Southampton Water UK

50.869653, -1.372339

Study A

Study A

Birds

Grey plover, Pluvialis squatarola

Ringed plover, Charadrius hiaticula

Oystercatcher, Haematopus ostralegus

Curlew, Numenius arquata

Bar-tailed gotwit, Limosa lapponica

Black-tailed gotwit, Limosa limosa

Dunlin, Calidris alpine

Redshank, Tringa tetanus

Turnstone,Arenaria interpres

Modelling

MORPH

Abstract

Overall abstract for PhD thesis:

European and UK legislation arising from The Convention on Biological Diversity 1993 aims to reduce biodiversity loss and to set guidelines for sustainable impacts of human activities. With predictions of increased biodiversity loss under climate change, it is paramount that present and future anthropogenic impacts on biodiversity are assessed, monitored and predicted. This thesis applies techniques of assessment, monitoring and prediction to cases of potential losses of ornithological diversity within the Solent, UK, through overexploitation of resources, disturbance and habitat loss.An annual commercial harvest of the eggs of Black-headed Gulls was studied to assess impacts on their breeding success and distribution within the Solent. From in-situ measurements of breeding success indicators, including egg volume, hatching success and chick survival, we were able to show that harvesting of eggs reduced the breeding success of gulls, over and above effects of colony size and nest position within the colony. Ex-situ measurements on the yolk-toalbumen ratio and eggshell thickness showed that harvesting reduced these components, over and above effects of laying date. Harvested sites also had a higher proportion of abnormallyformed eggs, particularly taking the form of small yolkless eggs and unpigmented eggs. These impacts are all consistent with known effects of depletion of the female’s endogenous reserves.

Data from long-term monitoring of seabirds breeding along the south coast of England indicated that egg harvesting and the associated disturbance may be directly and negatively influencing the breeding distribution of Black-headed Gulls and also the protected Mediterranean Gull that breeds in its colonies. Data suggests that egg harvesting has prevented the colonisation of Mediterranean Gulls on these sites, whereas un-harvested sites have seen rapid colonisation in the last 10 years. On this basis, both EU and UK legislation may be being violated, through infringement of the regulations surrounding the Mediterranean Gull as an Annex 1 (EC Birds Directive 1979) and Schedule 1 (Wildlife and Countryside Act 1981) species; and through the breeding habitat within the Solent being SACs and SPAs. Protected tern species that associate with Black-headed gull colonies start laying after the harvesting season, but are nevertheless susceptible to the collapse of harvested colonies.

As well as its gull colonies, the Solent sustains important populations of wintering shorebirds that rely on the food resource supplied by estuaries and tidal flats. The quantity and composition of macrobenthic invertebrate prey in the Southampton Water SPA was sampled with a stratified-random design for ANOVA. The split-plot ANOVA revealed a higher level of heterogeneity within the estuary than could be resolved from the multiple regression techniques that are normally applied to grid-based designs. Bootstrap resampling indicated that the ANOVA design predicted invertebrate assemblages with adequate precision to produce an individual-based predictive model of site quality for shorebirds over-wintering on Southampton Water. This model accurately predicted the observed shorebird distribution, on the assumption that non-starving birds moved within restricted sections of the site, consuming any prey that yielded a threshold energy assimilation rate. Dunlin and curlew were the species predicted to be most sensitive to loss of prey biomass or overall habitat area, with losses of 5-10% provoking significant impacts on survival. When the area for the proposed development of a port terminal at Dibden Bay was modelled as habitat loss, the impacts on shorebird survival were eliminated by the proposed mitigation. However, our model did not account for the years of habitat removal and construction of the mitigation sites. Despite these limitations the model indicated the potential for evaluating ornithological losses within the Solent from a small loss of intertidal habitat.

