus ostralegus. In recent years mussels have settled over parts of some cockle beds, preventing cockle fishery there and leading to a request by shellfishers to remove this 'mussel crumble'. Conservation managers, however, were concerned that the mussel crumble might be providing a high-quality food source for the oystercatchers, making its removal detrimental to the birds. A behaviour-based model of oystercatcher feeding on cockles and mussels was parameterised for the inlet and its predictions tested against the distribution of birds across the shellfish beds and the amount of time they spent feeding. The model was then used to explore whether the birds were currently food-limited and what would be the effects on their mortality rate and body condition if the mussel crumble were to be removed, thereby re-exposing underlying cockle beds. The model predicted successfully the proportion of birds feeding on the different types of food and the number of hours birds spent feeding on neap tides. It was predicted that, at current bird population sizes, there would have to be a 50% reduction in shellfish stocks and the areas of shellfish beds from 2000-01 levels to cause noticeable extra emigration or mortality. A given area of mussel bed was predicted to be able to support more birds than the same area of cockle bed, but the greater area of the cockle beds meant that they were more important than mussels in determining the number of birds supported by the inlet. The simulated removal of mussel crumble to expose underlying cockles had no effect on predicted bird mortality and body condition at 2000-01 shellfish stock levels. However, there were circumstances under which the mussel crumble was predicted to increase the inlet's capacity to support birds, particularly when the area of existing cockle and mussel beds was substantially reduced.
A modelling approach is used to explore the effect of age and sex differences in oystercatcher (Haematopus ostralegus) winter mortality on population size, population structure and the population response to habitat loss or change. Increasing the mortality of first and second year birds reduced population size, but had very little effect on the proportion of the population that were adults. Increasing female mortality reduced population size and resulted in a male-biased population. A sex bias amongst birds of breeding age meant that there were fewer potential breeding pairs for a given population size, reducing the size of the breeding population and the breeding output. Increasing the mortality of one sex relative to the other reduced population size, even when mean adult mortality rates remained unchanged. Increasing the strength of density-dependent mortality in young birds caused a greater reduction in population size as habitat was lost. Increasing the strength of female density-dependent mortality had the same effect, even though male density-dependent mortality had been correspondingly reduced. Increasing density-independent or density-dependent winter mortality in one sex relative to another also exaggerated the disproportional effect of winter habitat loss on separate breeding subpopulations using the same overwintering area. These results suggest that any study of population dynamics should be aware of both age and sex differences in mortality. Conservationists should be particularly aware of any age or sex differences in diet or habitat use that may result in a differential response to environmental change.
Human interests often conflict with those of wildlife. In the coastal zone humans often exploit shellfish populations that would otherwise provide food for populations of shorebirds (Charadrii). There has been considerable debate on the consequences of shellfishing for the survival of shorebirds, and conversely the effects of shorebird predation on the shellfish stocks remaining for human exploitation. Until now, it has been difficult to determine the impact of current shellfishery practices on birdsor to investigate how possible alternative policies would affect their survival and numbers. One long-running contentious issue has been how to manage mussel Mytilus edulis and cockle Cerastoderma edule shellfisheries in a way that has least effect on a co-dependent shorebird, the oystercatcher Haematopus ostralegus, which also consumes these shellfish. This study used a behaviour-based model to explore the effects that the present-day management regimes of a mussel (Exe estuary, UK) and a cockle (Burryinlet, UK) fishery have on the survival and numbers of overwintering oystercatchers. It also explored how alternative regimes might affect the birds. The model includes depletion and disturbance as two possibly detrimental effects of shellfishing and some of the longer-term effects on shellfish stocks. Importantly, model birds respond to shellfishing in the same ways as real birds. They increase the time spent feeding at low tide and feed in fields and upshore areas at other times. When shellfishing removes the larger prey, birds eat more smaller prey. The results suggest that, currently, neither shellfishery causes oystercatcher mortality to be higher than it would otherwise be in the absence of shellfishing; at present intensities, shellfishing does not significantly affect the birds. However, they also show that changes in management practices, such as increasing fishing effort, reducing the minimum size of shellfish collected or increasing the daily quota, can greatly affect oystercatcher mortality and population size, and that the detrimental effect of shellfishing can be greatly increased by periods of cold weather or when prey are unusually scarce. By providing quantitative predictions of bird survival and numbers of a range of alternative shellfishery management regimes, the model can guide management policy in these and other estuaries.
