|MIGRATAGIS - Wintering and migrating shorebirds as indicators of the quality of estuarine environments|
José Pedro Granadeiro
Execution dates - 2008-10-01 - 2012-03-31 (42 Months)
Funding Entity - FCT
Funding for CESAM - 135870 €
Total Funding - 163000 €
Proponent Institution - Universidade de Lisboa
Universidade de Aveiro* Instituto Superior de Psicologia APlicada
During the winter, many species of shorebirds feed on the macro-invertebrates in the intertidal sediments of estuaries during the low tide, and seek refuge in adjoining areas for resting and maintenance activities during the high tide. Hence, wintering shorebirds have the potential to act as integrative indicators of the quality of estuarine areas, reflecting not only the quality of the sediment flats, on which they depend for feeding, but also that of the surrounding habitats, which they seek as refuge. Some estuaries are also routinely used by very large numbers of actively migrating shorebirds. Each year, the fate of hundred of thousands migrants depends on the existence of a network of good quality stopover sites along their migratory flyway, which they use to rebuild their body condition between the successive legs of their migratory trajectories.
The Tagus estuary is located on a migratory pathway known as "East Atlantic Flyway", and supports a large number of shorebirds during the winter and in migration. The wintering shorebirds of the Tagus estuary have been the focus of recent research but many important ecological questions are still unresolved. The factors determining the spatio-temporal variation in the distribution of birds in the feeding area are only partially understood. Also, the scales at which these factors operate are now beginning to be unveiled. Further insights into these issues depend, on one hand, on long-term data about the distribution and abundance of prey and about their recruitment schedule, and on the other hand, on further correlative research on foraging strategies of birds.
The lack of knowledge is particularly acute in relation to numbers and behaviour of actively migrating birds in the Tagus estuary. The Tagus estuary is believed to act as a important stopover site, particularly during the northward migration. However, the magnitude of the migrating populations, the residence period of birds, the preferred foraging sites for refuelling, the rates of weight increase and many other parameters of the birds' migratory ecology are virtually unknown. This lack of knowledge prevents an adequate assessment of the quality of the Tagus estuary as a stopover site. Therefore, the main aims of this project are (1) to carry out an in-depth analysis of key factors influencing the use of tidal flats and high-tide roosts by shorebirds, (2) to develop methods to quantitatively assess the quality of different roosting sites for shorebirds, using eco-physiological indicators of stress and (3) to undertake the first quantitative assessment of several stopover parameters of shorebirds migrating through the Tagus estuary. We will define and implement a standardised monitoring scheme for main invertebrate prey at small and mesoscales, giving particular emphasis to the intra- and inter-annual patterns of abundance and to their recruitment schedules.
The value of these data is well beyond the objectives of this particular project, as it may be used as baseline data to quantify the impacts on the estuary of natural and man-made events. We will concurrently undertake regular counts and behavioural observations of birds at their feeding areas and at the roosts. Some birds will be individually marked and radio-tagged, and intensively monitored during the day and during the night using standard radio-tracking techniques based on mobile antennas. This will provide detailed data about daily and seasonal shifts in their foraging and roosting grounds, which we will correlate with behavioural data. Therefore, we will be able to map the most important foraging and roosting areas in the estuary.
We will also assess the quality of different roost sites by analysing the seric levels of corticosteroid hormones in birds. High levels of this hormone are known to correlate with above-normal stress levels, attributable to a wide variety of factors. These factors will be independently quantified on each study roost. Also, we plan to use very recent technological advances which now enable the use of bird faeces to measure hormone levels. This will facilitate the collection of data, and because it is a non-intrusive procedure will reduce biases in our results. We expect to develop eco-physiological standards to assess the quality of roosts for shorebirds. To study the migratory ecology of shorebirds, we will rely on intensive monitoring of roosting and feeding areas in order to detect the migratory peaks. We will use radio-tracking data and will log the tags with Automatic Radio Tracking Stations. This equipment will enable a continuous tracking all marked individual at selected locations, thus enabling the quantification of stopover periods. We expect to obtain the first estimates of the overall numbers using the Tagus estuary and of their stopover periods, using recent advances in survival models. We will also be able to identify the most important foraging and roosting areas for these transient populations.