Chapter 5:

European conservation law now requires environmental impact assessments of estuary sites of importance to over-wintering shorebirds. Reliable methodologies are consequently needed to monitor site quality and assess impacts of habitat loss. We developed an individual-based model of Southampton Water to evaluate site quality for eight shorebirds: dunlin Calidris alpina, ringed plover Charadrius hiaticula, ruddy turnstone Arenaria interpres, redshank Tringa totanus, grey plover Pluvialis squatarola, black-tailed godwit Limosa limosa, Eurasian oystercatcher Haematopus ostralegus and Eurasian curlew Numenius arquata. Over-winter survival was predicted both with and without 7% habitat loss for the proposed construction of a port terminal at Dibden Bay. The model accurately predicted the observed shorebird distribution if nonstarving birds were assumed to move within restricted sections of the site, consuming any prey which yielded a threshold energy assimilation rate. In contrast, the model predicted that too few patches were occupied if birds were assumed to consume only those prey that maximised energy assimilation rate. All species except turnstone and oystercatcher were reliant on the consumption of annelids to maintain high survival rates. Dunlin and curlew were predicted to be the species most likely to have reduced survival if either prey biomass or overall habitat area were reduced. In some simulations, the habitat loss caused by the Dibden Bay port terminal was predicted to decrease the survival rate of dunlin by 2.7%, turnstone by 0.9% and curlew by 1.7%, but did not effect the survival of any other species. The effect of habitat loss on these species was eliminated by the proposed mitigation of a tidal creek. The predicted success of the mitigation, however, did not account for the years required to construct the mitigation habitat, or any accumulative effects on the mortality of shorebirds which would be forced to feed from other sites within the estuary.

Funding and Collaboration

English Nature, ABP Marine Environmental Research, Beaulieu Estate

Study B

Study B

Birds

Golden plover, Pluvialis squatarola

Ringed plover, Charadrius hiaticula

Oystercatcher,Haematopus ostralegus

Curlew, Numenius arquata

Black-tailed gotwit, Limosa limosa

Dunlin, Calidris alpine

Redshank,Tringa tetanus

Modelling

MORPH

Abstract

The Solent coastline provides feeding grounds for internationally protected populations of overwintering waders and wildfowl, and is also extensively used for recreation. In response to concerns over the impact of recreational pressure on birds within protected areas in the Solent, the Solent Forum initiated the Solent Disturbance and Mitigation Project to determine visitor access patterns around the coast and how their activities may influence the birds. The project has been divided into two phases. Phase I collated and reviewed information on housing, human activities and birds around the Solent, and reviewed the potential impact of disturbance on birds. Phase II has involved a programme of major new data collection to (i) estimate visitor rates to the coast from current and future housing, (ii) measure the activities and distances moved by people on the shore and intertidal habitats, and (iii) measure the distances and time for which different bird species respond to different activities.

The current report represents the culmination of Phase II, in which the primary data are used to predict whether disturbance may be reducing the survival of birds. Predictions are derived for wader species by developing detailed computer models of birds and disturbance within Southampton Water and Chichester Harbour. These models create a virtual environment within the computer incorporating the intertidal invertebrate food supply of the birds, the exposure and covering of this food through the tidal cycle, disturbance from human activities, and the energy requirements and behaviour of the birds as they avoid humans and search for food. The invertebrate food supply of birds in the models was derived from previous intertidal surveys, and the exposure of intertidal habitat predicted from a tidal model of the Solent. The models incorporate the costs that birds incur when avoiding human activities (e.g. increased density in non-disturbed areas, reduced time for feeding and increased energy demands when flying away), but also their abilities to compensate for these costs (e.g. by feeding for longer or avoiding more disturbed areas). The predictions indicate how disturbance may be effecting the survival of waders throughout the Solent. The following waders were included in the models: Dunlin Calidris alpina, Ringed Plover Charadrius hiaticula, Redshank Tringa totanus, Grey Plover Pluvialis squatarola, Black-tailed Godwit Limosa limosa, Bar-tailed Godwit Limosa lapponica (Chichester Harbour model only), Oystercatcher Haematopus ostralegus and Curlew Numenius arquata. A simpler approach was used to assess how disturbance may be effecting Brent Geese in the Solent.

