Wetland Bird Survey
When should this method be used?
The Wetland Bird Survey (WeBS) method is applicable where wetland habitat(s) are present that have the potential to support priority waterbird species, for example open lakes, reservoirs, estuaries and intertidal habitats.
Waterbird species include divers, grebes, cormorants, herons, spoonbill, swans, geese, ducks, rails, cranes, waders, gulls, terns and kingfisher.
Surveys should seek to qualify the diversity and numbers of birds interacting with the wetland habitats, in the context of their specific ecology and population status. For example, a reservoir that supports staging or wintering waterfowl. Should these habitats be significantly disturbed or destroyed, those reliant birds are unlikely to reach breeding condition during spring.
The WeBS methodology requires monthly survey visits (i.e. one visit per month) to be undertaken. Where intertidal habitats are present, there may be a requirement to undertake high tide and low tide surveys.
High tide surveys typically record wetland birds congregated at traditional roosts or gathered on open waterbodies. As a consequence, wetland birds are generally easier to count at high tide. This is the core intertidal WeBS method, and is typically used to establish maximum counts of wetland birds within an intertidal wetland habitat.
Low tide counts assess the spatial distribution of non-breeding wetland bird species during low tide and the relative importance of the various parts of an intertidal waterbody (such as an estuary) for foraging birds. Low tide surveys are typically carried out in addition to high tide surveys, where deemed appropriate.
The number of visits will depend on the habitats present and the ecology of priority species that may occur on site. This will be determined by the desk study. For example, a site that is likely to support wintering birds may require monthly visits between November and February (the core winter months), whereas a site that has passage potential may require a wider window of survey (e.g., seven monthly visits between September and March inclusive). The BTO WeBS methodology typically consists of high tide surveys during the months of September to March inclusive, and low tide surveys during the core winter months of November to February inclusive. For particular target species, the BTO Bird track data can help identify periods of peak detectability, and this can inform the survey dates.
The number of surveys being undertaken must be supported with detailed and robust justification. Additional survey effort may need to be considered for large-scale projects with the potential to have significant impacts on birds, and/or for high profile, sensitive projects. On the other hand, fewer survey visits may be justified for projects with very limited impacts, or sites with habitats of low value for birds.
Additional surveys (such as non-breeding walkover survey, nocturnal survey or species-specific surveys) should also be considered and will depend on the habitats present and the ecology of the priority species that may occur. For particularly large sites, surveys may require several surveyors.
Survey timing should always be about maximising detection of species likely to be present on site. Unlike during the breeding period, when many species are detectable primarily on call or song, during the non-breeding season, audible detectability of many species will decrease, and surveyors must rely on visual identification.
The behaviour of many species is also likely to move from breeding and territorial behaviours to foraging and resource acquisition, and so birds present may be more obvious for longer periods (although not always the case). Therefore, there is less restriction on timings of surveys, and the majority of non-breeding walkover surveys will determined by visibility (i.e. undertaken during daylight hours).
Where intertidal habitats are present, surveys should be undertaken during daylight hours and within two hours either side of high or low tide (depending which is being surveyed).
Planning survey dates
The number of visits will depend on the habitats present and the ecology of priority species that may occur on site. For example, a site that is likely to support wintering birds may require monthly visits between November and February (the core winter months), whereas a site that has passage potential may require a wider window of survey (e.g., seven monthly visits between September and March inclusive). For particular target species, the BTO Bird track data can help identify periods of peak detectability, and this can inform the survey dates.
Within each month, the exact date is not important for non-intertidal sites, but ideally they will be spread fairly evenly between the months (e.g. all approximately at the beginning, middle or end of the month).
Factors to consider when planning non-intertidal Wetland Bird Survey times and dates:
- Weather conditions – has it been a particularly wet or cold season? For example, a mild winter may lead to later arrivals of wintering birds, whereas conversely a particularly cold snap early in winter may lead to earlier arrivals.
- Does your site have seasonally constrained features – such as temporary pools that might only be present early in the season or in wet years? If your survey coincides with a dry year you may underestimate the importance of a site or miss important birds such as lowland waders.
- Do you need data from more than one non-breeding season?
Spring tide refers to the ‘springing forth’ of the tide during new and full moon. Spring tides occur twice each lunar month all year long, without regard to the season. This is the period each month when the range of heights between high and low tide is the greatest.
High and low tide surveys should be undertaken as close to spring tide as possible. It is possible to check spring tide dates and sunrise/sunset times in advance when planning surveys. It will be necessary to plan high and/or low tide surveys on dates as close to a spring tide as possible, when the high and/or low tide survey window (i.e., the survey can be completed within two hours either side of high or low tide, depending which is being surveyed) falls within daylight hours.
Factors to consider when planning intertidal Wetland Bird Survey times and dates:
- What is the spring tide date?
- Will the survey window (i.e. the survey can be completed within two hours either side of high or low tide, depending which is being surveyed) fall within daylight hours?
- Do you need data from more than one non-breeding season?
Prior to starting the survey, record the date, start time, time of sunrise / sunset, temperature (°C), wind (Beaufort scale 0–12), cloud cover (Okta 0–9, ‘9 Okta’s represents sky obscured by fog or other meteorological phenomena’ and therefore is unlikely to be appropriate for a bird survey) and rain (as a brief description e.g. dry, light drizzle). The end time and closing weather conditions (if there has been a substantial change during the survey) should also be recorded.
The weather conditions are typically less restrictive during non-breeding surveys than surveys of breeding birds, and a range of weather conditions could help provide a representative assessment of the priority species present. However, typically surveys will need to be undertaken when there is good visibility, to enable the visual detection of priority species. If surveys are carried out in less-than-ideal conditions, this should be noted as limitation in the report, with justification and a consideration of potential impacts.
Key vantage point locations around the wetland survey area should be pre-determined. These will be repeated between survey visits, and will allow an accurate coverage of the wetland area being surveyed. For a linear feature such as a coast line this will consist of a transect being walked with several stopping points, whereas for an open reservoir this will include sufficient stopping points around the reservoir to enable an accurate survey of the entire reservoir.
Features, such as buoys, will be used where possible to ensure an accurate coverage of a waterbody, and to avoid overcounting.
The number and approximate distribution of waterbird species will be recorded on a map (typically a 1:25,000 scale map), using the BTO two-letter codes.
Additional consideration should be given to any hazards identified in the site-specific risk assessment. Under no circumstances should observers enter into a hazardous situation in order to complete a survey. Instead, surveys of inaccessible or hazardous habitats should be undertaken from a vantage point or other safe distance, and any limitations should be recorded in the report, with justification and a consideration of potential impacts. Where appropriate, these hazards should be reported and any site specific risk assessment changed in light of this new information.
The number and approximate distribution of waterbird species will be recorded on a map (typically a 1:25,000 scale map), using the BTO two-letter codes . Please note that it will be necessary to record waterbirds in groups, rather than the individual location of each bird.
Typically, all waterbird species will be recorded. Waterbird species include divers, grebes, cormorants, herons, spoonbill, swans, geese, ducks, rails, cranes, waders, gulls, terns and kingfisher. Any deviation (for example if the focus is on a particular group of waterbirds, or a particular target species) will need to be justified.
Observations of birds moving high overhead, and not associating with the site itself, should be summarised together with recordings of secondary species (non-waterbird species) or omitted all together.