1. The debate over the interaction between shellfishing and shorebirds is long-running. Behaviour-based models predict how animal populations are influenced by environmental change from the behavioural responses of individual animals to this change. These models are a potential tool for addressing shellfishery problems, but to be of value they must produce reliable predictions using data that are readily available or can be collected relatively quickly. 2. We parameterized a behaviour-based model for the oystercatcher population of the Wash, UK, for 1990-99 using data from shellfishery (mussels and cockles), shorebird and climate monitoring schemes. During the 1990s the overwinter mortality rates of Wash oystercatchers varied widely. The model correctly identified the years in which the observed overwinter mortality was either low (1-2%) or high (10-26%) from annual variation in the food supply, oystercatcher population size and temperature. 3. Many oystercatchers were observed and predicted to die when only a fraction of the available food was consumed. Within the model at least, this was because interference competition excluded the least dominant birds from part of the food supply and the least efficient foragers died before the food supply was fully depleted. A simplified model, which excluded interference and individual variation, incorrectly predicted that all birds survived in all years. Models that exclude these two components of behaviour will tend to underestimate the effect of mussel and cockle food shortage on oystercatchers. Shellfishery management based on such predictions may cause high oystercatcher mortality rates even though enough food would appear to be reserved for the birds. 4. Synthesis and applications. This study shows how a behaviour-based model can be parameterized and predict annual variation in oystercatcher mortality using data routinely collected from the Wash. The principle on which the model is based, that animals behave in order to maximize their chances of survival and reproduction, applies to any system, and the shellfishery, bird and climate data used to parameterize the model are widely available. The model can be used to advise how to manage shellfisheries, by predicting the proportion of the stock that needs to remain unfished in order to maintain low oystercatcher mortality rates.
Population models show that the response of migratory bird populations to a reduction in the area, or change in the quality, of their winter feeding areas depends critically on the shape (linear or non-linear) and strength (slope) of the relationship describing how the proportion dying from starvation changes with population density. Yet the parameters that define such density-dependent functions are extremely difficult to estimate from direct measurements of mortality at different population sizes. Even if they could be estimated, there would be uncertainty as to whether or not the relationship would remain the same, and thus provide reliable predictions, in the new circumstances for which forecasts are required. This paper summarizes studies of the Oystercatcher Haematopus ostralegus which aim to derive the shape and strength of the winter density-dependent mortality and emigration function for one estuary, under existing and new circumstances, from the responses of individual birds to each other and to their spatially and seasonally varying food supply. Based on these studies, an individuals-based, physiologically structured game theoretic distribution model has been built which predicts the carrying capacity and numbers of birds dying at different population sizes. The model also can be applied to Oyster-catchers occupying several estuaries distributed throughout their wintering range and can thus be extended to the entire biogeographical or global population. In addition, it can be used to identify some easily measured behavioural and ecological parameters that identify those species, from a wide range of taxa, that are most likely to be affected by habitat loss and change.
1. In order to assess the future impact of a proposed development or evaluate the cost effectiveness of proposed mitigating measures, ecologists must be able to provide accurate predictions under new environmental conditions. The difficulty with predicting to new circumstances is that often there is no way of knowing whether the empirical relationships upon which models are based will hold under the new conditions, and so predictions are of uncertain accuracy.