As with any models, the predictions of the models used in this project depend on the data with which they are parameterised and the assumptions they make about the real system. The current and future visitor rates used in the models were themselves predicted using statistical analyses of household survey and on-site visitor data. The responses of birds to disturbance were parameterised using on-site observations of the responses of birds to disturbance. Furthermore, models are a simplification of real systems, and it is important to recognise this when interpreting their predictions. The report considers how the model parameters and assumptions may influence predictions. These include: (i) the way in which the disturbance data were measured and assumptions made about how birds and people are distributed in space and time; (ii) the way in which the behaviour of birds to disturbance differs between sites; (iii) the effect of extreme weather on the birds; (iv) how rare or localised activities are incorporated into the models; and (v) how consumption of food by species other than waders is included. The project predicted changes in visitor numbers to the Solent coast. Local authorities in the Solent region provided projections of future housing developments in the region. These were combined with data on visitor rates to different parts of the coast and the distance travelled to visit the coast, to predict coastal visitor rates with current and future housing. Using current housing levels, 52 million household visits per year to the Solent coast were predicted (i.e. the shore from Hurst Castle to Chichester Harbour, including the north shore of the Isle of Wight). Using the housing data provided by local authorities, visitor numbers were predicted to rise by around 8 million household visits, to a total of 60 million, an overall increase of 15%.

Within Chichester Harbour, the food supply surveyed was not predicted to be able to support the majority of wading birds modelled. This implied that either the invertebrate survey underestimated the intertidal food supply, or that other food was available either terrestrially, or from neighbouring intertidal sites such as Langstone Harbour. Similar invertebrate surveys have been used to parameterise 17 other similar models, and in all cases birds were predicted to have survival rates close to, or higher than those expected. Due to uncertainties with the Chichester Harbour invertebrate data, it was decided not to use the Chichester Harbour model to predict the effect of disturbance on the birds. However, it is important to note what the effect of low food abundance would be on the effect of disturbance on the birds. The impact of disturbance on survival and body condition will depend on the birds’ ability to compensate for lost feeding time and extra energy expenditure. Birds will be better able to compensate when more food is available, and so lower food abundance in a site will make it more likely that disturbance decreases survival and body condition.

Within Southampton Water, in the absence of disturbance, all wader species modelled were predicted to have 100% survival and maintain their body masses at the target value throughout the course of winter. Disturbance from current housing was predicted to reduce the survival of Dunlin, Ringed Plover, Oystercatcher and Curlew. Increased visitor numbers as a result of future housing was predicted to further reduce the survival of Dunlin and Ringed Plover. Disturbance was predicted to have a relatively minor effect on the mean body mass of waders surviving to the end of winter, largely because the individuals with very low mass starved before the end of winter. The Southampton Water model provided evidence that current and future disturbance rates may reduce wader survival in this site. Hypothetical simulations were run to explore how intertidal habitat area, energy demands of the birds and the frequency of different activities may influence the survival of waders within Southampton Water. The survival rates of Dunlin, Ringed Plover, Oystercatcher and Curlew were predicted to be decreased by any reduction in intertidal habitat area (e.g. due to sea level rise) or increases in energy demands (e.g. due to disturbance at roosts or cold weather). Wader survival was predicted to increase if intertidal activities were moved to the shore. This meant that the disturbance from these activities was restricted to the top of the shore rather than the whole intertidal area, and so the proportion of intertidal habitat disturbed was reduced. Reductions in the number of dogs that were off leads were also predicted to increase the survival of some wader species. Removing bait digging from simulations did not increase wader survival. However, this happened because baitdigging was assumed to be a relatively infrequent activity. This does not mean that bait-digging could not adversely affect the birds if it occurs at a higher frequency, and the simulations did not incorporate the depletion of the invertebrate prey of the birds caused by bait digging, which would be an additional effect on the birds in addition to disturbance.

Brent Geese were considered in the light of the Solent Waders and Brent Goose Strategy. Important issues are the size of individual sites, their spacing and the ease with which birds can move between the sites. A high proportion of each site needs to be further away from visitor access routes than the distances over which birds are disturbed to ensure that disturbance to the birds is minimised. This could be achieved through a network of larger sites or by preventing visitor access through, or close to, smaller sites. Both intertidal and terrestrial food resources are important to the birds, intertidal food typically being of higher food value but dying back and / or becoming depleted during the autumn / early winter. Previous models of Brent Geese have predicted that the loss of terrestrial habitat typically has the highest effect on survival, and so such habitat is predicted to be particularly important for the birds. Maintaining a suitable network of saltmarsh sites will be increasingly important as the total area of saltmarsh declines with sea level rise. The findings of the present project are in general support with the recommendations of the Solent Waders and Brent Goose Strategy.

