Grey plover, Pluvialis squatarola
Ringed plover, Charadrius hiaticula
Bar-tailed godwit, Limosa lapponica
Black-tailed gotwit, Limosa limosa
Dunlin, Calidris alpine
Knot, Calidris canutus
Redshank, Tringa totanus
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.
Funding and Collaboration
ABP Marine Environmental Research and English Nature
Grey plover Pluvialis squatarola
Ringed plover Charadrius hiaticula
Oystercatcher Haematopus ostralegus
Bar-tailed godwitLimosa lapponica
Black-tailed godwit Limosa limosa
Dunlin Calidris alpina
Knot Calidris canutus
Redshank Tringa totanus
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, wecan aid the conservation and management of estuarine systems for wading birds.
Funding and Collaboration
Bournemouth University and HR Wallingford