2. We present a model, based on the optimality approach of behavioural ecology, that is designed to overcome this problem. The model's central assumption is that each individual within a population always behaves in order to maximize its fitness. The model follows the optimal decisions of each individual within a population and predicts population mortality rate from the survival consequences of these decisions. Such behaviour-based models should provide a reliable means of predicting to new circumstances because, even if conditions change greatly, the basis of predictions – fitness maximization – will not.
3. The model was parameterized and tested for a shorebird, the oystercatcher Haematopus ostralegus. Development aimed to minimize the difference between predicted and observed overwinter starvation rates of juveniles, immatures and adults during the model calibration years of 1976–80. The model was tested by comparing its predicted starvation rates with the observed rates for another sample of years during 1980–91, when the oystercatcher population was larger than in the model calibration years. It predicted the observed density-dependent increase in mortality rate in these years, outside the conditions for which it was parameterized.
4. The predicted overwinter mortality rate was based on generally realistic behaviour of oystercatchers within the model population. The two submodels that predicted the interference-free intake rates and the numbers and densities of birds on the different mussel Mytilus edulis beds at low water did so with good precision. The model also predicted reasonably well (i) the stage of the winter at which the birds starved; (ii) the relative mass of birds using different feeding methods; (iii) the number of minutes birds spent feeding on mussels at low water during both the night and day; and (iv) the dates at which birds supplemented their low tide intake of mussels by also feeding on supplementary prey in fields while mussel beds were unavailable over the high water period.
5. A sensitivity analysis showed that the model's predictive ability depended on virtually all of its parameters. However, the importance of different parameters varied considerably. In particular, variation in gross energetic parameters had a greater influence on predictions than variations in behavioural parameters. In accord with this, much of the model's predictive power was retained when a detailed foraging submodel was replaced with a simple functional response relating intake rate to mussel biomass. The behavioural parameters were not irrelevant, however, as these were the basis of predictions.
6. Although we applied the model to oystercatchers, the general principle on which it is based applies widely. We list the key parameters that need to be measured in order to apply the model to other systems, estimate the time scales involved and describe the types of environmental changes that can be modelled. For example, in the case of estuaries, the model can be used to predict the impact of habitat loss, changes in the intensity or method of shellfishing, or changes in the frequency of human disturbance.
7. We conclude that behaviour-based models provide a good basis for predicting how demographic parameters, and thus population size, would be affected by novel environments. The key reason for this is that, by being based on optimal decision rules, animals in these models are likely to respond to environmental changes in the same way as real ones would.
Conservation managers responsible for estuaries are often required to monitor their site to ensure that the conservation status of any bird species for which the site is considered important is not affected by deterioration of their habitat or by disturbance of the birds themselves. Here, we use an individuals-based model to predict the quality of the Wash embayment, UK, defined in this case as overwinter survival rate, for eight shorebird species. We use the model to predict how site quality would be affected by changes in the types of prey available, prey density, mudflat area and the rate at which birds are disturbed. The results suggested that Macoma, Hydrobia and Corophium had relatively little influence on site quality for any species modelled except black-tailed godwit, despite being the preferred prey for some bird species. Arenicola marina, other annelids and Cerastoderma edule were found to be important influences on site quality. Birds began to starve, when autumn, estuary-wide food biomass density was below about 5 g AFDM m−2 and survival rates fell below 90% at 4 g AFDM m−2. One possible conservation objective for the Wash estuary would be to monitor whether the 99% confidence limit of biomass density falls below one of these limits, to determine whether site quality is being maintained. The system as a whole was predicted to be relatively insensitive to habitat loss. Black-tailed godwits were the most sensitive species, but their survival was not affected until 40% of the feeding grounds were removed. The survival of all species in the model remained high at fewer than 20 disturbances/hour. Although disturbance rates on the Wash were not measured during this study it is unlikely that present-day rates of disturbance on the Wash represent a threat to the survival of the bird species modelled. Our results show how an individuals-based model can assess present-day site quality and how it may change in the future. The model predicted prey biomasses below which survival rate decreased, which shorebird species were most vulnerable to changes in site quality, and that prey density was a more important factor in shorebird survival than habitat area on the Wash. They also show such models can be used to set maximum disturbance rates for each species by predicting how disturbance rates influence shorebird survival.