Predicted current visitor rates varied widely throughout the Solent, but were relatively high within Southampton Water. The highest percentage increases in visitor rates were on the Isle of Wight (50-75%). Wader survival was predicted to be decreased in Southampton Water when daily visitor rates to coastal sections were greater than 30 per ha of intertidal habitat. The potential impact of visitors on wader survival throughout the Solent was calculated by comparing visitor densities throughout the Solent (expressed relative to maximum intertidal habitat area) to the visitor densities predicted to decrease bird survival within Southampton Water. The intertidal food supply within Chichester Harbour was insufficient to support the model birds and so any disturbance (by reducing feeding area or time, or increasing energy demands) would have decreased predicted survival in this site. There is also doubt as to the food supply within the other harbours and so some caution is appropriate when applying the results from Southampton Water to these sites. Coastal sections with daily visitor rates over 30 per ha are identified. The predictions of the Southampton Water model suggest that birds within these sections may have reduced survival due to disturbance from visitors. Whether or not such visitor rates will reduce survival will depend on the food abundance in the coastal sections themselves as well as that in neighbouring sections.

The area of overlap between an activity / development and the distribution of birds is often used as a measure of the impact of the activity on the birds, with 1% overlap often taken as the threshold for impact (note however that this 1% overlap does not necessarily mean that an activity will have an adverse effect on the survival or body condition of birds). Therefore, the percentage of intertidal habitat disturbed within each coastal section was calculated as an index of the potential impact of disturbance on the birds. Assuming the maximum intertidal area and only including intertidal visitors, over 50% of the area of many coastal sections was predicted to be disturbed, with an average of 42%.

Funding and Collaboration

Solent Forum

Study C

Study C

Birds

Grey plover, Pluvialis squatarola

Oystercatcher,Haematopus ostralegus

Curlew, Numenius arquata

Black-tailed gotwit, Limosa limosa

Dunlin, Calidris alpine

Redshank, Tringa tetanus

Turnstone,Arenaria interpres

Modelling

MORPH

Abstract

With the pressures that today’s ecosystems are being placed under, from both environmental change and anthropogenic developments, the speed at which management decisions need to be made has increased. Coastal development means that estuaries are particularly affected and their characteristic species, like wading birds (Charadrii), are now experiencing worldwide declines. In such situations there is a need for predictive ecology to understand in advance how species might react to future changes.

This thesis looks into how we can use individual-based models (IBM) to make accurate predictions of how wading birds are affected by environmental change. Starting with previously validated models I show the importance of measuring size of invertebrates though an IBM investigation into regime shifts and wading birds responses. The models show that by altering their diet preferences, birds adapt to regime shifts in their prey but that this maintenance of population size masks the true changes in the system and limits the use of waders as direct bio-indicators of ecosystem health. Using the current literature, an analysis on empirical responses of wader populations to environmental change revealed the lack of comparability between studies and the scarcity of studies on small scale events.

Data from literature and fieldwork was used to develop a comparable suite of individual-based models for five UK estuaries with up to eleven wading bird species. These models were validated using current BTO Wetland Bird Surveys data to increase confidence in final results. Using these new models, investigations of population thresholds and environmental change were carried out. Increases to current populations revealed that several estuaries are no longer able to support the number of birds around the time of Special Protection Area designation. This, alongside higher populations currently seen since the years of designation, indicates the need for re-assessment of SPA species numbers. When looking at the impacts of two types of environmental change, habitat loss and sea-level rise, certain species declined predictably across sites whilst the individual make up of each estuary had particular impacts on some waders more than others. The work of this thesis further indicates the great potential of using individual-based models to predict the effects of a wide range of environmental changes. With the new models and a quicker and systematic way of developing IBMs for additional areas, we can aid the conservation and management of estuarine systems for wading birds.

Funding and Collaboration

Bournemouth University and HR Wallingford

 

Related Paper:

Study A
Study A

Wood, P.J. (2007). Human impacts on coastal bird populations in the Solent. PhD thesis, University of Southampton.

 

Study B
Study B

Stillman, R.A., West, A.D., Clarke, R.T. & Liley, D. (2012) Solent Disturbance and Mitigation Project Phase II: Predicting the impact of human disturbance on overwintering birds in the Solent. Report to the Solent Forum. pp 119.

 

Study C
Study C

Bowgen, K.M., 2016. Predicting the effect of environmental change on wading birds: insights from individual-based models. PhD thesis, Bournemouth University in collaboration with HR Wallingford.