Skip to content

What Are Intertidal Bird Surveys?

Waders in flight

The UK’s coastline is of huge importance to a large number of bird species. This includes the area between low and high tides, the intertidal zone. This area is frequently used by different species in different ways. Because all birds are protected under the Wildlife and Countryside Act 1981 (as amended), it is a legal requirement to ensure that any planned developments that may encroach on or lie adjacent to these zones does not disturb its bird life. Intertidal surveys, employing a range of different methodologies, are therefore carried out to assess the impact of any proposed developments.

Intertidal Bird Surveys Through the Year

Surveys are predominantly carried out during the autumn and winter months; this is when this environment really comes into its own. Thousands of waterbirds use key areas between September and March, especially estuaries like the Wash that are rich in mud-dwelling invertebrates. To give an idea of the scale, during the peak winter months, 400-450,000 waterbirds use the Wash. In fact, our intertidal zones are of international importance because of the number of species and volume of birds they support during the winter months.

Brent Geese
Over 100,000 brent geese winter in the UK

These include birds that have migrated from their breeding grounds elsewhere, either further north above the Arctic Circle or inland in the UK. Some will stay for the whole winter while others will use the locations as stopping-off points en route to somewhere else. Geese, ducks and waders can all congregate in large numbers at this time of year. The survey period runs from August through to May if the area has been identified as important during migration periods. If not, surveys may only focus on a core span of November to February.

Sandwich tern and ringed plover
Sandwich terns and ringed plovers both nest close to intertidal zones

If a site also has potential for breeding species at the edge of the intertidal zone, surveys will need to be carried out for a full 12 months before development begins. Depending on habitat type, breeding terns, gulls or ringed plovers and oystercatchers may all nest very close to the intertidal zone. If the site includes any areas of saltmarsh, shelduck, redshank and curlew may also breed.

Survey Types

Before any surveys can begin, ecologists will usually carry out a desk-based study to find out what birds have been recorded in an area in the past. A key source for this information are past Wetland Bird Survey (WeBS) counts. These are monthly winter surveys that have been carried out every year since 1947 and are organised by the British Trust for Ornithology (BTO). The study will also highlight whether the proposed development site has any environmental designations attached to it or to adjacent land and if so, what the designation is for. This preliminary research will help determine what survey types, as well as survey timings, to use. For example, if the area is already known to be an important site for waders, low-tide surveys to cover feeding hours are crucial. And if the area is a known migration stopover site, the ecologist needs to survey from September through to at least March rather than just November to February. If birds are breeding there, a year of surveys will be needed.

Waders roosting intertidal bird surveys
Winter high tide roosts can include a number of wader species

Different survey methods are used because of the different ways birds use intertidal zones. Surveyors may use any of the following: core counts, low-tide counts, through the tide cycle counts (TTTCCs), night surveys using thermal imaging equipment or walkovers. Core and low-tide counts are monthly ‘look-see’ surveys, also used for WeBS monitoring. Surveyors scan across the whole area, counting how many of each species is present and noting behaviour. Both are made once a month, with core counts made at high tide when birds are usually roosting. Low-tide counts are important for monitoring those species that use the intertidal zone to feed, such as waders, shelducks and wigeon.

Pink footed geese
Pink-footed geese roost in the intertidal zone but usually feed elsewhere

Night surveys are useful for species, such as geese, that only use the site to roost at night but feed elsewhere. For areas of particular importance to waterbirds or flagged up as important to particularly sensitive or vulnerable species, it might be appropriate to carry out a TTTCC. A TTTCC surveys the area for the full 12 hours of a tidal cycle to get the fullest picture of which birds use the intertidal zone and how they use it. This removes the risk of something being missed. Breeding season will usually involve walkovers of a site under licence.

Surveys for all Seasons

A range of different project types have the potential for impacting intertidal zones. These include harbour developments, coastal reinforcement, pipeline installation and recreational facilities. Because intertidal zones are so important for thousands of wintering birds, comprehensive surveying is important before a project begins in order to reduce any impact to both birds and the development itself.

Waders feeding in the intertidal zone
Feeding times are limited between tides

Purple Plover is able to offer a full range of bird surveys, including intertidal bird surveys. We hold Schedule 1 licences and have years of experience monitoring on a range of coastal projects.