The numbers of Pink-footed Geese Anser brachyrhynchus wintering in Britain have been increasing exponentially since the 1950s. The numbers of geese at virtually all roost sites have increased, but the most dramatic increase has been in Norfolk, the southernmost region occupied in Britain. This redistribution was most likely caused either by the increase in the population forcing greater numbers of geese towards more southerly sites as the result of a buffer effect, by a decrease in the quality of sites elsewhere in the range or by an increase in the attractiveness of Norfolk. Co-ordinated counts of geese around Britain and historical data of changes in agricultural practice in Norfolk were used to examine these possibilities. No evidence was found for buffer effects, degradation of sites elsewhere or an increase in food availability in Norfolk. The major difference between Norfolk and other Pink-footed Goose sites is in the food type available in Norfolk, namely harvested Sugar Beet Beta vulgaris remains. This food is of high quality and the geese are not disturbed whilst feeding on it because of its limited commercial value. The pattern of redistribution of Pink-footed Geese may therefore be the result of cultural learning of the benefits of feeding on Sugar Beet.
Assessments of whether disturbance is having a deleterious effect on populations have often measured behavioural responses to disturbance and assumed that populations with a larger behavioural response are more susceptible to disturbance. However, there is no guarantee that the behavioural response to disturbance is related to the population consequence, measured in terms of decreased reproduction or increased mortality. Individual-based models, consisting of fitness-maximizing individuals, are one means of linking the behavioural responses to disturbance to population consequences. This paper reviews how individual-based models have been used to predict the effect of disturbance on populations of shorebirds and wildfowl at several European sites, and shows how these models could be improved in the future by incorporating a range of alternative responses to disturbance.
The Wash, in eastern England, supports internationally important populations of 11 species of shorebird. A major commercial shellfishery provides potential conflict between fishermen and nature conservation interests. During the 1990s, high fishing mortality and low recruitment substantially reduced the stocks of cockle (Cerastoderma edule) and mussel (Mytilus edulis). Population models, constructed from estimates of survival and recruitment, indicated that declines in the availability of cockles and mussels were associated with changes in oystercatcher (Haemotopus ostralegus) survival between 1970 and 1998, including three periods of mass mortality, and also the recruitment of juvenile birds to both oystercatcher and knot (Calidris canutus) populations. Emigration of knot may also have taken place. Cockle recruitment was dependent on climatic conditions, whereas mussel populations tended to be stable. The decline in mussel stocks, due to over-fishing, increased the vulnerability of the oystercatcher population to mass-mortality episodes in poor cockle years. The key to preventing major oystercatcher kills in future is to ensure sufficient mussels are available in poor cockle years. Recent cultivation of mussels in inter-tidal areas has been beneficial and is an important management tool for maintaining bird populations.
To assess the long-term effects of human disturbance on birds, ways of predicting its impacts on individual fitness and population size must be found. In this paper we use a behaviour-based model to predict the impact of human disturbance on oystercatchers (Haematopus ostralegus) on their intertidal feeding grounds in the Exe estuary in winter. The model predicted that, for the same overall area disturbed, numerous small disturbances would be more damaging than fewer, larger disturbances. When the time and energy costs arising from disturbance were included, disturbance could be more damaging than permanent habitat loss. Preventing disturbance during late winter, when feeding conditions were harder, practically eliminated its predicted population consequences. Although disturbance can cause increased mortality, it was not predicted to do so at the levels currently occurring in the Exe estuary.
1.1. Metabolisable energy ME intake in various mammals and birds under intensely energy-demanding conditions was found to average 1713 kJ kg0.72 per day.2.2. The implication of a limit to ME intake on activity and growth rate are mentioned briefly.
A behaviour-based model was used to explore the effect of an extension of the port at Le Havre (Port 2000), and the effect of proposed mitigation measures, on the mortality and body condition of the three main shorebird species that overwinter in the estuary of the river Seine, France. In the model, a 20% reduction in the area of mudflats on the north side of the estuary had little effect on curlew Numenius arquata mortality and body condition but significantly increased mortality and decreased body condition in dunlin Calidris alpina and oystercatchers Haematopus ostralegus. Disturbance of feeding birds both day and night had a significant effect on the mortality and body condition of all three shorebird species, as did disturbance of roosting birds. Disturbance of feeding birds in the daytime only had a significant effect on dunlin mortality and body condition, but not that of curlew and oystercatchers. In the model, the creation of a buffer zone to reduce disturbance of feeding birds restored shorebird mortality and body condition to pre-disturbance levels. A new mudflat area was also effective in mitigating the effect of habitat loss on all three shorebirds and in mitigating the effect of roost disturbance on dunlin and curlew. However, a new mudflat area was not effective in mitigating the effect of roost disturbance on oystercatcher mortality and body condition. The effectiveness of the mitigating mudflat depended as much on its size as its quality. We believe that this is the first time that anyone has been able to forecast the efficacy of proposed mitigation measures.
This paper describes an individual-based model, MORPH, that has been designed to predict the effect of environmental change on foraging animal populations. The key assumptions of MORPH are that individuals within populations behave in order to maximise their perceived fitness, but that perceived fitness may not always be positively related to the actual chances of survival and reproduction. MORPH has been parameterised for coastal birds on several European sites and predicted the effect of environmental change, caused by factors such as habitat loss, disturbance from humans and sea-level rise, on the survival and body condition of these species. However, MORPH contains a basic framework to describe animal physiology and foraging behaviour, and the distribution and abundance of the resources required by these animals. Therefore, MORPH is not restricted to coastal birds, and is potentially applicable to a wider range of systems. To be applied to a forager system, MORPH requires parameters describing (i) the distribution of the food supply and how food quality and abundance changes through time; (ii) the rate at which foragers consume food given the abundance of food and competitors; (iii) the amount of food the forager must consume each day to survive; (iv) the distribution and seasonal changes in other factors which influence the foraging behaviour and survival of foragers. The purpose of this paper is to (i) describe MORPH, (ii) give examples of its application, (iii) describe the types of systems to which MORPH can be applied, and (iv) publish its source code and a user guide.
Thesis (Ph. D.)--University of Oxford, 2000. Includes bibliographical references.
Individual behaviour, populations and conservation
- Goss-Custard
Goss-Custard, J.D., Sutherland, W.J., 1997. Individual behaviour, populations and
conservation. In: Krebs, J.R., Davies, N.B. (Eds.), Behavioural Ecology: An
Evolutionary Approach. Blackwell Science, Oxford, pp. 373-395.
Surveys of Cockle and Mussel Stocks in the Burry Inlet
- J Moore
Moore, J., 2009. Surveys of Cockle and Mussel Stocks in the Burry Inlet, 2004 to
2008. CCW Marine Monitoring Report No. 34, 51 p.
A Survey of the Cockle Stocks in the Burry Inlet
- K R Vanstaen
Vanstaen, K.R., 2009. A Survey of the Cockle Stocks in the Burry Inlet, South Wales,
November 2008.
Marine Monitoring Project: Modelling Shorebirds and their Food on the Dee Estuary
- A D West
- S Mcgrorty
- J D Goss-Custard
- W G Sanderson
- C Gray
West, A.D., McGrorty, S., Goss-Custard, J.D., Sanderson, W.G., Gray, C., 2005. Marine
Monitoring Project: Modelling Shorebirds and their Food on the Dee Estuary,
Traeth Lafan and Burry Inlet Spas to Inform Target Setting and Site Management
-Phase 2. Final Report. June 2005, CCW.
Predicting the Effect of Shellfish Stocks on the Oystercatcher and Knot Populations of the Burry Inlet and Three Rivers. Bournemouth University for the Countryside Council for Wales
- R A Stillman
Stillman, R.A., 2009. Predicting the Effect of Shellfish Stocks on the Oystercatcher
and Knot Populations of the Burry Inlet and Three Rivers. Bournemouth
University for the Countryside Council for Wales. Marine Monitoring Report No.
65, p. 45.
Wetland Bird Survey Alerts Changes in Numbers of Wintering Waterbirds in the Constituent Countries of the United Kingdom, Special Protection Areas (SPAs) and Sites of Special Scientific Interest (SSSIs)
- I M D Maclean
- G E Austin
- S K Malham
- A P Woolmer
- G Jones
- D Cock
- R Callaway
Maclean, I.M.D., Austin, G.E., 2008. Wetland Bird Survey Alerts 2004/2005 (Release 2): Changes in Numbers of Wintering Waterbirds in the Constituent Countries of the United Kingdom, Special Protection Areas (SPAs) and Sites of Special Scientific Interest (SSSIs). BTO Research Report 492. Malham, S.K., Woolmer, A.P., Jones, G., Cock, D., Callaway, R., 2008. A Report into the Causes of Mortality of the Edible Cockle (Cerastoderma edule) in the Burry Inlet and Three Rivers, South Wales. 73 p.
Waterbirds in the UK 2006/07: The Wetland Bird Survey
- G E Austin
- M P Collier
- N A Calbrade
- C Hall
- A J Musgrove
- Bto / Wwt / Rspb
- Jncc
- Thetford
- A N Banks
- I M D Maclean
- M P Collier
- I Hainsworth
- R J Howells
- D S Hughes
Austin, G.E., Collier, M.P., Calbrade, N.A., Hall, C., Musgrove, A.J., 2008. Waterbirds in the UK 2006/07: The Wetland Bird Survey. BTO/WWT/RSPB/JNCC, Thetford. Banks, A.N., Maclean, I.M.D., Collier, M.P., Hainsworth, I., Howells, R.J., Hughes, D.S., 2007. Monitoring Bird Distribution and Behaviour on the Carmarthen Bay & Estuaries SAC at Low Tide. British Trust for Ornithology Research Report No.
Table A7 Ash-free dry mass of mussel size classes at start of winter Size class ash-free dry is not calculated for size classes with zero density. Size class ash-free dry mass (g) Year Patch
- West
Table A7 Ash-free dry mass of mussel size classes at start of winter (Moore, 2009; West et al., 2005). Size class ash-free dry is not calculated for size classes with zero density. Size class ash-free dry mass (g) Year Patch 10–14
Monitoring Survival of Waders in Britain The Role of Night-feeding in Shorebirds in an Estuarine Environment with Specific Reference to Mussel-feeding Oysterscatchers
- R A Robinson
- N H K Burton
- J A Clark
- M M Rehfisch
Robinson, R.A., Burton, N.H.K., Clark, J.A., Rehfisch, M.M., 2007. Monitoring Survival of Waders in Britain. BTO Research Report No. 469. BTO, Thetford. Sitters, H.P., 2000. The Role of Night-feeding in Shorebirds in an Estuarine Environment with Specific Reference to Mussel-feeding Oysterscatchers. Ph.D. Thesis, University of Oxford, Oxford, 301 p.
Monitoring Bird Distribution and Behaviour on the Carmarthen Bay & Estuaries SAC at Low Tide
- A N Banks
- I M D Maclean
- M P Collier
- I Hainsworth
- R J Howells
- D S Hughes
Banks, A.N., Maclean, I.M.D., Collier, M.P., Hainsworth, I., Howells, R.J., Hughes, D.S.,
2007. Monitoring Bird Distribution and Behaviour on the Carmarthen Bay &
Estuaries SAC at Low Tide. British Trust for Ornithology Research Report No.
467.
Monitoring Bird Distribution and Behaviour on the Carmarthen Bay & Estuaries SAC at Low Tide in Winter
- N H K Burton
- N A Calbrade
- M P Collier
- I Hainsworth
- R J Howells
- D S Hughes
Burton, N.H.K., Calbrade, N.A., Collier, M.P., Hainsworth, I., Howells, R.J., Hughes,
D.S., 2008. Monitoring Bird Distribution and Behaviour on the Carmarthen Bay
& Estuaries SAC at Low Tide in Winter 2007/08. CCW Contract Science Report
No. 837, p. 73.
Monitoring Bird Distribution and Behaviour on the Carmarthen Bay & Estuaries SAC at Low Tide in Winter
- N H K Burton
- N A Calbrade
- R J Howells
- D S Hughes
- P Jenks
Burton, N.H.K., Calbrade, N.A., Howells, R.J., Hughes, D.S., Jenks, P., 2009. Monitoring
Bird Distribution and Behaviour on the Carmarthen Bay & Estuaries SAC at Low
Tide in Winter 2008/09. CCW Contract Science Report No. 880, p. 63.
- J D Goss-Custard
- A D West
- M Yates
- R W G Caldow
- R A Stillman
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- J Castilla
- M Castro
- V Dierschke
- S E A L V D Durell
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- B J Ens
- K M Exo
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- P N Ferns
- P A R Hockey
- J A Gill
- I Johnstone
- B Kalejta-Summers
- J A Masero
- F Moreira
- R V Nagarajan
- I P F Owens
- C Pacheco
- A Perez-Hurtado
- D Rogers
- G Scheiffarth
- H Sitters
- W J Sutherland
- P Triplet
- D Worrall
- Y Zharikov
- L Zwarts
- R A Pettifor
Goss-Custard, J.D., West, A.D., Yates, M., Caldow, R.W.G., Stillman, R.A., Bardsley, L.,
Castilla, J., Castro, M., Dierschke, V., Durell, S.E.A.l.V.d., Eichhorn, G., Ens, B.J.,
Exo, K.M., Udayangani-Fernando, P.U., Ferns, P.N., Hockey, P.A.R., Gill, J.A.,
Johnstone, I., Kalejta-Summers, B., Masero, J.A., Moreira, F., Nagarajan, R.V.,
Owens, I.P.F., Pacheco, C., Perez-Hurtado, A., Rogers, D., Scheiffarth, G., Sitters,
H., Sutherland, W.J., Triplet, P., Worrall, D., Zharikov, Y., Zwarts, L., Pettifor, R.A.,
2006. Intake rates and the functional response in shorebirds (Charadriiformes)
eating macro-invertebrates. Biological Reviews 81, 501-529.
A Report into the Causes of Mortality of the Edible Cockle
- S K Malham
- A P Woolmer
- G Jones
- D Cock
- R Callaway
Malham, S.K., Woolmer, A.P., Jones, G., Cock, D., Callaway, R., 2008. A Report into the
Causes of Mortality of the Edible Cockle (Cerastoderma edule) in the Burry Inlet
and Three Rivers, South Wales. 73 p.
The Role of Night-feeding in Shorebirds in an Estuarine Environment with Specific Reference to Mussel-feeding Oysterscatchers
- R A Robinson
- N H K Burton
- J A Clark
- M M Rehfisch
- Thetford Bto
- H P Sitters
Robinson, R.A., Burton, N.H.K., Clark, J.A., Rehfisch, M.M., 2007. Monitoring Survival
of Waders in Britain. BTO Research Report No. 469. BTO, Thetford.
Sitters, H.P., 2000. The Role of Night-feeding in Shorebirds in an Estuarine
Environment with Specific Reference to Mussel-feeding Oysterscatchers. Ph.D.
Thesis, University of Oxford, Oxford, 301 p.